Sunday, November 18, 2007

White horses and blonde humans: a genetic connection?   posted by p-ter @ 11/18/2007 06:10:00 PM

In PLoS Genetics, there's a report on the identification of a locus that leads to white coat color in horses. This locus is KIT, a proto-oncogene (ie. certain mutations in this gene lead to increased cell growth and sometimes cancer) important for the survival of melanoblasts early in development. It's a nice story on its own, and the authors have an interesting historical genetics perspective:
Two thousand years ago, the Romans already knew of the phenotypic differences of depigmented horses, which they described as candidus (white) or glaucus (grey). The Roman historian Tacitus described the use of sacred white horses for auguries by German tribes. The so-called white horse of the Saxons is depicted on the flags of the German states of Lower Saxony and North Rhine-Westphalia. It is thus of considerable historic interest to trace the origins of white horses, particularly because the nature of their white color can have different causes, some of which are KIT mutations such as those described here. We do not know whether the Roman terms candidus and glaucus actually correspond to our modern coat color designations of white and grey. Archaeogenetics on historic DNA samples may help to identify the genetic constitution of these horses.
But something about that gene name bothered me: where had I heard it before? Ah yes, there was a recent report of an association with variants near KITLG (KIT ligand; ie. a binding partner of KIT) and blonde hair in humans. The genetic architecture underlying pigmentation isn't all that different across mammals, of course, so this isn't surprising. But still, it's nice to see these connections-- sometimes, biology makes sense.

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