Autosomal dominant cerebellar phenotypes

The dominantly inherited ataxias comprise a series of clinical phenotypes that include ataxia, dysarthria, dysmetria, and intention tremor resulting from the involvement of the cerebellum and its afferent and efferent pathways. These inherited ataxias occur commonly throughout the world and represent an area of intense neurologic research. Although the clinical manifestations and neuropathologic findings of cerebellar disease are predominant, there may be characteristic changes in the basal ganglia, brainstem, spinal cord, optic nerves, retina, and peripheral nerve. In large families with dominantly inherited disease, there are many gradations, from pure cerebellar manifestations to mixed cerebellar and brainstem disorders, cerebellar and basal ganglia syndromes, and spinal cord or peripheral nerve disease. Rarely, dementia may be present as well. The clinical picture may be consistent within a family with dominantly inherited ataxia, but on occasion there is a characteristic syndrome in the majority of affected family members and an entirely different phenotype in one or several members. For these reasons, I suggested in 1990 ^[1] that for the autosomal dominant phenotypes, the genotype would be required to settle the issue of disease assignment and classification.

Neurologists have written extensively as to the appropriateness of various classifications and have debated, often passionately at meetings, the uniqueness and placement of newly evaluated families with inherited cerebellar disease. Categories of disease abound, therein satisfying the needs of selective investigators to be either unifiers or splitters, often based on quite arbitrary factors ^[1]. Scholarly, yet divergent, classifications of dominantly inherited syndromes have been formulated by Greenfield, ^[2] Konigsmark and Weiner, ^[3] Harding, ^[4] and the World Federation of Neurology Study Group on Cerebellar Ataxias (unpublished, 1993). Harding ^[4] separates the autosomal dominant cerebellar ataxias (ADCAs) into type I and type II, in which ataxia is combined to a varying degree with pyramidal and extrapyramidal signs …