TRINUCLEOTIDE (GAA)N REPEAT EXPANSION IN 2 FAMILIES WITH FRIEDREICHS ATAXIA WITH RETAINED REFLEXES

In occasional families in whom cases of classic Friedreich's ataxia (F RDA) coexist with affected cases with retained reflexes, linkage analy sis has shown that both map to the FRDA locus on chromosome 9q13-21.1. A gene X25 has been identified within the critical region of the FRDA locus, and an intronic expanded GAA trinucleotide repeat has been fou nd in most cases of FRDA. We report two further FRDA families in whom some patients with classic FRDA were areflexic whereas others had bris k reflexes. Molecular genetic analysis disclosed an abnormal trinucleo tide repeat expansion within intron 1 of the FRDA gene in both phenoty pes.