Clinical cytogenetic and molecular evidence in 1 patient with paternal uniparental disomy (UPD) for chromosome 15 is reported from the University of Florida College of Medicine, Gainesville, FL. The deletions of chromosome 15 q11-q13 were demonstrated with DNA probes. Twenty-seven patients with a clinical diagnosis of Angelman syndrome were evaluated in the laboratory by molecular genetic techniques. Twenty had a molecular deletion of 15 q11-q13, whereas 6 had biparental inheritance for chromosome 15 DNA markers. The 7th patient, who did not have a molecular deletion, had paternal UPD for chromosome 15. This is the first patient in whom UPD involved the critical chromosomal region. The overall frequency of paternal UPD was calculated at 3.7%. The low frequency of UPD in Angelman syndrome contrasts with the high frequency of 25% for maternal UPD in Prader-Willi syndrome. [1]

COMMENT. Angelman syndrome is characterized by severe mental retardation, absence of speech, inappropriate laughter, puppet-like ataxic movements, microbrachycephaly, seizures, an abnormal electrocephalogram, mild hypotonia, hypopigmentation and prognathism with tongue protrusion. Most cases of Angelman syndrome are due to deletions of exclusively maternal origin from a critical region in chromosome 15 q 11 -q 13. For a review of the diagnostic features of 36 cases of Angelman syndrome see Robb SA et al. [2, 3]