Fragile X with Reflex

Last Modified: 2/13/2019 3:30:42 PM


Medical Necessity Documentation:  
Client Notes:  
Patient Preparation:  
Specimen Requirements: 5.0 mL Whole Blood in a Lavender Top Tubes - EDTA
Collection Instructions:

Do not centrifuge specimen

Do not open specimen

Minimum Volume: 3.0 mL Whole Blood
Transport & Storage: Temperature/Stability:

8 days Ambient
8 days Refirgerated

Rejection Criteria: Frozen Specimen; extensive hemolysis observed
Reference Range:

 Refer to Interpretive Results

Critical Ranges:  
Test Comments:

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.

Methodology: Polymerase Chain Reaction (PCR) with Detection by Capillary Electrophoresis
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

Documentation:

If Fragile X, PCR result is not Normal, or Gray zone, Fragile X, Southern Blot will be performed at an additional charge (CPT codes(s): 81244)

Custom Panel: No

PRODUCTION SCHEDULE

Turn Around Time: 10 to 17 days
Days Performed: Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday
Sites Performed: Quest - Chantilly to San Juan Capistrano
PHL Test Code: FXSX
EPIC Test Code: LAB738
Send Out Test Code: 16313
Alternate Test Names: FMR1; Fra (X); FRAX; Martin-Bell Syndrome; XSense®; XSense®, Fragile X with Reflex
Included Tests:  
CPT Coding: 81243 (Reflex 81244)

Go back to the top of the page.