Loss of functional maternal UBE3A expression in the brain causes this neurodevelopmental disorder. Most cases are sporadic; deletion, imprinting defects, paternal uniparental disomy, and a maternal pathogenic variant are distinct mechanisms.
- Development: substantial developmental disability, very limited expressive speech, and nonverbal communication.
- Movement: ataxia, tremulous movements, hypotonia, and hand flapping; coordination problems increase trauma risk.
- Neurology: seizures, sleep disturbance, and sometimes microcephaly.
- Appearance: a wide mouth, protruding tongue, mandibular prominence, and a happy or excitable affect may occur.