NDP and Norrie disease: Highlighting the critical roles of Norrin‐FZD4 signaling in the retina, NDP, FZD4, LRP5, and TSPAN12 mutations were identified in a number of related congenital diseases with ocular manifestations, such as Norrie disease, osteoporosis‐pseudoglioma syndrome, and familial exudative vitreoretinopathy (FEVR; Warden et al, 2007; Baron & Kneissel, 2013; Gilmour, 2015), each of which are associated with hypovascularization of the retina and severe loss of visual function.