Setmelanotide Response Variability in Two Genetically Confirmed Pediatric Kidney Transplant Recipients with Bardet-Biedl Syndrome.

Bardet-Biedl syndrome (BBS) is a genetically heterogeneous ciliopathy associated with hyperphagic obesity and kidney disease. Evidence on setmelanotide after pediatric kidney transplantation is limited. We evaluated two children with BBS treated with setmelanotide after kidney transplantation, collecting anthropometric, hunger, metabolic, graft-function, cyclosporine and genetic data. Patient 1, a 17-year-old boy with a homozygous pathogenic SDCCAG8 exon deletion, improved over 12 months: weight 55.6 to 48.0 kg, BMI 26.6 to 23.0 kg/m2, BMI-for-age z-score +1.60 to +0.43, maximal-hunger score 8/10 to 5/10, and HbA1c 6.5% to 5.1%. Patient 2, an 8-year-old girl with a homozygous likely pathogenic BBS5 splice-site variant and a heterozygous PCSK1 N221D variant, showed reduced hunger and an initial z-score fall from +6.10 to +5.69 by month 2.5, meeting the 0.2-point threshold for clinically meaningful change; this was not sustained, and BMI rose from 38.0 to 42.7 kg/m2 by eight months despite a dose of 3 mg/day. Graft function and cyclosporine trough concentrations remained stable, and skin hyperpigmentation was the only treatment-related adverse effect. In these two patients, setmelanotide was not associated with graft deterioration or altered cyclosporine trough concentrations, although two cases cannot establish safety. The divergent trajectories highlight interindividual variability; the role of PCSK1 N221D remains uncertain, and these observations are hypothesis-generating.