Tag Archives: NIPT

by | January 8, 2022 · 5:25 PM

The Questions We Should Really Be Asking After Reading the NY Times Article About Prenatal cfDNA Screening For Microdeletions

As the genetic counseling world knows all too well, the New York Times recently published a story about prenatal cfDNA screening for chromosomal microdeletion syndromes. The gist of the article is that screening for microdeletions has a high number of false positives that produce significant patient anxiety and, in a very small number of cases, patients have elected to terminate a pregnancy before confirmatory diagnostic testing. The Times piece generated 1100+ comments on its site, including many from genetic counselors and physicians, not to mention vitriolic sturm und drang on various social media.

Clearly the article touched a collective genetic counselor nerve — a lot of the reaction has been more reflexive than reflective. Which is kind of surprising, considering that cfDNA for microdeletions is a so-so screen for a handful of rare conditions that genetic counselors have not widely agreed should be included on these tests.

Most of the criticism centered on the article not always making a clear and consistent technical distinction between a screaming test, er, uh, I mean, a screening test (which cfNDA is) and a diagnostic test (which cfDNA is not). This confusion has been an ongoing problem since the early to mid-1980s when AFP screening for neural tube defects — and maternal anxiety over testing — was first working its way into clinical practice (I remember one of my patients back then referring to AFP as “alpha-fucking protein”). Forty years later, and the anxiety and misunderstanding has not improved much.

Some of those criticisms are fair, particularly when the article describes cfDNA results as being “wrong” or “inaccurate.” To the specialist, the term false positive has a very specific definition,* and hence the source of the reaction to the article. But from a semantics standpoint, doesn’t the word false in false positive imply wrong? You can also think of calling a result “wrong” as an example of the tried and true counseling strategy of reframing, i.e. “Well, Jane, your test result actually says that there is more than an 80-90% chance your baby does not have a microdeletion.”

In my opinion the article otherwise does a decent job of highlighting the statistical complexities of cfDNA. The accompanying Figures are helpful in explaining what is essentially the positive predictive value of the tests. In fact, I think the graphics are better than the explanations and graphics on many of the testing laboratories’ websites. Many of these websites are even guiltier of muddling the differences between screening and diagnostic tests, and labs really should know better. It’s no wonder that patients might be confused and anxious when they read that a test is “highly accurate,” “an alternative to amniocentesis or CVS,” and can be assured of a “healthy baby” when results are normal. To be fair, some of the websites also address the distinctions between screening tests and diagnostic tests, but only if you click down into the rabbit warren of information.

I think most of the criticism by genetic counselors glosses over more important and fundamental questions that should be the focus of critiques of prenatal testing and our reaction to the Times piece (here I am defining prenatal testing as including screening and diagnosis). These critical questions include:

• Should we test for any condition prenatally? This is an ethically and for some a religiously complex question but it underlies all of the subsequent questions.

• If there is broad agreement that prenatal testing should be available, then what is its purpose? Realistically, with a few exceptions, is there any purpose beyond selective termination? While termination is an important option and benefit of the test for some, it’s not a course of action that all parents will choose. Some parents might decide to have prenatal testing for “preparation” but as I have argued elsewhere there is minimal data saying one way or another whether prenatal knowledge of a condition helps babies or their families, medically, emotionally, or developmentally (thought at least one study is beginning to address this shortcoming). If patients are going to be put through the emotional ringer of prenatal testing, we should be able to provide solid data on whether prenatal knowledge of a condition provides benefits in addition to the option of termination.

• What criteria should be used in determining which conditions should be subject to prenatal testing? Even if every genetic condition could be detected prenatally (and we might actually get close to that point one day), it wouldn’t make sense to test for many of them. Clinically rational and ethically acceptable criteria need to be developed to guide the selection of conditions to consider for prenatal testing.

• Who decides which conditions are screen-worthy? As Ilana Löwy and others have noted, commercial labs often spearhead this choice but decisions are reinforced and supported by the medical and genetics communities that order the testing. If no one ordered a test, labs wouldn’t offer it. As Liza Minelli, Joel Grey, and Scarface remind us, money makes the world go around. Are we screening for some conditions primarily because we can screen for them and labs offer it? What about input from patients, the public, multiple medical specialties, ethicists, social scientists, people with disabilities, and others?

• Is widespread screening for rare conditions the best use of laboratory and genetic counseling resources? Follow up of screen positive results consumes a significant amount of genetic counselor time and energy, to say nothing of patients’ anxiety and health care costs. Should these resources be focused on more pressing conditions?

• Many jobs in the genetics sector — labs and clinical providers — are dependent on the existence of genetic testing. Labs make their living off of testing but so do many genetic counselors working in clinics. While genetic counselors are not trying to push testing on patients, many genetic counseling jobs depend on the availability of genetic testing, either helping patients decide whether to have a test or explaining results to them once the testing has been completed. For better and worse, the genetic counseling profession has intimately identified itself with genetic testing. Clinics would employ far fewer prenatal, cancer, cardiogenetics, and other specialty genetic counseling jobs if there were not so many genetic tests. Think about how many clinical positions would evaporate if prenatal testing — or, really, almost any genetic testing — disappeared tomorrow. Some jobs would remain, for sure. But the demand for genetic counseling would likely drop off significantly if fewer tests were available. How much does this conflict of interest influence genetic counselors’ attitudes toward, and willingness to adopt, genetic tests, and how much does it subtly and subconsciously influence some of the strong reaction to the Times article?

• First and foremost, a patient’s decision to undergo — or not — prenatal testing should be preceded by a soul-searching exploration with partners and care providers about what parents want out of their children and addressing parental fears of disability, along with ethical and spiritual reflection. The decision requires more emotional expertise than numerical expertise. Should we be offering tests to all pregnant women that require them to master abstruse statistical knowledge in order to decide about whether to pursue testing? Even in a (unrealistic) world where all pregnant patients meet with a genetic counselor prior to testing and everything was explained in excruciating detail, many patients will misinterpret, forget, and misunderstand most of the technical information about false positives, false negatives, and distinctions between diagnostic tests and screening tests. What is the best way for patients to make medically and emotionally informed decisions? Laboratory website are less than ideal sources of information. Websites are essentially marketing tools, and marketing is antithetical to nondirectiveness. Chatbots alone don’t cut it for this purpose, although they could have an ancillary role.

• What message does it send to people with disabilities, their families, and their advocates if we continually add, seemingly willy-nilly, more and more genetic conditions to the prenatal testing list, especially, as I noted above, if they obtain no tangible benefit from testing? More testing readily begets further routinization of testing. And when you start testing lots of pregnancies for lots of conditions, you start creeping further into eugenic territory.

There are no easy solutions to any of these questions. Some may very well prove to be unanswerable and some parties will remain dissatisfied if we do manage to come up with some answers. It will involve vigorous and at times contentious debates among multiple viewpoints, and lots of people convinced that they are so damned right and why the hell can’t everybody else see that? But that doesn’t mean we shouldn’t be taking on the challenge. We may wind up with less than perfect answers, but they will be better than what we are doing now. The practice of genetic counseling demands it and patients deserve no less.

