Analysis of GJB2 mutation: evidence for a Mediterranean ancestor for the 35delG mutation

The GJB2 (Cx26) Gene Variants in Patients with Hearing Impairment in the Baikal Lake Region (Russia)

The GJB2 (Cx26) gene pathogenic variants are associated with autosomal recessive deafness type 1A (DFNB1A, OMIM #220290). Direct sequencing of the GJB2 gene among 165 hearing-impaired individuals living in the Baikal Lake region of Russia identified 14 allelic variants: pathogenic/likely pathogenic-nine variants, benign-three variants, unclassified-one variant, and one novel variant. The contribution of the GJB2 gene variants to the etiology of hearing impairment (HI) in the total sample of patients was 15.8% (26 out of 165) and significantly differed in patients of different ethnicity (5.1% in Buryat patients and 28.9% in Russian patients). In patients with DFNB1A (n = 26), HIs were congenital/early onset (92.3%), symmetric (88.5%), sensorineural (100.0%), and variable in severity (moderate-11.6%, severe-26.9% or profound-61.5%). The reconstruction of the SNP haplotypes with three frequent GJB2 pathogenic variants (c.-23+1G>A, c.35delG or c.235delC), in comparison with previously published data, supports a major role of the founder effect in the expansion of the c.-23+1G>A and c.35delG variants around the world. Comparative analysis of the haplotypes with c.235delC revealed one major haplotype G A C T (97.5%) in Eastern Asians (Chinese, Japanese and Korean patients) and two haplotypes, G A C T (71.4%) and G A C C (28.6%), in Northern Asians (Altaians, Buryats and Mongols). The variable structure of the c.235delC-haplotypes in Northern Asians requires more studies to expand our knowledge about the origin of this pathogenic variant.

Deep analysis of the LRTOMTc.242G>A variant in non-syndromic hearing loss North African patients and the Berber population: Implications for genetic diagnosis and genealogical studies

Autosomal recessive non‐syndromic hearing loss (ARNSHL) is the most common inherited sensory impairment. It is particularly frequent in North African populations who have a high rate of consanguineous marriage. The c.242G>A homozygous variant in LRTOMT gene was previously established as pathogenic and is associated with NSHL in both humans and mice. The aim of this study is to determine the carrier frequency for the LRTOMT c.242G>A variant and also to estimate its age in addition to evaluating its diagnostic potential as a deafness biomarker among various populations and ethnicities in Northern African countries. A total of 179 Tunisian and 34 Libyan unrelated deafness patients were screened for this variant. The homozygous c.242G>A variant was found in 5.02% and 2.94% in Tunisian and Libyan families, respectively. Subsequent screening for this variant in 263 healthy controls of various ethnicities (136 Tunisian Berbers, 32 Andalusian and 95 Tunisian from undefined ethnic origin) revealed higher frequency for the heterozygous state among Tunisians of Berber origin only (19.11%). Genotyping 7 microsatellite markers nearby the variant location in ARNSHL patients who had the homozygous variant revealed the same haplotype suggesting a common founder origin for this variant. The age of this variant was estimated to be between 2025 and 3425 years (this corresponds to 3400 years when the variant rate was set at 10⁻³ or 2600 years when the variant rate is set at 10⁻²), spreading along with the Berber population who migrated to North Africa. In conclusion, the LRTOMT c.242G>A homozygous variant could be used as a useful deafness biomarker for North African ARNSHL patients meanwhile the heterozygous variant could be utilized in genealogical studies for tracing those of the Berber ethnic group.

