)The methylation test that is performed for Angelman syndrome (a defect in UBE3A) looks for methylation on the gene's neighbor SNRPN (which is silenced by methylation on the maternal copy of the gene).While Angelman syndrome can be caused by a single mutation in the UBE3A gene, the most common genetic defect leading to Angelman syndrome is a ~4Mb (megabase) maternal deletion in chromosomal region 15q11-13 causing an absence of "UBE3A" expression in the paternally imprinted brain regions.