Prader-Willi Syndrome and Angelman Syndrome?
Within that region, there are multiple genes.


  Although the same gene may control imprinting for both disorders, the
  gene(s) causing their phenotypes differ. AS results from
  underexpression of a single gene, UBE3A, which codes for E6-AP, a
  protein that functions to transfer small ubiquitin molecules to
  certain target proteins, to enable their degradation. The genes
  responsible for PWS are not determined, although several maternally
  imprinted genes in 15q11-q13 are known. The most likely candidate is
  SNRPN


From this paper: http://www.ncbi.nlm.nih.gov/pubmed/11180221