Cytogenetic and molecular study of Angelman syndrome.

Six patients, including two sibs, with Angelman syndrome (AS; three females and three males, aged 11 to 18 years) were studied cytogenetically. Molecular analysis was also performed. Using high-resolution banding technique, we detected a microdeletion in the proximal region of chromosome 15q in four cases. The deleted segment was heterogenous between these patients, and the common deleted region appeared to be 15q11.2. Four patients with deleted 15q were all sporadic cases, whereas in the sib cases we could not detect a visible deletion in the long arm of chromosome 15. However, there was no clinical difference between sporadic cases and sib cases. Densitometric analysis of autoradiographic bands of Southern hybridization using two DNA segments, pML34 and pTD3-21, as probes demonstrated that two patients had only one copy for each of the probes. In the remaining four patients, including the sibs, two copies of each sequence were retained. The probes used here detect a molecular deletion in most Prader-Willi syndrome patients. Thus the segment causing AS is localized adjacent to the critical segment of Prader-Willi syndrome. There seemed to be heterogeneity for the molecular deletion within AS individuals.