Background: Huntington disease (HD) is a rare, progressive, and fatal autosomal dominant neurodegenerative disorder, typically of adult onset.

Methods: We reviewed the literature concerning the molecular diagnosis of HD.

Results: The discovery of the genetic etiology of HD, a trinucleotide expansion mutation on chromosome 4p, has led to the development of increasingly reliable and valid diagnostic tests that can be applied to symptomatic patients, individuals at risk for HD but currently asymptomatic, fetuses, and embryos. However, the unstable nature of the HD mutation, the lack of effective treatments for HD, the mid-adulthood age of disease onset, and the existence of disorders with the same clinical presentation but different etiology all complicates diagnostic testing.

Conclusion: Conscientious laboratory work, knowledgeable interpretation of genetic test results, and the availability of pre- and posttest counseling are essential components of HD diagnosis.