Here is
Greg Cochran's fascinating
piece on "Overclocking" over at
Jerry Pournelle's site.
The opening paragrah of his pithy essay will give you a good taste:
There is a good chance that an odd cluster of hereditary neurological diseases among the Ashkenazi Jews is a side-effect of strong selection for increased intelligence. The idea is not really new, but the evidence has gotten stronger with time, and I have recently found some intriguing supporting data.. Four of these syndromes - Tay-Sachs, Niemann-Pick, Gaucher's, and mucolipidosis type IV - are recessive lysosomal storage diseases. The first three of these are caused by deficient variants of enzymes that break down sphingolipids, which play a role in neuron membrane structure and also as signaling molecules. Homozygotes, who have no working copy of the breakdown enzymes, become ill. Tay-Sachs and Niemann-Pick cause retardation and death in childhood, but Gaucher's disease is milder and more variable. The form common in Ashkenazi Jews does not cause brain damage, although there can be other problems with the spleen and bones. . Mucolipidosis type IV probably involves a defect in endocytosis. It causes retardation and death in early life.
Thanks to
David Mercer for pointing it out to me.