SNRPN(Small Nuclear Ribonucleoprotein Polypeptide N), also called SMN, is a bicistronic imprinted gene that encodes 2 polypeptides, the SmN splicing factor, which is involved in RNA processing, and the SNRPN upstream reading frame (SNURF) polypeptide. The protein encoded by this gene is one polypeptide of a small nuclear ribonucleoprotein complex and belongs to the snRNP SMB/SMN family. SNRPN also encodes a long alternatively spliced transcript containing several small nucleolar RNAs (snoRNAs) and extends downstream to partially overlap the UBE3A gene in the antisense orientation. PWS arises from loss of function of genes in this region expressed exclusively from the paternal chromosome, suggesting that SNRPN may play a role in its etiology. The SNRPN gene is mapped on 15q11.2. Analysis of maternal DNA and of SNRPN cDNA confirmed that the maternal allele is not expressed in fetal brain and heart. Deletions in the transcription unit of the imprinted SNRPN gene occur in patients who have PWS or Angelman syndrome because of a parental imprint switch failure in this chromosomal domain.