Clinical and molecular studies of 73 Italian families with autosomal dominant cerebellar ataxia type I: SCA1 and SCA2 are the most common genotypes

We clinically and genetically evaluated 73 Italian families with autosomal dominant cerebellar ataxia (ADCA) type I. Spinocerebellar ataxia (SCA) type 1 was the most common genotype (SCAI), accounting for 41% of cases (30 fam ilies), SCA2 was slightly less frequent (29%, 21 families), and the remaini ng families were negative for the SCAI, SCA2, and SCA3 mutations. Among the positively genotyped families, SCAI was found most frequently in families from northern Italy (50%), while SCA2 was the most common mutation in famil ies from the southern part of the country (56%). Slow saccades and decrease d deep tendon reflexes were observed significantly more frequently in SCA2 patients, while increased deep tendon reflexes and nystagmus were more comm on in SCAI. In SCAI and SCA2 families there was a significant inverse corre lation between expansion size and age at onset. Analysis of triplet repeat numbers in parent offspring pairs showed greater meiotic instability, which was associated with an earlier onset of the disease in SCA2 families than in SCAI families.