Ordering Recommendation

Use to confirm common pathogenic and pseudodeficiency HEXA variants in individuals of Ashkenazi Jewish and French-Canadian descent with abnormal levels of HexA enzyme. For initial testing of Tay-Sachs disease, refer to Hexosaminidase A percent and Total Hexosaminidase in Leukocytes (2008125).

Mnemonic
HEXA
Methodology

Polymerase Chain Reaction/Fluorescence Monitoring

Performed

Tue, Fri

Reported

5-10 days

New York DOH Approval Status
This test is New York DOH approved.
Specimen Required
Patient Preparation
Collect

Lavender (EDTA), pink (K2EDTA), or yellow (ACD Solution A or B).

Specimen Preparation

Transport 3 mL whole blood. (Min: 1 mL)

Storage/Transport Temperature

Refrigerated.

Unacceptable Conditions

Specimens collected in sodium heparin or lithium heparin tubes.

Remarks
Stability

Ambient: 72 hours; Refrigerated: 2 weeks; Frozen: 1 month

Reference Interval

By report

Interpretive Data

Background information for Tay-Sachs Disease (HEXA), 7 Variants:
Characteristics:
Tay-Sachs disease is a lysosomal storage disease that, in the most severe childhood-onset form, leads to a loss of motor skills beginning at 3- to 6-months of age and progresses to blindness, seizures, total incapacitation, and eventual death by 4 years of age. Adult-onset Tay-Sachs is a milder disease with later onset and slower progression. In adults, Tay-Sachs disease is associated with variable neurological findings, including progressive dystonia, spinocerebellar degeneration, motor neuron disease, and bipolar form of psychosis.
Incidence:
1 in 3000 Ashkenazi Jewish individuals.
Inheritance:
Autosomal recessive.
Cause:
HEXA gene pathogenic variants.
Variants Tested:
Four pathogenic 7.6kb del, c.1073+1G>A, p.Y427Ifs (c.1274_1277dup TATC), c.1421+1G>C; one mild pathogenic p.G269S (c.805G>A); and two pseudodeficiency alleles p.R247W (c.739C>T) and p.R249W (c.745C>T).
Clinical Sensitivity:
94 percent in Ashkenazi Jewish individuals, 59 percent in other ethnicities.
Methodology:
Polymerase chain reaction (PCR) and fluorescence monitoring.
Analytical Sensitivity and Specificity:
Greater than 99 percent.
Limitations:
HEXA variants other than those specified above will not be detected. Diagnostic errors can occur due to rare sequence variations.

Compliance Category

Laboratory Developed Test (LDT)

Note
Hotline History
N/A
CPT Codes

81255

Components
Component Test Code* Component Chart Name LOINC
0051430 Tay-Sachs Disease (HEXA), Allele 1 38900-7
0051431 Tay-Sachs Disease (HEXA), Allele 2 38900-7
0051432 Tay-Sachs Disease (HEXA), Interpretation 51773-0
2001315 Tay-Sachs Disease (HEXA), Specimen 31208-2
* Component test codes cannot be used to order tests. The information provided here is not sufficient for interface builds; for a complete test mix, please click the sidebar link to access the Interface Map.
Aliases
  • Hexosaminidase A
  • Hexosaminidase A Deficiency DNA assay
  • TSD molecular assay
Tay-Sachs Disease (HEXA), 7 Variants