An individual with late-onset ataxia was found to be heterozygous for an un
usual (GAAGGA)(65) sequence and a normal GAA repeat in the frataxin gene. N
o frataxin point mutation was present, excluding a form of Friedreich ataxi
a. (GAAGGA)(65) did not have the inhibitory effect on gene expression in tr
ansfected cells shown by pathogenic GAA repeats of similar length. GAA repe
ats, but not (GAAGGA)(65), adopt a triple helical conformation in vitro. We
suggest that such a tripler structure is essential for suppression of gene
expression.