The inherited ataxias

Hereditary ataxias have attracted neurologic attention for many years and have been the subject of several earlier reviews. Classification has been notoriously difficult; at the present time there is no widely accepted standard for classification. There are two general philosophies espoused by the 'lumpers' and the 'splitters'. The former attempts to simplify the classification by accepting only the most concrete evidence for distinguishing subgroups. The 'splitters', in an effort to produce a very accurate descriptive system, tend to set up a new diagnostic group to accommodate apparently distinctive features. Much of the confusion arises from insufficient attention to genetic issues. There are three large groups of patients encountered by the neurologist: dominant, recessive, and sporadic ataxias. The sporadic ataxias, which may account for one-third of the patients with chronic, progressive ataxia, will not be discussed in detail. The dominant and recessive ataxias each account for an additional third of the patients. With smaller family sizes, it is sometimes difficult to distinguish recessive from sporadic ataxias.