Rp1l1, short for Retinitis pigmentosa 1-like 1, is a component of the photoreceptor cilium. Although its exact function remains unknown, it is crucial in photoreceptor biology [1,2]. The photoreceptor cilium is involved in vital processes related to vision, suggesting that Rp1l1 may participate in pathways related to maintaining normal photoreceptor function and thus normal vision.

Pathogenic variants in Rp1l1 lead to photoreceptor diseases. It has been associated with occult macular dystrophy (a cone-degeneration disorder) and retinitis pigmentosa (a rod-degeneration disorder) [1,2]. In a study of 1204 Japanese patients with retinitis pigmentosa, Rp1l1 variants were among the six genes that caused the disease in a significant proportion of patients [3]. Inherited eye diseases research in a Chinese cohort found that RP1L1 had a diagnostic yield of de novo mutations of 5.88% [4]. A case report of an Indian patient with a homozygous variant in Rp1l1 presented with RP1L1 maculopathy, showing ill-defined foveal mottling, sub-foveal hyper-reflective deposits, and outer retinal layer disruption [5]. Another study on early age-related macular degeneration found an association between RP1L1 rs3924612 polymorphism and the early development of AMD, especially in females and the 56-68-year-old age group [6]. In patients with macular and cone/cone-rod dystrophy, mutations in Rp1l1 were identified, contributing to the understanding of the genetic causes of these diseases [7]. In RP1L1-associated occult macular dystrophy, the disease was characterized by deterioration of L-and M-cone-driven function in the perifovea [8]. In Taiwanese patients with inherited retinal degeneration, RP1L1 was among the genes where variants led patients to seek medical help earlier [9]. A Chinese family was identified with a maculopathy case caused by new recessive compound heterozygous variants of Rp1l1, expanding the understanding of its phenotype and genotype [10].

In conclusion, Rp1l1 is essential for photoreceptor biology, and its variants are strongly associated with various photoreceptor-related diseases such as retinitis pigmentosa, occult macular dystrophy, and maculopathy. Research on Rp1l1 provides insights into the genetic mechanisms underlying these eye diseases, which may help in developing targeted diagnostic and therapeutic strategies for inherited retinal disorders.