Intrafamilial phenotype variation in Friedreich's disease: possible exceptions to diagnostic criteria.

Three families are described which include members with "typical" Friedreich's disease (FD) and others who are ataxic but do not satisfy all the diagnostic criteria for that disease. In family A two patients have an early-onset, rapidly progressive FD, while two others have a late-onset, more benign form. In families B and C one member has "typical" FD, and another has a similar ataxic syndrome, except for preservation of knee jerks. Laboratory evaluation is consistent with the diagnosis of FD in all cases. FD diagnosis appears justified in secondary cases with late onset or preserved tendon reflexes, provided that the index case fulfils all diagnostic criteria. Whether the diagnosis of FD is tenable in sporadic "atypical" cases remains to be seen. Echocardiographic and neurophysiological examination may be valuable in classifying such cases.