Genetic cerebellar ataxias.

This review broadly covers the commoner genetic ataxias, concentrating on their clinical features. Over the last two decades there has been a potentially bewildering profusion of newly described genetic ataxias. However, at least half of dominant ataxias (SCAs) are caused by (CAG)n repeat expansions resulting in expanded polyglutamine tracts (SCAs 1, 2, 3, 6, 7, 17, and DRPLA), although of the remainder only SCAs 8, 10, 12, 14, 15/16, and 31 are frequent enough that the described phenotype is probably representative. Though the SCAs can be difficult to separate clinically, variations in prevalence in different populations, together with various clinical and radiological features, at least help to order the pretest probabilities. The X-linked disorder, fragile-X tremor ataxia syndrome occurs in fragile-X permutation carriers, and typically causes a late-onset ataxia-plus syndrome. The recessive ataxias are not named systematically: The most frequent are Friedreich, ataxia telangiectasia, ARSACS, AOA1 and 2, and the various POLG syndromes. Although rare, several other recessive disorders such as AVED are potentially treatable and should not be missed. Another group of genetic ataxias are the dominant episodic ataxias, of which EA1 and EA2 are the most important. Lastly, the neurologist's role in ongoing management, rather than just diagnosis, is addressed.