Figure 5.

Summary of the genetic and expression map of chromosomal region 15q11.2–q13. The position of genes and genetic markers (circles) are shown. In the PWS region (shown in blue), there are six paternal-only (PWS region) expressed unique copy genes (MKRN3, MAGEL2, NECDIN, C15ORF2 and SNURF- SNRPN and a family of five paternal-only expressed snoRNA genes). Only UBE3A and ATP10A (shown in red), related to Angelman syndrome (AS), have maternal-only expression in mouse and humans, and this imprinted expression is limited to certain tissue-specific regions (ie, brain). The bipartite imprinting center (IC) lies proximal to SNURF-SNRPN and within the 3 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 black). The jagged vertical lines denote the common 5–7 Mb AS and PWS deletion breakpoints, which lie within the segmental duplications associated with BP1, BP2 and BP3.⁴⁵ There are two common proximal breakpoints and one distal common breakpoint.⁴⁴ In between BP1 and BP2 lie four additional, non-imprinted genes GCP5 (TUBGCP5), CYFIP1, NIPA2 and NIPA1.⁴⁶ Type 1 deletions extend from BP1 to BP3 and type 2 deletions extend from BP2 to BP3. Note that there are more copies of the HBII-85 and HBII-52 genes than are shown.