Angelman syndrome is a neurodevelopmental disorder typically characterized by severe developmental delays appearing in the first year of life. In most patients, development plateaus between 24 and 30 months and shows no further progression. Language skill development in children diagnosed with Angelman syndrome is marked by the absence of speech in most cases, and in a small number, only a single-word vocabulary. Despite delays in all neurodevelopmental skills, social interaction abilities can vary. Although children with Angelman syndrome characteristically display a cheerful demeanor, they may exhibit various behavioral challenges, including a short attention span, hyperactivity, aggression, temper tantrums, and other behavioral dysregulations. Furthermore, balance disturbances are observed early in a significant portion of these children.

The expected clinical findings in Angelman syndrome, listed by frequency, are as follows:
* Epileptic seizures
* Sleep disturbances
* Behavioral disorders
* Motor developmental delay
* Feeding difficulties
* Microcephaly (head circumference below average for age and sex)
* Typical facial appearance
* Strabismus
* Scoliosis