Bardet-Biedl Syndrome 18
A number sign (#) is used with this entry because of evidence that Bardet-Biedl syndrome-18 (BBS18) can be caused by homozygous mutation in the BBIP1 gene (613605) on chromosome 10q25. One such patient has been reported.
DescriptionBBS18 is an autosomal recessive ciliopathy described in a single patient and characterized by retinitis pigmentosa, obesity, kidney failure, and cognitive disability (Scheidecker et al., 2014).
For a general phenotypic description and a discussion of genetic heterogeneity of Bardet-Biedl syndrome, see BBS1 (209900).
Clinical FeaturesScheidecker et al. (2014) studied a patient with Bardet-Biedl syndrome (BBS) who was the only affected sib of 4 born to consanguineous Italian parents. He had been diagnosed at age 49 based on the presence of 4 major features (retinitis pigmentosa, obesity, kidney failure, cognitive disability) and 1 minor feature (brachydactyly). Visual impairment was severe, with dense cataracts in addition to retinal dystrophy. End-stage renal failure occurred 4 years after diagnosis.
Molecular GeneticsIn a 49-year-old Italian man, born of consanguineous parents, with BBS18, Scheidecker et al. (2014) identified a homozygous truncating mutation in the BBIP1 gene (L58X; 613605.0001). In vitro functional expression studies in HEK cells showed that the mutant L58X protein was not incorporated into the BBSome, and morpholino knockout of the Bbip1 ortholog in zebrafish embryos recapitulated the ciliopathy phenotype.