Autism-World

In the child in whom the diagnosis is suspected, a high resolution chromosome analysis is often first performed to insure that no other chromosome disorder is present, since features such as mental delay, microcephaly, or seizures can be seen in other chromosome abnormalities. Concurrent with the chromosome test, a fluorescent in situ hybridization (FISH) analysis is usually ordered. This test uses molecular tags to detect the deletion on chromosome 15.

The tags are directly applied to the chromosome and it is examined under a microscope after special stains are applied. The FISH test is far superior to the usual chromosome test. The child with AS should have their chromosomes 15 fully studied to insure that they are structurally normal; a maternal chromosome study as well provides additional confirmation that the maternal chromosome 15 is structurally normal. In the diagnostic testing for AS, a “DNA methylation” test may be ordered first or ordered in conjunction with chromosome and FISH testing. The methylation test can detect the large common deletion type of AS, as well as those with uniparental disomy or defects in the imprinting center (IC). Confirmation of uniparental disomy needs to be made by additional molecular testing (usually, study of parental blood is required) and confirmation of IC mutations requires specific molecular deletion analysis in the IC area. About 80-85% of individuals with AS will be diagnosed by a combination of these tests, but there still remain a small group in whom additional genetic testing of the UBE3A gene may then detect an abnormality. At this time, molecular analysis for UBE3A is available for clinical use in a few referral laboratories but the testing is expensive. Molecular testing of the IC region is not commercially available for clinical use but is being performed in some research labs.

Technorati : Angelman Syndrome

This entry was posted on Monday, September 10th, 2007 at 5:06 pm and is filed under Angelman Syndrome.