Genetics and meta-analysis of recessive non-syndromic hearing impairment and Usher syndrome in Maghreb population: lessons from the past, contemporary actualities and future challenges

Hereditary hearing impairment (HI) is a heterogeneous condition with over 130 genes associated with genetic non-syndromic HI (NSHI) and Usher syndrome (USH). Approximately 80% of hereditary NSHI cases have autosomal recessive (AR) mode of inheritance. The high rate of consanguinity and endogamy in the Maghreb countries, including Tunisia, Algeria and Morocco, represents a major contributing factor to the development of ARHI. Since the 90s, those populations, with their particular large familiar structure, represented an effective key towards the discovery of the first HI loci and genes. In this study, we performed a deep literature database search to analyze the mutational spectrum and the distribution of pathogenic variants responsible of USH and the NSHI among those populations. To date, 124 pathogenic variants were identified in 32 genes of which over 70% represent population-specific variants. The particular variants' distribution is related to the high rate of consanguinity as well as the multiple shared features such as demographic history of migrations and social behavior that promoted the spreading of several founder mutations within those countries. This is the first study to report lessons from the past and current actualities of HI within the three Maghreb countries. However, despite the great impact placed by such population for the HI genetic studies, only a few next-generation sequencing platforms have so far been implemented with those countries. We, therefore, believe that those countries should be supported to implement this technology that would definitely be of great value in the discovery of additional novel HI genes/variants.

High Rates of Three Common GJB2 Mutations c.516G>C, c.-23+1G>A, c.235delC in Deaf Patients from Southern Siberia Are Due to the Founder Effect

The mutations in the GJB2 gene (13q12.11, MIM 121011) encoding transmembrane protein connexin 26 (Cx26) account for a significant portion of hereditary hearing loss worldwide. Earlier we found a high prevalence of recessive GJB2 mutations c.516G>C, c.-23+1G>A, c.235delC in indigenous Turkic-speaking Siberian peoples (Tuvinians and Altaians) from the Tyva Republic and Altai Republic (Southern Siberia, Russia) and proposed the founder effect as a cause for their high rates in these populations. To reconstruct the haplotypes associated with each of these mutations, the genotyping of polymorphic genetic markers both within and flanking the GJB2 gene was performed in 28 unrelated individuals homozygous for c.516G>C (n = 18), c.-23+1G>A (n = 6), or c.235delC (n = 4) as well as in the ethnically matched controls (62 Tuvinians and 55 Altaians) without these mutations. The common haplotypes specific for mutations c.516G>C, c.-23+1G>A, or c.235delC were revealed implying a single origin of each of these mutations. The age of mutations estimated by the DMLE+ v2.3 software and the single marker method is discussed in relation to ethnic history of Tuvinians and Altaians. The data obtained in this study support a crucial role of the founder effect in the high prevalence of GJB2 mutations c.516G>C, c.-23+1G>A, c.235delC in indigenous populations of Southern Siberia.

The spectrum of GJB2 gene mutations in Algerian families with nonsyndromic hearing loss from Sahara and Kabylie regions

INTRODUCTION

DFNB1, caused by mutations of GJB2 or GJB6, is the most prevalent genetic form of nonsyndromic (i.e., isolated) congenital deafness in countries located around the Mediterranean Sea. Because some mutations are restricted to specific ethnic-geographic groups, we studied the prevalence and spectrum of GJB2/GJB6 mutations in deaf patients originating from two different Algerian regions, Kabylie and Sahara.

PATIENTS AND METHODS

Among 91 reportedly unrelated Algerian patients affected by prelingual deafness, 80 patients (41 from Kabylie and 39 from Sahara) were diagnosed with isolated deafness. All had profound deafness, except one patient with mild deafness. They were screened for the presence of GJB2 mutations by direct sequencing of the single coding exon of GJB2. Patients without mutations were then screened for the presence of the most frequent two deletions of GJB6: del(GJB6-D13S1854) and del(GJB6-D13S1830).

RESULTS

Causative mutations were found in 13 and 8 patients from Kabylie and Sahara, respectively, accounting for more than a quarter of the cohort. The c.35delG, p.Gly12Valfs*2 mutation remains the most important mutation both in Kabylie (10 patients) and Sahara (7 patients). All detected patients were homozygous for this mutation. In addition, two other mutations (c.139G > T, p.Glu47* and c.167delT, p.Leu56Argfs*26) were found homozygous in one family each, and two patients were compound heterozygotes for (c.35delG p.Gly12Valfs*2/c.139G > T, p.Glu47*). No deletion of GJB6 was detected.

