Atypical presentation of Angelman syndrome with intact expressive language due to low‐level mosaicism

Background Angelman syndrome (AS) occurs due to a lack of expression or function of the maternally inherited UBE3A gene. Individuals with AS typically have significant developmental delay, severe speech impairment with absent to minimal verbal language, gait abnormalities including ataxia, and an incongruous happy demeanor. The majority of individuals with AS also have seizures and microcephaly. Some individuals with mosaic AS have been reported to have expressive language and milder levels of developmental delay. Case Report We report a male patient presenting with mild to moderate intellectual disability, hyperphagia, obesity, and the ability to communicate verbally. His phenotype was suggestive of Prader‐Willi syndrome. However, methylation testing was positive for Angelman syndrome and additional methylation specific multiplex ligation‐dependent amplification (MS‐MLPA) study revealed low‐level mosaicism for AS. Conclusion A broader phenotypic spectrum should be considered for AS as patients with atypical presentations may otherwise elude diagnosis. We report on a patient who had an atypical presentation of Angelman syndrome with mild intellectual disability, obesity, and ability to communicate verbally. Additional analysis using methylation specific multiplex ligation‐dependent amplification has identified low level mosaicism. A broader phenotypic spectrum should be considered for Angelman syndrome since patients with atypical presentations may be missed.