Recent studies of rare human translocation patients narrowed the PWS critical genes to a 121-kb region containing PWCR1/HBII-85 and HBII-438 snoRNA genes.
As part of the PWCR1/HBII-85 snoRNA cluster is highly conserved between human and mice, while no copy of HBII-438 has been found in mouse, we conclude that PWCR1/HBII-85 snoRNAs is likely to play a major role in the PWS- phenotype.