Bardet-Biedl Ciliopathy Renal Mechanism — ESENeph MCQ

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HardTubular DisordersBardet-Biedl Ciliopathy Renal MechanismESENeph

A 30-year-old man with Bardet-Biedl syndrome (BBS) has progressive CKD. He has retinitis pigmentosa, obesity, polydactyly, learning difficulties, and hypogonadism. His eGFR is 35 mL/min/1.73m2. Renal biopsy shows tubulointerstitial nephritis with mild cyst formation. What is the underlying cellular mechanism?

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Correct answer: D — Ciliary dysfunction (ciliopathy)

Bardet-Biedl syndrome (BBS) is a ciliopathy — caused by mutations in genes encoding proteins of the BBSome complex, which is essential for primary cilium function and intraflagellar transport. Primary cilia on renal tubular epithelial cells act as mechanosensors and signalling hubs (Hedgehog, Wnt, planar cell polarity pathways). Ciliary dysfunction leads to cyst formation, tubulointerstitial fibrosis, and progressive CKD. The multi-system features of BBS (retinal dystrophy from photoreceptor ciliopathy, polydactyly from Hedgehog signalling defects, obesity from hypothalamic ciliary dysfunction, cognitive impairment) all stem from the same ciliary defect. Other ciliopathies include ADPKD, nephronophthisis, Joubert syndrome, and Meckel-Gruber syndrome.

Reference: Forsythe & Bhatt 2013 – BBS Clinical Management; Hildebrandt et al 2011 – Ciliopathies