Fragile X Syndrome Testing (FRX)
Information for Ordering
Acceptable Specimen Types
- Fresh blood sample: 3–6 mL EDTA; no time limitations associated with receipt
Turnaround Time
- Blood: Average of 15 working days
Price, CPT Codes, and Z Code
- Tier 1 PCR analysis: $280 USD institutional/self-pay price
- Tier 1 PCR with reflex Tier 2 Southern blot (if indicated): $560 USD institutional/self-pay price
- CPT code: 81243, with reflex to 81404 when indicated
- Z code: ZB6A7
Candidates for Testing
Individuals with intellectual disability, developmental delay, autism spectrum disorder, or a family history suggestive of Fragile X syndrome.
Specimen Shipping and Handling
Please refer to the specimen requirements listed above.
Blood specimens should be shipped at room temperature. Do not ship specimens on ice.
Specimens must be packaged to prevent breakage. Absorbent material must be included to contain liquids if breakage occurs. Specimens must also be shipped in double watertight containers, such as a specimen pouch placed inside the shipping company's diagnostic envelope.
To request a collection kit, please complete the Collection Kit Request Form.
Before shipping a specimen, please contact the UAB Medical Genomics Laboratory by email at medgenomics@uabmc.edu or by phone at 205-934-5562. Please provide the specimen type, shipment date, and package tracking number so the laboratory can help ensure proper and timely receipt.
Required Forms
About
Disorder Background
Fragile X syndrome is one of the most common inherited causes of intellectual disability, with an estimated incidence of approximately 1 in 4,000–6,250 males. Affected males typically have moderate intellectual disability and may present with characteristic physical findings, including a long face, prominent ears, and macroorchidism. Approximately 50% of females with a full mutation are clinically affected, although manifestations are generally milder than those observed in males.
Fragile X syndrome is usually caused by expansion of the CGG trinucleotide repeat within the FMR1 gene on the X chromosome. Typical individuals have fewer than 45 CGG repeats. Intermediate ("gray zone") alleles generally contain 45–54 repeats, premutation alleles contain 55–200 repeats, and full mutations contain more than 200 CGG repeats.
Test Description
Testing is performed using a two-tier approach.
Tier 1 consists of polymerase chain reaction (PCR) analysis to determine the CGG repeat size within the FMR1 gene.
If PCR identifies or suggests a premutation or full mutation, or if a homozygous female result requires further characterization, Tier 2 testing is performed. Tier 2 consists of EcoRI and EagI restriction enzyme digestion followed by Southern blot analysis using the StB12.3 probe to evaluate methylation status and estimate the number of CGG repeats. PCR analysis is also used to further refine repeat sizing when appropriate.
View references for this testing.
Other Related Test Options
For more information, test requisition forms, or collection kits, please contact the UAB Medical Genomics Laboratory at 205-934-5562 or medgenomics@uabmc.edu.