A mutation in SLC22A4 encoding an organic cation transporter expressed in the cochlea strial endothelium causes human recessive non-syndromic hearing loss DFNB60.

The high prevalence/incidence of hearing loss (HL) in humans makes it the most common sensory defect. The majority of the cases are of genetic origin. Non-syndromic hereditary HL is extremely heterogeneous. Genetic approaches have been instrumental in deciphering genes that are crucial for auditory function. In this study, we first used NADf chip to exclude the implication of known North-African mutations in HL in a large consanguineous Tunisian family (FT13) affected by autosomal recessive non-syndromic HL (ARNSHL). We then performed genome-wide linkage analysis and assigned the deafness gene locus to ch:5q23.2-31.1, corresponding to the DFNB60 ARNSHL locus. Moreover, we performed whole exome sequencing on FT13 patient DNA and uncovered amino acid substitution p.Cys113Tyr in SLC22A4, a transporter of organic cations, cosegregating with HL in FT13 and therefore the cause of ARNSHL DFNB60. We also screened a cohort of small Tunisian HL families and uncovered an additional deaf proband of consanguineous parents that is homozygous for p.Cys113Tyr carried by the same microsatellite marker haplotype as in FT13, indicating that this mutation is ancestral. Using immunofluorescence, we found that Slc22a4 is expressed in stria vascularis (SV) endothelial cells of rodent cochlea and targets their apical plasma membrane. We also found Slc22a4 transcripts in our RNA-seq library from purified primary culture of mouse SV endothelial cells. Interestingly, p.Cys113Tyr mutation affects the trafficking of the transporter and severely alters ergothioneine uptake. We conclude that SLC22A4 is an organic cation transporter of the SV endothelium that is essential for hearing, and its mutation causes DFNB60 form of HL.

Genome-wide analysis reveals a novel autosomal-recessive hearing loss locus DFNB80 on chromosome 2p16.1-p21.

Hearing impairment (HI) is the decreased ability to hear and discriminate among sounds. It is one of the most common birth defects. Epidemiological data show that more than one child in 1000 is born with HI, whereas more than 50% of prelingual HI cases are found to be hereditary. So far, 95 published autosomal-recessive nonsyndromic HI (ARNSHI) loci have been mapped, and 41 ARNSHI genes have been identified. In this study, we performed a genome-wide linkage study in a consanguineous Tunisian family, and report the mapping of a novel ARNSHI locus DFNB80 to chromosome 2p16.1-p21 between the two single-nucleotide polymorphisms rs10191091 and rs2193485 with a maximum multipoint logarithm of odds score of 4.1. The screening of seven candidate genes, failed to reveal any disease-causing mutations.

Screening of the DFNB3 locus: identification of three novel mutations of MYO15A associated with hearing loss and further suggestion for two distinctive genes on this locus.

Recessive mutations of MYO15A are associated with nonsyndromic hearing loss (HL) in humans (DFNB3) and in the shaker-2 mouse. Human MYO15A has 66 exons and encodes unconventional myosin XVA. Analysis of 77 Tunisian consanguineous families segregating recessive deafness revealed evidence of linkage to microsatellite markers for DFNB3 in four families. In two families, sequencing of MYO15A led to the identification of two novel homozygous mutations: a nonsense (c.4998C>A (p.C1666X) in exon 17 and a splice site mutation in intron 54 (c.9229 + 1G>A). A novel mutation of unknown significance, c.7395 + 3G>C, was identified in the third family, and no mutation was found in the fourth family. In conclusion, we discovered three novel mutations of MYO15A, and our data suggest the possibility that there are two distinct genes at the DFNB3 locus.

TMC1 but not TMC2 is responsible for autosomal recessive nonsyndromic hearing impairment in Tunisian families.

Hereditary nonsyndromic hearing impairment (HI) is extremely heterogeneous. Mutations of the transmembrane channel-like gene 1 (TMC1) have been shown to cause autosomal dominant and recessive forms of nonsyndromic HI linked to the loci DFNA36 and DFNB7/B11, respectively. TMC1 is 1 member of a family of 8 genes encoding transmembrane proteins. In the mouse, MmTmc1 and MmTmc2 are both members of Tmc subfamily A and are highly and almost exclusively expressed in the cochlea. The restricted expression of Tmc2 in the cochlea and its close phylogenetic relationship to Tmc1 makes it a candidate gene for nonsyndromic HI. We analyzed 3 microsatellite markers linked to the TMC1 and TMC2 genes in 85 Tunisian families with autosomal recessive nonsyndromic HI and without mutations in the protein-coding region of the GJB2 gene. Autozygosity by descent analysis of 2 markers bordering the TMC2 gene allowed us to rule out its association with deafness within these families. However, 5 families were found to segregate deafness with 3 different alleles of marker D9S1837, located within the first intron of the TMC1 gene. By DNA sequencing of coding exons of TMC1 in affected individuals, we identified 3 homozygous mutations, c.100C-->T (p.R34X), c.1165C-->T (p.R389X) and the novel mutation c.1764G-->A (p.W588X). We additionally tested 60 unrelated deaf Tunisian individuals for the c.100C-->T mutation. We detected this mutation in a homozygous state in 2 cases. This study confirms that mutations in the TMC1 gene may be a common cause for autosomal recessive nonsyndromic HI.

Single-isomer R-salbutamol is not superior to racemate regarding protection for bronchial hyperresponsiveness.

Bronchial hyper-reactivity (BHR) has been suggested to follow cessation of regular medication with racemic salbutamol. This study aimed at investigating the effects from medication with R,S- and R-salbutamol on bronchial response to provocation with isocapnic hyperventilation of cold air (IHCA). Twenty-six patients with mild to moderate asthma were enrolled in a double-blind, randomised, cross-over study. Bronchial response to provocation was measured before and after 1 week's medication. Doses of 0.63 mg R-salbutamol or 1.25 mg R/S-salbutamol were inhaled three times daily during medication-weeks and a wash-out week intervened. Tests were performed 6 h after the last dose of test drug. Impulse oscillometry and forced expiratory volume during one second were methods used to identify bronchial response to provocation. Two patients withdrew from the investigation due to side-effects, one from R- the other from R,S-salbutamol. Comparable resting bronchial conditions were indicated by differences in baseline lung function values of <2% between study days. No statistically significant medication-dependent differences in BHR could be demonstrated between treatment groups. However, 15 patients exhibited higher (P = 0.03) post-treatment BHR after pure R-salbutamol than after R,S-salbutamol. Furthermore, plasma concentrations of R-salbutamol tended to be lower (P = 0.08) after medication with R- than after R,S-salbutamol despite equal doses of R-salbutamol given during the two separate treatment periods. We also found that considerable amounts of S-salbutamol were retrieved in plasma after medication with pure R-salbutamol. We conclude that we were unable to demonstrate favourable effects of R-salbutamol over R,S-salbutamol regarding response to provocation with IHCA after regular medication of 1 week's duration.