Angelman syndrome is due to loss of function of the maternally inherited ubiquitin protein ligase E3A (UBE3A) allele, while Rett syndrome is due in the majority of cases to loss of function mutation in the X-linked methyl-CpG- binding protein 2 (MECP2) gene. The gene discussed is UBE3A; the disease is atypical Rett syndrome.