Prader Willi syndrome (PWS) is a contiguous gene syndrome, which presents with obesity and variable clini­cal manifestations. The full phenotype is evident at the age of 3-5 years. Angelman syndrome (AS) is a single gene disorder with lack of speech and ataxic gait. The two syndromes share the same cytogenetic alterations (mainly deletions) in the chromosomal region 15q11-13, but differ in parental origin of the deletions, suggesting genomic imprinting of the area. Clinical evaluation and DNA anal­ysis was performed in 171 Greek patients referred for PWS and AS syndromes during the period 1994-2001. Forty out of 114 (35%) PWS cases and 32/57 (56%) of AS cases met the typical diagnostic criteria. DNA analysis confirmed the diagnosis in 39/114 (34%) PWS and 18/57 (32%) AS patients. Deletions were detected in 28/39 PWS patients, while 11/39 had uniparental disomy (UPD). Deletions were also detected in all 18 AS patients. Among the confirmed cases were a pair of twins with PWS and a pair of twins with AS. Reasons for PWS referrals are often insufficient and include mainly neonatal hypotonia, obe­sity and learning difficulties, leading to misdiagnosis of the syndrome. Although clinical presentation of AS seems more reliable, it is possible that the routine molecular analysis performed in the present study is not specific enough to confirm diagnosis in all AS cases.

Key words: Prader Willi syndrome (PWS); Angelman syndrome (AS); 15q11-13 deletions; Dinucleotide repeat polymorphism( DNRP) analysis; Fluorescent in situ hy­bridization (FISH) analysis; twin gestation.

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Department of Medical Genetics, University of Athens Med­ical School, Aghia Sophia Children's Hospital, Athens, Greece