While Angelman Syndrome can be misdiagnosed as cerebral palsy or an autistic spectrum disorder, there are several other syndromes that share characteristics with AS and should be considered in making a diagnosis including known mimicking syndromes;
Prader-Willi Syndrome – also results from a deletion on Chromosome 15 that is inherited paternally. As this syndrome presents with severe hypotonia and feeding difficulties, it could be misdiagnosed as Angelman Syndrome and vice-versa. Methylation testing is required to determine if deletions on Chromosome 15 are maternal (Angelman Syndrome) or paternal (Prader-Willi Syndrome) in origin.
X-linked Mental Retardation Syndrome (XLMR), Christianson Type – This syndrome is caused by mutations in SLC9A6 gene and has been referred to as an «Angelman-like Syndrome.»
Rett Syndrome – A neurodevelopmental disorder that occurs almost exclusively in girls. Characterized by mental retardation, seizures, loss of speech and regression of acquired skills.
Chromosome 22q13.3 Deletion Syndrome (Phelan-McDermid) – This syndrome is characterized by hypotonia, absent or severely delayed speech and autistic behavior.
Mowat-Wilson Syndrome – a complex developmental disorder that presents with mental retardation, delayed motor development and epilepsy.
Monosomy 1p36 Syndrome – deletion of the 1p36 region leads to multiple congenital abnormalities and mental retardation.
Smith-Magenis Syndrome – deletion of the 17p11.2 regions leads to mental retardation, hypotonia, speech delay and sleeping disorders.
Chromosome 17q21.31 Microdeletion Syndrome – this deletion leads to mental retardation, hypotonia, and a friendly disposition with characteristic facial anomalies.
Pitt-Hopkins Syndrome – caused by haploinsufficiency of the TCF4 gene on 18q21. This syndrome can present with behavioral characteristics similar to Angelman Syndrome including lack of speech and happy disposition, but also has distinctive facial and hand features. *
Chromosome 2q23.1 Microdeletion Syndrome – this syndrome was recently described in Pubmed; it includes microcephaly, seizures and short stature. The report states that individuals originally thought to have Angelman Syndrome, Prader-Willi, or Smith-Magenis have tested positive for this deletion. Deletions studied to date remove the MBD5 gene suggesting the absence of this gene may cause the clinical features of this syndrome.
Mutation of HERC2 – also known as MRT38 – autosomal recessive, mental retardation) located on 15q13.1; disruption of HERC2 function relates to a reduction in E6-AP activity, resulting in global developmental delay and autistic features similar to AS. Individuals may also have blue irides (eyes).
*While the OMIM description does not suggest Angelman Syndrome, please see this recent publication where children given a clinical diagnosis of Angelman Syndrome, Prader-Willi Syndrome or Rett Syndrome were found to have Pitt-Hopkins Syndrome PMID 18781613