Congenital stationary night blindness: an update and review of the disease spectrum in Saudi Arabia.

Congenital stationary night blindness (CSNB) is a group of rare, mainly stationary disorders of the retina, resulting from dysfunction of several specific and essential visual processing mechanisms. The inheritance is often recessive and as such, CSNB may be more common among populations with a high degree of consanguinity. Here, we present a topic update and a review of the clinical and molecular genetic spectrum of CSNB in Saudi Arabia. Since a major review article on CSNB in 2015, which described 17 genes underlying CSNB, an additional four genes have been incriminated in autosomal recessive CSNB: RIMS2, GNB3, GUCY2D and ABCA4. These have been associated with syndromic cone-rod synaptic disease, ON bipolar cell dysfunction with reduced cone sensitivity, CSNB with dysfunction of the phototransduction (Riggs type) and CSNB with cone-rod dystrophy, respectively. In Saudi Arabia, a total of 24 patients with CSNB were identified, using a combination of literature search and retrospective study of previously unpublished cases. Recessive mutations in TRPM1 and CABP4 accounted for the majority of cases (5 and 13 for each gene, respectively). These genes were associated with complete (cCSNB) and incomplete (icCSNB), respectively, and were associated with high myopia in the former and hyperopia in the latter. Four novel mutations were identified. For the first time, we describe the fundus albipunctatus in two patients from Saudi Arabia, caused by recessive mutation in RDH5 and RPE65, where the former in addition featured findings compatible with cone dystrophy. No cases were identified with any dominantly inherited CSNB.