Laboratory Test Guide

Huntington Disease DNA Screen

General Information

Lab Name

Huntington Disease

Lab Code

HDTEST

Epic Name

HUNTINGTON DISEASE

Description

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:

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.

References

  • Bean L and Bayrak-Toydemir P. American College of Medical Genetics and Genomics Standards and Guidelines for Clinical Genetics Laboratories, 2014 edition: technical standards and guidelines for Huntington disease. Genet Med 2014, 16:e2. 25356969
  • Kremer B, et al. A worldwide study of the Huntington's disease mutation. The sensitivity and specificity of measuring CAG repeats. N Engl J Med 1994, 330:1401-6. 8159192
  • Mahbubul H, Hayden MR. Huntington Disease. In: GeneReviews at GeneTests: Medical Genetics Information Resource (database online). Copyright, University of Washington, Seattle. Available at https://www.ncbi.nlm.nih.gov/books/NBK1305/
  • Margolis RL and Ross CA. Diagnosis of Huntington disease. Clin Chem 2003, 49:1726-32. 14500613

Synonyms

Huntington's Chorea

Components

Code Name
HDA1 HD Allele 1
HDA2 HD Allele 2
HDCI HD Clinical Information
HDIN HD Interpretation
HDMTH HD Methods

Interpretation

Method

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.

Reference Range

See individual components

Ref. Range Notes

Expansion of a CAG repeat in the HTT gene is present in about 98% of Huntington disease cases and is essentially absent in normal controls. Alleles with 40 or more CAG repeats are abnormal, alleles with 36 to 39 repeats are abnormal with reduced penetrance, alleles with 27 to 35 repeats are normal but potentially mutable upon transmission to offspring, and alleles with 26 or fewer repeats are normal (Bean et al 2014).

Guidelines

Ordering & Collection

Specimen Type

Blood/Extracted DNA from the whole blood sample. For any other sample type, including prenatal testing: contact Genetics laboratory (206)598-7021 for approval.

Collection

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

Forms & Requisitions

Genetics Requisition

Handling Instructions

  • 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.

Quantity

requested: Entire specimen
minimum: Blood: 1 mL. If volume is less than 1mL, do not cancel. Send to Genetics lab.

Processing

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.

Performance

LIS Dept Code

Genetics (GEN)

Performing Location(s)

UW-MT Genetics

Attention: Genetics Lab
Clinical lab, Room NW220
University of Washington Medical Center
1959 NE Pacific Street
Seattle, WA 98195

Tel: 206-598–6429 M–F (7:30 AM–4:00 PM)
Fax: 206-616-4584
Lab email: cgateam@uw.edu

Tel (EXOME only): 206-543-0459

Faculty
Jillian Buchan, PhD, FACMG
Runjun Kumar, MD, PhD
Regina Kwon, MD, MPH
Christina Lockwood, PhD, DABCC, DABMGG
Abbye McEwen, MD, PhD
Colin Pritchard, MD, PhD
Vera Paulson, MD, PhD
Eric Konnick, MD, MS
He Fang, PhD

Frequency

Performed weekly. Results within 2-3 weeks.

Available STAT?

No

Billing & Coding

CPT codes

81271

Billing Comments

For pricing information, contact Client Support Services 206-520-4600 or 800-713-5198.

LOINC

53783-7

Interfaced Order Code

UOW850