Prader-Willi/Angelman
Methylation Studies
Prader-Willi and Angelman syndromes are examples
of disorders involving imprinted genes. Imprinted genes are only
expressed from either the maternally or paternally derived member
of a homologous chromosome pair.
Prader-Willi syndrome results from the loss of
genes that are expressed only from the paternally derived chromosome
15, either through a deletion on the paternally derived chromosome
15 or a maternal uniparental disomy for the chromosome 15 pair. Angelman
syndrome results from the loss of genes that are expressed only from
the maternally derived chromosome 15 via a deletion on the maternally
derived chromosome 15 or a paternal uniparental disomy for the
chromosome 15 pair. This differential gene expression is thought
to be controlled by methylation of the DNA on the maternally
versus the paternally derived chromosome 15. Southern blot analysis
using methylation sensitive restriction enzymes illustrates whether
the patient has both maternally derived and paternally derived
material in the critical region of chromosome 15.
The molecular
diagnosis of Prader-Willi and Angelman syndromes is part of a
comprehensive package of services recommended for referred individuals.
High resolution cytogenetic analysis, FISH deletion analysis,
and/or UPD analysis complete the recommended diagnostic work-up.
All of these services are offered at the Greenwood Genetic Center.
Prenatal testing is available. Please contact the
Molecular Diagnostic Laboratories for details.
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.
If necessary, ACD solution A Vacutainer 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: Please contact the Molecular Diagnostic Laboratory Coordinator
(1-800-473-9411) for shipping
information. 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.
Analysis standards: Analysis will be completed within
2 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 (x2), 83894, 83898, 83912
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