Huntington Disease DNA Screen

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General Information

Lab Name
Huntington Disease
Lab Code
HDTEST
Epic Ordering
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:

  • Patient information is available on the UWMC's HDSA Center of Excellence Website (https://depts.washington.edu/hdcoe/).
  • A printable patient brochure "Testing for Huntington's Disease: Making an Informed Choice" is available at: UW Department of Neurology website.
  • For current guidelines and protocols on genetic testing for Huntington disease, please refer to the American College of Medical Genetics website 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.

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
Forms & Requisitions

Genetics Requisition

Synonyms
Huntington's Chorea
Components

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).

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
Guidelines

Ordering & Collection

Specimen Type
Blood, amniocytes, chorionic villus tissue or cultured cells.
Collection

BLOOD:

  • Adult: 5 mL LAVENDER TOP tube
  • Child: 2 mL LAVENDER TOP tube
  • Also acceptable: YELLOW TOP (ACD) tube
  • Unacceptable: Heparin green top tubes

AMNIOCYTES or CULTURED CHORIONIC VILLUS CELLS:

  • Two (2) T23 or One (1) T75 flask (minimum 1-T25 flask)

CHORIONIC VILLIS and/or TISSUE:

  • In sterile tube or culture media, at least 5 mg tissue.

Prenatal testing requires concomitant testing for maternal cell contamination (see Online Test Guide, Lab Mnemonic Maternal Cell Contamination [MCC] for ordering and specimen requirements)

Forms & Requisitions

Genetics Requisition

Handling Instructions

Blood: Refrigerate whole blood up to 1 week.

Amniocytes & cultured CVS cells: hold flasks at room temperature.

Chorionic villi &/or tissue: hold at room temperature.

Outside Laboratories: Ship whole blood at ambient temperature for receipt within 1 week of specimen collection.- For cultured amniocytes or chorionic villus cells and for CVS or other tissue, transport and store at room temperature within 24 hours of obtaining CV or removing cultured cells from incubator.

Quantity
requested: Entire specimen
minimum: Blood: 1 mL. Amniocytes, cultured chorionic villus cells, chorionic villi or tissue: as above.

Processing

Processing

Please notify genetics about amniocytes, cultured chorionic villus cells, chorionic villi or tissue.

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: 206-598–0304
Lab email: genelab@uw.edu

Tel (EXOME only): 206-543-0459

Manager

Rebecca Gaulin, rgaulin@uw.edu

Genetic Counselors

Angela Jacobson, MS, LGC agibson@uw.edu
Sarah Paolucci, MA, MS, LGC, spaolucc@uw.edu
Jenna Huey, MS, LGC, jlhuey@uw.edu
Sandra Coe, MS,LGC, scoe20@uw.edu
Dru Leistritz, MS, LGC, dru2@uw.edu (EXOME testing only)

Variant Review Scientist

Ankita Jhuraney, PhD

Faculty

Colin C. Pritchard, MD, PhD
Brian H. Shirts, MD, PhD
Christina Lockwood, PhD, DABCC
Stephen Salipante, MD, PhD
Eric Konnick, MD, MS
Niklas Krumm, MD,PhD
Vera Paulson, MD, PhD
Jillian Buchan, PhD, FACMG

Frequency
Performed weekly. Results within 2 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