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.
Other
During the post-operative recovery period for a tonsillectomy or adenoidectomy, it is common for adult patients to experience a lack of appetite until their throat significantly heals (usually 10–14 days). Altitude sickness
Significant emotional pain caused by an event (rather than a mental disorder) can cause an individual to temporarily lose all interest in food. Several Twelve-step programs including Overeaters Anonymous tackle psychological issues members believe lead to forms of deprivation
Psychological stress
Experiencing grotesque or unappealing thoughts or conversations, or viewing similar images
Being in the presence of unappealing things such as waste matter, dead organisms, or bad smells

Complications
Complications of anorexia may result due to poor food intake. Poor food intake can lead to dehydration, electrolyte imbalances, anemia and nutritional deficiencies. These imbalances will worsen the longer that food is avoided. Sudden cardiac death
Anorexia is a relatively common condition that can lead patients to have dangerous electrolyte imbalances, leading to acquired long QT syndrome which can result in sudden cardiac death. This can develop over a prolonged period of time, and the risk is further heightened when feeding resumes after a period of abstaining from consumption. Refeeding syndrome
Care must be taken when a patient begins to eat after prolonged starvation to avoid the potentially fatal complications of refeeding syndrome. The initial signs of refeeding syndrome are minimal, but can rapidly progress to death. Thus, the reinitiation of food or oral intake is usually started slowly and requires close observation under supervision by trained healthcare professionals. This is usually done in a hospital or nutritional rehabilitation center.