Figure 3

Summary of the genetic and expression map of chromosomal region 15q11.2-q13. The Prader-Willi syndrome (PWS) region (shown in blue) has five paternal-only (PWS region) expressed unique copy genes that encode polypeptides (MKRN3, MAGEL2, NECDIN, and SNURF-SNRPN) and a family of six paternal-only expressed snoRNA genes. Only UBE3A and ATP10A (shown in orange), related to Angelman syndrome (AS), have preferential maternal-only expression, and this imprinted expression is limited to certain tissue specific regions (specifically brain). The bipartite imprinting center (IC) lies proximal to the bicistronic SNURF-SNRPN gene and within the 2.5 Mb PWS/AS imprinted region. The cluster of GABA receptor genes (GABRB3, GABRA5, and GABRG3), OCA2 (type II albinism), and HERC2 are not imprinted and have biparental expression (shown in green). The jagged vertical lines denote the three common 5–6 Mb PWS and AS deletion breakpoints, BP1, BP2, and BP3. On rare occasions, there will be a distal breakpoint at BP4 or BP5. In between BP1 and BP2 lie four additional, nonimprinted genes, NIPA1, NIPA2, CYFIP1, and GCP5.⁹⁴ Type 1 deletions (T1D) extend from BP1 to BP3, and type 2 deletions (T2D) extend from BP2 to BP3. Note that there are more copies of the SNORD116 and SNORD115 genes than are shown, and the map has not been precisely drawn to scale.