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HEXA Gene Sequencing
Test Code16612
Physician Attestation of Informed Consent
This germline genetic test requires physician attestation that patient consent has been received if ordering medical facility is located in AK, DE, FL, GA, IA, MA, MN, NV, NJ, NY, OR, SD or VT or test is performed in MA.
Includes
If amniotic fluid or chorionic villi sampling (CVS) is received, then an additional charge will be added for cell culture work (CPT code(s): 88235) if not already ordered
Preferred Specimen
5 mL whole blood collected in an EDTA (lavender-top) tube
Minimum Volume
3 mL whole blood • 10 mL amniotic fluid • Cultured cells 75% confluent • 10 mg chorionic villi
Other Acceptable Specimens
10 mL amniotic fluid collected in a sterile, leak-proof container • 10 mg chorionic villi collected in a sterile tube filled with sterile culture media • Cultured cells collected in each of two sterile T-25 flasks
Instructions
Do not hold specimen; forward to laboratory when specimen arrives. Contact performing laboratory for stability determination. For any other sample type call 866-GENE-INFO (1-866-436-3463).
Whole blood (preferred): Normal phlebotomy procedure. Specimen stability is crucial. Store and ship room temperature immediately. Do not freeze.
For fetal testing:
1) Please call 1-866-GENE-INFO (1-866-436-3463) prior to submission
2) Documentation of parental carrier status must be provided
3) It is required that Maternal Cell Contamination Study, STR Analysis be ordered in conjunction with fetal testing. A separate tube of maternal blood (EDTA) is required for this test. Do not hold cells; forward to laboratory when cells arrive.
Amniotic fluid (acceptable): Normal collection procedure. Specimen stability is crucial. Store and ship at room temperature immediately. Do not refrigerate or freeze; forward to laboratory when sample arrives.
Amniocyte or Chorionic Villus (CVS) culture (acceptable): Two sterile T25 flasks, 75% confluent, filled with culture medium. Specimen stability is crucial. Store and ship at room temperature immediately. Do not refrigerate or freeze; forward to laboratory when cells arrive.
Dissected Chorionic Villus (CVS) biopsy (acceptable): 10-20 mg dissected chorionic villi collected in a sterile tube, filled with sterile culture medium. Specimen stability is crucial. Store and ship at room temperature immediately. Do not refrigerate or freeze; forward to laboratory when sample arrives.
Whole blood (preferred): Normal phlebotomy procedure. Specimen stability is crucial. Store and ship room temperature immediately. Do not freeze.
For fetal testing:
1) Please call 1-866-GENE-INFO (1-866-436-3463) prior to submission
2) Documentation of parental carrier status must be provided
3) It is required that Maternal Cell Contamination Study, STR Analysis be ordered in conjunction with fetal testing. A separate tube of maternal blood (EDTA) is required for this test. Do not hold cells; forward to laboratory when cells arrive.
Amniotic fluid (acceptable): Normal collection procedure. Specimen stability is crucial. Store and ship at room temperature immediately. Do not refrigerate or freeze; forward to laboratory when sample arrives.
Amniocyte or Chorionic Villus (CVS) culture (acceptable): Two sterile T25 flasks, 75% confluent, filled with culture medium. Specimen stability is crucial. Store and ship at room temperature immediately. Do not refrigerate or freeze; forward to laboratory when cells arrive.
Dissected Chorionic Villus (CVS) biopsy (acceptable): 10-20 mg dissected chorionic villi collected in a sterile tube, filled with sterile culture medium. Specimen stability is crucial. Store and ship at room temperature immediately. Do not refrigerate or freeze; forward to laboratory when sample arrives.
Transport Temperature
Room temperature
Specimen Stability
Whole blood
Room temperature: 14 days
Refrigerated: 14 days
Frozen: Unacceptable
Fetal specimens
Room temperature: 48 hours
Refrigerated: Unacceptable
Frozen: Unacceptable
Room temperature: 14 days
Refrigerated: 14 days
Frozen: Unacceptable
Fetal specimens
Room temperature: 48 hours
Refrigerated: Unacceptable
Frozen: Unacceptable
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Do not reject. Forward to performing laboratory for evaluation of sample.
Methodology
Next Generation Sequencing
FDA Status
This test was developed and its analytical performance characteristics have been determined by Quest Diagnostics. It has not been cleared or approved by FDA. This assay has been validated pursuant to the CLIA regulations and is used for clinical purposes.
Setup Schedule
Set up: as needed; Report Available: 4 weeks following setup
Limitations
This test will identify greater than 99% of disease-causing mutations. It will also identify the known pseudodeficiency variants that are not associated with the disease but which lead to reduced enzyme activity when the standard enzyme assay is used to measure Hex A activity. Large rearrangements (deletions/insertions) are rare and not detectable by this test method. If no mutation is found by the testing procedure, it does not mean that the risk of carrying or developing TSD is not present. It simply means that this risk is significantly reduced.
Clinical Significance
Tay-Sachs disease (TSD) is a progressive neurodegenerative disease. It is caused by pathogenic variants in the HEXA gene. Gene sequencing would be appropriate for individuals who have had a positive or equivocal Tay-Sachs enzyme carrier result and are negative for a panel of common pathogenic variants.
