Prader-Willi Syndrome (PWS) and Angelman Syndrome (AS) are distinct neurogenetic disorders caused by the loss of function of genes on chromosome 15 (bands 15q11-13), on either the paternally or maternally inherited chromosome, respectively1. In 70% of patients, a large interstitial deletion of 3-4Mb is observed1,2. In around 3% of patients, an imprinting defect is observed, caused by either an epimutation or a microdeletion of the Imprinting Centre (IC)1,3. Uniparental disomy, in which both chromosome 15s are inherited from the same parent, accounts for most of the remaining patients with PWS/AS1.
The SNRPN gene is one of four imprinted loci that are expressed from the paternal chromosome 15 region (15q11-13) and maps to the minimally deleted region (MDR) involved in PWS5. Its chromosomal location and imprinting status suggest it plays a possible role in the aetiology of PWS4.
The imprinting centre (IC) maps to a 100kb region proximal to SNRPN. Parental deletions or mutations in the IC impair the imprinting process in 15q11-13 and cause one of two distinct diseases in their offspring5,6. Most of the PWS imprinting deletions involve SNRPN and are approximately 200kb in size. The AS imprinting deletions are small (approximately 40kb), involve the BD3 region, and do not include SNRPN.
SNRPN, 15q11.2, Red
15qter, 15q26.3, Green