Tay-Sachs Disease Detection: Carrier Screening, Prenatal, and Newborn Testing

Early detection of Tay-Sachs disease (TSD) enables reproductive planning and, for affected infants, prompt supportive care. Multiple complementary methods exist.

1. Carrier Screening (Preconception / Prenatal)

• Enzyme assay: Serum/leukocyte HexA activity (fluorometric). Heat-inactivation step distinguishes HexA (heat-labile) from HexB (heat-stable). Limitation: Pseudodeficiency alleles cause false-positive carrier results.
• Molecular (DNA) testing: Targeted mutation panel (ethnic-specific) or full HEXA sequencing. Detects >95% mutations in Ashkenazi Jews; lower sensitivity pan-ethnic unless sequenced.
• Combined approach (recommended): Enzyme + molecular → resolves pseudodeficiency, maximizes detection.

2. Prenatal Diagnosis (If Both Parents Carriers)

• Chorionic Villus Sampling (CVS): 10–13 weeks; HexA activity on direct prep + culture; molecular confirmation.
• Amniocentesis: 15–20 weeks; amniocyte culture for HexA activity + DNA.
• Preimplantation Genetic Testing (PGT-M): IVF + embryo biopsy; select unaffected embryos.

3. Newborn / Infant Diagnosis (Symptomatic)

• Enzyme assay: Leukocyte HexA activity (gold standard for diagnosis).
• Molecular: HEXA sequencing (confirms, predicts phenotype).
• Ophthalmologic: Cherry-red spot (supportive, not diagnostic alone).
• Biochemical: Urinary G2 ganglioside (research).

4. Population Screening Programs

• Ashkenazi Jewish: Community-based carrier screening since 1970s → >90% reduction in TSD births.
• French Canadian, Cajun: Targeted programs.
• General population: ACMG recommends pan-ethnic carrier screening for TSD among other conditions.

Interpretation Pitfalls

• Pseudodeficiency allele (R247W/R249W): Low serum HexA but normal leukocyte activity vs. natural substrate. Molecular testing clarifies.
• Leukocyte vs. serum: Leukocyte preferred (less interference).
• Pregnancy: Serum HexA increases (placental HexA); use leukocyte or adjust cutoffs.

Follow-Up for Carrier Couples

• Genetic counseling: recurrence risk, reproductive options, prenatal diagnosis timing.
• Psychosocial support.
• Cascade testing of relatives.

Combined enzyme + DNA testing provides the most accurate carrier detection and prenatal diagnosis.