currently commercially available for 14 SCA types, including SCA1. In cases where SCAs are not present in family history or where family history is unavailable, testing for the 4 most common SCAs will return positive results for 50% of suspected SCA cases. Individuals who are at risk of inheriting SCA1 but are currently presymptomatic can also be screened with molecular genetic testing. Genetic testing Genetic testing is the only definitive way to differentiate between spinocerebellar ataxia types because of the similarity between clinical characteristics of these diseases and the large variance between cases. Genetic testing is available for many SCA types, including the relatively common types SCA1, 2, 3, 6, and 7; and the less common SCA8, 10, 12, 14, and 17. However, genetic testing is high in cost and has a low diagnostic yield, with positive diagnoses being found in only 24% of tests ordered by a subspecialist and 10% overall. Genetic testing can be administered at various stages of disease progression. When genetic testing is administered after the onset of symptoms, the test is said to be diagnostic; in adults prior to onset of symptoms it is presymptomatic, and the test can be performed for prenatal or preimplantation diagnoses. The European Molecular Quality Genetics Network (EMQN) recommends criteria for each type, which must be met before testing can begin. The EQMN recommends that labs receive a written clinical evaluation of symptoms by a neurologist and a disclosure of family history, or lack of history, before initiating diagnostic genetic testing. Because no preventative or curative treatments are known for SCAs, genetic testing for at risk individuals is not recommended for all cases, and is typically issued on an individual basis. Presymptomatic, prenatal, and preimplantation testing are typically requested through a genetic counsellor and require existing family history and documentation of informed consent of the consultand. Spinocerebellar ataxia type 1 was one of the first late onset diseases for which presymptomatic testing was demonstrated effective and predictive; prior to the development of testing for SCA1, Huntington's disease was the only similar disease for which presymptomatic testing was available. Molecular genetic testing of SCAs must be able to differentiate samples with the pathogenic allele from those without and be able to accurately measure the number of repeats in repeat expansion disorders. Capillary electrophoresis (CE) is one method that has met these criteria and is recommended by the EMQN. Another method that