Truncating mutations in BBS10 and BBS12 impair proteostasis and ciliary architecture in Bardet-Biedl Syndrome.

**What the researchers found:** Scientists studied two families with children who have Bardet-Biedl Syndrome and discovered new genetic mutations in two specific genes called BBS10 and BBS12. These mutations cause the proteins made by these genes to become unstable and break down too quickly in cells. The children in both families showed the typical BBS symptoms including obesity, extra fingers or toes (polydactyly), and serious eye problems that affect vision. When the researchers looked closely at the eye problems, they found specific patterns of damage to the retina (the part of the eye that detects light). **Why this matters for patients:** This research helps doctors better understand how certain BBS mutations actually cause the disease symptoms. The scientists found that these particular mutations damage tiny cellular structures called cilia - small hair-like projections that help cells communicate and function properly. When cilia don't work correctly, it leads to the various symptoms seen in BBS. This study was done using laboratory cell cultures, so it's still early-stage research, but it provides important clues about how the disease works. **Looking ahead:** While this study doesn't offer new treatments yet, understanding exactly how these mutations cause problems is an important step toward developing better therapies in the future. The research helps confirm genetic diagnoses for families and adds to scientists' knowledge about which parts of these proteins are most critical for normal function.

Bardet-Biedl Syndrome (BBS) is a rare autosomal recessive ciliopathy characterized by genetic heterogeneity. Despite significant progress in understanding the BBSome-coding genes associated with ciliopathies, the pathogenesis linked to mutations in chaperonin-coding genes (BBS6, BBS10, and BBS12) remains poorly defined. This study aims to confirm the genetic diagnosis of BBS and elucidate the pathological mechanisms in causative genes of BBS10 and BBS12. Clinical evaluations were performed on BBS patients, followed by targeted next-generation sequencing (NGS) to identify disease-causing variants. Pathogenicity was assessed using computational prediction tools. Mutant BBS10 and BBS12 constructs were transfected into HEK293T cells for protein stability (Western blot) and interaction analyses (co-immunoprecipitation). Ciliogenesis was evaluated in hTERT-RPE1 cell model via immunofluorescence. The results identified novel compound heterozygous mutants in BBS10 (c. 1391G > C, c.2056 G > A) and BBS12 (c.590-591del AT, c.2102 C > G) in probands from two families. These mutations correlated with the classical BBS features: obesity, polydactyly, and retinal dystrophy. Ophthalmic examinations revealed bone spicule-like deposits, macular outer nuclear layer thinning, and photoreceptor loss in the retina. Comparative analysis across species revealed that these mutations occurred at conserved residues. Structural predictions indicated truncation at the protein's C-terminus. Transfection studies in HEK293T and hTERT-RPE1 cells showed that although the mutant protein localized to primary cilia similar to their wild-type counterparts, their stability was compromised, leading to accelerated degradation through ubiquitin-proteasome pathway. Our findings showed that C-terminal deletions in chaperonin-like BBS proteins significantly impaired their function, particularly affecting protein-protein interactions with each other and with the core BBSome subcomplex protein BBS7. The identified novel compound heterozygous mutations in BBS10 and BBS12 significantly affected ciliary length and protein-protein interactions critical for BBSome assembly, contributing to the manifestation of BBS symptoms.