Imprinting on human chromosome 15 is regulated by an imprinting centre, which has been mapped to a 100–kb region including exon 1 of SNRPN. From this region we have identified novel transcripts, which represent alternative transcripts of the SNRPN gene. The novel exons lack protein coding potential and are expressed from the paternal chromosome only. We have also identified intragenic deletions and a point mutation in patients who have Angelman or Prader–Willi syndrome due to a parental imprint switch failure. This suggests that imprint switching on human chromosome 15 may involve alternative SNRPN transcripts.