[Genetic diagnosis, classification and clinical hereditary ataxia disease entities]

Hereditary ataxias are a heterogeneous group of neurodegenerative diseases. Neither the clinical features nor the findings at autopsy provide a satisfactory basis for the isolation of distinct categories and classification. Recently, several gene loci responsible for inherited ataxias have been identified. For several hereditary ataxias even the disease causing mutations have been described. These findings lead to a new classification of the inherited ataxias based on genotypes rather than pathology or phenotypes. Such a classification will potentially gain wide acceptance since it derives from the molecular genetic cause of the diseases. Furthermore, recent advances in molecular biology improved the understanding of the clinical variability of hereditary ataxias that occurs even within the same family. All forms of progressive dominant ataxias are most likely caused by the same type of mutation: an unstable and expanded trinucleotide repeat. The repeat expansion is moderate in patients with later onset and mild progression but is extensive in juvenile cases with a more rapid course of the disease. Furthermore, the extent of the expansion seems to be at least partially responsible for the development of different phenotypes. The identification of gene loci and mutations allows reliable diagnosis even at a presymptomatic or prenatal stage for an increasing number of inherited ataxias. Although molecular genetics has improved the diagnosis and understanding considerably for most forms of hereditary ataxias a causal therapy is still missing. Therefore, it is essential that presymptomatic analysis is always performed according to the international guidelines. They include genetic counselling by a team of experienced neurologists, geneticists, psychologists and social workers.