Résumé
ObjectiveRetinitis pigmentosa (RP) is the most common inherited retinal disease (IRD). It is characterized by degeneration of the light-sensing photoreceptors and/or the supporting retinal pigment epithelium, which leads to progressive vision loss. RP is clinically and genetically heterogeneous with over 90 causative genes. Currently the genetic causes in approximately 40% of cases are unresolved. To resolve such cases, we performed whole exome sequencing of 3 unrelated families presenting with RP and identified 4 patients carrying variants in TBC1D32. TBC1D32 belongs to a family of Rab GTPase-activating proteins and has been shown to have a role in regulating the primary cilium of the neural tube. To date, TBC1D32 variants have not been associated with an IRD.MethodsTo determine the role of TBC1D32 in the retina, and to validate TBC1D32 as a putative RP-causative gene, we developed and characterized induced pluripotent stem cell (iPSC)-derived retinal pigment epithelium (RPE) and retinal organoids from control and RP individuals.ResultsOur data showed that TBC1D32 was expressed at the level of the primary RPE cilium and that it played an important role in retinal pigment epithelium (RPE) ciliogenesis. Disrupted TBC1D32 expression provoked elongated ciliary defects that resulted in disrupted apical tight junctions, loss of functionality (delayed retinoid cycling and altered secretion balance), and the onset of an epithelial-mesenchymal transition–like phenotype. Furthermore, using patient-derived iPSC-derived retinal organoids, we detected connecting cilium anomalies that resulted in impaired trafficking to the outer segments of photoreceptors, where light interaction takes place.ConclusionOverall, using human iPSC-derived retinal models, we identify a critical role for TBC1D32 in retinal ciliogenesis and demonstrate that TBC1D32 variants lead to RP. We thus identify TBC1D32 as a novel IRD-causative gene, which has implications for alleviating current diagnostic deadlocks.