The impact of molecular genetics in the unequivocal diagnosis of certain neurological disorders is unprecedented. The appropriate assignment of the genetic basis of a movement disorder in a symptomatic patient provides not only closure in the clinical diagnosis, but also provides crucial genetic information for the patient's immediate and extended family.
The dynamic mutations causing virtually all cases of Huntington's disease (HD), Spinocerebellar ataxia type 1 (SCA 1), Spinocerebellar ataxia type 2 (SCA 2), Spinocerebellar ataxia type 3 (SCA 3) also known as Machdo-Joseph Disease (MJD), Spinocerebellar ataxia type 6 (SCA 6), Spinocerebellar ataxia type 7 (SCA 7), and Dentatorubral pallidoluysian atrophy (DRPLA) are now all amenable to direct diagnostic testing using a PCR assay on DNA isolated from a peripheral blood sample.
The clinical diagnosis of these disorders is confounded by marked phenotypic heterogeneity in presentation especially in the dominantly inherited ataxias (SCA 1, SCA 2, SCA 3, SCA 6, SCA 7). The accuracy and cost-effectiveness of DNA testing for individuals having any one of these disorders is unparalleled by any other clinical diagnostic assay.
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