*If prior authorization is not submitted, test may be delayed.
Test Overview
Fragile X fragment analysis, performed using the Asuragen AmplideX PCR/CE FMR1 Reagents, uses GC-rich optimized polymerase chain reaction (PCR) and capillary electrophoresis to determine the number of cytosine-guanine-guanine (CGG) repeats in the Fragile X Messenger Ribonucleoprotein 1 (FMR1) gene 5’ untranslated region. A PCR primer pair amplifies the entire CGG repeat region, and a separate primer randomly anneals inside and amplifies different portions of the CGG repeat region resulting in small fragments of three nucleotides difference (CGG primed “shoulder” peaks). Reported CGG repeat sizes may vary by +/- 2 repeats. Because the FMR1 gene is located on the X chromosome, most individuals assigned male at birth are expected to have one CGG repeat allele, and most individuals assigned female at birth are expected to have two CGG repeat alleles. Detection of only one CGG repeat allele in an individual assigned female at birth suggests that the two alleles are the same or of a similar size (PMID: 20616364).
The repeat expansion interpretation is based on the following ranges:
Normal 5-44 CGG repeats
Intermediate 45-54 CGG repeats
Premutation 55-200 CGG repeats
Full mutation >200 CGG repeats
FMR1 methylation analysis, performed using the Asuragen AmplideX mPCR FMR1 Kit, uses methylation-sensitive enzyme digestion followed by PCR and capillary electrophoresis to determine the methylation status of the FMR1 5’ untranslated region. Methylation analysis is only performed for a patient with a premutation, or a full mutation CGG repeat expansion.
The methylation interpretation is based on the following ranges:
Unmethylated: <20% methylation
Partially methylated: 20-80% methylation
Fully methylated: >80% methylation
Analysis of CGG repeats present in the FMR1 gene in a patient with clinical features consistent with Fragile X Syndrome or determination of the carrier status of a family member.
*Reference ranges may change over time. Please refer to the original patient report when evaluating results.
* Reference ranges may change over time. Please refer to the original patient report when evaluating results.
This assay can accurately detect repeat numbers up to 200 CGG repeats in the FMR1 gene locus. Samples containing >200 CGG repeats will be reported as "full mutation (>200 CGG repeats)". This assay will not detect Fragile X syndrome caused by other types of variants in the FMR1 gene. If the clinical phenotype is consistent with FXS, then additional testing which includes sequence and deletion/duplication analyses of the FMR1 gene may be considered. Fewer than 1% of patients with FXS have a sequence variant, a partial deletion, or a full deletion of FMR1 (PMID: 29178241).
Test Details
21 days
- Fragile X Mutation Detection by Fragment Analysis
- Fragile X Syndrome
- x-linked mental retardation
- Fragile X tremor ataxia syndrome
- Fragile X associated premature ovarian insufficiency (FXPOI)
- Autism / Intellectual Disability
Specimen Requirements
Collect blood specimen in a EDTA lavender top tube. Send it within 24 hours if stored at room temperature or within 5 days if stored refrigerated.
Fill out a MLabs Molecular test requisition (or place an e-order if applicable):
https://mlabs.umich.edu/media/166
Fill out a Clinical History Form for Insurance Prior Authorization (include all required documentation indicated at the bottom of this form):
https://mlabs.umich.edu/sites/default/files/2020-08/file/mlab11618clini…
Fill out a UMHS Request and Consent for Genetic Testing form:
https://mlabs.umich.edu/sites/default/files/2023-04/file/germline-conse…
Michigan State law requires the ordering provider to obtaining informed consent from the patient prior to prognostic or predictive genetic testing. Contact a MLabs Client Services Center at 800-862-7284 to request paper copies or to setup a client account.
See "Fragile X Syndrome Mutation (Non-Blood Specimen)" for other specimen types accepted for this testing.
5 mL whole blood
1 mL whole blood (0.5 mL infants)
Additional Information
The American College of Medical Genetics recommends that both a routine karotype (Chromosome Analysis, Blood, Constitutional) AND a molecular test (Fragile X Syndrome Mutation Detection) be performed. Most insurance carriers require prior authorization for genetic testing. Testing will not begin until insurance prior authorization is received by the laboratory or it is confirmed that prior authorization is not required. The ordering health care provider can obtain the prior authorization or request the laboratory to submit it. To obtain BCN prior authorization call Joint Venture Hospital Laboratories (JVHL) at 800-445-4979; for all other insurances, contact the plan directly. By ordering this test the clinician acknowledges that informed consent, https://mlabs.umich.edu/sites/default/files/2023-04/file/germline-conse…, has been obtained from the patient as required by applicable state or federal laws and the ordering clinician has authorization from the patient permitting MLabs to report the test results to the ordering clinician. Test includes medical geneticist interpretation of results billed as a separate additional charge. This test is not available without interpretation.