The clinical diagnosis of autosomal dominant spinocerebellar ataxias

The spinocerebellar ataxias (SCAs) are a heterogeneous group of autosomal dominantly inherited progressive ataxia diseases. Up to now, almost 30 different gene loci have been found. In 14 of them, the underlying mutations have been identified. The more common SCAs, SCA1, 2, 3 and 6 are due to translated CAG repeat expansions that code for an elongated polyglutamine tract within the respective proteins. These diseases belong to a larger group of polyglutamine disorders that also includes Huntington's disease. Epidemiological studies conducted in different European regions found prevalence rates of SCAs ranging from 0.9 to 3.0 : 100,000. In all SCAs, ataxia is the prominent symptom. However, the majority have a complex phenotype in which ataxia is accompanied by varying non-ataxia symptoms. In all ataxia patients with proven or suspected autosomal dominant mode of inheritance, the available molecular genetic tests for SCA mutations should be performed. Depending on the geographical origin of the family, these tests will lead to positive diagnostic results in at least half of the families.