Evidence of a genetic marker associated with early onset in Friedreich's ataxia.

We evaluated the association between age at onset of Friedreich's ataxia and alleles of two restriction fragment length polymorphisms (RFLP) at D9S15 and D9S5 in the 9q13-9q21.1 region. We studied 65 Italian patients from 49 families. Age at onset was not normally distributed in our patients, suggesting allelic heterogeneity. Patients homozygous for allele 1 of MspI RFLP detected by probe MCT112 at D9S15 (M1) had an earlier onset (mean 9.3, SD 3.4 years) than patients homozygous for allele 2 (M2; mean 12.1, SD 4.3). Heterozygotes had an onset age similar to that of the M2 homozygotes. These findings suggest that the M1 allele might be a marker of one allelic early-onset Friedreich's ataxia mutation.