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Lynch et al¹ have written a lucid review of the genetic pathophysiologic characteristics of Friedreich ataxia and its clinical applications. In discussing the differential diagnosis of patients who have a Friedreich-like phenotype but no GAA expansion, they mention other genetic scenarios (2 individual point mutations or linkage to another genetic locus, FRDA2) and several overlapping conditions (ataxia with vitamin E deficiency, autosomal recessive spastic ataxia of Charlevoix-Saguenay, posterior column ataxia with retinal pigmentary changes, early-onset cerebellar atrophy with retained reflexes, complicated Charcot-Marie-Tooth disease, and other mitochondrial disorders). They neglect to mention the adult form of hexosaminidase A deficiency (late-onset Tay-Sachs disease), which is seen not just in the Ashkenazi Jewish population but also in French Canadians and others.

First reported by Rapin et al² in 1976 and elegantly reviewed by Navon³ in 1991, data have shown that individuals who are compound heterozygotes for the classic Tay-Sachs mutation and a . . . [Full Text of this Article]