Analysis of mitochondrial alterations in Brazilian patients with sensorineural hearing loss using MALDI-TOF mass spectrometry

Review and research gap identification in genetics causes of syndromic and nonsyndromic hearing loss in Saudi Arabia

Congenital hearing loss is one of the most common sensory disabilities worldwide. The genetic causes of hearing loss account for 50% of hearing loss. Genetic causes of hearing loss can be classified as nonsyndromic hearing loss (NSHL) or syndromic hearing loss (SHL). NSHL is defined as a partial or complete hearing loss without additional phenotypes; however, SHL, known as hearing loss, is associated with other phenotypes. Both types follow a simple Mendelian inheritance fashion. Several studies have been conducted to uncover the genetic factors contributing to NSHL and SHL in Saudi patients. However, these studies have encountered certain limitations. This review assesses and discusses the genetic factors underpinning NSHL and SHL globally, with a specific emphasis on the Saudi Arabian context. It also explores the prevalence of the most observed genetic causes of NSHL and SHL in Saudi Arabia. It also sheds light on areas where further research is needed to fully understand the genetic foundations of hearing loss in the Saudi population. This review identifies several gaps in research in NSHL and SHL and provides insights into potential research to be conducted.

Mitochondrial mutations in protein coding genes of respiratory chain including complexes IV, V, and mt-tRNA genes are associated risk factors for congenital heart disease

Most studies aiming at unraveling the molecular events associated with cardiac congenital heart disease (CHD) have focused on the effect of mutations occurring in the nuclear genome. In recent years, a significant role has been attributed to mitochondria for correct heart development and maturation of cardiomyocytes. Moreover, numerous heart defects have been associated with nucleotide variations occurring in the mitochondrial genome, affecting mitochondrial functions and cardiac energy metabolism, including genes encoding for subunits of respiratory chain complexes. Therefore, mutations in the mitochondrial genome may be a major cause of heart disease, including CHD, and their identification and characterization can shed light on pathological mechanisms occurring during heart development. Here, we have analyzed mitochondrial genetic variants in previously reported mutational genome hotspots and the flanking regions of mt-ND1, mt-ND2, mt-COXI, mt-COXII, mt-ATPase8, mt-ATPase6, mt-COXIII, and mt-tRNAs (Ile, Gln, Met, Trp, Ala, Asn, Cys, Tyr, Ser, Asp, and Lys) encoding genes by polymerase chain reaction-single stranded conformation polymorphism (PCR-SSCP) in 200 patients with CHD, undergoing cardiac surgery. A total of 23 mitochondrial variations (5 missense mutations, 8 synonymous variations, and 10 nucleotide changes in tRNA encoding genes) were identified and included 16 novel variants. Additionally, we showed that intracellular ATP was significantly reduced (P=0.002) in CHD patients compared with healthy controls, suggesting that the mutations have an impact on mitochondrial energy production. Functional and structural alterations caused by the mitochondrial nucleotide variations in the gene products were studied in-silico and predicted to convey a predisposing risk factor for CHD. Further studies are necessary to better understand the mechanisms by which the alterations identified in the present study contribute to the development of CHD in patients.

A fully integrated SNP genotyping system for hereditary hearing-loss detection

Hereditary hearing loss is one of the most common human neurosensory disorders, and there is a great need for early intervention methods such as genetically screening newborns. Single nucleotide polymorphisms (SNPs) are the major genetic targets for hearing-loss screening. In this study, a fully integrated SNP genotyping system was constructed to identify hereditary hearing loss-related genetic markers from human whole blood. The entire detection process, including blood cell lysis, nucleic acid extraction, the reaction mixture distribution, the chambers sealing and the two-colour multiplex competitive allele-specific polymerase chain reaction (KASP), can be automatically conducted in a self-contained cassette within 3 hours. To critically evaluate the performance of the system, its specificity, sensitivity and stability were assessed. Then, 13 clinical samples were genotyped with this fluidic cassette system to detect seven hotspot deafness-associated mutations in three genes (MT-RNR1, GJB2 and SLC26A4). The detection results of the cassette system were 100% concordant with those obtained by Sanger sequencing, proving its accuracy in the genetic screening of inherited hearing loss.

