Clinical characteristics: Spinocerebellar ataxia type 7 (SCA7) comprises a phenotypic spectrum ranging from adolescent- or adult-onset progressive cerebellar ataxia and cone-rod retinal dystrophy to infantile or early-childhood onset with multiorgan failure, an accelerated course, and early death. Anticipation in this nucleotide repeat disorder may be so dramatic that within a family a child with infantile or early-childhood onset may be diagnosed with what is thought to be an unrelated neurodegenerative disorder years before a parent or grandparent with a CAG repeat expansion becomes symptomatic. In adolescent-onset SCA7, the initial manifestation is typically impaired vision, followed by cerebellar ataxia. In those with adult onset, progressive cerebellar ataxia usually precedes the onset of visual manifestations. While the rate of progression varies in these two age groups, the eventual result for almost all affected individuals is loss of vision, severe dysarthria and dysphagia, and a bedridden state with loss of motor control.
Diagnosis/testing: The diagnosis of SCA7 is established in a proband by the identification of a heterozygous abnormal CAG trinucleotide repeat expansion in ATXN7 by molecular genetic testing.
Management: Treatment of manifestations: Multidisciplinary care involves supportive treatment of: neurologic manifestations – physical and occupational therapy to help maintain mobility and function, and pharmacologic treatment to reduce symptoms; dysarthria – speech and language therapy and alternative communication methods; dysphagia – feeding therapy to improve nutrition and reduce the risk of aspiration; and reduced vision – use of low vision aids and consultation with agencies for the visually impaired.
Surveillance: Routine follow up with multidisciplinary care providers.
Agents/circumstances to avoid: Avoid: alcohol intake (especially if excessive) as it can further impair cerebellar function; foods identified by a registered dietitian as possible causes of dizziness or disorientation.
Therapies under investigation: Several ongoing clinical trials for medications used as treatment for ataxia.
Genetic counseling: SCA7 is inherited in an autosomal dominant manner. Offspring of an affected individual have a 50% chance of inheriting an abnormal CAG repeat expansion in ATXN7. Once an ATXN7 CAG repeat expansion has been identified in an affected family member, prenatal testing for a pregnancy at increased risk and preimplantation genetic testing for SCA7 are possible.
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