Bardet-Biedl Syndrome 7

A number sign (#) is used with this entry because Bardet-Biedl syndrome-7 (BBS7) is caused by homozygous mutation in the BBS7 gene (607590) on chromosome 4q27.

Description

BBS7 is an autosomal recessive disorder characterized by retinitis pigmentosa, postaxial polydactyly, mental retardation, obesity, renal anomalies, and hypogenitalism (Harville et al., 2010). Zaghloul and Katsanis (2009) estimated the contribution of BBS7 gene mutations to the total BBS mutational load to be 1.50%.

For a general phenotypic description and a discussion of genetic heterogeneity of Bardet-Biedl syndrome, see BBS1 (209900).

Clinical Features

The 4 affected children with BBS7 from the consanguineous family studied by Najmabadi et al. (2011) had severe intellectual disability, polydactyly, and obesity.

The patients from 4 families studied by Harville et al. (2010) with BBS7 had retinitis pigmentosa, polydactyly, obesity, hypogonadism, and renal anomalies. Three of the families were consanguineous.

Molecular Genetics

In 3 of 84 independent families of primarily European ancestry with BBS, Badano et al. (2003) identified biallelic mutations in the BBS7 gene (607590.0001-607590.0003).

By homozygosity mapping followed by exon enrichment and next-generation sequencing in 136 consanguineous families (over 90% Iranian and less than 10% Turkish or Arabic) segregating syndromic or nonsyndromic forms of autosomal recessive intellectual disability, Najmabadi et al. (2011) identified homozygosity for a 6-bp deletion in the BBS7 gene (607590.0004) in affected members of a family (M324) segregating Bardet-Biedl syndrome.

Harville et al. (2010) used homozygosity mapping in a worldwide cohort of 45 BBS families to identify 17 causative homozygous mutations in 20 families. Four of these mutations occurred in the BBS7 gene.