Analysis of CAG repeats in five SCA loci in Mexican population: epidemiological evidence of a SCA7 founder effect.

Spinocerebellar ataxias (SCA) are a heterogeneous group of neurodegenerative disorders. CAG (cytosine-adenine-guanine) trinucleotide repeat expansions in the causative genes have been identified as the cause of different SCA. In this study, we simultaneously genotyped SCA1, SCA2, SCA3, SCA6, and SCA7 applying a fluorescent multiplex polymerase chain reaction assay. We analyzed 10 families with SCA (64 patients) from five different communities of Veracruz, a Mexican southeastern state, and identified 55 patients for SCA7 and 9 for SCA2, but none for SCA1, SCA3, or SCA6. To our knowledge, this sample represents one of the largest series of SCA7 cases reported worldwide. Genotyping of 300 healthy individuals from Mexican population and compiled data from different ethnicities showed discordant results concerning the hypothesis that SCA disease alleles arise by expansion of large normal alleles.