Identification of a novel mutation confirms the implication of IFT172(BBS20)in Bardet–Biedl syndrome

Bardet–Biedl syndrome (BBS; MIM 209900) is a recessive heterogeneous ciliopathy characterized by retinitis pigmentosa (RP), postaxial polydactyly, obesity, hypogonadism, cognitive impairment and kidney dysfunction. So far, 20 BBS genes have been identified, with the last reported ones being found in one or very few families. Whole-exome sequencing was performed in a consanguineous family in which two affected children presented typical BBS features (retinitis pigmentosa, postaxial polydactyly, obesity, hypogonadism and cognitive impairment) without any mutation identified in known BBS genes at the time of the study. We identified a homozygous splice-site mutation (NM_015662.2: c.4428+3A>G) in both affected siblings in the last reported BBS gene, namely, Intraflagellar Transport 172 Homolog (IFT172). Familial mutation segregation was consistent with autosomal recessive inheritance. IFT172mutations were initially reported in Jeune and Mainzer–Saldino syndromes. Recently, mutations have also been found in isolated RP and Bardet–Biedl-like ciliopathy. This is the second report of IFT172mutations in BBS patients validating IFT172as the twentieth BBS gene (BBS20). Moreover, another IFTgene, IFT27, was already associated with BBS, confirming the implication of IFTgenes in the pathogenesis of BBS.