Unique origin and specific ethnic distribution of the Friedreich ataxia GAA expansion

The GAA triplet repeat expansion that causes Friedreich ataxia is found onl y in individuals of European, North African, Middle Eastern, or Indian orig in (Indo-European and Afro-Asiatic speakers). Analysis of normal alleles of the GAA repeat and of closely linked markers suggests that expansions aros e through a unique two-step process. A major implication of these findings is that Friedreich ataxia may not exist among sub-Saharan Africans, Amerind ians, and people from China, Japan, and Southeast Asia.