Mutations in a novel isoform of TRIOBP that encodes a filamentous-actin binding protein are responsible for DFNB28 recessive nonsyndromic hearing loss.

In a large consanguineous Palestinian kindred, we previously mapped DFNB28--a locus associated with recessively inherited, prelingual, profound sensorineural hearing impairment--to chromosome 22q13.1. We report here that mutations in a novel 218-kDa isoform of TRIOBP (TRIO and filamentous actin [F-actin] binding protein) are associated with DFNB28 hearing loss in a total of nine Palestinian families. Two nonsense mutations (R347X and Q581X) truncate the protein, and a potentially deleterious missense mutation (G1019R) occurs in a conserved motif in a putative SH3-binding domain. In seven families, 27 deaf individuals are homozygous for one of the nonsense mutations; in two other families, 3 deaf individuals are compound heterozygous for the two nonsense mutations or for Q581X and G1019R. The novel long isoform of TRIOBP has a restricted expression profile, including cochlea, retina, and fetal brain, whereas the original short isoform is widely expressed. Antibodies to TRIOBP reveal expression in sensory cells of the inner ear and colocalization with F-actin along the length of the stereocilia.

Genetics of congenital deafness in the Palestinian population: multiple connexin 26 alleles with shared origins in the Middle East.

In some Palestinian communities, the prevalence of inherited prelingual deafness is among the highest in the world. As an initial step towards understanding the genetic causes of hearing loss in the Palestinian population, 48 independently ascertained probands with non-syndromic hearing loss were evaluated for mutations in the connexin 26 gene. Of the 48 deaf probands, 11 (23%) were homozygous or compound heterozygous for mutations in GJB2. Five different mutations were identified: ivs1(+1) G-->A, 35delG, 167delT, T229C, 235delC. Nine deaf probands were homozygous and only two compound heterozygous. Among 400 hearing Palestinian controls, one carrier was observed (for 167delT). We show that GJB2 ivs1(+1) G-->A disrupts splicing, yielding no detectable message. Linkage disequilibrium analysis suggests, in the Palestinian and Israeli populations, a common origin of the 35delG mutation, which is worldwide, and of 167delT, which appears specific to Israeli Ashkenazi and Palestinian populations. A high prevalence of deafness, high frequency of homozygosity rather than compound heterozygosity among deaf, and low mutation carrier frequency together reflect the high levels of consanguinity of many extended Palestinian families. Some of the 25 families with multiple cases of inherited prelingual deafness and wildtype GJB2 sequences may represent as-yet-unknown genes for inherited hearing loss.