--there are a awful lot of genetic syndromes among Jews of Eastern European background (and a rather high incidence of autoimmune disease among people of such backgrounds as well, and we know Alan has psoraisis . . .)

There are some well known hereditary neuropathies such as the Charcot-Marie-Tooth variants, and some not so well known ones, such as the hereditary sensory neuropathies associated with point mutations:

http://neuromuscular.wustl.edu/time/hsn.htm

http://neuromuscular.wustl.edu/time/hmsn.html

As you can see, it's a long list, and these are only the ones that have been documented to this point . . .