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*- Another source of confusion here is the distinction between the false positive rate and a false positive result. The false positive rate is the number of pregnancies that do not have a condition but test positive. Thus, a lab can accurately claim that cfDNA for microdeletions has a false positive rate below 1%. You can see why a patient with a positive result might misinterpret that to mean there is over a 99% chance that her baby does indeed have a microdeletion. On the other hand, a false positive result is one specific patient’s test result which incorrectly indicates that a condition is present. Thus a patient who has a positive microdeletion result has an 80-90% chance that her baby does not have a microdeletion. Lord have mercy! You can see why pregnant patients might be confused. Then try to sort through all that while experiencing the joys of hyperemesis, or if you are a non-English speaking immigrant from a village in Central America working through an interpreter, or if you are also trying to figure out at about the same time the meaning of your rubella result, your HIV status, your nuchal thickness scan, and the results of your carrier testing.

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by | April 25, 2016 · 6:14 PM

Appearances Are Important

About two months ago a story about conflict of interest in the Boston Globe caused a bit of a kerfuffle in the genetic counseling community. The article reported on the experiences of some pregnant women who felt that financial conflict of interest on the part of a few genetic counselors had resulted in the patients being given misinformation about the results of their non-invasive prenatal testing (NIPT). The counselors mentioned in the study had either received speaking fees from the lab where the testing had been performed or was an employee of a lab.

In my reading, the source of the patients’ understandable frustrations stemmed not so much from conflicts of interest on the part of the genetic counselors as it did from misunderstandings on the part of the patients and their physicians about the distinction between the false positive rate and the positive predictive value of NIPT. These two very different statistical measures can easily be confused with one another and this confusion has haunted maternal serum screening since AFP screening for spina bifida was introduced in the early 1980s (we sometimes used to darkly joke that the A in AFP stood for Anxiety and the F stood for an impolite word that would be familiar to Boston Red Sox fans when they describe their nemesis Bucky Dent). Providers and patients often incorrectly interpret a false positive rate of, say, 0.2% to mean that a positive test indicates a 99.8% probability the baby will be affected with the disorder in question. Who would not be anxious if they were convinced that there was over a 99% chance that their baby has a potentially serious health condition?

I am sure that the genetic counselors in the story understood the distinction between positive predictive value and false positive rates, and tried very hard to convey this to the patients. These counselors are well-respected and highly ethical colleagues. Really, they could have been any of us. We all have been in these counselors’ shoes and we were all feeling their pain – as well as the patients’ pain – when we read the story. Did some blind spot on the part of the genetic counselors not allow them to see how their counseling may have been influenced by an unacknowledged conflict of interest? Perhaps, and that is a point worth considering seriously. But as every genetic counselor knows, the anxiety and emotional fragility of couples faced with threatening information, particularly during pregnancy, usually dominate genetic counseling sessions and can result in patients coming away with a less than perfect comprehension of statistical fine points. We humans are emotional creatures, not Vulcans.

I think that the evidence for overt financial conflict of interest on the part of these genetic counselors was not strong. The counselors were certainly not exploiting these patients “for personal advantage, profit, or interest,” in the words of the Code of Ethics of the National Society of Genetic Counselors (NSGC). My guess is that the concern about conflict of interest arose from at least one of the patients not finding out about the counselor’s relationship with the lab until afterwards (from the article it is not clear if at the time of genetic counseling the patient was aware of the counselor’s financial ties to the lab but it seems that she learned about it only later).

And therein lies a critical point about conflict of interest – the appearance of financial conflict of interest can be just as corrosive as actual conflict of interest. Grumble though we may about the article, by bringing this to our attention, the reporter, Beth Daley, performed an important service for genetic counselors and our patients and we should be thankful for it. Public trust in our professional skills and judgement can be seriously compromised if patients perceive us to have a financial conflict of interest. Unless we openly and honestly confront conflict of interest in all its many forms, rather than deny its existence or ignore its potential, problems and misconceptions stemming from the appearance of conflict of interest will only worsen. And, possibly, a more blatant financial conflict of interest scandal may one day rear its ugly head (it would be astonishingly naive to believe that “It can’t happen here.”).

So how can the NSGC and individual genetic counselors help reduce the appearance of conflict of interest? We should be in the vanguard of addressing financial conflict of interest and demonstrate that we take it seriously. To this end, I have one concrete suggestion – the on-line NSGC directory of genetic counselors should include voluntarily provided information about the financial relationships of genetic counselors with any company other than their employers. And the directory should also clearly state who the employer is in situations where genetic counselors are employed by labs but working in hospitals and providers’ offices. While we are at it, maybe the American Board of Genetic Counseling should also consider doing this with its directory of certified genetic counselors. The Affordable Care Act requires this of physicians but for now the law does not apply to genetic counselors.

I am guessing that this suggestion might not immediately sit well with some of us. But once you get past your initial reaction and think about it a bit more clearly, it is a simple and powerful idea. It is also consistent with Section 1 of the NSGC Code of Ethics, which states that genetic counselors should:

Acknowledge and disclose circumstances that may result in a real or perceived conflict of interest.
Avoid relationships and activities that interfere with professional judgment or objectivity.

Actions are more powerful than words. Voluntarily including this information in the NSGC directory demonstrates that genetic counselors recognize that conflict of interest is a real problem and that we are not sitting around waiting to do something only if some federal law eventually requires us to do so. It allows patients to learn beforehand about a genetic counselor’s financial ties and gives patients the opportunity to discuss it openly with counselors. Or, if patients are so inclined, they can seek an alternative counselor or a second opinion.

Transparency is always the best policy – for us and for our patients.

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by | December 30, 2015 · 8:52 AM

The Top Ten Stories in Genetics, 2015: A Bacterial Editing System Goes Viral

Genetic modification was not invented in 2015. DNA was edited before CRISPR/Cas 9, just as books were printed before the Gutenberg Bible. Is it crazy to compare CRISPR to the printing press? Perhaps, time will tell. But the comparison does illustrate the enormous transformative power of technology made cheaper, faster and more efficient. It is hard to overstate the likely impact of CRISPR on medicine; it is already revolutionizing the development of new therapeutics from gene therapy to stem cell therapy to customized cell lines for drug development. Improvements to the technology and new applications for use have come so thick and fast that at times it seems like #crisprfacts, the hashtag invented to mock the CRISPR hype, can hardly keep up.

crispr facts 2

crisprfacts

crispr facts

Here’s mine…

Now is the winter of our discontent made glorious summer by CRISPR. #crisprfacts

Oh, yeah, and some other things happened too. Here’s the countdown:

  1. Roche Buys Billion Dollar Stake in Foundation Medicine

In January 2015, the Swiss pharmaceutical company Roche spent just over 1 billion dollars to obtain a majority stake in Foundation Medicine, a pioneer in cancer genomic testing. The deal not only symbolizes but may catalyze the mainstream role of genomics in cancer therapy, as tumor testing continues its rapid ascent from cameo performer to standard of care.

