Case report: A novel missense variant in melanopsin associates with delayed sleep phenotype: Whole genome sequencing study.

Melanopsin (OPN4) is a blue light-sensitive opsin-type G-protein coupled receptor. It is highly expressed in photosensitive retinal ganglion cells which mediate responses to light, including regulation of sleep, circadian photoentrainment, and pupillary light response. Mutations in were shown to affect responses to light, ultimately affecting the regulation of circadian rhythms and sleep. In this study, we describe a male carrier of the missense variant diagnosed with delayed sleep-wake phase disorder (DSWPD), with a consistent recurrent pattern of delayed sleep onset The rs143641898 [NM_033282.4:c.502C>T p.(Arg168Cys)] variant in the gene was shown in a functional study to render the OPN4 protein non-functional. The variant is rare and likely increases the risk of DSWPD its direct effect on the melanopsin pathway. This study offers useful insights for the differential diagnosis and ultimately treatment of DSWPD risk in which patients carry pathogenic variants in the gene.