Genetic etiology of non-syndromic hearing loss in Latin America

Latin America comprises all countries from South and Central America, in addition to Mexico. It is characterized by a complex mosaic of regions with heterogeneous genetic profiles regarding the geographical origin of the ancestors and proportions of admixture between the Native American, European and African components. In the first years following the findings of the role of the GJB2/GJB6 genes in the etiology of hearing loss, most scientific investigations about the genetics of hearing loss in Latin America focused on assessing the frequencies of pathogenic variants in these genes. More recently, modern techniques allowed researchers in Latin America to make exciting contributions to the finding of new candidate genes, novel mechanisms of inheritance in previously known genes, and characterize a wide diversity of variants, many of them unique to Latin America. This review aimed to provide a general landscape of the genetic studies about non-syndromic hearing loss in Latin America and their main scientific contributions. It allows the conclusion that, although there are similar contributions of some genes, such as GJB2/GJB6, when compared to European and North American countries, Latin American populations revealed some peculiarities that indicate the need for tailored strategies of screening and diagnosis to specific geographic regions.

Impact of an MT-RNR1 Gene Polymorphism on Hepatocellular Carcinoma Progression and Clinical Characteristics

Mitochondrial DNA (mtDNA) mutations are highly associated with cancer progression. The poor prognosis of hepatocellular carcinoma (HCC) is largely due to high rates of tumor metastasis. This emphasizes the urgency of identifying these patients in advance and developing new therapeutic targets for successful intervention. However, the issue of whether mtDNA influences tumor metastasis in hepatoma remains unclear. In the current study, multiple mutations in mtDNA were identified by sequencing HCC samples. Among these mutations, mitochondrially encoded 12S rRNA (MT-RNR1) G709A was identified as a novel potential candidate. The MT-RNR1 G709A polymorphism was an independent risk factor for overall survival and distant metastasis-free survival. Subgroup analysis showed that in patients with cirrhosis, HBV-related HCC, α-fetoprotein ≥ 400 ng/mL, aspartate transaminase ≥ 31 IU/L, tumor number > 1, tumor size ≥ 5 cm, and histology grade 3-4, MT-RNR1 G709A was associated with both shorter overall survival and distant metastasis-free survival. Mechanistically, MT-RNR1 G709A was clearly associated with hexokinase 2 (HK2) expression and unfavorable prognosis in HCC patients. Our data collectively highlight that novel associations among MT-RNR1 G709A and HK2 are an important risk factor in HCC patients.

Detecting Rare Variants and Heteroplasmy of Mitochondrial DNA from High-Throughput Sequencing in Patients with Coronary Artery Disease

Background

Although mutations and dysfunction of mitochondrial DNA (mtDNA) are related to a variety of diseases, few studies have focused on the relationship between mtDNA and coronary artery disease (CAD), especially the relationship between rare variants and CAD.

Material/Methods

Two-stage high-throughput sequencing was performed to detect mtDNA variants or heteroplasmy and the relationship between them and CAD phenotypes. In the discovery stage, mtDNA was analyzed by high-throughput sequencing of long-range PCR products generated from the peripheral blood of 85 CAD patients and 80 demographically matched controls. In the validation stage, high-throughput sequencing for mtDNA target regions captured by GenCap Kit was performed on 100 CAD samples and 100 controls. Finally, tRNA fine mapping was performed between our study and the reported Chinese CAD study.

Results

Among the tRNA genes, we confirmed a highly conserved rare variant, A5592G, previously reported in the Chinese CAD study, and 2 novel rare mutations that reached Bonferroni’s correction significance in the combined analysis were found (P=7.39×10⁻⁴ for T5628C in tRNA^Ala and P=1.01×10⁻⁵ for T681C in 12S rRNA) in the CAD study. Both of them were predicted to be pathological, with T5628C disrupting an extremely conservative base-pairing at the AC stem of tRNA^Ala. Furthermore, we confirmed the controversial issue that the number of non-synonymous heteroplasmic sites per sample was significantly higher in CAD patients.

Conclusions

In conclusion, our study confirmed the contribution of rare variants in CAD and showed that CAD patients had more non-synonymous heterogeneity mutations, which may be helpful in identifying the genetic and molecular basis of CAD.

Mitochondrial mutations in non-syndromic hearing loss at UAE

INTRODUCTION

Hearing loss (HL) is a common sensory disorder over the world, and it has been estimated that genetic etiology is involved in more than 50% of the cases in developed countries. Both nuclear and mitochondrial genes were reported as responsible for hereditary HL. Mitochondrial mutations leading to HL have so far been reported in the MT-RNR1 gene, mitochondrially encoded 12S rRNA.