Foundation, which has yet to turn a profit, offers separate tests for solid tumors and blood-based malignancies. The tests offer sequencing of a large number of genes known to be implicated in cancer, but fall short of exome sequencing and examine only cancerous cells and not the germline comparison. Foundation reports are intended to help oncologists choose therapeutic options, including drugs and clinical trials. Roche’s involvement should increase marketing of the tests in the U.S. and abroad, and they likely hope that it will bolster research, such as identifying the markers of tumor DNA that could provide the basis for the highly anticipated ‘liquid biopsies’.

 

  1. Matchmaker Exchange Goes Live

Screen Shot 2015-12-29 at 9.15.23 PM

When you’re driving in traffic, other people are annoying. When you are in line at the supermarket, other people are annoying. But when you are trying to solve medical mysteries with a genetic test, other people are the answer.

Parenting a child with an undiagnosed genetic disease is a trip without guidebooks. Treatment is a series of guesses, prognosis is unknown. No one can warn you about what’s to come, or reassure you about what will pass. Genetic testing may reveal the apparent cause, but in cases where the variant has not been seen before it can only be confirmed by the second case. Patient networks built around genotype can improve treatment, clarify reproductive risk and provide emotional support.

Because clinically significant genetic changes are individually rare and collectively common, finding another person with the same gene variant or the same mutation in a tumor requires access to vast amounts of information and the means of searching it. Fortunately for us, we live in an age defined by the ability to access vast amounts of information and the means search it. But sharing genetic information on the internet has been complicated by rules designed to protect patient privacy and the hot mess that is our patient records system.

In September, a team led by Heidi Rehm announced the launch of the Matchmaker Exchange, a collaboration with multiple partners that provides secure sharing of patient information linking phenotype and genotype. Rehm described the new venture as “a reliable, scalable way to find matching cases and identify their genetic causes.” Congratulations to the field of genomics, and welcome to the Internet Age.

 

  1. Illumina Launches Helix, a Consumer Genomics Platform

Helix

In 2015, the consumer genomics industry is not so much an industry as it is a high tech field of dreams, a plowed-under cornfield in the cloud, waiting for the crowds to arrive. “They will come,” says the prophet in the James Earl Jones voiceover voice, “not even knowing for sure why they’re doing it. They’ll arrive at your door as innocent as children, longing for the future. They will pass over the money without even thinking about it; for it is money they have and peace they lack.”

But while back in Iowa poor Ray had to fight the bankers to keep his dream of a self-sustaining ghost baseball industry alive, capitalists are lining up to host the field of genomes. Both Google and Apple have cloud-based storage systems for DNA sequence data; Illumina’s proposal is unique in that you pay not for storage but for use. The company is betting that multiple third parties will develop consumer applications that require genomic information, smartphone apps that personalize your risk for side effects from pharmaceuticals or calculate the degree of relationship between you and your Tinder match. Helix holds onto your genomic digits the way Amazon holds onto your credit card information, making it easier for each new purchase to flow through them.

Illumina, the undisputed heavyweight champion of second generation sequencing, makes a forward-looking move here, tilling the soil in a hypothetical ecosystem. Two years ago, the ‘consumer genomics industry’ was a fancy synonym for 23andMe, one single tree that dominated the landscape. Ironically, the FDA pruning of 23andMe in 2013 that cut back their health and wellness business provided a little sunshine for smaller farmers, and in 2015 the first green leaves of a thousand consumer genomics products popped up out of the dirt, offering gene-based advice on the treatment of mental illness, on diets to suit your metabolic type, on the probability of cardiac events. These new shoots are individually weak – in many cases not rooted in the science, in others likely to be mown down by regulatory mechanisms not yet in place – but collectively they represent a widespread belief that there is money to be made in these fields.

 

  1. In Memento Moratorium

 “It is easier to stay out than to get out.”

                                                –Mark Twain

On April 18th, a group of Chinese scientists led by Junjio Huang published a paper in Protein and Cell describing their attempt to edit (but not implant) human embryos using the CRISPR/Cas 9 system. The goal was to alter the hemoglobin-B gene, which happened in 4 out of 54 embryos, although all 4 were mosaic – some cells were altered and others were not. This, the authors concluded, was not a success. Improving “fidelity and specificity,” they wrote, is a “prerequisite for any clinical applications of CRISPR/Cas 9-mediated editing.”

But failure or no, the publication ignited a firestorm of debate. On one thing the scientific community agreed: the experiment was evidence that the question of to edit or not to edit is in the offing. Improvements in the efficiency of gene editing are occurring so fast that the technology used in the study was itself a generation or so out of date before it made it into print. Can we do this? Not yet, say the authors of this paper. Should we do this? That is a much harder question, a question that launched a thousand editorials in 2015.

Early debates about what should or should not be allowed in DNA engineering did not focus on the human germline, but the consensus that evolved drew a line between somatic human uses for gene therapy, and changes that would affect eggs, sperm or embryos. Avoiding changes that would be passed down through generations confined any unintended effects to the individual, and sidestepped all the societal issues wrapped up in the concept of ‘designer babies.’ The moratorium that some scientists called for after word spread of the beta thal experiment is not new, and if heeded would reinstate a tacit agreement that had been in place since the 1970’s.

Oh, but it is easy to say you wouldn’t do something when you can’t. The Chinese paper resulted in an international summit on human gene editing in December, hosted by the National Academy of Sciences. The statement produced after 3 days of meetings endorsed somatic uses and germline research, but labeled any clinical use (i.e., use that could result in a baby with edited genes) irresponsible – for now. The note of caution may have obscured what is effectively a rejection of any hard and fast limitations. “As scientific knowledge advances and societal views evolve,” the organizers wrote, “the clinical use of germline editing should be revisited on a regular basis.”

 

  1. Sequenom Introduces a Non-Invasive Scan of the Genome

 “Facts are stubborn, but statistics are more pliable.”

                                                            –Mark Twain

 In September 2015, Sequenom launched MaterniT Genome, an expanded version of its non-invasive prenatal screen designed to catch all microdeletions or duplications greater than or equal to 7 MB. This is simultaneously not that important at all and an illustration of everything we are dealing with now and a window into the future.

The new Sequenom test joins its stablemates VisiblitiT (tests for trisomies 21 and 18) and MaterniT Plus (tests for all the trisomies plus select, well-characterized microdeletion syndromes like Wolf-Hirschorn or Cri-du-chat).   All the tests report on fetal sex. Everybody reports on sex, and the most common form of informed consent for testing consists of an obstetrician asking the patient “do you want to do the test for gender?” (I can’t prove this but it’s true. Ask around.).

