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Epic Code LAB848 Huntington Disease, Molecular Analysis, Varies

Important Note

Presymptomatic testing requires documented informed consent and both neurological and psychological evaluation. Please contact Genetic Services for more information (616-391-2700).

Order as Reference Miscellaneous #LAB848; indicate complete test name when ordering.

Additional Codes

Mayo Code: HAD

 

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Useful 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

Specimen Type

Varies


Shipping Instructions


 



Necessary 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 Special Container
Varies Ambient (preferred)
  Frozen 
  Refrigerated 

Reject Due To

All specimens will be evaluated by Mayo Clinic Laboratories for test suitability.

Day(s) Performed

Wednesday

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.

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.

Cautions

For predictive testing, it is important to first document the presence of a CAG-repeat amplification in the HTT gene in an affected family member to confirm that molecular expansion is the underlying mechanism of disease in the family.

 

It is strongly recommended that patients undergoing predictive testing receive genetic counseling both prior to testing and after results are available.

 

Predictive testing of an asymptomatic child is not recommended.

 

Test results should be interpreted in the context of clinical findings, family history, and other laboratory data. Errors in the interpretation of results may occur if the information given is inaccurate or incomplete.

Interpretation

The provided interpretive report includes an overview of the findings as well as the associated clinical significance.

Reporting Name

Huntington Disease Analysis

Method Name

Polymerase Chain Reaction (PCR)

Method Description

A polymerase chain reaction-based assay is utilized to detect expansions of a CAG trinucleotide tract in exon 1 of the HTT gene.(Unpublished Mayo method)

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

Report Available

7 to 11 days upon receipt of sufficient clinical information for testing

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.

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

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.