Genetic and clinical profile of the spinocerebellar ataxias followed in the Calgary Movement Disorders Clinic

Kraft, Scott W. (2003) Genetic and clinical profile of the spinocerebellar ataxias followed in the Calgary Movement Disorders Clinic. Masters thesis, Memorial University of Newfoundland.

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Abstract

The adult onset spinocerebellar ataxias are a genetically and clinically heterogeneous group of neurodegenerative disorders. The relative frequencies of these disorders vary within different ethnic groups and geographical locations. We sought to identify the relative frequencies of these disorders in the Calgary Movement Disorders Clinic, as well as to determine the proportion of patients that have a positive family history and to determine the diagnostic utility of genetic testing in individuals with and without family members with similar symptoms. -- A retrospective chart review of individuals given a clinical diagnosis of adult onset spinocerebellar ataxia in the Calgary Movement Disorders Clinic was carried out. Testing for SCA types 1, 2, 3, 6, 7, and 8 as well as Friedreich's Ataxia and the fragile X premutation tremor/ataxia syndrome was performed on at least one member of each family. -- A total of 69 patients in 60 families presented with an adult onset progressive ataxic disorder. Twenty-one (35.0%) of the families had a pedigree suggestive of an autosomal dominant disorder. An apparent autosomal recessive pattern of inheritance was present in 3.3%. A positive but undefined family history was noted in 15.0%. Sporadic disease appeared to be present in 43.3%. Two patients (3.3%) were adopted. The most commonly found mutation in the autosomal dominant families was SCA3 (5 families - 23.8%). This was followed by SCA2 (3 families - 14.3%) and SCA6 (2 families - 9.5%). The SCA1 and SCA8 expansions were only identified in 1 family (4.8%) each. Although the family history was suggestive of a dominant disorder, one patient was found to have Friedreich's Ataxia. A patient in one of the two autosomal recessive appearing families tested positive for Friedreich’s ataxia. One individual (11.1 %) with a positive but undefined family history tested positive for SCA6. A single sporadic patient had a positive test which was SCA3. Neither of the two adopted patients had a positive test. DRPLA testing was performed on 21 of the families and no positive tests were found. No expansions of the fragile X mental retardation gene were found. -- A positive test result was found in 61.9% of autosomal dominant pedigrees, 50% of autosomal recessive pedigrees, and 11.1% of patients with positive but undefined family histories. Of the sporadic patients only 1 of 26 (3.8%) was found to have a positive genetic test. -- SCA3 is the most common mutation found in our clinic patients followed by SCA2 and SCA6. A positive test result is uncommon in individuals without any family history of a similar disorder. The fragile X tremor/ataxia syndrome was not identified in our SCA patient population.

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