Of the three other U.S. purveyors of non-invasive testing, only Natera includes the option of a microdeletion panel. Although NIPT is the hottest selling thing in the universe, reaction to the microdeletion panels have been lukewarm, and here’s why: math. The Achilles heel of NIPT is positive predictive value, or the percent of the time that the test flags a pregnancy and is wrong. Even when a test is very accurate, the rarer the condition, the higher the percentage of false positives. Doctors and genetic counselors don’t like false positives because in real life a ‘false positive’ is a very frightened and very upset patient, and in real life some of these patients have ignored advice for follow up and terminated pregnancies that turned out to be unaffected (this sounds very extreme but remember that they are looking at a test labeled 99+% accurate, and under intense time pressure at just around the point when most people go public with a pregnancy).

Microdeletion syndromes are rarer than trisomies, so even as accuracy remains high, positive predictive value drops precipitously. Sequenom offers no estimates of PPV, and Natera’s own numbers suggest a PPV of just 5.3% for 22q11 deletion syndrome. In this context, the Sequenom genome-wide test seems like a curious step. Not only does it raise serious questions about PPV, but most of the deletions and duplications would be uncharacterized, meaning that counseling patients on the predicted effect of the change would be complex. None of this is exactly obvious in the Sequenom promotional material, which highlights 99.9% specificity and 92.9% sensitivity.

Why is a test likely to be used sparingly a top story for 2015? Because it has a ‘more information/less clarity’ aspect that is very 2015. Because it shows the quandaries into which we wander, when we take our limited 2015 knowledge into the realm of prenatal testing. And… because limited use may grow over time, as Sequenom no doubt knows, so that this may well be a first look at the prenatal testing of the future.

 

  1. Gene Expression? There’s a CRISPR for that.

crisperizer

When exactly did the reports on CRISPR start to sound like an infomercial? Maybe it was March of 2015, when scientists from Duke University led by Timothy Reddy and Charles Gersbach published an article describing their success using an adapted CRISPR/Cas 9 system to create a targeted increase in gene production.

CRISPR! It slices, it dices… No wait, there’s more…

In this case, the modified CRISPR program links a guide RNA that searches out the target DNA with a protein that catalyzes acetylation – so instead of gripping and snipping, your bonus CRISPR tool finds the appointed enhancer region and flips a switch, turning gene production on. And voila: “A programmable, CRISPR-Cas9-based acetyltransferase…leading to robust transcriptional activation of target genes from promoters and both proximal and distal enhancers.”

Clap on, clap off… the Clapper!ld0oalpb8u8le

Debates may yet rage about the nature of epigenetics and its intergenerational significance (hell, spellcheck still refuses to recognize it as a word) but no one argues about the importance of gene expression. Changes in gene expression are central to both development and stasis; altering gene expression provides a possible avenue of control of every process from learning to aging.

Amazing! And for far less than you might think! Does it come in red?

 

  1. A Prenatal Genetic Test Reveals Cancer in the Mom-to-Be

In the four years since non-invasive prenatal testing was introduced it has grown into a market worth over half a billion dollars annually in the US alone, with double digit growth projected for years to come. The number of invasive procedures has fallen off a cliff, with many women opting not to do amniocentesis or CVS after reassuring results on a non-invasive prenatal screen. But not everyone has been reassured. In March of this year, Virginia Hughes at Buzzfeed reported on the case of Eunice Lee, who learned she had cancer after the lab reported unusual results on her non-invasive screen.

This rare event – Sequenom suggested that one in 100,000 of their tests results pointed at a malignancy, with just over half of those subsequently confirmed – affects only the (thankfully) limited universe of pregnant women with cancer, but the story is more universally significant for at least two reasons.

The first is how it reflects the challenges surrounding non-invasive testing, the first major testing modality to roll out as an industry unto itself. Since it’s inception, this technology has developed in a highly competitive and market-oriented environment (one Sequenom executive lied about early test results and would have gone to jail if she hadn’t died first) and many people have suggested that their pre-market studies were inadequate and self-serving. The FDA has pointed to non-invasive testing as an example of why laboratory-developed tests need more regulation. All of this criticism has continued despite the fact that the tests are extremely popular and largely successful, and have decreased the need for more expensive and more dangerous invasive testing. Because it is so new and because the early studies were limited, these funky results are an anomaly that put the testing company into an awkward spot. Although they look like cancer, they can’t be officially reported as cancer, because there are no studies to validate that claim. Ignoring them, on the other hand, seems like an ethical breach to me, given that there is some evidence that suspicions are correct. Sequenom chose to call the test non-informative, but alert the physician to their hunch. Other companies have chosen to say nothing in similar circumstances.

The second take home point of this story is how close we are to a new type of cancer diagnostic, one that will be used both as a screen and a test for recurrence or the effectiveness of chemotherapy. If prenatal testing is any model (and it is) it will appear soon, all the companies involved will sue one another frequently, and we will all work out the bumps as we go along. One of these days we will all be surprised to read about someone concerned about cancer who discovered she was pregnant.

Eunice Lee and Benjamin

Eunice and Benjamin  Lee

Ms. Lee, by the way, was successfully treated for colon cancer with surgery alone, and gave birth to Benjamin, a healthy baby boy.

 

 

 

 

 

 

  1. Baby With Cancer Responds to Treatment Using Genetically Modified Cells

The headline for this segment should have been, First Clinical Use of CRISPR Technology Saves Baby With Cancer, except no part of that sentence is true. The gene modification technology used wasn’t CRISPR but Talens, an older approach that is more expensive, less flexible and more technically demanding. It wasn’t the first use of gene modification as a therapy, just the first that presents a promising path to widespread use. And let’s not jinx the baby, five months into remission, with an overconfident use of the word cured.

And yet, 18-month-old Layla Richards is home with her dad and mom (probably mum; they say mum in Britain) 6 months after doctors counseled the family to consider palliative care for acute lymphoblastic anemia. If there was a miracle involved, it was simply the miracle of being in the right time and the right place – Great Ormond Street Hospital in London, which had on hand modified T cells intended for use in a clinical trial for the French biotech company Cellectis, slated to begin in 2016. The Cellectis process involves knocking out a gene in donor T cells so that they cannot attack host tissues – a step that eliminates the need to use the patient’s own cells, a personalized approach that makes it slower and more expensive. Several companies that have been developing autologous approaches saw their stock prices fall in the wake of this announcement. In the case of baby Layla, doctors say they were unable to find enough T cells to extract for treatment.

Who did what first is a subject best left to the historians (and the patent lawyers). This story represents where we stand in 2015, on the cusp of therapeutic innovation built not on serendipity, the great innovative engine of the past, but on knowledge and engineering. We are entering an age of miracles that are not miracles at all, because we can both explain and reproduce them. And we are entering it fast, with technology out of date before the gun goes off, like thoroughbreds groomed and trained who show up at the starting gate to find themselves racing unicorns.

 

  1. First Analysis of Large Data Sets Suggests: When It Comes to Variant Classification, It’s Clinician Beware, At Least For Now

 “The trouble with the world is not that people know too little; it’s that they know so many things that just aren’t so.”

