Screening of the eight BBS genes in Tunisian families: no evidence of triallelism.

PURPOSE To study Bardet-Biedl syndrome (BBS) in the Tunisian population and determine the presence of triallelism in the eight identified BBS genes. METHODS DNA samples were collected from 19 consanguineous Tunisian families with BBS. Genome-wide scans were performed with microsatellite markers in 12 families, and two-point linkage analyses were performed. Direct sequencing was used to screen patients with BBS for mutations in all eight identified BBS genes. RESULTS Mutations in the BBS genes were identified in nine families. In addition, a large consanguineous family (57004) showed linkage to the BBS7 locus, although no mutation was identified. Five novel mutations were present in the nine families: one in BBS2 (c.565C>T, p.ArgR189Stop), one in BBS5 (c.123delA, p.Gly42GlufsX11), one in BBS7 (g.47247455_47267458del20004insATA, p.Met284LysfsX7), and two in BBS8 (c.459+1G>A, p.Pro101LeufsX12 and c.355_356insGGTGGAAGGCCAGGCA, p.Thr124ArgfsX43). CONCLUSIONS All families in which mutations were identified show changes in both copies of the mutant gene, and inheritance patterns in all families are consistent with autosomal recessive inheritance excluding any evidence of triallelism in the BBS genes in Tunisia.