Molecular investigation of pediatric portuguese patients with sensorineural hearing loss

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.

Prevalence of GJB2 gene mutations correlated to presence of clinical and environmental risk factors in the etiology of congenital sensorineural hearing loss of the Romanian population

Although etiologically heterogeneous at least 50% of all early on-set hearing losses have a genetic cause and of these, the large majority, 75-80% are most probably autosomal recessive and 70% are non-syndromic. The rest of the congenital hearing losses are determined by clinical and environmental factors such as ototoxic medication, prematurity, and complications at birth. During the last decade it became clear that 50-80% of all such afflictions result from mutations in a single gene, GJB2, which encodes the protein Connexin 26. In order to, at least partially clarify this problem, especially in an emerging country such as Romania, where the problem is not studied adequately, we developed a comprehensive study of genetic, clinical and environmental risk factors for congenital hearing loss. The two most common variations of this gene, 35delG and W24X in children with positive diagnosis of bilateral severe to profound sensorineural hearing loss were investigated. A cohort of 34 children (20 female and 14 male), ages between 2 and 10 (mean age 4.62 years), coming from 33 non-related families were evaluated. All cases were diagnosed with severe or profound bilateral congenital SNHL. A statistical comparison of genetic and environmental/clinical prevalence was also attempted since the presence of a genetic disorder cannot rule out the role of other documented risk factors in the etiology of SNHL. The results showed that, 29.4% of cases (10/34) were homozygotic for the 35delG mutation 35delG/35delG), also known as genotype Δ/Δ. 5.88% of cases (2/34) belong to the heterozygotic bi-genic group 35delG/W24X. The clinical factors with high statistical significance for SNHL in a non-genetic group have no significance for genetic SNHL patients. Thus, the present study confirms the relatively high prevalence of the 35delG and W24X mutations in cases of congenital non-syndromic severe of profound bilateral SNHL.

GJB2 and GJB6 genes mutations in children with non-syndromic hearing loss

Introduction. At the moment there is not enough data in Romania about the incidence of the main genetic mutations which can cause hearing loss.

Objective. The current research aims to determine on a representative sample the prevalence of two mutations of genes GJB2 -c.35delG and p.W24X- and two mutations of genes GJB6 -del(GJB6-D13S1830), del(GJB6-D13S1854) respectively - in patients with congenital nonsyndromic sensorineural hearing loss (CNSHL).

Methods: The sample group included 179 children with CNSHL. The evaluation consist in: a.Clinical, laboratory and imagistic examination; b.ENT exam and audiological evaluation. c.Two methods (semi-nested PCR technique followed by RFLP, validated with ARMS-PCR analysis) for detection of c.35delG and pW24X mutations; d.PCR-multiplex technique for detecting del(GJB6-D13S1830) and del (GJB6-D13S1854).

Results: The audiological diagnosis was: profound hearing loss in 116 patients (64.8%), severe hearing loss in 29 children (16.2%) and moderate hearing loss in 34 patients (representing 19% of the trial patients). The prevalence for the three mutations was: 27.3 % for c.35delG, 3.6 % for p.W24X and 0.28% for del(GJB6-D13S1830). The detection of the three mutations (two on GJB2 gene and one on GJB 6 gene) has allowed to establish the genetic cause for deafness in 45 patients, representing 25.14% of the sample group. Our study is reporting the first case in Romania with a mutation of gene GJB6. Mutation del(GJB6-D13S1854) lacked in all 179 patients.

Conclusion: The prevalence data obtained in the current research are comparable to data communicated by studies from other European countries.

Study of Met34Thr variant in nonsyndromic hearing loss in four Portuguese families

Objective

The purpose of this work was to characterize the Met34Thr variant in a group of patients with nonsyndromic hearing loss, in order to establish a genotype-phenotype correlation.

Methods

13 cases from 4 unrelated Portuguese families were selected, in which one or more hearing-impaired members had Met34Thr variant.

Results

Met34Thr variant was identified in 11/13 cases. Two cases have an additional mutation - Val153Ile and 35delG. Hearing loss was mild in 2 patients (Met34Thr/Val153Ile; Met34Thr/Met34Thr), moderate in 3(Met34Thr/WT; Met34Thr/35delG; Met34Thr/Met34Thr), severe in 2 (2 Met34Thr/WT) and profound in 1 (Met34Thr/WT). Three individuals with Met34Thr had normal hearing thresholds.

Conclusion

The present data corroborate the hypothesis that the Met34Thr variant is associated with mild-to-severe forms of deafness and that this variant seems to segregate with a dominant hearing loss with incomplete penetrance and a variable expression of the phenotype. However, other factors are likely to also have a pathologic effect.

Ethnic-specific spectrum of GJB2 and SLC26A4 mutations: their origin and a literature review

OBJECTIVE

The mutation spectrum of the GJB2 and SLC26A4 genes, the 2 most common genes causing deafness, are known to be ethnic specific. In this study, the spectrum of the reported GJB2 and SLC26A4 mutations in different populations are reviewed and considered from a human migration perspective.

METHODS

Fifty-two and 17 articles on GJB2 and SLC26A4 mutations, respectively, were reviewed through the PubMed database from April 1996 to September 2014. The 4 most prevalent mutations were selected and compared. A cluster analysis was subsequently performed for these selected mutations.

RESULTS

The present review of frequent mutations shows the ethnic-specific GJB2 and SLC26A4 gene mutation spectrum. A cluster analysis of the GJB2 and SLC26A4 genes revealed similarities between ethnic populations.

CONCLUSION

The mutation spectrum reviewed in this study clearly indicated that the frequent mutations in the GJB2 and SLC26A4 genes are consistent with the founder mutation hypothesis. A comparison with the Y-chromosome phylogenetic tree indicated that these mutations may have occurred during human migration.