Angelman syndrome assessed by neurological and molecular cytogenetic investigations.

Angelman syndrome (AS) is characterized by severe psychomotor retardation, speech impairment, happy disposition with bursts of laughter, ataxia, convulsions, and some distinct physical anomalies. Correct diagnosis of AS is important because of its clinical implications, and once the disease is confirmed, familial genetic counseling becomes crucial. We evaluated 22 patients with a putative diagnosis of AS by both clinical and molecular cytogenetic analysis. A deletion of the region 15q11-13 could be identified cytogenetically in 11 cases by high-resolution technique (group I). Four additional cases were confirmed by fluorescence in situ hybridization (FISH) study with D15S11, SNRPN, D15S10, and GABRB 3 [Prader-Willi syndrome (PWS)/AS region probes] (group II). The common deletion of GABRB 3 was documented in those AS cases (n = 15) by FISH. The other 7 cases exhibited no deletion over 15q11-13 at either the cytogenetic or molecular level (group III). We compared the following associated neurological disorders: convulsions and abnormal EEG, microcephaly, sleep and behavior problems, brain anomalies proved by image studies, sexual precocity with pineal tumor among the three groups, as well as other clinical conditions including congenital heart disease, obesity, scoliosis, and hypopigmentation. In the present study, the differences in neurological and facial characteristics were not distinct among these groups. However, the associated conditions were more frequently observed in the patients with deletion than in those without deletion. The EEG features of AS appear to be less sufficient in helping identify patients at an early age before the clinical features become obvious. Therefore, a region involved in the major As phenotypes may contain only one or more tightly contiguous genes around the GABRB 3 locus, which may explain the clinical heterogeneity in AS.