Examples include mapping of a severe autosomal recessive RP to subsequently identify a causative mutation in MERTK [33]; mapping of an autosomal recessive early onset generalized dystonia to subsequently identify a causative mutation in THAP1 [34]; and homozygosity mapping in one affected member of a consanguineous family segregating an autosomal recessive RP to identify three candidate regions, totaling 46 Mb, enabling subsequent identification of the causative mutation in C8orf37 [35]. The gene discussed is CFAP418; the disease is retinitis pigmentosa 1.