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).
- Patient Preparation
- Lavender (EDTA), pink (K2EDTA), or yellow (ACD Solution A or B).
- Specimen Preparation
- Transport 3 mL whole blood. (Min: 1 mL)
- Storage/Transport Temperature
- Unacceptable Conditions
- Specimens collected in sodium heparin or lithium heparin tubes.
- Ambient: 72 hours; Refrigerated: 2 weeks; Frozen: 1 month
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.
Counseling and informed consent are recommended for genetic testing. Consent forms are available online.
|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