                                                                                                -Mark Twain

Anyone arrogant enough to believe we were equipped to interpret the human genome must have found the last few years humbling, poor foolish person. But most of us, veterans of the diagnostic odyssey and the variant of uncertain significance, were prepared to admit that it was early days. The collective need for more information has in recent years overcome proprietary and competitive instincts, and convinced many researchers and commercial laboratories to share their data. The top story for 2014 was ExAC, a Broad Institute initiative that has aggregated exome data from over 60,000 healthy adults.

Preliminary analysis of that data is in, with a couple of headlines. One – no surprise – there’s a lot we don’t know. As expected, mutations that result in a loss of function are constrained in genes associated with severe disease – in healthy individuals, you should see limited loss of function in genes where disruption causes a severe phenotype. We saw this purifying effect in many genes, and 79% of them are not yet associated with human disease. That’s the knowledge gap that we need to fill.

Headline number two: lots of things we thought we knew are wrong. The extent of this may qualify as a surprise, although careful observers will not be shocked. Plenty of evidence existed that existing databases and analyses were larded with inaccuracies. The database ClinGen reported in June that among the 12,895 unique variants with clinical interpretation from more than one source, 17% were interpreted differently by the submitters. The ACMG guidelines for variant interpretations published in March stressed that variant “analysis is, at present, imperfect, and the variant category reported does not imply 100% certainty.” Analysis of ExAC, a preliminary report suggests, shows that most individuals carry a rare and presumably deleterious variant in a gene associated with dominant disease. Beyond inaccurate classification, this may be evidence of incomplete penetrance, subclinical presentations, or simply the resilience of the genome. Take home point, as stated by Dan MacArthur et al, “The abundance of rare functional variation in many disease genes in ExAC is a reminder that such variants should not be assumed to be causal or highly penetrant with careful segregation or case-control analysis.”

 

  1. The Power of Gene Drive

“The only difference between reality and fiction, is that fiction needs to be credible.”                                                                                                 –Mark Twain

Do you know that moment in the movie when the hero has to decide whether or not to commit some morally ambiguous act in order to save thousands of lives? Remember that? Well, forget about it. That make-believe drama cannot compare with the real life dilemma facing scientists, regulators — all of us, actually – in light of this year’s signature story, a CRISPR-mediated system that can rewrite the laws of evolution to propagate traits devised in the laboratory.

Gene drive is a term for a biological process that increases the probability that a given gene will be passed along to the next generation. In 2014, Kevin Esvelt and George Church at Harvard (et al) wrote a paper describing how CRISPR could be used to insert a tricked-out version of an edited gene that included the machinery to hack out the corresponding gene from the other parent and replace it with a copy of itself, complete with the gene drive complex. Introduce this zombie gene into any fast-replicating population and the allele frequency doubles with each new generation until there aren’t so many wildtype alleles left to convert.

Welcome to 2015, when a hypothetical is always just one grad student project away from reality. In November, Sharon Begley at STAT reported that success with fruit flies in the UC San Diego lab of Ethan Bier had led to a collaboration with UC Irvine’s Anthony James, who has developed an edited mosquito gene that destroys the parasite that causes malaria. Success could mean the most effective means of malarial control ever devised, and one that effectively spreads itself.

Herein lies the dilemma: this intervention is not so much introduced as unleashed. Although Church and Esvelt recently published a paper detailing strategies for containment and reversal of gene drives, concerns remain over the specter of unintended consequences. The Pentagon and the United Nations are reported to be concerned about the potential for weaponized insects. Scientists and ethicists have expressed alarm about the unknowns associated with any disruption of an evolved ecosystem. But the WHO reports that in 2015 there were 214 million cases of malaria and almost half a million deaths. So here’s the movie pitch: the mosquito is a terrorist killing 1500 children every day. You, the scientist, can reprogram the mosquito, with unknown impact on the entire planet. The developing and developed world can’t overcome their mutual distrust to make a plan. Do you release the zombie mosquito?

Buy it as a movie? No one would. It’s just too out there.

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by | August 17, 2015 · 10:11 PM

Guest Post: Sometimes It’s Okay To Fail

by Lisa Demers and Stephanie Snow

Stephanie Snow, MS, CGC has 11 years of prenatal genetic counseling experience. She worked as a clinical site coordinator and genetic counselor for the FASTER study and as a clinical research coordinator for the NEXT study. Lisa Demers, MS, LGC has 12 years of prenatal genetic counseling experience and currently works with Ariosa Diagnostics as a Medical Science Liaison.

The landscape of prenatal screening is changing. The use of non-invasive prenatal testing (NIPT) in clinical practice is already common and is being adopted quickly by generalist obstetricians and maternal fetal medicine specialists. While the cell-free DNA technology is innovative and the impact on patient care is significant, there is a rising chatter about NIPT failures – the 1-8% (depending on the company) of reports that return without a test result. This is a dual issue – there’s the underlying “annoyance” that NIPT occasionally fails to produce a result, and then there are publications suggesting an association between fetal aneuploidy and test failure. The latter is a conversation for another day.

Although these “no call” results frustrate patients and their doctors, the negativity surrounding these failures is surprising. The concept of a test failing is not new in medicine, and certainly not within prenatal medicine. Increasing rates of maternal obesity are just one reason for limited prenatal surveillance, with one study demonstrating that 41% or less of fetal survey ultrasounds on patients with a BMI of 30 or higher were able to be completed on the first try. When it comes to first trimester measurement of nuchal translucency (NT), the FASTER trial noted an overall 7.5% failure rate, either because of an inability to measure or due to inaccurate measurement. In a review of patients within one clinic, where nearly 50% of patients had a BMI over 25 and 25% had a BMI of 30 or more, 4% of patients had an NT failure on the first attempt and of those who opted for a second attempt, 18% failed. Overall in this population, 2.7% of patients did not achieve a NT measurement.

This is not to say that test failures are necessarily bad. When an NIPT test fails, it is often because quality metrics are in place to ensure proper test performance – just as there are standards for NT measurement which are established by the Fetal Medicine Foundation (FMF) and the Nuchal Translucency Quality Review (NTQR) program. An NT may “fail” because a patient presents for screening outside of the appropriate gestational age requirements or because of suboptimal fetal positioning. The nuchal translucency measurement is critical in obtaining aneuploidy risk assessment when combined with serum biochemistry, and even the slightest over or under estimation dramatically impacts clinical care. Such is the case with NIPT quality metrics. These metrics are in place to ensure appropriate risk assessment for the pregnancy, with the most important of these being fetal fraction. Fetal fraction is greatly affected by maternal weight, with obese women less likely having the required minimum concentration of fetal DNA in circulation. Here again, maternal obesity reduces our ability to accurately assess the well-being of a fetus.

In reality, any test failure rate can be a nuisance to a busy clinic. Having patients return for an additional visit is inconvenient to patient and provider alike. However, there are biological and technical reasons for at least some NIPT tests to fail. The thoughtful provider will consider the various metrics involved with the NIPT options and select one that balances high quality metrics (including fetal fraction) and low rate of technical failures.

