The journal Evolution, Medicine, and Public Health has a section entitled clinical briefs, that are short entries on the evolutionary considerations of common diseases and clinical medical issues. These open access articles are an excellent way to convey evolutionary ideas in a digestible and effective way. One entry that seems appropriate to current cultural events is entitled Clone Wars: the evolution of therapeutic resistance in cancer. This work explores chemotherapy resistance that leads to cancer relapse in an evolutionary context.
I have encouraged my students to read these clinical briefs and we discuss patient problems in real time using a similar format. I will be posting some of my most recent explorations of topics with my students on this blog, in a even more concise format – the Evo Med Mini. It goes like this:
I. The Patient and the Problem
In an example from my ER shift last night with two evolutionary medicine elective students, we saw a 36 year old woman (details will be slightly changed for this and future examples) who presented with left leg swelling and tightness. Our concern was deep vein thrombosis (DVT), a potentially lethal diagnosis that can proceed to pulmonary embolism if missed. One risk factor for deep vein thrombosis is Factor V Leiden, a mutation affecting Factor V so that its carriers clot more readily.
II. The Conventional Wisdom
Factor V Leiden is one of a variety of gene variants that increase the risk of DVT and pulmonary embolism.
III. The Evolutionary Insight
Carriage of the Factor V Leiden (FVL) mutation exceeds 1 in 20 in Caucasians, far more than would be expected for a sporadic mutation. Indeed FVL is typically inherited and its penetrance in human populations suggests that it has been maintained by natural selection, perhaps by balancing selection, and perhaps is an example of a heterozygote advantage.
Two hypotheses for a heterozygote advantage for FVL are protection from mortality during childbirth from hemorrhage and protection from sepsis.
IV. Translational Impact
What is the impact of the evolutionary hypothesis, if true? The impact for a given DVT sufferer is not great, since the treatment plan would be unchanged. On a scale of 1-10, the translational impact = 2. As important, these hypotheses have yet to be substantiated by concrete clinical evidence, limiting their translational importance.
V. Future directions. Asking the question – what is a possible selective benefit for FVL? – is useful. This line of inquiry may eventually lead to changes in the treatment of clotting disorders, and possibly sepsis. Keep an eye on this space!
Emergency Physician, Educator, Researcher, interested in the microbiome, evolution, and medicine