The Expanding World of Trinucleotide Repeats

A paper in this week's issue of Science (Campuzano et al. , p. 1423 ) reports that Friedreich's ataxia has now joined the list of diseases caused by expanding trinucleotide repeats. In his Perspective, S. Warren discusses how some unusual features of the repeats in this disease challenge some generalizations that have been made about the mechanisms by which these unusual mutations cause disease.