NDP and Norrie disease: Previous reviews have found no clear pattern in the nature of NDP mutations and their association with either FEVR or Norrie disease (Nikopoulos et al., 2010), with the exceptions that cysteine residue mutations have been associated with Norrie Disease (Wu et al., 2007) and that truncating mutations are associated with more severe visual loss than missense mutations (Smith et al., 2012).