Redouane Boulouiz

Mutations in TPRN Cause a Progressive Form of Autosomal-Recessive Nonsyndromic Hearing Loss

We performed genome-wide homozygosity mapping in a large consanguineous family from Morocco and mapped the autosomal-recessive nonsyndromic hearing loss (ARNSHL) in this family to the DFNB79 locus on chromosome 9q34. By sequencing of 62 positional candidate genes of the critical region, we identified a causative homozygous 11 bp deletion, c.42_52del, in the TPRN gene in all seven affected individuals. The deletion is located in exon 1 and results in a frameshift and premature protein truncation (p.Gly15AlafsX150). Interestingly, the deleted sequence is part of a repetitive and CG-rich motive predicted to be prone to structural aberrations during crossover formation. We identified another family with progressive ARNSHL linked to this locus, whose affected members were shown to carry a causative 1 bp deletion (c.1347delG) in exon 1 of TPRN. The function of the encoded protein, taperin, is unknown; yet, partial homology to the actin-caping protein phostensin suggests a role in actin dynamics.

No association between T222P/LGR8 mutation and cryptorchidism in the Moroccan population.

Background: Cryptorchidism is the most common genital anomaly in men. The INSL3/LGR8 system is involved in testicular descent via gubernacular development. INSL3 binds with high affinity to its receptor LGR8 and receptor activation is associated with cAMP signaling. Analysis of human INSL3 and LGR8 mutations confirms that some cases of cryptorchidism are caused by mutations in these genes. The T222P mutation is the only one within the LGR8 gene associated with the cryptorchidism phenotype. A strong association of the T222P mutation with cryptorchidism was found in an Italian population. Due to the same mutation being found in patients within the Mediterranean area, a possible founder effect of this mutation is supposed. Methods: We screened 109 patients with cryptorchidism and 250 controls in a Moroccan population. Results: We found that 3 of the 109 patients tested carry the T222P mutation and 4 individuals in the control group also carry the mutation. Conclusions: Our results show in fact that the same mutation is present in the Moroccan population, but an association between cryptorchidism and the T222P mutation was not found.

Prevalence of the mitochondrial A 1555G mutation in Moroccan patients with non-syndromic hearing loss

UNLABELLED Mutations in mitochondrial DNA (mtDNA), especially the A1555G transition in the 12S rRNA gene, are one of the causes of both aminoglycoside-induced and non-syndromic sensorineural hearing loss. OBJECTIVE The aim of this study was to determine the prevalence of the A1555G mitochondrial mutation in Moroccan patients. METHODS We performed molecular characterization by PCR-RFLP and direct sequencing of one hundred and sixty four patients (84 unrelated familial and 80 sporadic cases) with a congenital sensorineural non-syndromic hearing loss and one hundred normal hearing controls for the occurrence of the A1555G mutation. RESULTS Mutational analysis of the mtDNA showed the presence of the homoplasmic A1555G mutation in three families, leading to a frequency of 3.6% similar to that reported for European-populations. No A1555G mutation was detected in sporadic and controls cases. However, we detected in twenty normal hearing controls a novel polymorphism A1557C, which was not found in patient samples. We further evidenced the presence of the A1438G mitochondrial polymorphism in four patients with sensorineural hearing loss and in five controls. CONCLUSION Our results show that the occurrence of the A1555G mutation in hearing impaired patients accounts for 3.6% in a Moroccan patients and those novel mtDNA polymorphisms might contribute to a novel sub-haplogroup specific of the Magrheb.