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by | May 4, 2015 · 12:24 PM

Guest Post: PPV Puffery? Sizing Up NIPT Statistics

by Katie Stoll and Heidi Lindh

Heidi and Katie are genetic counselors and both work with the newly established charitable nonprofit, the Genetic Support Foundation (twitter @GeneticSupport), geneticsupportfoundation.org.

The importance of the Positive Predictive value (PPV) in interpreting Noninvasive Prenatal Testing (NIPT) results is increasingly on the minds of providers as evidenced by frequent discussions, presentations, and publications on the topic. But what if, in an effort to make their lab look like the best lab, the NIPT PPV was overstated in marketing materials or even on test reports? And what if providers and patients believed this information without question or further investigation?

Until 2014, four labs (Sequenom, Verinata Health/Illumina, Ariosa and Natera) were the only companies in the United States that offered NIPT. Over the past year, we have seen a burgeoning of new labs offering their own branded NIPT tests. In some cases, the 4 original companies act as “pass-through” labs in which the testing is branded and advertised through a secondary lab however the sample is ultimately sent to the primary lab for analysis and interpretation. In other cases, referral labs have brought NIPT testing in-house, developing their own algorithms and reporting, such as the case for the InformaSeqTM test offered by LabCorp and Integrated Genetics. In a recently published marketing document, Illumina lists 16 laboratory “partners” that all offer a version of the Illumina NIPT. The other primary NIPT labs are also distributing their tests through other labs as well; Quest Diagnostics and the Mayo Clinic have been secondary labs for the Sequenom NIPT (Quest also has their own brand, the “Q-Natal Advanced”and Natera’s NIPT is available through GenPath and ARUP).

The growing number of laboratories that offer some version of NIPT presents a significant challenge for healthcare providers who are struggling to navigate the various testing options to determine what is in the best interest of their patients. The competitive commercial landscape and aggressive marketing of NIPT to both patients and providers can further confound clinical decision-making given the paucity of information available to providers that is not delivered with an angle aimed at selling the test.

NIPT Statistics in Marketing Materials

We have noted that multiple labs offering testing have promoted extraordinarily high positive predictive values (PPVs) in their marketing materials distributed over the past year and on their websites ^ and on laboratory test reports. These tables include information regarding PPV frequently reference data from the Illumina platform and VerifiTM methodology and a study by Futch et al. as the source.

 

Performance Data Presented in Marketing Brochures for NIPT
Condition PPV NPV Sensitivity Specificity
T21 0.994 0.999 >99.9% 99.8%
T18 0.910 0.999 97.4% 99.6%
T13 0.843 0.999 87.5% >99.9%

These figures (or slight variations thereof) have been observed in the marketing materials for multiple laboratories offering NIPT. These specific statistics were reproduced from an InformaSeq brochure and sample test reports available online. 

 

The PPVs reported in this table – being widely distributed on test reports and as educational information for providers – have NOT been demonstrated by the referenced study by Futch et al. or any published NIPT studies of which we are aware.

Of course, the PPV of a screening test depends on the prevalence of the condition in the population being screened. Using the sensitivity and specificity of testing accompanying these predictive value data in the same brochure, one could only derive PPV of >99% if the prevalence of Down syndrome in the screened population was 25% or 1 in 4 pregnancies, far higher than the a priori risk for the vast majority of women undergoing prenatal screening.

PPV = (sensitivity x prevalence) / ((sensitivity x prevalence) + (1 – specificity)(1 – prevalence))

.994 = (.999x.25)/((.999x.25) + (1-.998)(1-.25)

In contrast, if we utilize performance statistics provided by the laboratories, we calculate a PPV of 33% in a population with a prevalence of 1 in 1,000 (which is similar to the prevalence for women in their 20’s) and a PPV of 83% in a population with a prevalence of 1 in 100 (which is similar to the prevalence in women age 40).

The Futch Factor

The study by Futch and colleagues that is frequently cited in marketing materials for NIPT does not demonstrate the high PPVs that are referenced, although we suspect that these statistics were arrived at through a series of assumptions about the Futch data that we will attempt to outline.

This study reported that in a cohort of 5,974 pregnant women tested, there were 155 positive calls for T21, 66 positive calls for trisomy 18, and 19 positive calls for trisomy 13. In this published report, only a fraction of the positive NIPT results had confirmation of the fetal karyotype, 52/155 cases of Down syndrome (33.5%); 13/66 cases of trisomy 18 (19.7%); and 7/19 cases of trisomy 13 (53.8%). There was 1 case of Trisomy 21 that had a normal NIPT result (false negative result), however negative test results were not methodically followed-up, so the true false negative rate for the screened conditions is unknown.

In analyzing the data presented by Futch et al, for marketing materials to derive PPVs of >99% for Down syndrome, 91% for trisomy 18 and 84% for trisomy 13 would require that all of the positive calls WITHOUT follow-up by karyotype confirmation were true positives.

 

Outcomes data from Futch et al, 2013 and projected PPVs based on category inclusion or exclusion as true positive.
T21 T18 T13
NIPT Positive 155 66 19
Confirmed (karyotype or birth outcome) 52 13 7
Discordant (Unexplained NIPT results that do not match karyotype from a source or birth outcome) 1 6 3
No information (laboratory did not obtain any information on outcomes) 22 12 0
Pregnancy loss (miscarriage , demise or termination without karyotype) 7 5 2
Unconfirmed (no karyotype or birth outcome known but history of clinical findings suspicious of aneuploidy such as ultrasound findings or high-risk biochemical screening results ) 73 30 7
Total Positive NIPTs where follow-up karyotype not confirmed 102 47 9
High End PPV* 99.4 90.1 84.2
Low end PPV** 33.5 19.7 36.8

*High end PPV- It appears that marketing material PPVs are considering all categories, including confirmed, no information, pregnancy loss, and unconfirmed to be TRUE positives in determination of PPVs.

**Low end PPV- calculated considering all cases, which were not discordant to be false positive results. A minority of positive NIPT results were confirmed with birth outcome or fetal karyotype information.

 

Given that Futch et al. did not have confirmed fetal karyotype or birth outcome follow-up for the majority of positive calls, it seems at best unlikely, and at worst impossible, that all of these positive NIPT results were correctly called, rendering claims of such high PPVs in the marketing materials based on this assumption to be unfounded. On the other end of the spectrum, if the PPV was calculated to include the not-karyotyped/no-birth outcome information pregnancies as false positive, the assumed PPVs would be 33.5% for Down syndrome, 19.7% for trisomy 18 and 36.8% for trisomy 13. Since the study does not report follow-up karyotype for the majority of positive test results, the true PPV for these NIPTs test likely lies somewhere in-between the high end PPV and low end PPV, perhaps closer to the 40-45% (for T18 and T21) previously reported in another Illumina sponsored study.

While the PPV of NIPT for Down syndrome, trisomy 18 and trisomy 13 exceeds that of traditional biochemical screening, no studies have demonstrated test performance as high as those presented in many of the PPV/NPV tables that are being provided to healthcare providers in marketing materials and, in some cases, on test reports.

