[Linkage study of hereditary spinocerebellar ataxia, and probable correlation for the loci to the disease phenotypes].

To study gene loci and disease phenotypes, 18 families with dominant OPCA were subjected for linkage analysis to SCA1- or SCA2-linked microsatellites. Total individuals consisted of 190. Among them, 77 were affected. Consequently, 10 families were 6p-linked, 7 were 12q-linked, and one was type-undetermined. These results indicate that the majority of dominant OPCA in Japan are composed with these two genotypes. Clinically, these two disorders show progressive ataxia, Babinski reflexes, and terminal amyotrophy. Other common features in SCA1 were hyperreflexia, spasticity, mild nystagmus at early stage, slow saccade, and external ophthalmoparesis (EOP) at advanced stage. In contrast SCA2 showed progressive hyporeflexia and slow saccade from early stage. Moreover, choreiform movement, tremor, and rhythmic myoclonus were more frequent in the latter. Neuropathologically, dentate nucleus, brainstem motor nuclei, spinocerebellar tract were involved more severely in SCA1 than SCA2. Degeneration of substantia nigra is more marked in SCA2 than SCA1. These observations strongly indicate that there are correlations between genotypes and phenotypes in dominant OPCAs. Conversely, it is possible to diagnose these two genetic disorders from the clinico-pathological findings.