The clinical manifestations of Angelman syndrome (AS) in 12 patients without a cytogenetic or molecular defect and 28 with a deletion were compared at the Department of Neurology, Leiden University Medical Center, and other hospitals in the Netherlands. Two minor differences were uncovered: mandibular prognathism was present in 100% of patients with a defect and 58% of those without; truncal hypotonia occurred in only 54% of the group with a genetic defect and in 91% of those without. All other characteristics, including seizures and EEG abnormalities, occurred with the same frequency in both groups. The absence of a detectable chromosome 15q11-13 anomaly does not change the AS phenotype. 
COMMENT. The clinical manifestations of Angelman syndrome with a chromosome defect include delayed motor milestones, ataxic puppet-like gait, absent speech, paroxysmal laughter, mandibular prognathism, macrostomia, brachycephaly, hyperreflexia, truncal hypotonia, and scoliosis. Patients without detectable chromosomal anomaly have a higher frequency of truncal hypotonia and less frequent prognathism. Otherwise the AS phenotype is essentially the same. In a previous study at the University of Pisa, Italy, the puppet-like movements were a manifestation of cortical myoclonus. (Progress in Pediatric Neurology III. 1997;p 390).