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Algorithm for preconception carrier testing for disease variants in HEXA (Tay-Sachs gene)

Algorithm for preconception carrier testing for disease variants in HEXA (Tay-Sachs gene)
Any child born to a parent who is a carrier of a HEXA disease variant has an approximately 1 in 2 chance of being a carrier. A child born to parents who are both carriers has an approximately 1 in 4 chance of being affected with TSD and an approximately 1 in 2 chance of being a carrier. Among unaffected siblings, the chance of being a carrier is 2 in 3; thus, if embryos that are homozygous or compound heterozygous for a HEXA disease variant are excluded by PGT, resulting offspring have a 2 in 3 chance of being a carrier. These children can defer testing for carrier status until they are themselves considering childbearing. Refer to UpToDate for additional information on Tay-Sachs disease.

TSD: Tay-Sachs disease; IVF: in vitro fertilization; PGT: preimplantation genetic testing; PV: pathogenic variant; LPV: likely pathogenic variant; VUS: variant of uncertain significance.

* If one member of a couple is from a high-risk group based on their ancestry or positive family history, they should be tested first; in these individuals, targeted testing for PVs may be adequate.
  • Known familial HEXA variant – Test for the familial variant.
  • Known Ashkenazi (Eastern European) Jewish ancestry – Test for the three common Ashkenazi Jewish variants.
  • All others◊ – Perform HEXA gene sequencing coupled with enzymatic testing (enzymatic testing can be done concurrently or if genetic testing is positive for a PV, LPV, or VUS).

¶ Positive results include PVs or LPVs, as long as appropriate quality controls have been used in a Clinical Laboratory Improvement Amendments (CLIA)-certified laboratory. Refer to UpToDate for important caveats regarding review and interpretation of genetic test results.

Δ Reasons for concern may include a partner with a positive family history of TSD or strong desire for testing due to ancestry from a group with a high carrier frequency.

◊ Includes general population, other groups with high carrier frequency, and individuals of unknown ancestry.
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