AS is a developmental disorder that affects movement, speech, and social demeanor. The disorder is caused by a deficiency of a maternally transmitted gene and is inherited at birth. Children with AS, however, are often not diagnosed until they are between 3 and 7 years old. Symptoms of AS may include, but are not limited to, functionally severe developmental delay; speech impairments; movement or balance problems; and behavioral uniqueness, including any combination of frequent laughter or smiling, apparent happy demeanor, easily excitable personality, hand flapping movements, and short attention span. There are four molecular variations of AS, but past clinical studies have been inconsistent in highlighting the phenotypic differences between them. This study will gain a better understanding of the disease progression and clinical features of AS by observing children with AS over a period of 5 to 10 years. The study will also attempt to establish genotype-phenotype correlations, which might aid in future clinical care of AS patients.

Participation in this observational study will be limited to current or future patients at one of the four study sites. A clinical evaluation will be performed at baseline, including a general patient history, physical and neurological examinations, a nutritional assessment, neuro-imaging, electroencephalography, laboratory testing, and neurodevelopmental testing. A blood sample or mucosal sample will also be taken at baseline to acquire DNA for potential genetic testing. All assessments except the neuro-imaging, electroencephalography, and blood sampling will be repeated at yearly study visits for a total of 5 years. In addition, participants will be photographed and perhaps videotaped on a yearly basis in order to document clinical phenotypes and any neurologic abnormalities. Participants may be followed-up for a total of 10 years.