Carrier Frequencies of Mutations/Polymorphisms in the Connexin 26 Gene (GJB2) in the Moroccan Population

Mutations in the Connexin 26 gene (GJB2/Cx26) are responsible for more than half of all cases of prelingual nonsyndromic recessive deafness in Caucasians. The carrier frequency of the 35delG-GJB2 mutation was found to be as high as 2-4% in the Mediterranean populations. Different GJB2 mutations were reported in the Moroccan patients with autosomal recessive nonsyndromic hearing loss; however, rare studies were carried out on the carrier frequencies of these mutations in the healthy populations. The aim of this study was to estimate the carrier frequencies of the GJB2 mutations in the Moroccan population. The molecular analysis of the 35delG mutation and other GJB2 sequence variations was performed in 386 healthy unrelated Moroccan individuals with no known hearing loss. Five GJB2 sequence variations at heterozygous state were found: two mutations, 35delG and 109G > A (V37I), and three polymorphisms, 79G > A (V27I), 341G > A (E114G), and 457G > A (V153I). The carrier frequency of the 35delG mutation was the highest with 2.07% [95% confidence interval (0.90-4.04%)], followed by that of the V37I mutation with 1.43% (0.06-5.39). The carrier frequency of V27I, E114G, and V153I changes was estimated to be 0.71% (0.01-4.34). This finding shows that the 35delG carrier frequency found here is similar to the one observed in Mediterranean populations. It provides new information about GJB2 carrier rates facilitating the diagnosis and the genetic counseling in the Moroccan population.

Molecular analysis of the TMPRSS3 gene in Moroccan families with non-syndromic hearing loss.

Autosomal recessive non-syndromic hearing impairment (ARNSHI) is the most common type of inherited hearing impairment, accounting for approximately 80% of inherited prelingual hearing impairment. Hearing loss is noted to be both phenotypically and genetically heterogeneous. Mutations in the TMPRSS3 gene, which encodes a transmembrane serine protease, are known to cause autosomal recessive non-syndromic hearing impairment DFNB8/10. In order to elucidate if the TMPRSS3 gene is responsible for ARNSHI in 80 Moroccan families with non-syndromic hearing impairment, the gene was sequenced using DNA samples from these families. Nineteen TMPRSS3 variants were found, nine are located in the exons among which six are missense and three are synonymous. The 10 remaining variations are located in non-coding regions. Missense variants analysis show that they do not have a significant pathogenic effect on protein while pathogenicity of some variant remains under discussion. Thus we show that the TMPRSS3 gene is not a major contributor to non-syndromic deafness in the Moroccan population.

The analysis of three markers flanking GJB2 gene suggests a single origin of the most common 35delG mutation in the Moroccan population

In Caucasian populations a single mutation, 35delG, accounts for the majority of GJB2 gene mediated hearing loss, with carrier frequencies estimated between 2-4%, possibly resulting from a founder effect rather than from a mutational hot spot. In Moroccan population, the 35delG mutation accounts for 90.8% of all GJB2 mutated alleles in deaf patients with a carrier frequency of 2.65%. The aim of this study was to evaluate whether the 35delG mutation has derived from a single origin in the Moroccan population. We enrolled 30 unrelated deaf patients homozygous for the 35delG mutation and 165 unrelated control individuals negative for this mutation, and genotyped three microsatellite markers flanking the GJB2 region: D13S141, D13S175 and D13S143. Data analysis revealed that the 35delG mutation is associated with particular alleles of these markers, with significant linkage disequilibrium for the 125 and 105 nucleotide long alleles of D13S141 and D13S175, and that a single specific haplotype accounts for 68% of the chromosomes carrying the 35delG mutation. The estimate age of 35delG mutation is 135 generations or approximately 2700 years old. Like in other Mediterranean populations, our results suggest that in the Moroccan population the 35delG mutation has derived from a single origin in a common founder process.

Recessive TBC1D24 Mutations Are Frequent in Moroccan Non-Syndromic Hearing Loss Pedigrees.

