RS1 and X-linked retinoschisis: Loss-of-function mutations in the RS1 gene cause X-linked retinoschisis (XLRS), a disease with a prevalence of 1:5000–1:25,000 that is characterized by the splitting of retinal layers, intraretinal cystic cavities, and a decreased b/a-wave amplitude ratio in scotopic ERG recordings, indicating impaired signal transmission from photoreceptor cells to bipolar cells [24,25,26,48].