Angelman syndrome is a neuro-genetic disorder characterized by intellectual disability, developmental delays, ataxia, and severe speech and language impediments. Most affected individuals also have epilepsy and microcephaly and many tend to have a happy personality with frequent laughing and smiling. Most cases result from deletions in the 15q11.2-q13 region which carries the Ube3a gene. Loss of Ube3a is considered a diagnostic tool.

General information links for Angelman syndrome:
NLM/NIH's Genetic and Rare Disease Information Center
OMIM
Genetics Home Reference