Nick Wade indicates that genetic drift, not selective pressures might have resulted in the high rates of lysosomal diseases among Ashkenazi Jews. Lots of thoughts can come out of this, but I’ll let readers weigh in…. (thanks to Steve Sailer for the link, you might want to read Greg Cochran’s essay on overclocking too).
Update: From the message board (and this does tend to make sense to me-Wade’s article was a little garbled it seems)-
Risch doesn’t make a lot of sense. One of the key arguments is that high frequencies of _multiple_ mutations of the same gene or worse yet multiple mutations in each of a number of metabolically related genes, is incredibly unlikely. But that has happened: there are three overly common Tay-Sachs mutations among the Ashkenazi, two overly commom Gaucher mutations, three Niemann-Pick mutations of roughly equal frequency, two elevated mucolipidosis type IV mutations. Tay-Sachs, Gaucher, and Niemann-Pick all invovle sphingolipd degradation, and the sphingolipids that pile up in mutant homozygotes (and are presumably mildly elevated in heterozygotes) are nerve growth factors.
Boas calculated that the probability of the Gaucher mutation distribution alone is less than 1 in 500: Risch doesn’t address this at all.
I have no idea what his point is in comparing geographic distributions of lysosomal- and non-lysosomal mutations, considering that many or most of the non-lysosomal mutations have _also_ been made common by selection. CF has, almost certainly. There’s evidence that strong selection is occuring at the BRCA1 locus (again two mutations). Slatkin has said that there must have been selection elevating the factor XI clotting disorder mutations ( again two different mutations). The connextin-26 deafness mutation has clearly been favored by natural selction in many populations, probably as a disease defense.
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