CONCLUSION

We confirm that mutations in GJB2, mainly c.35delG, are one of the most prevalent causes of nonsyndromic congenital deafness in Algeria, whereas the del (GJB6-D13S1854) and del (GJB6-D13S1830) deletions of GJB6 contribute little, if any. Further investigation is needed to identify the cause of deafness in other patients without diagnostic.

Updated carrier rates for c.35delG (GJB2) associated with hearing loss in Russia and common c.35delG haplotypes in Siberia

Background

Mutations in GJB2 gene are a major causes of deafness and their spectrum and prevalence are specific for various populations. The well-known mutation c.35delG is more frequent in populations of Caucasian origin. Data on the c.35delG prevalence in Russia are mainly restricted to the European part of this country. We aimed to estimate the carrier frequency of c.35delG in Western Siberia and thereby update current data on the c.35delG prevalence in Russia. According to a generally accepted hypothesis, c.35delG originated from a common ancestor in the Middle East or the Mediterranean ~ 10,000–14,000 years ago and spread throughout Europe with Neolithic migrations. To test the c.35delG common origin hypothesis, we have reconstructed haplotypes bearing c.35delG and evaluated the approximate age of c.35delG in Siberia.

Methods

The carrier frequency of c.35delG was estimated in 122 unrelated hearing individuals living in Western Siberia. For reconstruction of haplotypes bearing c.35delG, polymorphic D13S141, D13S175, D13S1853 flanking the GJB2 gene, and intragenic rs3751385 were genotyped in deaf patients homozygous for c.35delG (n = 24) and in unrelated healthy individuals negative for c.35delG (n = 67) living in Siberia.

Results

We present updated carrier rates for c.35delG in Russia complemented by new data on c.35delG carrier frequency in Russians living in Western Siberia (4.1%). Two common D13S141-c.35delG-D13S175-D13S1853 haplotypes, 126-c.35delG-105-202 and 124-c.35delG-105-202, were reconstructed in the c.35delG homozygotes from Siberia. Moreover, identical allelic composition of the two most frequent c.35delG haplotypes restricted by D13S141 and D13S175 was established in geographically remote regions: Siberia and Volga-Ural region (Russia) and Belarus (Eastern Europe).

Conclusions

Distribution of the c.35delG carrier frequency in Russia is characterized by pronounced ethno-geographic specificity with a downward trend from west to east. Comparative analysis of the c.35delG haplotypes supports a common origin of c.35delG in some regions of Russia (Volga-Ural region and Siberia) and in Eastern Europe (Belarus). A rough estimation of the c.35delG age in Siberia (about 4800 to 8100 years ago) probably reflects the early formation stages of the modern European population (including the European part of the contemporary territory of Russia) since the settlement of Siberia by Russians started only at the end of sixteenth century.

Electronic supplementary material

The online version of this article (10.1186/s12881-018-0650-5) contains supplementary material, which is available to authorized users.

The OTOGL p.Arg925* Variant is Associated with Moderate Hearing Loss in a Syrian Nonconsanguineous Family

AIM

To screen for the genetic basis of congenital hearing loss in a Syrian family.

METHODS

A Syrian patient living in Lebanon presented with moderate congenital hearing loss. The patient's large nonconsanguineous family was recruited. DNA was extracted from blood samples and sent for whole-exome sequencing. A detailed clinical examination along with audiograms was obtained for all subjects.

RESULTS

Hearing loss was noted to be mild to moderate in the low and mid frequencies, sloping to moderate to severe in the high frequencies for all affected members. Results of DNA analysis showed the presence of a previously described p.Arg925* mutation in the OTOGL gene on both alleles in affected family members, whereas nonaffected members either had the wild type or one copy of the mutated allele.

DISCUSSION

Mutations affecting the OTOGL gene have been recently connected with nonsyndromic sensorineural hearing loss. Seven such mutations have already been described. The p.Arg925* reported in this study has been found once in a French family. The current report is the first to describe this mutation in a Middle Eastern family.

