Senior–Løken syndrome: A syndromic form of retinal dystrophy associated with nephronophthisis

► Senior–Løken syndrome (SLS) is an autosomal recessive disease. ► A combination of RP or LCA and nephronophthisis develop in patients with SLS. ► Mutations in the majority of the 13 known nephrocystin (NPHP) genes cause SLS. ► The biochemistry, cell biology and existing animal models for all NPHPs are reviewed. Senior–Løken syndrome (SLS) is an autosomal recessive disease characterized by development of a retinitis pigmentosa (RP)- or Leber congenital amaurosis (LCA)-like retinal dystrophy and a medullary cystic kidney disease, nephronophthisis. Mutations in several genes (called nephrocystins) have been shown to cause SLS. The proteins encoded by these genes are localized in the connecting cilium of photoreceptor cells and in the primary cilium of kidney cells. Nephrocystins are thought to have a role in regulating transport of proteins bound to the outer segment/primary cilium; however, the precise molecular mechanisms are largely undetermined. This review will survey the biochemistry, cell biology and existing animal models for each of the nephrocystins as it relates to photoreceptor biology and pathogenesis of retinal degeneration.