Huntington Disease DNA Screen

Huntington disease (HD) is an autosomal dominant genetic disorder. Expansion of a CAG trinucleotide repeat in the HTT gene occurs in 98-99% of Huntington disease cases, and is essentially absent in normal controls (Kremer et al. 1994). The number of CAG repeats does not reliably predict the age of onset, the rate of disease progression, or the severity of symptoms for an individual patient.

Indications for testing include:

• Confirmation of a clinical diagnosis of Huntington disease
• Presymptomatic testing for Huntington disease

Restrictions/exclusions from testing include:

• Presymptomatic testing of minors (< age 18) (including evaluations for adoptions)
• Anonymous testing

For additional information:

• Patient information is available on the UWMC's HDSA Center of Excellence Website (https://depts.washington.edu/hdcoe/).
• For current guidelines and protocols on genetic testing for Huntington disease, please refer to the American College of Medical Genetics or see Bean et al. 2014 edition.

Genetic Counseling can be useful to patients and families considering genetic testing. The laboratory can provide referrals to genetics clinics.

If confidentiality is an issue, please call Genetics Lab 206-598-6429. Anonymous testing is NOT performed. Testing on children requires prior approval by Genetics Lab.

Polymerase Chain Reaction (PCR)/Capillary Electrophoresis

The region of the HTT gene containing the CAG repeat is amplified and its size measured by capillary electrophoresis calibrated against HTT-specific cloned size standards. Precision (1 SD) is better than 0.5 CAG repeat units. This test was developed and its performance characteristics determined by the Department of Laboratory Medicine at the University of Washington.

Acceptable:

1. Whole blood: 5 mL lavender top (EDTA) tube or yellow (ACD) top tube or 2 mL microtainer lavender top tube
   
   
2. Extracted DNA from approved sample type (blood): 500 ng (concentration >10 ng/uL)

Unacceptable: Heparin green top tubes, buccal swab

• Whole blood samples in EDTA or ACD: Refrigerate upon receipt.
  
  
• Extracted DNA: Refrigerate upon receipt or keep frozen if the sample was received frozen.

Call Genetics lab for any questions at (206)598-7021.

For clients outside of UW, please include any relevant clinical history. Testing on pediatric patients is only available if individuals are symptomatic. Presymptomatic testing on pediatric patients is not available.

If fetal tissue (cultured amniocytes or chorionic villi) was received for prenatal testing, consultation with the laboratory is required. Please notify the Genetics lab about prenatal studies via email at geneticshelp@uw.edu or call 206-598-7021.