NADf chip, a two-color microarray for simultaneous screening of multigene mutations associated with hearing impairment in North African Mediterranean countries

Hearing impairment (HI) is the most frequent sensory defect. Genetic causes are involved in two thirds of prelingual cases. Moreover, the autosomal recessive HI frequency is increased in countries where there is a high rate of consanguinity, such as in North African Mediterranean countries. This population shares several features, including history and social behavior, that promote the spread of founder mutations. HI is characterized by tremendous heterogeneity in both the genetic and clinical aspects. The identification of the causal mutation is important for early diagnosis, clinical follow-up, and genetic counseling. Addressing the extreme genetic heterogeneity of HI using classic molecular methods would be expensive and time-consuming. We designed a cost-effective North African Deafness chip for rapid and simultaneous analysis of 58 mutations using multiplex PCR coupled with dual-color arrayed primer extension. These mutations are found in North African HI patients and are distributed over 31 exons and five introns in 21 distinct genes. Assay specificity was initially optimized using 103 archived DNA samples of known genotypes. Blind validation of HI-unrelated patients revealed mutant alleles in 13 samples, and these mutations were confirmed by Sanger sequencing. The North African Deafness chip allows for simultaneous genotyping of eight different samples, at a minimal cost and in a single day, and is therefore amenable to large-scale molecular screening of HI in North Africa.

GJB2 and GJB6 screening in Tunisian patients with autosomal recessive deafness

Autosomal recessive nonsyndromic deafness (ARNSD or DFNB) is a very common genetically heterogenous disorder. Although DFNB1 mutations are known to be the most frequent cause of this disorder, they are largely dependent on ethnic groups. The aims of our study are to specify the prevalence and the spectrum of GJB2 mutations as well as the prevalence of GJB6 large deletion in Tunisian population.

PATIENTS AND METHODS

95 unrelated patients with moderate to severe sensorineural hearing loss have been tested. The GJB2 coding region has been studied by PCR/Sequencing and the del(GJB6-D13S1830) mutation has been screened by fluorescent PCR multiplex.

RESULTS

27.36% of patients present mutations on both alleles of GJB2 gene and no one has the del(GJB6-D13S1830) mutation. The c.35delG mutation represents 86.5% of GJB2 deafness alleles and is found in homozygous state in 22 patients and in heterozygous state in one patient. Four other mutations are detected in four probands: two are compound heterozygous for the p.V37I/p.E47X and the c.35delG/p.R184P mutations, and two are homozygous for the p.E47X and the c.333-334delAA mutations.

CONCLUSION

Our results showed that c.35delG is the most common but not the only GJB2 mutation and that the del(GJB6-del D13S1830) is absent in our cohort. Consequently, we propose a systematic sequencing of GJB2 coding region for ARNSD Tunisian patients and we suggest additional studies to specify the real prevalence of del(GJB6-D13S1830) in our population.

Founder mutations in Tunisia: implications for diagnosis in North Africa and Middle East

Background

Tunisia is a North African country of 10 million inhabitants. The native background population is Berber. However, throughout its history, Tunisia has been the site of invasions and migratory waves of allogenic populations and ethnic groups such as Phoenicians, Romans, Vandals, Arabs, Ottomans and French. Like neighbouring and Middle Eastern countries, the Tunisian population shows a relatively high rate of consanguinity and endogamy that favor expression of recessive genetic disorders at relatively high rates. Many factors could contribute to the recurrence of monogenic morbid trait expression. Among them, founder mutations that arise in one ancestral individual and diffuse through generations in isolated communities.

Method

We report here on founder mutations in the Tunisian population by a systematic review of all available data from PubMed, other sources of the scientific literature as well as unpublished data from our research laboratory.

