Tay-Sachs Disease (HEXA) Sequencing and 7.6kb Deletion
2009298
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).
Mnemonic
HEXA FGS
Methodology
Polymerase Chain Reaction/Sequencing
Performed
Varies
Reported
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
  
Collect
Lavender (EDTA), pink (K2EDTA), or yellow (ACD Solution A or B).  
Specimen Preparation
Transport 3 mL whole blood. (Min: 1 mL)  
Storage/Transport Temperature
Refrigerated.  
Unacceptable Conditions
  
Remarks
  
Stability
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:
Characteristics:
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).
Incidence:
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.
Inheritance:
Autosomal recessive.
Cause:
Two pathogenic germline HEXA gene mutations on opposite chromosomes.
Clinical Sensitivity:
99 percent.
Methodology:
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.
Limitations:
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.



Counseling and informed consent are recommended for genetic testing. Consent forms are available online at www.aruplab.com.

See Compliance Statement C: www.aruplab.com/CS  
Note
 
CPT Code(s)
81406; 81479
Components
Component Test Code*Component Chart Name
2009299Tay-Sachs Disease (HEXA) Seq, Specimen
2009300Tay-Sachs Disease (HEXA) Seq, Interp
* Component test codes cannot be used to order tests. The information provided here is not sufficient for interface builds; for a complete test mix, please click the sidebar link to access the Interface Map.
Aliases