Mutations ofGJB2in three geographic isolates from northern Tunisia: evidence for genetic heterogeneity within isolates

Geographically isolated populations have been successfully used to localize genes for recessive inherited diseases, including non-syndromic sensorineural recessive deafness (NSRD). To date, 25 loci for NSRD have been localized on human chromosomes (DFNB loci), and six of the corresponding genes have been identified. Here, we report on the contribution of the DFNB1 locus (GJB2 gene) to NRSD in seven affected families living in three northern Tunisian geographic isolates, and we provide evidence for genetic heterogeneity within isolates. This finding challenges the classical view of a single 'founder' mutation segregating in such isolates.