Results

We identified two different classes of founder mutations. The first includes founder mutations so far reported only among Tunisians that are responsible for 30 genetic diseases. The second group represents founder haplotypes described in 51 inherited conditions that occur among Tunisians and are also shared with other North African and Middle Eastern countries. Several heavily disabilitating diseases are caused by recessive founder mutations. They include, among others, neuromuscular diseases such as congenital muscular dystrophy and spastic paraglegia and also severe genodermatoses such as dystrophic epidermolysis bullosa and xeroderma pigmentosa.

Conclusion

This report provides informations on founder mutations for 73 genetic diseases either specific to Tunisians or shared by other populations. Taking into account the relatively high number and frequency of genetic diseases in the region and the limited resources, screening for these founder mutations should provide a rapid and cost effective tool for molecular diagnosis. Indeed, our report should help designing appropriate measures for carrier screening, better evaluation of diseases burden and setting up of preventive measures at the regional level.

Did the GJB2 35delG mutation originate in Iran?

Mutations in GJB2 are a major cause of autosomal recessive non-syndromic hearing loss (ARNSHL) in many populations. A single mutation of this gene (35delG) accounts for approximately 70% of GJB2 mutations that are associated with ARNSHL in Caucasians in many European countries and also in Iranian. In this study, we used PCR and restriction digestion to genotype five single nucleotide polymorphisms (SNPs) that define the genetic background of the 35delG mutation over an interval of 98 Kbp that includes the coding and flanking regions of GJB2. Two microsatellite markers, D13S175 and D13S141, were also analyzed in patients and controls. These data suggest that the 35delG mutation originated in northern Iran.

The IVS1-2A>G mutation in the SRD5A2 gene predominates in Cypriot patients with 5α reductase deficiency

BACKGROUND

5α steroid reductase deficiency (5αSRD) is an autosomal recessive enzymatic deficiency and mutations in the 5α steroid reductase type 2 gene (SRD5A2) result in male pseudohermaphrodism caused by decreased dihydrotestosterone (DHT) synthesis.

AIM

To identify the specific mutations of the SRD5A2 gene in Cypriot patients with 5αSRD.

SUBJECTS AND METHODS

Five unrelated patients with 46,XY karyotype were examined. Four of them were born with ambiguous genitalia and 1 patient, who was raised as girl, presented with primary amenorrhea. The hCG test was informative (elevated testosterone/DHT) of 5αSRD in 3 out of 4 subjects. Sequencing of the SRD5A2 gene was completed for all patients. Genomic DNA was also isolated from a total of 204 healthy unrelated Cypriot subjects. Screening for the IVS1-2A>G mutation was performed by using direct sequencing and restriction enzyme analysis.

RESULTS

The IVS1-2A>G was identified in homozygosity in 3 patients and in a compound heterozygote state in the other 2 patients, in combination with p.P181L and p.R171S in exon 3, respectively. The carrier frequency in the Cypriot population for the IVS1-2A>G mutation was estimated to be 0.98% or 2 in 204.

CONCLUSIONS

The same IVS1-2A>G mutation in the SRD5A2 gene seems to characterize all Cypriot patients with 5αSRD diagnosed so far. Furthermore this relatively rare genetic defect, which has only been reported previously in a single case in the Eastern Mediterranean region, is very likely to be the result of a founder effect.

High frequency of the p.R34X mutation in the TMC1 gene associated with nonsyndromic hearing loss is due to founder effects

Founder mutations, particularly 35delG in the GJB2 gene, have to a large extent contributed to the high frequency of autosomal recessive nonsyndromic hearing loss (ARNSHL). Mutations in transmembrane channel-like gene 1 (TMC1) cause ARNSHL. The p.R34X mutation is the most frequent known mutation in the TMC1 gene. To study the origin of this mutation and determine whether it arose in a common ancestor, we analyzed 21 polymorphic markers spanning the TMC1 gene in 11 unrelated individuals from Algeria, Iran, Iraq, Lebanon, Pakistan, Tunisia, and Turkey who carry this mutation. In nine individuals, we observed significant linkage disequilibrium between p.R34X and five polymorphic markers within a 220 kb interval, suggesting that p.R34X arose from a common founder. We estimated the age of this mutation to be between 1075 and 1900 years, perhaps spreading along the third Hadramaout population movements during the seventh century. A second founder effect was observed in Turkish and Lebanese individuals with markers in a 920 kb interval. Screening for the TMC1 p.R34X mutation is indicated in the genetic evaluation of persons with ARNSHL from North African and Southwest Asia.

