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HelpTest ID: HAD Huntington Disease, Molecular Analysis, Varies
Reporting Name
Huntington Disease AnalysisUseful For
Molecular confirmation of clinically suspected cases of Huntington disease (HD)
Presymptomatic testing for individuals with a family history of HD and a documented expansion in the HTT gene
Clinical Information
Huntington disease (HD) is an autosomal dominant progressive neurodegenerative disorder associated with progressive involuntary and voluntary motor disturbances (chorea, dystonia, dysarthria, gait disturbance, postural instability, oculomotor dysfunction), cognitive decline leading to dementia, and a wide range of neuropsychiatric problems including apathy, depression, anxiety, and other behavioral disturbances. Onset occurs typically in the late 30's to early 40's, but rare individuals may present with juvenile onset.
Huntington disease is caused by a CAG (cystine, adenine, guanine) repeat expansion in the HTT gene and is associated with genetic anticipation, whereby repeat sizes may expand with transmission to subsequent generations. Correlation exists between the size of the CAG repeat and disease onset and severity, with larger alleles associated with earlier onset and more severe disease presentation. Full penetrance HTT expansions are greater than 39 repeats, while normal alleles are less than 27 repeats. Allele sizes between 36 and 39 repeats are associated with reduced penetrance of clinical HD symptoms. Intermediate alleles (27-35 repeats) are not typically associated with clinical symptoms; however, both reduced penetrance and intermediate alleles may expand into the full penetrance range with transmission to offspring.
Identification of a disease-associated repeat expansion has important implications for family members. Testing of at-risk individuals is possible, but it is recommended that predictive testing be performed in conjunction with appropriate pre- and post-test counseling. Additionally, presymptomatic testing of minors is strongly discouraged.
Interpretation
The provided interpretive report includes an overview of the findings as well as the associated clinical significance.
Report Available
7 to 11 days upon receipt of sufficient clinical information for testingDay(s) Performed
Wednesday
Clinical Reference
1. Bean L, 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(12):e2. doi:10.1038/gim.2014.146
2. Testa C, Jankovic J. Huntington disease: A quarter century of progress since the gene discovery. J Neurol Sci. 2019:396:52-68. doi:10.1016/j.jns.2018.09.022
Method Name
Polymerase Chain Reaction (PCR)
Specimen Type
VariesNecessary Information
Molecular Genetics: Neurology Patient Information or a recent clinical note is required. Testing cannot proceed without this information.
Specimen Required
Patient Preparation: A previous bone marrow transplant from an allogenic donor will interfere with testing. For instructions for testing patients who have received a bone marrow transplant, call 800-533-1710.
Specimen Type: Whole blood
Container/Tube: Lavender top (EDTA) or yellow top (ACD)
Specimen Volume: 3 mL
Collection Instructions:
1. Invert several times to mix blood.
2. Send whole blood specimen in original tube. Do not aliquot.
Additional Information:
1. Specimens are preferred to be received within 4 days of collection. Extraction will be attempted for specimens received after 4 days, and DNA yield will be evaluated to determine if testing may proceed.
2. To ensure minimum volume and concentration of DNA is met, the preferred volume of blood must be submitted. Testing may be canceled if DNA requirements are inadequate.
Specimen Minimum Volume
See Specimen Required
Specimen Stability Information
| Specimen Type | Temperature | Time |
|---|---|---|
| Varies | Ambient (preferred) | |
| Frozen | ||
| Refrigerated | ||
Special Instructions
Reference Values
Normal alleles: <27 CAG repeats
Intermediate alleles: 27-35 CAG repeats
Reduced penetrance: 36-39 CAG repeats
Full penetrance: >39 CAG repeats
An interpretive report will be provided.
Test Classification
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.CPT Code Information
81271-HTT (huntingtin) (eg, Huntington disease) gene analysis; evaluation to detect abnormal (eg, expanded) alleles
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| HAD | Huntington Disease Analysis | 21763-8 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| 52885 | Result Summary | 50397-9 |
| 52886 | Result | 53782-9 |
| 52887 | Interpretation | 69047-9 |
| 52888 | Reason for Referral | 42349-1 |
| 52889 | Specimen | 31208-2 |
| 52890 | Source | 31208-2 |
| 52891 | Released By | 18771-6 |
Forms
1. Molecular Genetics: Neurology Patient Information is required.
2. New York Clients-Informed consent is required. Document on the request form or electronic order that a copy is on file. The following documents are available:
-Informed Consent for Genetic Testing (T576)
-Informed Consent for Genetic Testing-Spanish (T826)
3. If not ordering electronically, complete, print, and send a Neurology Specialty Testing Client Test Request (T732) with the specimen.
mml-Movement-Disorders