OBSOLETE: Uniparental disomy of chromosome 15

Uniparental disomy of chromosome 15 (UPD15) is an obsolete Orphanet entry that previously described a chromosomal mechanism rather than a single distinct clinical entity. Uniparental disomy of chromosome 15 occurs when both copies of chromosome 15 are inherited from a single parent instead of one from each parent. Because chromosome 15 contains an imprinted region (15q11-q13), the clinical consequences depend entirely on which parent contributed both copies. When both copies come from the mother (maternal UPD15), the result is Prader-Willi syndrome, characterized by neonatal hypotonia, feeding difficulties in infancy followed by hyperphagia and obesity in childhood, intellectual disability, hypogonadism, short stature, and behavioral problems. When both copies come from the father (paternal UPD15), the result is Angelman syndrome, characterized by severe intellectual disability, absent or minimal speech, movement and balance disorders (ataxia), seizures, and a characteristically happy demeanor with frequent laughing and smiling. This Orphanet entry has been marked as obsolete because UPD15 is a genetic mechanism rather than a standalone diagnosis. Patients are now classified under the specific clinical syndromes that result — Prader-Willi syndrome (Orphanet: 739) or Angelman syndrome (Orphanet: 72) — each of which can also arise through other genetic mechanisms such as deletions or imprinting defects. Management is syndrome-specific: Prader-Willi syndrome treatment includes growth hormone therapy, dietary management, and behavioral interventions, while Angelman syndrome management focuses on seizure control, physical therapy, and communication support. There is no cure for either condition, and care is multidisciplinary and lifelong.

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