Interpretive Handbook

Test 61622 :
Huntington Disease, Molecular Analysis

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Huntington disease (HD) is an autosomal dominant progressive neurodegenerative disorder caused by a CAG repeat expansion in the HTT gene. HD is associated with cognitive impairment leading to dementia and a wide range of neuropsychiatric problems including apathy, depression, anxiety, and other behavioral disturbances. Additionally, affected individuals typically develop extrapyramidal symptoms (eg, dystonia, dysarthria, chorea, gait disturbance, postural instability, oculomotor dysfunction).

Useful For Suggests clinical disorders or settings where the test may be helpful

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

Interpretation Provides information to assist in interpretation of the test results

An interpretive report will be provided.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

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.


We strongly recommend 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 our interpretation of results may occur if information given is inaccurate or incomplete.


A previous bone marrow transplant from an allogenic donor will interfere with testing. Call Mayo Medical Laboratories at 800-533-1710 for instructions for testing patients who have received a bone marrow transplant.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

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 References Provides recommendations for further in-depth reading of a clinical nature

1. American College of Medical Genetics/American Society of Human Genetics Huntington Disease Genetic Testing Working Group: Laboratory guidelines for Huntington disease genetic testing. Am J Hum Genet 1998;62:1243-1247

2. Potter NT, Spector EB, Prior TW: Technical standards and guidelines for Huntington disease testing. Genet Med 2004;6:61-65