Genotype/phenotype correlation in a SCA1 family: anticipation without CAG expansion

We report on a family with spinocerebellar ataxia type 1 (SCA1), in which the age at onset and the se- verity of the disease do not correlate with the number of CAG repeat units. Although a marked anticipation was observed in the proband, it was not a consequence of an expansion of the CAG tract. None of the expanded alleles contained CAT interruptions. The pathologic expansion in this family was stable during the paternal but not ma- ternal transmission, where it expanded by one trinucleotide and unexpectedly did not lead to anticipation. Our ob- servations suggest that factors other than the length of the CAG repeat play a considerable role in determination of the disease course.