Investigation of UBE3A and MECP2 in Angelman syndrome (AS) and patients with features of AS.
Angelman syndrome (AS) is an imprinted neurobehavioral disorder characterized by mental retardation, absent speech, excessive laughter, seizures, ataxia, and a characteristic EEG pattern. Classical lesions, including deletion, paternal disomy, or epigenetic mutation, are confirmatory of AS diagnoses in 80% of cases. Loss-of-function mutations of the UBE3A gene have been identified in approximately 8% of AS cases, failing to account for the remaining patient population, and there appears to be a higher prevalence of mutations in familial than sporadic cases. We screened UBE3A in 45 index cases of AS without obvious 15q11-13 abnormalities. Pathological mutations were identified in 3/6 (50%) familial and 4/39 (>10%) sporadic cases. By combining our data with those of the literature, we demonstrate statistically that the frequency of UBE3A mutations is significantly higher in the familial than sporadic subsets of AS. This indicates that an independent molecular mechanism or 'phenocopy' exists for the sporadic group. Rett syndrome (RS), caused by mutations of the MECP2 gene, and patients with deletions of 22q13.3 --> qter, have overlapping clinical features with AS. We screened 24 of the sporadic AS cases without detectable UBE3A mutations for mutations of MECP2, but found none. A separate cohort of 43 atypical patients with features common to AS and RS, in whom 15q11-13 lesions and 22q13.3 --> qter deletion had been ruled out, were also screened for MECP2 mutations. One male patient was mosaic for a frameshift mutation of this gene (previously reported). While MECP2 mutations can cause a phenotype reminiscent of AS in rare cases, they fail to account for the excess of sporadic patients with a definitive clinical diagnosis of AS.
Molecular Embryology Unit, Institute of Child Health and Great Ormond Street Hospital, University College London, London, United Kingdom. M.Hitchins@ich.ucl.ac.uk
Megan P
MP
Hitchins
Sarah
S
Rickard
Fatima
F
Dhalla
Una L
UL
Fairbrother
Bert B A
BB
de Vries
Robin
R
Winter
Marcus E
ME
Pembrey
Sue
S
Malcolm
D017204:Angelman Syndrome / Q000235:genetics*; D002868:Chromosomal Proteins, Non-Histone; D002884:Chromosomes, Human, Pair 15 / Q000235:genetics*; D002892:Chromosomes, Human, Pair 22 / Q000235:genetics; D015331:Cohort Studies; D004268:DNA-Binding Proteins / Q000235:genetics*; D017353:Gene Deletion; D005820:Genetic Testing; D018392:Genomic Imprinting; D006801:Humans; D008214:Lymphocytes / Q000378:metabolism / Q000473:pathology; D008297:Male; D051783:Methyl-CpG-Binding Protein 2; D009030:Mosaicism; D009154:Mutation / Q000235:genetics*; D010641:Phenotype; D018807:Polymorphism, Single-Stranded Conformational; D012097:Repressor Proteins; D015518:Rett Syndrome; D044767:Ubiquitin-Protein Ligases / Q000235:genetics*
D002868:Chromosomal Proteins, Non-Histone; D004268:DNA-Binding Proteins; C497392:MECP2 protein, human; D051783:Methyl-CpG-Binding Protein 2; D012097:Repressor Proteins; C471639:UBE3A protein, human; D044767:Ubiquitin-Protein Ligases