Fragile X syndrome (FMR1)
|Disorder||Fragile X syndrome|
|Clinical info||Fragile X Syndrome is the most common form of inherited intellectual disability. Approximately 1/1250 males and 1/2500 females are affected by the condition. Some population studies have shown the carrier frequency to be as high as 1/250 individuals. The American College of Medical Genetics policy statement on Fragile X testing recommends consideration of testing for males or females with intellectual disability, developmental delay or autism, those with a family history of Fragile X syndrome or unexplained intellectual disability. Additionally, prenatal testing should be offered to known carrier females. Trinucleotide repeat analysis is the standard for Fragile X diagnosis. Patients with the above characteristics who had a previously normal cytogenetic Fragile X results should also be considered for trinucleotide repeat analysis.|
|Indications||Molecular testing is useful to confirm the diagnosis and to identify the disease causing mutation within a family to allow for carrier testing and prenatal diagnosis.|
|Detection||More than 99% of cases are due to the expansion of a polymorphic (CGG) repeat within the FMR1 gene. Fragile X testing at the Greenwood Genetic Center involves two independent molecular approaches. PCR analyses are performed initially to determine if an expanded allele is present as well as to size normal alleles. Samples with normal allele sizes of less than 45 repeats are reported out in approximately 7-10 days. If an allele size of 45 or greater is detected, the sample will be reflexed to Southern blotting to size the allele and determine methylation status.|
|Specimen Requirements||5 to 10 ml of peripheral blood collected in an EDTA (lavender top) Vacutainer tube is preferred. The minimal blood needed for reliable DNA isolation is 3 ml|
|Transport||The specimen should be kept at room temperature and delivered via overnight shipping. FedEx is preferred. If shipment is delayed by one or two days, the specimen should be refrigerated and shipped at room temperature. Do not freeze the specimen. Samples collected on Friday can be safely designated for Monday delivery.|
|Turnaround time||7-10 days for samples with <45 repeats
3 weeks for samples with > 45 repeats
|Prenatal testing||Prenatal diagnosis via amniocentesis is available if the familial mutation is known. Additional fees for cell culture and maternal cell contamination may apply. Maternal cell contamination studies are required for all prenatal molecular tests. Contact the laboratory to discuss options for individual cases prior to sending a sample.|
Prenatal diagnosis is $1000. Please contact the laboratory for more information.
Molecular Diagnostic Lab
The Molecular Diagnostic Lab offers DNA analysis for many genetic disorders via gene sequencing, targeted mutation analysis, MLPA deletion/duplication testing, trinucleotide repeat analysis and next generation sequencing panels.