Tay-Sachs Disease, DNA Analysis

CPT: 81255
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Test Details

Synonyms

  • Hexosaminidase A Deficiency

Use

Pre- and postnatal determination of Tay-Sachs disease carrier status; resolution of pseudodeficiency allele status

Limitations

More than 95% of the mutant alleles in persons with Ashkenazi Jewish heritage are detected. In persons with French-Canadian ancestry, 80% of the mutations are detected, and 25% of mutations in non-Jewish Caucasians are also detected.

Methodology

Polymerase chain reaction (PCR); primer extension; flow-sorted bead array analysis for five mutations and two pseudodeficiency alleles in the hexosaminidase A gene

Additional Information

Tay-Sachs disease is an autosomal recessive lysosomal storage disorder that causes progressive neurological deterioration ranging in severity from forms with infantile onset to those with adult onset. If the individual tested by DNA analysis is not of Ashkenazi Jewish descent, carrier testing by enzyme analysis is strongly recommended. Couples who are both carriers have a one in four risk of having a child with Tay-Sachs disease. DNA test results should be combined with enzyme test results and clinical information for the most accurate interpretation. The mutations tested include: 1278insTATC, G269S, IVS9+1 G>A, 1421+1 G>C, and 7.6 kb deletion. Pseudodeficiency alleles tested include: R247W and R249W.

Note: The pseudodeficiency mutation, R247W, accounts for 32% of enzyme-defined carriers in the non-Jewish population, while R249W accounts for 4% of pseudodeficiency among Ashkenazi Jews. These mutations affect the enzyme test, but do not affect in vivo function of beta-hexosaminidase A. Carriers of these mutations are not at increased risk to have children with Tay-Sachs disease.

Specimen Requirements

Specimen

Whole blood, amniotic fluid, chorionic villus sample (CVS) (submission of maternal blood is required for fetal testing), or LabCorp buccal swab kit (buccal swab collection kit contains instructions for use of a buccal swab)

Volume

7 mL whole blood, 10 mL amniotic fluid, 20 mg CVS, or LabCorp buccal swab kit

Minimum Volume

3 mL whole blood, 5 mL amniotic fluid, 10 mg CVS, or two buccal swabs

Container

Lavender-top (EDTA) tube, yellow-top (ACD) tube, sterile plastic conical tube or two confluent T25 flasks for fetal testing, or LabCorp buccal swab kit

Storage Instructions

Maintain specimen at room temperature.

Causes for Rejection

Frozen specimen; hemolysis; quantity not sufficient for analysis; improper container; one buccal swab; wet buccal swab

Clinical Information

Special Instructions

A completed screening questionnaire must accompany specimens. Call 800-345-4363 to request forms, or photocopy the Tay-Sachs Disease Screening Questionnaire from the Genetics Appendix online.

References

American College of Obstetricians and Gynecologists Committee on Genetics. ACOG committee opinion. Nº 298, August 2004. Prenatal and preconceptional carrier screening for genetic diseases in individuals of Eastern European Jewish descent. Obstet Gynecol. 2004 Aug; 104(2):425-428. 15292027
American College of Obstetricians and Gynecologists Committee on Genetics. ACOG committee opinion Nº 162: Screening for Tay-Sachs disease. Washington, DC: ACOG;1995 Nov.
Monaghan KG, Feldman GL, Palomaki GE, Spector EB; Ashkenazi Jewish Reproductive Screening Working Group; Molecular Subcommittee of the ACMG Laboratory Quality Assurance Committee. Technical standards and guidelines for reproductive screening in the Ashkenazi Jewish population. Genet Med. 2008 Jan; 10(1):57-72. 18197058
Triggs-Raine BL, Feigenbaum AS, Natowicz M, et al. Screening for carriers of Tay-Sachs disease among Ashkenazi Jews. A comparison of DNA-based and enzyme-based tests. N Engl J Med. 1990 Jul 5; 323(1):6-12. 2355960

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
510404 Tay-Sachs, DNA Analysis 510407 Tay-Sachs, DNA 32632-2
510404 Tay-Sachs, DNA Analysis 511961 PDF Pending
510404 Tay-Sachs, DNA Analysis 511005 Jewish Heritage Putaway N/A

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