Mutations in the TBC1D24 gene are responsible for four neurological presentations: infantile epileptic encephalopathy, infantile myoclonic epilepsy, DOORS (deafness, onychodystrophy, osteodystrophy, mental retardation and seizures) and NSHL (non-syndromic hearing loss). For the latter, two recessive (DFNB86) and one dominant (DFNA65) mutations have so far been identified in consanguineous Pakistani and European/Chinese families, respectively. Here we report the results of a genetic study performed on a large Moroccan cohort of deaf patients that identified three families with compound heterozygote mutations in TBC1D24. Four novel mutations were identified, among which, one c.641G>A (p.Arg214His) was present in the three families, and has a frequency of 2% in control Moroccan population with normal hearing, suggesting that it acts as an hypomorphic variant leading to restricted deafness when combined with another recessive severe mutation. Altogether, our results show that mutations in TBC1D24 gene are a frequent cause (>2%) of NSHL in Morocco, and that due to its possible compound heterozygote recessive transmission, this gene should be further considered and screened in other deaf cohorts.

A novel mutation in the Espin gene causes autosomal recessive nonsyndromic hearing loss but no apparent vestibular dysfunction in a Moroccan family

Redouane Boulouiz,* Yun Li, Hafid Soualhine, Omar Abidi, Abdelaziz Chafik, Gudrun Nurnberg, Christian Becker, Peter Nurnberg, Christian Kubisch, Bernd Wollnik, and Abdelhamid Barakat Department of Genetics, Institut Pasteur du Maroc, Casablanca, Morocco Faculte des Sciences Universite Chouaib Doukkali, El-Jadida, Morocco Center for Molecular Medicine Cologne (CMMC), University of Cologne, Cologne, Germany Institute of Human Genetics, University of Cologne, Cologne, Germany Cologne Center for Genomics, University of Cologne, Cologne, Germany Institute for Genetics, University of Cologne, Cologne, Germany

Absence of GJB3 and GJB6 mutations in Moroccan familial and sporadic patients with autosomal recessive non-syndromic deafness.

UNLABELLED Deafness is an etiologically heterogeneous trait with a wide variety of genetic and environmental causes. It is generally considered that genetic factors account for at least half of all cases of profound congenital deafness, which can be classified in two categories - dominant or recessive - according to the mode of inheritance and in two types - syndromic or non-syndromic - according to the presence or absence of some other specific clinical features. Mutations in the gene GJB2, encoding the gap junction protein connexion 26, are considered to be responsible for up to 50% of familial cases of autosomal recessive non-syndromic hearing loss and for up to 15-30% of the sporadic cases. It has also been reported that mutations in the GJB6 and GJB3 genes contribute to autosomal recessive and autosomal dominant hearing defects in many populations. OBJECTIVE The aim of this study was to screen mutations in GJB6 and GJB3 genes in Moroccan patients with autosomal non-syndromic hearing loss. METHODS We carried out 95 patients with non-syndromic hearing loss. The patients, who were negative for homozygous mutations in GJB2 gene and GJB6-D13S1830 deletion, were tested for the coding regions of GJB6 and GJB3 genes by direct sequencing. RESULTS No deleterious mutation in GJB6 and GJB3 genes was detected in all deaf patients tested. Only a C357T silent transition in heterozygous state was found in the GJB3 gene in one patient. CONCLUSION The present data demonstrated that mutations in the GJB6 and GJB3 genes are an infrequent cause of non-syndromic deafness in Morocco.

Mutation rate at 17 Y-STR loci in “Father/Son” pairs from moroccan population

Precise knowledge of mutation rate at Y-STRs loci is essential for a correct evaluation of typing results in forensic casework and specially kinship genetic studies. In this study, we have examined 252 confirmed and unrelated father/son sample pairs from Moroccan population using the 17 Y-STR markers DYS19, DYS389I, DYS389II, DYS390, DYS391, DYS392, DYS393, DYS385a, DYS385b, DYS437, DYS438, DYS439, DYS448, DYS456, DYS458, DYS635, and Y-GATA-H4 of the AmpFlSTR Yfiler™ kit used in routine casework. We observed a total of 15 single repeat mutations between fathers and sons as mutational events. Nine mutations resulted in the gain of a repeat in the son and six resulted in a loss of a repeat. The average mutation rate in the studied sample is 3.5×10(-3) (95% CI 2-5.8×10(-3)). Furthermore, Y-STRs mutation occurrence seems to be 4 times more frequent than autosomal STRs mutation in this sample.