Ordering Recommendation

Use to confirm pathogenic and pseudodeficiency HEXA gene variants in individuals with abnormal levels of HEX A enzyme. For initial testing of Tay-Sachs disease, refer to Hexosaminidase A percent and Total Hexosaminidase in Leukocytes (2008125).

Mnemonic
HEXA FGS
Methodology

Polymerase Chain Reaction/Sequencing/Gel Electrophoresis

Performed

Varies

Reported

21-28 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.

Compliance Category

Laboratory Developed Test (LDT)

Note
Hotline History
N/A
CPT Codes

81406; 81479

Components
Component Test Code* Component Chart Name LOINC
2009299 Tay-Sachs Disease (HEXA) Seq, Specimen 31208-2
2009300 Tay-Sachs Disease (HEXA) Seq, Interp 35473-8
* 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
Tay-Sachs Disease (HEXA) Sequencing and 7.6kb Deletion