A Call For Truth In Advertising And In Test Reporting

Honest communication about test performance metrics must be available to providers so that they can provide accurate counseling to patients making critical decisions about their pregnancies. While most labs do state that NIPTs are screening tests and that confirmatory testing of positive results is recommended, it is not surprising that providers and patients are having difficulty appreciating the possibility of false positive results when the laboratories are incorrectly reporting positive predictive values that exceed 99%. The consequences of relying on lab-developed materials rather than a careful analysis of the available literature are significant. There are reports of patients terminating pregnancies based on NIPT results alone. It is not surprising that some women choose not to pursue diagnostic testing to confirm abnormal NIPT results given the very high stated predictive value.

It is imperative that we recognize not only the potential benefits of these new technologies but also their risks and limitations. Testing companies are primarily responsible to their shareholders and investors, so information provided by companies about their products is largely aimed at increasing test uptake. Professional societies need to call for independent data and federal funds need to be made available to support independent research related to NIPT. Policies and best practices cannot arise from the industry-influenced studies that are currently available. While some regulatory oversight of marketing materials will likely be necessary, we urge the laboratories to consider their marketing approach and how it is affecting patients and providers. If laboratories want to truly partner with patients and providers, they need to provide accurate and straight-forward information to limit provider liability and likewise, help patients avoid making life-changing decisions based on inaccurate and/or confusing information related to test performance. As a medical profession can we come together and make this change without regulatory oversight? Now that would be a medical breakthrough.

^ – Notably, Counsyl has also recently produced a table that provides more accurate estimates of their NIPT predictive values

 

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by | November 4, 2013 · 10:25 PM

Guest Post: NIPS And The Threat To Informed Decision Making

by Katie Stoll

Katie Stoll is a genetic counselor in Washington State. She graduated from the Brandeis University training program in 2003 and since that time has held positions in the areas of prenatal, pediatric and cancer genetic counseling.

A few months ago, I reached out to the DNA Exchange readership and called for more truth in advertising by the Noninvasive Prenatal Screening companies regarding the accuracy of test results. I recently returned from the National Society of Genetic Counselors meeting where I had the opportunity to survey the marketing and patient materials from labs offering NIPS and to learn about the experiences of my fellow genetic counselors with these new tests.

Not surprisingly, in this dynamic and rapidly evolving field, all of the companies have updated their materials. Some brochures proudly acknowledge how quickly this testing is being integrated into clinical use. It feels like we are being patted on the back for adopting this new test quickly and without question.

I remain very concerned about the misleading claims in the marketing materials aimed at providers and in the patient directed brochures. It is easy to see how the language of the brochures could lead healthcare providers and patients to conclude that these tests are diagnostic or near-diagnostic. These quotes from the materials illustrate my point:

v  “Definite, informative results.”

v  “Positive or negative results.  Never maybe.”

v  “No confusion.  Just simple, clear results.”

To my knowledge, there are no new large studies to dispel my concerns about the positive predictive value of NIPS. Depending on the prior probability, a significant portion of positive results may be false positives– especially with rarer conditions such as Trisomy 18 and Trisomy 13. And because these technologies have been rapidly integrated into clinical practice based on limited research, we do not have robust outcome data to see how false positive and false negative data are playing out in clinical practice.

Since most NIPS testing is done outside of a clinical research protocol, the labs that choose to put resources into follow-up are at the mercy of the providers to share that outcomes information.  Even in the best scenarios, voluntarily reported outcome data are not likely to tell the whole story. I spoke with a testing company representative regarding a poster presented at ACMG last year which based its false positive and false negative results on ad hoc feedback. When I inquired about the meaning of ad hoc feedback, it was explained to me that the company didn’t have the resources to track outcomes so were relying on providers to let them know if the testing results were incorrect. Of course, if a patient terminates her pregnancy based on a false positive test result, nobody will know that the NIPS result was incorrect.

Don’t think a patient would terminate based on NIPS alone? We all hope that women who receive adequate counseling about the limitations of the testing would confirm results with a diagnostic test, but this is not always the case. At a presentation during the recent NSGC Annual Education Conference, one lab referenced preliminary data showing some patients are terminating pregnancies without first getting diagnostic testing, and in the absence of ultrasound findings. While this tracking has some limitations, this lab should be applauded for investing resources in tracking outcomes data and for sharing these data with genetic counselors. Hopefully we will see it published soon and other labs will follow suit.

This situation of patients making reproductive decisions based only on NIPS results may be particularly problematic in communities that don’t have ready access to genetic counseling and/or maternal fetal medicine services.

Imagine this scenario:  a 35-year-old woman living in small town, USA who has limited access to abortion services beyond the first trimester, receives a positive result for Trisomy 13. Based on positive predictive values calculations, there is an 8% chance that her “positive” result is a true positive. But, the patient – and her doctor – may think the probability is much higher, maybe even close to 100%, based on the reporting practices of the labs, which may say “Aneuploidy detected” or “Positive” for Trisomy 13. This does not support informed reproductive decisions.

This patient has 3 options:

  1.  Wait for an appointment at a high risk referral center, at some distance from her home to undergo diagnostic testing. This may limit her reproductive options by delaying time to diagnosis (the later a pregnancy termination occurs, the more expensive it is, and pregnancy termination outside of the first trimester is often not available in many smaller communities).
  2. Seek out pregnancy termination options in her local community based on the NIPS results alone – knowing that she is up against a gestational age ticking clock.
  3. Decline further testing and continue the pregnancy.

If the patient feels that she would not want to continue a pregnancy given a Trisomy 13 diagnosis, and she understands the limitations of the testing, I would imagine that she likely would feel it was worth the wait and the travel for diagnostic testing. However, given the emphasis on the accuracy of NIPS based on the lab reports, and the misconception by OB providers that this testing is “nearly diagnostic”, it is easy to imagine a scenario where she may elect to have a termination based on NIPS alone.

Based on an aggregate of data from the NIPS companies from the first quarter of 2013, one health economist estimates that NIPS is utilized by 40% of the high-risk population in the US, and this number is growing rapidly. So while the patients you see in your genetic counseling practice may be very informed about the limitations of the testing given your expert counsel, this statistic suggests that most NIPS is probably taking place outside of our offices.

We must continue the conversation about how NIPS is marketed and used in prenatal care. While the advantages to a more sensitive screening test are obvious (e.g. fewer women needing to undergo diagnostic testing), we must recognize the largely undisclosed limitations and dangers. Without adequate counseling, patients are being harmed by the misleading claims about the accuracy

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by | July 11, 2013 · 10:27 PM

Guest Post: NIPS Is Not Diagnostic – Convincing Our Patients And Convincing Ourselves

By Katie Stoll, MS

Katie Stoll is a genetic counselor in Washington State. She graduated from the Brandeis University training program in 2003 and since that time has held positions in the areas of prenatal, pediatric and cancer genetics.

