Iqcb1, also known as NPHP5 (nephrocystin-5), is a gene encoding a ciliary protein. It plays a crucial role in ciliary function, especially in the formation of photoreceptor outer segments in the retina [7]. Mutations in Iqcb1 are associated with ciliopathies, including Senior-Løken syndrome characterized by Leber congenital amaurosis and nephronophthisis, as well as isolated retinopathy [1,2,3,4,5,6,7].

In Nphp5-knockout mice, absence of scotopic and photopic electroretinogram responses was observed, resembling Leber congenital amaurosis. There was abnormal accumulation of outer segment transmembrane protein in the endoplasmic reticulum, and the transition zones of photoreceptors were aberrant with reduced diameter. Photoreceptor degeneration was complete at 1 month of age, but was significantly delayed in cone-only retina (Nphp5 -/-;Nrl -/-) [7]. In in vitro studies using patient-derived cells, mutations in IQCB1 led to aberrantly elongated ciliary axonemes in fibroblasts and RPE, impaired development of outer segment structures in retinal organoids, and mislocalization of visual pigments, which could be rescued by AAV-mediated IQCB1 gene augmentation therapy [4].

In conclusion, Iqcb1 is essential for photoreceptor outer segment formation and normal ciliary function in the retina. The study of Iqcb1 knockout mouse models and patient-derived cells has provided insights into the pathogenesis of ciliopathies such as Senior-Løken syndrome and Leber congenital amaurosis, offering potential directions for therapeutic interventions [4,7].