Signs and symptoms
Signs and symptoms of Angelman syndrome and their relative frequency in affected individuals are:

Consistent (100%)
Developmental delay, functionally severe
Speech impairment, no or minimal use of words; receptive and non-verbal communication skills higher than verbal ones
Movement or balance disorder, usually ataxia of gait and/or tremulous movement of limbs
Behavioral characteristics of the following types: any combination of atypical frequent laughter/smiling; atypically happy demeanor; easily excitable personality, often with hand flapping movements; hypermotoric behavior; short attention span

Frequent (more than 80%)
Delayed, disproportionate growth in head circumference, usually resulting in microcephaly (absolute or relative) by age 2
Seizures, onset usually less than 3 years of age
Abnormal EEG, characteristic pattern with large amplitude slow-spike waves

Associated (20–80%)
Cause
Angelman syndrome is caused by the lack of expression of a gene known as UBE3A during development. This gene is located within a region of chromosome 15 known as 15q11-q13 and is part of the ubiquitin pathway. In fact, UBE3A codes for a very selective E6-AP ubiquitin ligase for which MAPK1, PRMT5, CDK1, CDK4, β-catenin, and UBXD8 have been identified as ubiquitination targetsTypically, a fetus inherits a maternal copy of UBE3A and a paternal copy of UBE3A. In certain areas of the developing brain, the paternal copy of UBE3A is inactivated through a process known as imprinting and the fetus relies on the functioning maternal copy of UBE3A in order to develop normally. In an individual with AS, however, the maternal UBE3A gene is absent or not functioning normally.
Sexual development is thought to be unaffected, as evidenced by a single reported case of a woman with Angelman syndrome conceiving a female child who also had Angelman syndrome.The majority of those with AS achieve continence by day and some by night. Angelman syndrome is not a degenerative syndrome, and thus people with AS may improve their living skills with support.Dressing skills are variable and usually limited to items of clothing without buttons or zippers. Most adults can eat with a knife or spoon and fork, and can learn to perform simple household tasks. Particular problems which have arisen in adults are a tendency to obesity (more in females), and worsening of scoliosis if it is present. The affectionate nature may also persist into adult life where it can pose a problem socially, but this problem is not insurmountable. People with Angelman syndrome appear to have a reduced but near-normal life expectancy, dying on average 10 to 15 years earlier than the general population. Epidemiology
Though the prevalence of Angelman syndrome is not precisely known, there are some estimates. The best data available are from studies of school age children, ages 6–13 years, living in Sweden and from Denmark where the diagnosis of AS children in medical clinics was compared to an 8-year period of about 45,000 births. The Swedish study showed an AS prevalence of about 1/20,000 and the Danish study showed a minimum AS prevalence of about 1/10,000. History
Harry Angelman, a pediatrician working in Warrington, England, first reported three children with this condition in 1965.