Polyglutamine Disorders

Alice Karam, Yvon Trottier, Karam, Alice, Trottier, Yvon

Spinocerebellar Ataxia type 7 (SCA7, OMIM # 164500) is an autosomal dominant neurodegenerative disorder characterized by adult onset of progressive cerebellar ataxia and blindness. SCA7 is part of the large family of autosomal dominant cerebellar ataxias (ADCAs), and was estimated to account for 1-11.7% of ADCAs in diverse populations. The frequency of SCA7 is higher where local founder effects were observed as in Scandinavia, Korea, South Africa and Mexico. SCA7 is pathomechanistically related to the group of CAG/polyglutamine (polyQ) expansion disorders, which includes other SCAs (1-3, 6 and 17), Huntington's disease, spinal bulbar muscular atrophy and dentatorubro pallidoluysian atrophy. Two distinctive characteristics of SCA7 are the strong anticipation by which earlier onset and more severe symptoms are observed in successive generations of affected families, and the loss of visual acuity due to cone-rod dystrophy of the retina. The pathology is caused by an unstable CAG repeat expansion coding for a polyQ stretch in Ataxin-7 (ATXN7). PolyQ expansion in ATXN7 confers toxic properties and leads to selective neuronal degeneration in the cerebellum, the brain stem and the retina. Herein, we summarize the genetic, clinical and pathological features of SCA7 and review our current knowledge of pathomechanisms and preclinical studies.