Fragile X Syndrome, Molecular Analysis, Varies
Use
Fragile X syndrome (FXS) is an X-linked disorder primarily affecting individuals due to an expansion of the CGG trinucleotide repeat in the FMR1 gene on the X chromosome. This test is useful for confirming diagnoses of FXS, fragile X tremor/ataxia syndrome, and premature ovarian insufficiency caused by FMR1 expansions. It is essential for determining carrier status in individuals with a family history of FXS or X-linked intellectual disability and is also significant for prenatal diagnosis when an FMR1 expansion is documented in the family. Expansion of CGG repeats causes various related disorders, with the test facilitating accurate diagnosis and carrier identification.
Special Instructions
For testing involving chorionic villus specimens, FMR1-methylation status cannot be assessed. Consultation with a molecular genetic counselor is advised prior to sending these specimens. Additional protocols are required for prenatal testing, including maternal blood specimens for maternal cell contamination analysis. The test may involve various reflex tests based on specimen type and findings.
Limitations
The test may not reliably determine disease severity prenatally due to variable expression and incomplete penetrance of the FMR1 expansion. Less than 1% of individuals with fragile X syndrome do not present the CGG expansion mutation and may have other mutations within the FMR1 gene. Errors can occur if the specimen or clinical data is incorrect or if the patient had a recent allogeneic bone marrow transplant. Methylation status will not be assessed on chorionic villus specimens or if the reported sex is female.
New York Approved
Methodology
PCR-based (PCR)
Biomarkers
LOINC Codes
- 81856-7
- 50397-9
- 81856-7
- 69047-9
- 42349-1
- 31208-2
- 85069-3
- 18771-6
Result Turnaround Time
8-10 days
Related Documents
For more information, please review the documents below
Specimen
Whole Blood
Volume
3 mL
Minimum Volume
Not provided
Container
Lavender top (EDTA) or yellow top (ACD); green top (Sodium heparin) acceptable
Collection Instructions
Invert several times to mix blood. Send whole blood specimen in original tube. Do not aliquot. Whole blood collected postnatal from an umbilical cord is also acceptable.
Patient Preparation
Previous bone marrow transplant from an allogeneic donor will interfere with testing.
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 4 days |
| Refrigerated | 4 days |
| Frozen | 4 days |