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


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


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)

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