"Only six of the 21 disease genes that we examined showed evidence of selection," Bray says. "This supports the argument that most of the Ashkenazi-prevalent diseases are not generally being selected for, but instead are likely a result of a genetic bottleneck effect, followed by random drift."
Besides examining the genes responsible for previously identified diseases, Bray and colleagues went on to look for other regions of the Ashkenazi Jewish genome that display signs of selection, in comparison to European genomes. The two strongest differences between the Ashkenazi and European populations were on chromosome 2 and 12. A region including the lactase gene, which confers lactose tolerance, on chromosome 2 showed signs of strong selection in Europeans but not the Ashkenazi.
"A variant of the lactase gene swept through Europe at around the same time as the domestication of cattle several thousand years ago," Bray says. "This result suggests the selection preceded the European establishment of the Ashkenazi Jewish population, which is consistent with the historical record."
In addition, a region on chromosome 12 showed selection in the Ashkenazi Jewish population but not Europeans. This area encompasses 18 genes but the investigators noticed that one of these, ALDH2, is important in alcohol metabolism, and genetic variation in ALDH2 has previously been shown to affect alcohol consumption, Bray says.
"This is consistent with historical and modern reports of lower alcoholism rates in Jews, although social and religious practices are also thought to play a role," he says. "However, a more detailed analysis of variants in the ALDH2 gene would be necessary to show a mechanistic link."
|Contact: Holly Korschun|