Spinocerebellar ataxia type 7

Spinocerebellar ataxia type 7, abbreviated SCA7, is a rare inherited disorder passed on in an autosomal dominant pattern. It results from an expanded run of CAG repeats in the ATXN7 gene, which lengthens a polyglutamine tract in the protein and places the condition among the polyglutamine disorders. Symptoms usually begin between the ages of 20 and 40 and include ataxia, slurred speech, slow eye movements, pyramidal signs, difficulty swallowing and ophthalmoplegia. A cone-rod dystrophy of the retina can progress to blindness and is one of the distinctive signs of the disease. The course usually runs 20 to 30 years but varies with the age at onset. It is reported at fewer than 1 in 300,000 people and accounts for about 2 percent of spinocerebellar ataxia cases, with more than 1,000 people described, and it is seen more often in Scandinavia, Africa and Mexico because of a founder effect.