Autosomal dominant cerebellar ataxia type I. Clinical and molecular study in 36 Italian families including a comparison between SCA1 and SCA2 phenotypes.

We studied 83 patients from 36 Italian families with autosomal dominant cerebellar ataxia type I. Mean onset age +/- SD was 34.2 +/- 12.8 years with a mean anticipation of 12.8 +/- 15.1 in 52 parent-offspring pairs. Onset age anticipation occurred predominantly through paternal transmission. Mean age at death was at 56.5 +/- 15.5 years. The most common associated features were supranuclear ophthalmoplegia, corticospinal signs, peripheral neuropathy and cognitive impairment. Cerebellar atrophy was constant at MRI and usually associated with shrinkage of the pons and degeneration of the pontine transverse fibres. Direct mutation analysis in 29 families showed two families with SCA1 and none with Machado-Joseph/SCA3 mutation. We performed linkage analysis in the ten largest families. Two of them showed linkage to SCA2 locus and none to SCA4 and SCA5 loci. SCA2 patients showed higher occurrence of peripheral neuropathy and slow saccades, rarer corticospinal signs and a milder course of the disease in comparison with SCA1 patients.