A couple of years ago we were just beginning to learn about a new prenatal testing technology termed Noninvasive Prenatal Diagnosis. It was soon relabeled as Noninvasive Prenatal Testing, and now the American College of Medical Genetics and Genomics recommends this be taken one step further by terming it Noninvasive Prenatal Screening (NIPS) to highlight the limitations of this new technology.

As currently reported by labs, NIPS presents new challenges for genetic counselors. Of particular importance is figuring out how to convey to patients and healthcare providers why relying on sensitivity and specificity alone may lead to misinterpreted results. In the absence of positive and negative predictive values there may be a tendency to assume that the high sensitivity and specificity reported with NIPS means that these tests are more powerful – more diagnostic – than they actually are.  

It is imperative that we understand both what the terms mean and how they relate to a person’s likelihood of having a condition.   Sensitivity measures the true positive rate – the proportion of actual positives which are correctly identified as such (e.g., the percentage of fetuses with Down syndrome (DS) who have a positive test result). Specificity measures the true negative rate – the proportion of actual negatives which are correctly identified as such (e.g., the percentage of fetuses who do not have Down syndrome who have a negative NIPS result for DS).

A test can have both a high sensitivity and specificity without being a good predictor of whether the condition is actually present. The likelihood that a positive test is a true positive result also depends on the incidence of the condition.

Sensitivity Graph

Genetic counselors are used to thinking about aneuploidy screening in terms of PPV, as this is generally the format for reporting maternal analyte screening such as Integrated , Quad screens, etc. Analyte screening takes into account the prior probability based on maternal age and provides a PPV as the end result. For instance, an analyte screen result may be reported as Positive with a 1 in 50 chance of Down syndrome. The PPV with analyte screening lets us know how many patients with a “positive” test will actually have a pregnancy affected with the condition and reporting results this way makes it clear that this is a screening test.

Can we apply the same interpretation to NIPS results?  Some labs provide a “risk score” which appears similar to what we see with analyte screening, but I am told by the labs that the vast majority will be reported as either >99% chance or <.01% chance.  Some labs do not report a risk score, instead giving essentially a positive or negative result. But does this mean that greater than 99% of women who receive a >99% or a positive result are actually carrying a fetus with Down syndrome or other chromosome condition?

Given that women 35 year and older are a population targeted for NIPS let me work out the expected NIPS results given the approximate sensitivities and specificities reported for a hypothetical population of 100,000 thirty-five-year old women (while I cannot tell you the specific number of women age 35 who give birth per year, CDC data suggests that for the past several years about 400,000 – 500,000 women in the age 35-39 have given birth each year in the United States – so 100,00 births annually by 35-year-old mothers is probably in the ball park of the national trend.

The performance data vary significantly from lab to lab – for the purpose of this illustration, I am using sensitivity and specificity in the range of what has been reported.  The data below are based on the chance of Trisomy 21, 18 and 13 at the time of amniocentesis for a woman 35 at time of EDD1.

Down Syndrome

Trisomy 18

Trisomy 13
Incidence

1/250

1 / 2000

1 / 5000
Affected Fetuses

400

50

20
Sensitivity

99.5%

98.0%

90.0%
Specificity

99.9%

99.6%

99.8%
Total test positives

498

449

218
True test positives

398

49

18
False positives

100

400

200
Positive Predictive Value

80%

11%

8%

If we add all of the positive results together in a population of 100,000 thirty-five-year old women we see that 1165 (1.2%) have positive test results for Trisomy 21, Trisomy 18 or Trisomy 13.  Note, though, that only 465 of these results will be true positives. This indicates that the majority of the time (greater than 60% using these statistics), a positive result on NIPS for a 35-year-old woman will be a false positive – and this doesn’t even include calculations for sex chromosome aneuploidy which some NIPS labs also screen for.

Notably, the negative predictive value for NIPS is very high indicating that a negative test result is a true negative >99% of the time. But how do we reconcile that for many women, the chance of a false positive with NIPS may be higher than the chance of a true positive result when that seems to be contradicted by way the labs are reporting the results? 

In trying to explain the chance of a false positive result to patients with a “positive” test report in hand, I have found that I am met with disbelief. I can understand why – if a test says there is a>99% chance of Down syndrome and the lab says the test has >99% sensitivity and >99% specificity, how could this test be wrong?

While genetic counselors understand the limitations, the reporting practices of the labs place us in a position in which we have to work hard to convince our patients that NIPS is only a screening test.

Currently four labs offer NIPS in the U.S. and all have different strengths and weaknesses in their reporting practices. All could be improved by making the limitations of this technology more obvious.  In some cases the language used in the reports gives the appearance that NIPS is diagnostic. For example, one company’s report suggests that the healthcare provider should advise for “additional diagnostic testing”.  The labs vary in whether the need for genetic counseling following a positive result is recommended.  Additionally there is variability in the transparency of how the performance data are derived.

Given that the performance statistics vary significantly, we need to be sure to take these details into account when considering PPV. I  encourage genetic counselors and other healthcare providers to critically look at how the performance data are derived.  The sample sizes on which these numbers are based are often quite small and the confidence intervals can be broad.  I was surprised to see in the fine print of one report that the performance data “excludes cases with evidence of fetal and/or placental mosaicism.” Given that mosaicism is a known cause of false positive results and because mosaicism cannot be definitively determined through NIPS, it doesn’t seem accurate that these cases should be excluded from calculations of test performance.

The pitfalls of interpreting NIPS results is a challenge we need to address because NIPS is increasingly taking place without the involvement of genetic counselors in pretest or post-test counseling. There is real concern that patients are making pregnancy decisions based on screening tests with the misunderstanding that NIPS is diagnostic. 

I write this as call to the NIPS labs to change their reporting practices to better emphasize the screening nature of this technology. Providing some positive predictive value estimates would be tremendously helpful as we try to make sense of NIPS results for our patients. While it may be difficult to provide individualized risk assessment, a general table of how prior probability impacts individual test performance would be beneficial for interpretation. Furthermore, eliminating language from the reports that suggests these tests are diagnostic and giving more transparency to ways in which performance data are calculated would also be welcome changes.

As genetic counselors, we strive to ensure informed decision-making for the clients we see. Key to informed decision-making is an understanding of the limitations of this evolving technology. As fellow patient advocates, I hope the genetic counseling community will join me in requesting increased accountability and responsible reporting on the part of the labs regarding NIPS.

I would like to acknowledge Evan Stoll, retired GAO data analyst for his contributions to this piece.

Please Note: Authors who contribute to The DNA Exchange cannot offer medical advice. Many commenters have raised interesting and thoughtful questions about NIPS. If you have undergone NIPS and have questions, you should meet with a certified genetic counselor. To locate a genetic counselor, go to the  Find A Genetic Counselor section of  the website of  The National Society of Genetic Counselors.

  1. Hook EB. Prevalence, risks and recurrence. In: Brock DJH, Rodeck CH, Ferguson-Smith MA, editors. Prenatal Diagnosis and Screening. Edinburgh: Churchill Livingston, 1992.

 

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