BBS21 is an autosomal recessive ciliopathy characterized by obesity, postaxial polydactyly, retinal degeneration, and mild cognitive impairment ({1:Heon et al., 2016}; {2:Khan et al., 2016}).nnFor a general phenotypic description and a discussion of genetic heterogeneity of Bardet-Biedl syndrome, see BBS1 (OMIM:209900).