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One hundred forty of the 187 patients,with ages at onset ranging from 2 to 51 years,were homozygous for a CAA expansion that had 120 to 1700 repeats of the trinucleotides.About one quarter of the patients,despite being homozygous,had atypical Friedreich's ataxia;they were older at presentation and had intact tendon reflexes.Larger GAA expansions correlated with earlier age at onset and shorter times to loss of ambulation.The size of the GAA expansions(and particularly that of the smaller of each pair)was associated with the frequency of cardiomyopathy and loss of reflexes in the upper limbs.The GAA repeats were unstable during transmission.The clinical spectrum of Friedreich's ataxia is broader than previously recognized,and the direct molecular test for the GAA expansion on chromosome 9 is useful for diagnosis,determination of prognosis,and genetic counseling. |
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