XSense®, Fragile X with Reflex

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

Test Codes

EPIC: LAB1232252, Beaker: XSENSE, Quest: 16313

Department

Send Outs

Instructions

If Fragile X, PCR result is not normal, or gray zone, then Fragile X Methylation Analysis will be performed.

Specimen Collection Criteria

Collect: One Lavender-top EDTA tubes or One Pink EDTA top.

Also acceptable: One Green-top Sodium Heparin tube.

Physician Office/Draw Specimen Preparation

Do not centrifuge. Maintain specimens at room temperature (20-26°C or 68-78.8°F) prior to transport.

Preparation for Courier Transport

Transport: 4.0 mL whole blood, at room temperature (20-26°C or 68-78.8°F). (Minimum: 3.0 mL)

Rejection Criteria

• Centrifuged specimens.
• Frozen specimens.
• Gross hemolysis
• Specimens not collected and processed as indicated.
• This test will only be performed once in a lifetime for a patient.

In-Lab Processing

Do not centrifuge. Maintain specimens at room temperature (20-26°C or 68-78.8°F) prior to transport.

Transport: 4.0 mL whole blood, at room temperature (20-26°C or 68-78.8°F). (Minimum: 3.0 mL)

Storage

Specimen Stability for Testing:

Room Temperature (20-26°C or 68-78.8°F): 8 days
Refrigerated (2-8°C or 36-46°F): 8 days
Frozen (-20°C/-4°F or below): Unacceptable

Specimen Storage in Department Prior to Disposal:

Specimen retention time is determined by the policy of the reference laboratory. Contact the Send Outs Laboratory with any questions.

Laboratory

Sent to Quest Diagnostics, Wood Dale, IL.

Performed

Information unavailable.

Reference Range

Interpretation is provided with the report.

Test Methodology

Southern Blot and Polymerase Chain Reaction (PCR) based assays.

Clinical Utility

XSense^®, Fragile X with Reflex – 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.

CPT Codes

81243, 81244 if needed (G0452).

Contacts

Last Updated

4/29/2026