American Board of Psychiatry and Neurology (ABPN) Practice Exam

What is the gold standard test for diagnosing Huntington's disease?

1. Karyotype of chromosomes

2. Serum ceruloplasmin

3. Serum polymerase chain reaction (PCR)

4. Cerebrospinal fluid assay for 14-3-3 protein

The correct answer is: Serum polymerase chain reaction (PCR)

The gold standard test for diagnosing Huntington's disease is based on genetic testing, specifically looking for the CAG repeat expansion in the HTT gene on chromosome 4, which is responsible for the disorder. While PCR (polymerase chain reaction) techniques can be used to amplify specific sequences of DNA, the definitive diagnosis is achieved through genetic testing that quantifies the number of CAG repeats. Individuals with Huntington's disease typically have 36 or more repeats, while individuals without the disease usually have fewer than 36 repeats. This test is important because it allows for pre-symptomatic testing, identification of at-risk individuals, and confirmation of a diagnosis in symptomatic individuals. Knowledge of CAG repeat length can also provide prognostic information regarding the age of onset and progression of the disease. The other tests mentioned are not pertinent to diagnosing Huntington's disease. Karyotype analysis is generally utilized for identifying chromosomal abnormalities, serum ceruloplasmin is associated with Wilson's disease, and a cerebrospinal fluid assay for 14-3-3 protein is related to diagnosing creutzfeldt-jakob disease and other prion diseases, not Huntington's disease. Thus, the identification of the CAG repeat in the HTT gene through genetic testing remains