The diagnosis of<unk>  is based on: * A history of delayed motor milestones and then later a delay in general development, especially of speech * Unusual movements including fine tremors, jerky limb movements, hand flapping and a wide-based, stiff-legged gait. * Characteristic facial appearance (but not in all cases). * A history of epilepsy and an abnormal EEG tracing. * A happy disposition with frequent laughter * A deletion or inactivity on chromosome 15 by array comparative genomic hybridization (aCGH) or by BACs-on-Beads technology. Diagnostic criteria for the disorder were initially established in 1995 in collaboration with the<unk>  Foundation (US); these criteria underwent revision in 2005. Seizures are a consequence, but so is excessive laughter, which is a major hindrance to early diagnosis. Differential diagnosis Other conditions that can appear similar include: * Autism spectrum * Cerebral palsy * Rett<unk>  * Mowat–Wilson<unk>  * Adenylosuccinate lyase deficiency * Pitt–Hopkins<unk>  * Phelan–McDermid<unk>  * Prader–Willi<unk>
Angelman syndrome
Cerebral palsy
Gitelman syndrome
Prader–Willi syndrome
FG syndrome
Rett syndrome
Perlman syndrome
Autism spectrum