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XSense®, Fragile X with Reflex
Test CodeFRAGILEX
Quest Code
16313
Alias/See Also
Fragile X Dna Analysis with Reflex to Karyotyping
FMR1
FMR1
CPT Codes
81243<br />
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 Fragile X, PCR result is not Normal, or Gray zone, then Fragile X Methylation Analysis will be performed at an additional charge (CPT codes(s): 81244)
Preferred Specimen
4 mL whole blood collected in EDTA (lavender-top) tube
Minimum Volume
3 mL
Other Acceptable Specimens
Acid citrate dextrose ACD-A-B (yellow-top), or sodium heparin (green-top) tube
Instructions
Normal phlebotomy procedure. Specimen stability is crucial. Store and ship room temperature immediately. Do not freeze.
Transport Temperature
Room temperature
Specimen Stability
Room temperature: 8 days
Refrigerated: 8 days
Frozen: Do not freeze
Refrigerated: 8 days
Frozen: Do not freeze
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Extensive hemolysis observed • Sample received frozen
Methodology
Polymerase Chain Reaction (PCR) with Detection by Capillary Electrophoresis
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: Daily night; Report available: 12 days (5 days for PCR and 7 days additional if reflex required)
Limitations
This analysis evaluates only the size of the FMR1 CGG repeat and cannot detect other possible chromosomal or DNA abnormalities. This assay cannot rule out the possibility of Fragile X syndrome caused by any other type of mutation in the FMR1 gene. In addition, this assay may not detect a FMR1 CGG expansion that presents with low-level mosaicism (this means that the expansion is present in only some cells not all cells). DNA analysis can predict the occurrence of Fragile X syndrome, but not the severity of the condition.
Reference Range
See Laboratory Report
Clinical Significance
Fragile X syndrome (FXS OMIM # 300624) is the most common inherited mental retardation syndrome, affecting approximately 1:4000 males and approximately 1:8000 females. The disease is caused by the expansion of a trinucleotide CGG repeat in the 5'-untranslated (UTR) region of the FMR1 gene. Methylation of the expanded CGG tract leads to silencing of expression of the FMR1 gene. The American College of Medical Genetics defines a normal repeat length as between 5 and 44. Intermediate alleles of between 45-54 repeats almost never expand to full mutations in a single meiosis. Premutation alleles are defined as 55-200 CGG. Premutation alleles of less than 90 repeats have a variable risk for expansion to full mutations whereas larger premutation alleles almost always expand when inherited through a female. Full mutation alleles are defined as >200 repeats. FXS in an X-linked dominant disease. The test is used to detect the presence of expanded alleles in the FMR1 gene and to distinguish normal homozygous females from full mutation carriers.
Performing Laboratory
| Quest Diagnostics Nichols Institute-San Juan Capistrano, CA |
| 33608 Ortega Highway |
| San Juan Capistrano, CA 92675-2042 |
Last Updated: September 12, 2019
