I am unabashedly the pedigree’s biggest fan.* Although those new-fangled “-omics” testing technologies may soon surpass the analytic power of the pedigree, I suspect that pedigrees will be a critical part of genetic counseling for as long as it is practiced in its current form.
I have resisted using family history questionnaires because for most patients those questionnaires probably just feel like homework assignments. Besides, I am not convinced that questionnaires really save much clinic time. More critically, the process of constructing a pedigree provides great insight into a patient’s understanding of genetics, disease, and family dynamics. And, truth be told, a questionnaire lacks a pedigree’s minimalist elegance and concise pictorial encapsulation of complex information. Ludwig Mies van der Rohe would have embraced the simple rhythmic modularity of a multi-generation pedigree.
But pedigrees are not measures of scientific realities like the speed of light in a vacuum or the Avogadro constant. Pedigree nomenclature is a product of the sociocultural background of the geneticists who devised it. Pedigree symbols were formalized a century ago by scientists (eugenicists, if we are to be honest about it) raised in the Western Judeo-Christian tradition, a tradition that reflects
the background of many current genetic counselors.
The sociocultural biases of pedigree nomenclature are most apparent in its limits. So, what are some of those limitations and what do they have to tell us?
Simply put, pedigree nomenclature functions best for people who have one mating partner for life as well as for kindreds with few or no consanguineous matings, and further assumes that people can be neatly placed into one of two discrete gender categories.
Let me expand on these points. Pedigrees are best suited for a simple family structure that broadly reflects the Christian ideal of a single spouse for life. Sure, pedigrees are capable of including a second partner, but they quickly grow into a mess of confusingly angled lines and icons when someone has more than two mating relationships. This problem is compounded when the proband’s relatives also have multiple mates.
In some non-Western societies, people are expected to marry their cousins whereas Westernized societies generally stigmatize consanguineous matings. Christianity grudgingly allows for the occasional cousin marriage but marrying a first cousin can require special dispensation from the Vatican. Frequent cousin marriages within a family are discouraged. The pedigree of a patient whose family includes multiple generations of consanguineous matings is a complex web of double mating lines and hooked or crisscrossed lines of descent. Such families are better described by inbreeding coefficients than by ideograms.
Pedigree nomenclature also assumes that people are either male or female, just like God created Adam and Eve. This is a peculiar assumption, considering that intersex individuals are not uncommonly encountered in the genetics clinic. It is probably more accurate to say that gender and sexuality represent a spectrum, with male heterosexual at one end and female heterosexual at the other. Yes, I know that the nomenclature allows for the depiction of people who may not phenotypically, socially, or genetically fit neatly into either male or female. But the technique is awkward, and was developed almost a century after pedigrees had become part of the genetics toolkit. They are literally square pegs in round holes.
There are other subtle psychological aspects of pedigree nomenclature. For example, it reinforces mendelian and reductionist views of complex biological phenomena. Those neat arrangements of squares, circles, and lines can
subconsciously seduce the clinician to think “Oh it must be a dominant condition with variable penetrance or reduced expressivity” or “With all those inbreeding loops it surely must be a recessive trait.” When you construct a figure intended to illustrate mendelism, everything starts to look mendelian. And, as eugenicists knew all too well, the ability of those dark and light geometric shapes to reify cultural constructs like feeble-mindedness or pauperism can make the pedigree a magnificently effective propaganda device.
Don’t get me wrong. I do not advocate eliminating pedigrees from the clinic or changing the nomenclature. Far from it. Hey, I was part of the group that established standards for modern pedigree nomenclature. But we must be willing to make the difficult acknowledgment that pedigrees are not objective scientific tools that take honest and accurate measure of biological traits. All kinship systems reflect the culture that developed them. Pedigrees are the product of geneticists, with all of their faults, prejudices, strengths, and humanity.
* – Okay, maybe I am second to Robin Bennett.