-year-old boy with obesity, hypogonadism, and small hands and feet who also has short stature and developmental delay. B, Angelman syndrome in a 4-year-old girl. Note wide stance and position of arms. C, Chromosomal microarray detection of approximately 5-Mb deletion in 15q11.2-q13.1 (red). D, Schematic of the 15q11.2-q13 region. The PWS region (shaded in blue) contains a series of imprinted genes (blue) that are expressed only from the paternal copy. The AS region (shaded in pink) contains two imprinted genes that are expressed only from the maternal copy, including the UBE3A gene, which is imprinted in the central nervous system and mutations in which can cause AS. The region is flanked by nonimprinted genes (purple) that are expressed from both maternal and paternal copies. Common deletions of the PWS/AS region, caused by recombination between pairs of segmental duplications, are shown in green at the bottom. Smaller deletions of the imprinting center (IC; orange) and of a subset of genes in the small nucleolar RNA (snoRNA) gene cluster can also lead to PWS. cen, Centromere; tel, telomere. See Sources & Acknowledgments.
TABLE 6-4
Genomic Mechanisms Causing Prader-Willi and Angelman Syndromes
| Mechanism | Prader-Willi Syndrome | Angelman Syndrome |
| 15q11.2-q13 deletion | ≈70% (paternal) | ≈70% (maternal) |
| Uniparental disomy | ≈20-30% (maternal) | ≈7% (paternal) |
| Imprinting center mutation | ≈2.5% | ≈3% |
| Gene mutations | Rare (small deletions within snoRNA gene cluster) | ≈10% (UBE3A mutations) |
| Unidentified | <1% | ≈10% |
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
