Fragile X Syndrome
Fragile X Syndrome is the most common form of inherited mental
retardation. More than 99% of cases are due to the expansion
of a polymorphic (CGG) repeat within the FMR1 gene. 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 under the following circumstances:
- Individuals of either sex with mental retardation, developmental
delay, or autism
- Individuals with a family history of Fragile X syndrome or
unexplained MR
- Prenatal testing of fetuses of known carrier mothers
- Patients with negative cytogenetic fragile X testing results
who have clinical symptoms of Fragile X syndrome
Fragile X testing at the Greenwood Genetic Center involves
two independent molecular approaches. Southern blotting and subsequent
analysis allows the repeat segment size and methylation status of a sample
to be determined. Polymerase chain reaction analysis is utilized to more
accurately determine (CGG) repeat numbers in high normal and premutation
ranges. Prenatal testing is available, please contact the
Molecular
Diagnostic Laboratory for details.
Specimen Requirements: 5 to 10 ml of peripheral blood
collected in an EDTA (lavender top) VacutainerTM tube is preferred. The minimal
blood needed for reliable DNA isolation is 3 ml. If necessary, ACD solution A
VacutainerTM tubes (yellow top) may be substituted. Prenatal studies require two
confluent T-25 flasks containing amniocytes. A maternal blood sample is also
requested for prenatal analysis.
Transport: The specimen should be kept at room
temperature and delivered via overnight shipping. FedEx delivery 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 a Friday can be safely designated for Monday delivery. Please contact JoAnne Babb
(1-800-473-9411), the Molecular Diagnostic Laboratory coordinator, for shipping
information.
Analysis Standards: Analysis will be completed within
2-3 weeks from sample receipt. The quality and interpretation of test results
are assessed by the laboratory director. Technical staff independently assess
the quality and interpretation of the test. The Greenwood Genetic Center
Molecular Diagnostic Laboratory is CLIA certified and actively participates in
CAP proficiency surveys.
Reporting of Test Results: Test results and their
interpretation will be mailed and/or faxed following completion of the test.
Verbal reports will be telephoned to the person(s) requesting the test when an
abnormal test result occurs. Consultation with the laboratory director is
available and explanations of testing protocols will be supplied upon request.
CPT Codes: 83890, 83892, 83896, 83898,
83909, 83912
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