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Laboratory Test Directory

Fragile X Repeat Analysis with Reflex to Methylation

Components

Name Method Department Units
Fragile X Repeat Analysis with Reflex to Methylation Polymerase chain reaction (PCR)
CGG Repeat Primed PCR
Methylation PCR
Molecular Genetics

Specimen Requirements

Whole blood

Container Type Container Size Specimen Volume
Preferred

Purple tube (EDTA)

4 mL 4 mL - 8 mL
Stability

Room temperature - 24 hour(s)
Refrigerated - 72 hour(s)

Specimen Preparation

  • Do not centrifuge
  • Do not freeze
  • Transport to laboratory as soon as possible

Reasons for Rejection

  • Wrong collection tube
  • Centrifuged specimen
  • Delayed or improper handling
  • Frozen specimen
  • Clotted specimen

Comments

This test detects the number of trinucleotide CGG repeats in the 5’-untranslated region (UTR) of the FMR1 gene.  Disorders associated with the FMR1 CGG repeat expansion include X-linked fragile X syndrome, fragile X-associated tremor/ataxia syndrome (FXTAS), and FMR1-related primary ovarian insufficiency (POI). The American College of Medical Genetics and Genomics (ACMG) defines a normal repeat length as less than or equal to 44 CGG repeats, an intermediate/gray zone as 45-54 repeats, a premutation category as 55-200 repeats, and a full mutation as over 200 repeats. More than 99% of patients with fragile X syndrome have aberrant FMR1 methylation caused by CGG repeat expansion (typically >200 repeats).

If patient is undergoing diagnostic testing, reflex to methylation will occur if the patient has a premutation or full mutation allele. If patient is undergoing carrier testing, reflex to methylation will occur if patient has a full mutation allele.

Forms

Lab Form

CPT Code

  • 81243
  • 81244