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HelpTest Code HEXAZ Tay-Sachs Disease, HEXA Gene, Full Gene Analysis, Varies
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
Special Instructions
Method Name
Polymerase Chain Reaction (PCR) Amplification/DNA Sequencing
Reporting Name
HEXA Gene, Full Gene AnalysisSpecimen Type
VariesShipping 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 800-533-1710 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 | Special Container |
|---|---|---|---|
| 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.
Cautions
A small percentage of individuals who are carriers or have a diagnosis of Tay-Sachs disease (TSD) may have a mutation that is not identified by this method (eg, large genomic deletions, promoter mutations). The absence of a mutation(s), therefore, does not eliminate the possibility of positive carrier status or the diagnosis of TSD. For carrier testing, it is important to first document the presence of a HEXA gene mutation in an affected family member.
In some cases, DNA alterations of undetermined significance may be identified.
Rare polymorphisms exist that could lead to false-negative or false-positive results. If results obtained do not match the clinical findings, additional testing should be considered.
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.
Day(s) Performed
Performed weekly
Report Available
14 to 20 daysPerforming Laboratory
Mayo Clinic Laboratories in Rochester
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
81406
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| HEXAZ | HEXA Gene, Full Gene Analysis | 76033-0 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| 53943 | Result Summary | 50397-9 |
| 53944 | Result | 82939-0 |
| 53945 | Interpretation | 69047-9 |
| 53946 | Additional Information | 48767-8 |
| 53947 | Specimen | 31208-2 |
| 53948 | Source | 31208-2 |
| 53949 | Released By | 18771-6 |
Testing Algorithm
Tay-Sachs and Related Disorders Diagnostic Testing Algorithm
Forms
1. 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.
2. Molecular Genetics: Biochemical Disorders Patient Information (T527) in Special Instructions.
3. If not ordering electronically, complete, print, and send a Biochemical Genetics Test Request (T798) with the specimen.