Tay-Sachs Disease (HEXA) Sequencing and 7.6kb Deletion
Ordering Recommendation
Molecular (DNA) test to confirm pathogenic and pseudodeficiency mutations for Tay Sachs disease. For initial testing for Tay Sachs, refer to Hexosaminidase A Percent and Total Hexosaminidase in Leukocytes (2008125).
Polymerase Chain Reaction/Sequencing
Within 28 days  
New York DOH Approval Status
Specimens from New York clients will be sent out to a New York DOH approved laboratory, if possible.
Specimen Required
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
Ambient: 72 hours; Refrigerated: 1 week; Frozen: Unacceptable  
Reference Interval
By report  
Interpretive Data
Background for Tay-Sachs Disease (HEXA) Sequencing and 7.6kb Deletion:
Hexosaminidase A (HEX A) enzyme deficiency is characterized by neuronal deterioration resulting in intellectual disability and motor retardation. Clinical severity is variable. Onset by six months of age with rapid progression is seen with Tay-Sachs disease (acute infantile form), while juvenile and adult-onset forms manifest a less severe course. HEX A deficiency results in the accumulation and lysosomal storage of GM2 (ganglioside).
Varies by ethnicity. 1 in 3,000 for Ashkenazi Jewish and French Canadians; other high-risk populations include Louisiana Cajuns and Old Order Amish. 1 in 300,000 for the general population.
Autosomal recessive.
Two pathogenic germline HEXA gene mutations on opposite chromosomes.
Clinical Sensitivity:
99 percent.
Bidirectional sequencing of all coding regions and intron/exon boundaries of the HEXA gene. Agarose gel electrophoresis to assess for the 7.6kb deletion.
Analytical Sensitivity and Specificity:
99 percent.
Diagnostic errors can occur due to rare sequence variations. Regulatory region mutations and deep intronic mutations will not be detected. Large deletions/duplications in HEXA, other than the 7.6kb deletion, will not be detected.

Compliance Statement C: The performance characteristics of this test were validated by ARUP Laboratories. The U.S. Food and Drug Administration (FDA) has not approved or cleared this test; however, FDA approval or clearance is currently not required for clinical use of this test. The results are not intended to be used as the sole means for clinical diagnosis or patient management decisions. ARUP is authorized under Clinical Laboratory Improvement Amendments (CLIA) and by all states to perform high-complexity testing.

Counseling and informed consent are recommended for genetic testing. Consent forms are available online.
CPT Code(s)
81406; 81479
Component Test Code*Component Chart NameLOINC
2009299Tay-Sachs Disease (HEXA) Seq, Specimen 
2009300Tay-Sachs Disease (HEXA) Seq, Interp 
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