Spinocerebellar ataxia type 20 is genetically distinct from spinocerebellar ataxia type 5

The autosomal dominant spinocerebellar ataxias (SCAs) are inherited neurodegenerative diseases with heterogeneous etiology and clinical presentation. The SCAs are primarily characterized by a progressive loss of coordination that affects gait, limb, and eye movement, speech, and swallowing.1 More than 28 different forms of SCA have been genetically mapped, and the number of loci responsible for SCAs continues to grow. In 2004, a family of Anglo-Celtic origin that presented a distinct form of SCA was reported.2 In addition to the classic incoordination found among patients with ataxia, most affected family members are clinically characterized by palatal tremor and dysphonia, whereas neuroradiologic studies show calcification of the dentate nuclei, which is not found in other forms of dominant ataxia. Genetic testing demonstrated the family did not carry the mutation for SCA1, 2, 3, 6 to 8, or 17, and linkage …