Biomedical subjects

Mirna Mustapha

Publications and source records attributed to Mirna Mustapha.

7 recordsLinked to original sources

PubMed2003

Usher syndrome type I G (USH1G) is caused by mutations in the gene encoding SANS, a protein that associates with the USH1C protein, harmonin.

Usher syndrome type I (USH1) is the most frequent cause of hereditary deaf-blindness in humans. Seven genetic loci (USH1A-G) have been implicated in this disease to date, and four of the corresponding genes have been identified: USH1B, C, D and F. We carried out fine mapping of USH1G (chromosome 17q24-25), restricting the location of this gene to an interval of 2.6 Mb and then screened genes present within this interval for mutations. The genes screened included the orthologue of the Sans gene, which is defective in the Jackson shaker deaf mutant and maps to the syntenic region in mice. In two consanguineous USH1G-affected families, we detected two different frameshift mutations in the SANS gene. Two brothers from a German family affected with USH1G were found to be compound heterozygotes for a frameshift and a missense mutation. These results demonstrate that SANS underlies USH1G. The SANS protein contains three ankyrin domains and a sterile alpha motif, and its C-terminal tripeptide presents a class I PDZ-binding motif. We showed, by means of co-transfection experiments, that SANS associates with harmonin, a PDZ domain-containing protein responsible for USH1C. In Jackson shaker mice the hair bundles, the mechanoreceptive structures of inner ear sensory cells, are disorganized. Based on the known interaction between USH1B (myosin VIIa), USH1C (harmonin) and USH1D (cadherin 23) proteins and the results obtained in this study, we suggest that a functional network formed by the USH1B, C, D and G proteins is responsible for the correct cohesion of the hair bundle.

Adaptor Proteins, Signal Transducing↗

PubMed2003

Defects in whirlin, a PDZ domain molecule involved in stereocilia elongation, cause deafness in the whirler mouse and families with DFNB31.

The whirler mouse mutant (wi) does not respond to sound stimuli, and detailed ultrastructural analysis of sensory hair cells in the organ of Corti of the inner ear indicates that the whirler gene encodes a protein involved in the elongation and maintenance of stereocilia in both inner hair cells (IHCs) and outer hair cells (OHCs). BAC-mediated transgene correction of the mouse phenotype and mutation analysis identified the causative gene as encoding a novel PDZ protein called whirlin. The gene encoding whirlin also underlies the human autosomal recessive deafness locus DFNB31. In the mouse cochlea, whirlin is expressed in the sensory IHC and OHC stereocilia. Our findings suggest that this novel PDZ domain-containing molecule acts as an organizer of submembranous molecular complexes that control the coordinated actin polymerization and membrane growth of stereocilia.

Amino Acid Sequence↗

PubMed2002

Otoancorin, an inner ear protein restricted to the interface between the apical surface of sensory epithelia and their overlying acellular gels, is defective in autosomal recessive deafness DFNB22.

A 3,673-bp murine cDNA predicted to encode a glycosylphosphatidylinositol-anchored protein of 1,088 amino acids was isolated during a study aimed at identifying transcripts specifically expressed in the inner ear. This inner ear-specific protein, otoancorin, shares weak homology with megakaryocyte potentiating factor/mesothelin precursor. Otoancorin is located at the interface between the apical surface of the inner ear sensory epithelia and their overlying acellular gels. In the cochlea, otoancorin is detected at two attachment zones of the tectorial membrane, a permanent one along the top of the spiral limbus and a transient one on the surface of the developing greater epithelial ridge. In the vestibule, otoancorin is present on the apical surface of nonsensory cells, where they contact the otoconial membranes and cupulae. The identification of the mutation (IVS12+2T>C) in the corresponding gene OTOA in one consanguineous Palestinian family affected by nonsyndromic recessive deafness DFNB22 assigns an essential function to otoancorin. We propose that otoancorin ensures the attachment of the inner ear acellular gels to the apical surface of the underlying nonsensory cells.

Amino Acid Sequence↗

PubMed2002

A novel locus for Usher syndrome type I, USH1G, maps to chromosome 17q24-25.

Usher syndrome (USH) is an autosomal recessive disorder associated with sensorineural hearing impairment and progressive visual loss attributable to retinitis pigmentosa. This syndrome is both clinically and genetically heterogeneous. Three clinical types have been described of which type I (USH1) is the most severe. Six USH1 loci have been identified. We report a Palestinian consanguineous family from Jordan with three affected children. In view of the combination of profound hearing loss, vestibular dysfunction, and retinitis pigmentosa in the patients, we classified the disease as USH1. Linkage analysis excluded the involvement of any of the known USH1 loci. A genome-wide screening allowed us to map this novel locus, USH1G, in a 23-cM interval on chromosome 17q24-25. The USH1G interval overlaps the intervals for two dominant forms of isolated hearing loss, namely DFNA20 and DFNA26. Since several examples have been reported of syndromic and isolated forms of deafness being allelic, USH1G, DFNA20, and DFNA26 might result from alterations of the same gene. Finally, a mouse mutant, jackson shaker ( js), with deafness and circling behavior has been mapped to the murine homologous region on chromosome 11.

Adult↗

PubMed2002

DFNB31, a recessive form of sensorineural hearing loss, maps to chromosome 9q32-34.

We report the identification of a novel locus responsible for an autosomal recessive form of hearing loss (DFNB) segregating in a Palestinian consanguineous family from Jordan. The affected individuals suffer from profound prelingual sensorineural hearing impairment. A genetic linkage with polymorphic markers surrounding D9S1776 was detected, thereby identifying a novel deafness locus, DFNB31. This locus could be assigned to a 9q32-34 region of 15 cM between markers D9S289 and D9S1881. The whirler (wi) mouse mutant, characterised by deafness and circling behaviour, maps to the corresponding region on the murine chromosome 4, thus suggesting that DFNB31 and whirler may result from orthologous gene defects.

Alleles↗

PubMed2002

Non-syndromic recessive deafness in Jordan: mapping of a new locus to chromosome 9q34.3 and prevalence of DFNB1 mutations.

Non-syndromic recessive deafness (NSRD) is the most commonly encountered form of hereditary hearing loss. The majority of NSRD cases in the Mediterranean area are linked to the DFNB1 locus (the connexin 26 GJB2 gene). Unrelated NSRD patients issued from 68 Jordanian families, were tested for mutations of the GJB2 gene by sequencing. Sixteen per cent of the families tested were linked to the DFNB1 locus. The 35delG was the only GJB2 mutation detected in these families. One of these families, presenting with four affected members and not linked to the gene, was subjected to a genome-wide search and was found to be mapped to 9q34.3 with a multipoint lodscore of 3.9. One candidate gene in the interval, coding for the chloride intracellular channel 3, CLIC3, was tested and excluded. The identification of a new NSRD locus, DFNB33, in one Jordanian family, shows the wide genetic heterogeneity that characterizes hearing impairment and the genetic diversity in Middle-Eastern populations.

Chromosome Mapping↗

PubMed2002

DFNB21.

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Adult↗