X-inactivation Studies

Turnaround Time

2 weeks

CPT Code(s)

81204

Cost

$350

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. 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. In approximately 10% of cases, the testing is uninformative due to the presence of the same allele size on both X chromosomes.

X-inactivation studies are useful in diagnosing some X-linked recessive disorders and determining carrier status of family members.

The preferred sample type is peripheral blood collected in an EDTA (purple top) tube - at least 2-3ml for pediatric patients and 5-6ml for adult patients. Extracted DNA, dried blood spots, and saliva are also accepted for this test. Saliva samples must be submitted in an approved saliva kit. Contact the lab to receive a saliva kit or to have one sent to your patient.

The specimen should be kept at room temperature and delivered via overnight shipping. 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.