XSense®, Fragile X with Reflex : 16313

FXD or 16313

Fragile X with Reflex, Fragile X Syndrome (FXS), Martin-Bell Syndrome, Fra(X), FMR1, FRAX

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)  (non-orderable reflex code FXDB IC 16313-2 )

Lavender (EDTA), yellow (ACD Solution A or B), or Green (no gel) (heparin) tube.

Transport 4 mL whole blood. (Min: 3 mL)

Refrigerated.

Extensive hemolysis observed, Sample received frozen.

Sunday - Saturday

10 days (4 days for PCR and 6 days additional if reflex required)  (From receipt at performing laboratory)

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.

See laboratory report.

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.