Table 1.

Clinical characteristics of Angelman syndrome (adapted from Williams et al. [30]).

Consistent (100%)	Frequent (>80%)	Associated (<80%)
Normal prenatal and birth history, no major birth defects Normal metabolic, hematologic, and chemical laboratory results Severe developmental delay Movement or balance disorder, usually ataxia of gait and/or tremulous movement of the limbs Behavioral uniqueness: frequent laughter/smiling; apparent happy demeanor; excitability, often with hand-flapping movements; hypermotoric behavior; short attention span Speech impairment: none or minimal use of words, non-verbal communication skills higher than verbal ones	Delayed or disproportionately slow growth in head circumference: usually resulting in absolute or relative microcephaly by age 2 years Epilepsy: usually starting before age 3 years Abnormal electroencephalogram (EEG): a characteristic pattern of large-amplitude slow-spike waves	Flat occiput; Occipital groove; Protruding tongue; Tongue thrusting; Suck/swallowing disorders; Feeding problems and/or muscle hypotonia during infancy; Prognathia; Wide mouth, wide-spaced teeth; Frequent drooling; excessive chewing/mouthing behaviors; Strabismus.