There are four possible explanations for the high frequency of Tay-Sachs disease among AshkenazicJews. The first explanation is the appearance of new copies of the gene caused by the mutation, while existing copies disappear. If to follow this hypothesis, it turns out that the mutation rate of the Ashkenazim gene is more than 110 times higher than that of any human gene. The second possible explanation is that the gene is passed from other people with a high gene frequency to Ashkenazim. This explanation might work according to some historical information about the origination of Ashkenazim.
However, those are not enough to be strong evidence for the explanation. The third hypothesis is based on the genetic processes, namely the founder effect and genetic drift. These theories explain how a rare gene may be spread among a small population. The fourth explanation suggests that something about Ashkenazim favored the accumulation of ganglioside and related fats. That means that the possibility of the several different mutations along the DNA stretch, where two of them are much more frequent in the Ashkenazim population being accidental, is unlikely. Thus, the chances of it being coincidental are miserable.