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Test ID: HEXAZ Tay-Sachs Disease, HEXA Gene, Full Gene Analysis

Useful For

Second-tier test for confirming a biochemical diagnosis of Tay-Sachs disease (TSD)

 

Carrier testing of individuals with a family history of TSD but an affected individual is not available for testing or disease-causing mutations have not been identified

 

Testing individuals with enzyme activity consistent with carrier status but negative molecular testing by a panel of common mutations

Method Name

Polymerase Chain Reaction (PCR) Amplification/DNA Sequencing

Reporting Name

HEXA Gene, Full Gene Analysis

Specimen Type

Varies


Shipping Instructions


Specimen preferred to arrive within 96 hours of draw.



Specimen Required


Patient Preparation: A previous bone marrow transplant from an allogenic donor will interfere with testing. Call Mayo Medical Laboratories for instructions for testing patients who have received a bone marrow transplant.

Specimen Type: Whole blood

Container/Tube:

Preferred: Lavender top (EDTA) or yellow top (ACD)

Acceptable: Any anticoagulant

Specimen Volume: 3 mL

Collection Instructions:

1. Invert several times to mix blood.

2. Send specimen in original tube.


Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time
Varies Ambient (preferred)
  Frozen 
  Refrigerated 

Clinical Information

Tay-Sachs disease (TSD) is an inherited lysosomal storage disease caused by a deficiency of the enzyme beta-hexosaminidase A. It is characterized by accumulation of GM2 gangliosides in cells of the brain and central nervous system. The HEXA gene encodes the alpha subunit of beta-hexosaminidase A and mutations in this gene cause TSD. TSD occurs in approximately 1 in 200,000 live births with a carrier frequency of 1 in 250 to 1 in 300 in the general population. The carrier frequency for this disease in individuals of Ashkenazi Jewish ancestry is 1 in 31.

 

The classic form of TSD becomes apparent in infancy when mild motor weakness is noted along with impaired visual acuity and the presence of a "startle response." Other manifestations include progressive neurodegeneration, seizures, and blindness, leading to total incapacitation and death. The subacute and adult-onset types of TSD are characterized by later ages of onset and a broad spectrum of disease symptoms and severity.

 

TSD is inherited in an autosomal recessive manner. Several common mutations in the HEXA gene account for 92% of disease-causing mutations in the Ashkenazi Jewish population. Testing for these mutations is available as a panel, TSDP / Tay-Sachs Disease, Mutation Analysis, HEXA. In non-Ashkenazi Jewish individuals, the detection rate for the common mutations is significantly decreased. Sequencing of the entire HEXA gene detects less common disease-causing mutations.

 

The recommended first-tier test for TSD carrier screening and diagnosis in all patients is a biochemical test that measures hexosaminidase A activity in white blood cells, NAGW / Hexosaminidase A and Total Hexosaminidase, Leukocytes.

Reference Values

An interpretive report will be provided.

Interpretation

All detected alterations are evaluated according to American College of Medical Genetics recommendations.(1) Variants are classified based on known, predicted, or possible pathogenicity and reported with interpretive comments detailing their potential or known significance.

Clinical Reference

1. Richards S, Aziz N, Bale S, et al: Standards and guidelines for the interpretation of sequence variants: a joint consensus recommendation of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology. Genet Med 2015 May;17(5):405-424

2. Gravel RA, Kaback MM, Proia RL, et al: The GM2 gangliosidosis. In The Metabolic and Molecular Bases of Inherited Disease. Eigth edition. Edited by CR Scriver, AL Beaudet, WS Sly, et al. New York, McGraw-Hill Book Company, 2001, pp 3827-3876

3. ACOG Committee on Genetics: ACOG Committee Opinion #318; Screening for Tay-Sachs disease. Obstet Gynecol 2005;106(4):893-894

Day(s) and Time(s) Performed

Performed weekly, varies

Analytic Time

14 days

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information

81406-HEXA (hexosaminidase A, alpha polypeptide) (eg, Tay-Sachs disease), full gene sequence

LOINC Code Information

Test ID Test Order Name Order LOINC Value
HEXAZ HEXA Gene, Full Gene Analysis In Process

 

Result ID Test Result Name Result LOINC Value
53943 Result Summary 50397-9
53944 Result In Process
53945 Interpretation In Process
53946 Additional Information 48767-8
53947 Specimen 31208-2
53948 Source 31208-2
53949 Released By No LOINC Needed

Testing Algorithm

The following algorithms are available in Special Instructions:     

Tay-Sachs Disease Carrier Testing Protocol

Tay-Sachs and Related Disorders Diagnostic Testing Algorithm

Forms

1. Molecular Genetics: Biochemical Disorders Patient Information (T527) in Special Instructions

2. New York Clients-Informed consent is required. Please document on the request form or electronic order that a copy is on file. An Informed Consent for Genetic Testing (T576) is available in Special Instructions.

Mayo Medical Laboratories | Genetics and Pharmacogenomics Catalog Additional Information:

mml-inherited-molecular