Bi-allelic loss-of-function variants in POC5 cause a syndromic retinal, endocrine and neuromuscular ciliopathy

A homozygous loss-of-function (LoF) variant in POC5 centriolar protein (POC5) was previously described in an individual with retinitis pigmentosa. We identified POC5 variants in twelve probands with a syndromic phenotype. We aim to define the phenotype spectrum and molecular mechanism associated with bi-allelic POC5 LoF variants. We studied a cohort of twelve families with bi-allelic LoF POC5 variants and performed detailed phenotype analysis. POC5 localization studies were performed in three proband-derived fibroblast cell lines. Detailed phenotyping of probands with POC5 variants expands the phenotype spectrum beyond ocular manifestations. This syndrome causes not only rod-cone dystrophy but also diabetes mellitus with severe insulin resistance and partial lipodystrophy, kidney disease, and muscle cramps. The POC5 protein plays an essential role during cell cycle and cilium formation. Interestingly, POC5 localization studies in three proband-derived fibroblast cell lines show aberrant localization suggesting a ciliary defect. The phenotypes of the twelve families in this study fit well within the ciliopathy phenotype spectrum, except for lipodystrophy, which is not common in ciliopathies. We describe a multi-organ syndrome caused by bi-allelic LoF variants in POC5. This underscores the pleiotropic effects of POC5 variants and highlights the significance of adipose tissue and metabolic dysfunction in ciliopathies.