Test Id : HAD
Huntington Disease, Molecular Analysis, Varies
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
Method Name
A short description of the method used to perform the test
Polymerase Chain Reaction (PCR)
NY State Available
Indicates the status of NY State approval and if the test is orderable for NY State clients.
Reporting Name
Lists a shorter or abbreviated version of the Published Name for a test
Aliases
Lists additional common names for a test, as an aid in searching
HD
Huntington Chorea
Chorea
HTT
Specimen Type
Describes the specimen type validated for testing
Varies
Necessary Information
Molecular Genetics: Neurology Patient Information or a recent clinical note is required. Testing cannot proceed without this information.
Specimen Required
Defines the optimal specimen required to perform the test and the preferred volume to complete testing
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.
Special Instructions
Library of PDFs including pertinent information and forms related to the test
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.
Specimen Minimum Volume
Defines the amount of sample necessary to provide a clinically relevant result as determined by the testing laboratory. The minimum volume is sufficient for one attempt at testing.
See Specimen Required
Reject Due To
Identifies specimen types and conditions that may cause the specimen to be rejected
Specimen Stability Information
Provides a description of the temperatures required to transport a specimen to the performing laboratory, alternate acceptable temperatures are also included
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Varies | Ambient (preferred) | ||
| Refrigerated | |||
| Frozen | |||
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
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 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.
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.
Interpretation
Provides information to assist in interpretation of the test results
The provided interpretive report includes an overview of the findings as well as the associated clinical significance.
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.
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.
Clinical Reference
Recommendations for in-depth reading of a clinical nature
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 Description
Describes how the test is performed and provides a method-specific reference
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)
PDF Report
Indicates whether the report includes an additional document with charts, images or other enriched information
Day(s) Performed
Outlines the days the test is performed. This field reflects the day that the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time before the test is performed. Some tests are listed as continuously performed, which means that assays are performed multiple times during the day.
Wednesday
Report Available
The interval of time (receipt of sample at Mayo Clinic Laboratories to results available) taking into account standard setup days and weekends. The first day is the time that it typically takes for a result to be available. The last day is the time it might take, accounting for any necessary repeated testing.
Specimen Retention Time
Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded
Performing Laboratory Location
Indicates the location of the laboratory that performs the test
Fees :
Several factors determine the fee charged to perform a test. Contact your U.S. or International Regional Manager for information about establishing a fee schedule or to learn more about resources to optimize test selection.
- Authorized users can sign in to Test Prices for detailed fee information.
- Clients without access to Test Prices can contact Customer Service 24 hours a day, seven days a week.
- Prospective clients should contact their account representative. For assistance, contact Customer Service.
Test Classification
Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR) product.
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
Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Clinic Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
CPT codes are provided by the performing laboratory.
CPT codes are provided by the performing laboratory.
81271-HTT (huntingtin) (eg, Huntington disease) gene analysis; evaluation to detect abnormal (eg, expanded) alleles
LOINC® Information
Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the order and results codes of this test. LOINC values are provided by the performing laboratory.
| Test Id | Test Order Name | Order LOINC Value |
|---|---|---|
| HAD | Huntington Disease Analysis | 21763-8 |
| Result Id | Test Result Name |
Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
|
|---|---|---|
| 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 |