Loss-of-function mutations in human BBS9 and other members of the BBSome cause Bardet-Biedl syndrome, associated with a series of clinical features including obesity, renal anomalies, and retinopathy, with the obese phenotype as one of the key features of Bardet-Biedl syndrome patients. Here, BBS9 is linked to obesity due to melanocortin 4 receptor deficiency.