X-inactivation
Determination of maternal and paternal X chromosome activation
status is useful in the diagnostic analysis of nonrandom patterns.
Skewed patterns of inactivation in female carriers of a number
of X-linked recessive disorders and asymptomatic female carriers
of some X-linked dominant diseases have been observed. X-inactivation
studies are useful in diagnosing such disorders and determining
carrier status of family members.
By using the methylation-sensitive restriction enzyme HpaII
and the polymerase chain reaction, the methylation status of
both the maternal and paternal X chromosome is determined. Methylation
of the HpaII restriction endonuclease site in the human
androgen-receptor gene, HUMARA, correlates with X-inactivation.
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 submitted. Please contact the laboratory for more
information.
Transport: Please contact the
Molecular Diagnostic Lab Coordinator (1-800-473-9411) for shipping
information. 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.
Analysis standards: Analysis will be complete within
2 weeks of sample receipt. The lab director assesses the quality
and interpretation of results. Technical staff members 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 with 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 and explanations of testing protocols
will be supplied upon request.
CPT Codes: 83890, 83898 (x2),
83909, 83912
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