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.

Mutation in gap and tight junctions in patients with non-syndromic hearing loss

Biallelic mutations in the GJB2, GJB3, GJB6 and CLDN14 genes have been implicated in autosomal recessive non-syndromic hearing impairment (ARNSHI). Moreover, a large number of GJB2 heterozygous patients was reported. The phenotype was in partly justified by the occurrence of two deletions including GJB6. We analysed GJB2, GJB6, GJB3 and CLDN14 in 102 Tunisian patients with ARNSHI. The deletions del(GJB6-D13S1830) and del(GJB6-D13S1854) were also screened. The c.35delG in GJB2 was the most frequent mutation (21.57%). It was detected at heterozygous state in 2 patients. The del(GJB6-D13S1830) was identified in one case at heterozygous state. No other mutation in studied gap junction genes was detected in heterozygous patients. Several polymorphisms were identified in GJB3, GJB6 and CLDN14. Our study confirms the importance of GJB2 screening in ARNSHI and suggests that in consanguineous populations, a single DFNB1 mutant allele in individuals with HI is likely due to a coincidental carrier state.

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.

High prevalences of carriers of the 35delG mutation of connexin 26 in the Mediterranean area

OBJECTIVE

Mutation 35delG in the connexin 26 gene is the main cause of recessive deafness in Europe. The prevalence of carriers varies, with a mean value proportion of 1/31 in Mediterranean countries. The aim of this study is to determinate the percentage of carriers in seven populations of the Mediterranean area and to compare prevalence of the mutation in seventeen other published populations in the same area.

METHODS

This study has been carried out on the genomic DNAs out of a total of 886 healthy subjects, originating from Sevilla (Spain), Genoa, Sicily (Italy), Alexandria (Egypt), Libya, Algier (Algeria) and Tangier (Morocco), genotyped by Taqman assay.

RESULTS

The approximate proportions of the 35delG mutation are <1/149 in Sevilla, 1/129 in Genoa, 1/34 in Sicily, 1/54 in Alexandria, 1/41 in Libya, 1/141 in Algier and 1/123 in Tangier. When compared to other Mediterranean populations, the mean prevalence of the mutation is 1/49. One of the most elevated values of 35delG prevalence corresponds to Greece (1/28); the pattern of various 35delG prevalences is interpretated in the present meta-analysis as the result of Ancient Greek colonizations of the "Magna Grecia" in historical times.

[The mutation 35delG of the gene of the connexin 26 is a frequent cause of autosomal-recessive non-syndromic hearing loss in Morocco]

Mutations of the connexin 26 gene, GJB2, are the most common cause of non syndromic autosomal-recessive hearing loss. One of the GJB2 mutations, the 35delG, is recurrent in European and Mediterranean populations with allelic frequency of at least 70% in patients with hearing loss caused by GJB2 impairment.

OBJECTIVES

To determine the prevalence of the 35delG mutation in non-syndromic autosomal-recessive deafness in Morocco.

PATIENTS AND METHODS

We looked for the 35delG mutation among 25 non-related Moroccan children suffering from an autosomal recessive hearing loss. A screening for GJB2 mutations, and then a search for GJB6 deletions were carried out among patients who do not bear the 35delG.

RESULTS

Twelve patients were homozygous for the 35delG mutation. This mutation was responsible for almost half of the hearing loss among our patients (48%). There was no other GJB2 or GJB6 mutation among 13 patients.

CONCLUSION

This study underlines the advantages of a systematic search for this mutation among deaf children when environmental causes are considered irrelevant. The identification of this genetic anomaly signs the etiologic diagnosis of deafness, which allows a relevant genetic advice, and a better treatment of patients.