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).
Polymerase Chain Reaction/Fluorescence Monitoring
Lavender (EDTA), pink (K2EDTA), or yellow (ACD Solution A or B).
Transport 3 mL whole blood. (Min: 1 mL)
Specimens collected in sodium heparin or lithium heparin tubes.
Ambient: 72 hours; Refrigerated: 2 weeks; Frozen: 1 month
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.
Laboratory Developed Test (LDT)
|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|
- Hexosaminidase A
- Hexosaminidase A Deficiency DNA assay
- TSD molecular assay