METHODS

To study the molecular contribution of mitochondrial 12S rRNA gene mutations in UAE-HL, a cohort of 74 unrelated UAE patients with no gap junction protein beta 2 (GJB2) mutations were selected for mitochondrial 12S rRNA gene mutational screening using Sanger sequencing and whole-exome sequencing. Detected DNA variants were analyzed by bioinformatics tools to predict their pathogenic effects.

RESULTS

Our analysis revealed the presence of two known deafness mutations; m.669T > C and m.827A > G in two different deaf individuals. Furthermore, whole-exome sequencing was done for these two patients and showed the absence of any nuclear mutations. Our study supports the pathogenic effect of the m.669T > C and m.827A > G mutations and showed that mitochondrial mutations have a contribution of 2.7% in our cohort.

CONCLUSIONS

This is the first report of mtDNA mutations in the UAE which revealed that both variants m.669T > C and m.827A > G should be included in the molecular diagnosis of patients with maternally inherited HL in UAE.

Genetics of Postlingual Sensorineural Hearing Loss

Literature and clinical practice around adult-onset hearing loss (HL) has traditionally focused on environmental risk factors, including noise exposure, ototoxic drug exposure, and cardiovascular disease. The most common diagnosis in adult-onset HL is presbycusis. However, the age of onset of presbycusis varies, and patients often describe family history of HL as well as individual variation in progression and severity. In recent years, there has been accumulating evidence of gene-environment interactions underlying adult cases of HL. Susceptibility loci for age-related HL have been identified, and genes related to postlingual nonsyndromic HL continue to be discovered through individual reports and genome-wide association studies. This review will outline main concepts in genetics as related to HL, identify implicated genes, and discuss clinical implications. Laryngoscope, 131:401-409, 2021.

The prevalence of mitochondrial mutations associated with aminoglycoside-induced deafness in ethnic Latvian population: the appraisal of the evidence

Aminoglycosides are potent antibiotics which are used to treat severe gram-negative infections, neonatal sepsis, and multidrug-resistant tuberculosis. Ototoxicity is a well-known side effect of aminoglycosides, and a rapid, profound, and irreversible hearing loss can occur in predisposed individuals. MT-RNR1 gene encoding the mitochondrial ribosomal 12S subunit is a hot spot for aminoglycoside-induced hearing loss mutations, however, a variability in the nature and frequency of genetic changes in different populations exists. The objective of this study was to analyze MT-RNR1 gene mutations in a Baltic-speaking Latvian population, and to estimate the prevalence of such genetic changes in the population-specific mitochondrial haplogroups. In the cohort of 191 ethnic non-related Latvians, the presence of two deafness-associated mutations, m.1555A>G and m.827A>G, three potentially pathogenic variations, m.961insC(n), m.961T>G and m.951G>A, and one unknown substitution, m961T>A was detected, and the aggregate frequency of all variants was 7.3%. All genetic changes were detected in samples belonged to the haplogroups H, U, T, and J. The presence of several aminoglycoside ototoxicity-related MT-RNR1 gene mutations in Baltic-speaking Latvian population indicates the necessity to include ototoxicity-related mutation analysis in the future studies in order to determine the feasibility of DNA screening for patients before administration of aminoglycoside therapy.

Investigation of the mtDNA mutations in Syrian families with non-syndromic sensorineural hearing loss

OBJECTIVE

Hearing loss is a common sensory disorder, and at least 50% of cases are due to a genetic etiology. Several mitochondrial DNA mutations (mtDNA) have been reported to be associated with nonsyndromic hearing loss (NSHL) in different population. However, There is no previous available data about the frequency of mtDNA mutations as etiology for deafness in Syrian. The aim of present study is to investigate the incidence of common mt DNA mutations in our families with congenital hearing loss and not related to the ototoxicity or aminoglycosides.

METHODS

A total of 50 deaf families were enrolled in the present study. Direct sequencing and PCR-RFLP methods were employed to detect seven mt DNA mutations, including A1555G, A3243G, C1494T, G3316A, T7510C, A7445G, and 7472insC.

RESULTS

Our results revealed a high prevalence of mt DNA mutation (10%) in deaf families (5/50). In surprising, the unexpected mutations were observed. The G3316A mutation was found in 2 families as homoplasmic genotype. Also, we found the homoplasmic and heteroplasmic genotype for the C1494T mutation in two families. In one family the heteroplasmic genotype for T7510C mutation was observed; this family harbor 35delG mutation in GJB2 gene. None of the common mtDNA mutations (A1555G, A3243G) and other mutations (A7445G, 7472insC) were detected here.

CONCLUSION

Our findings indicate to significant contribution of the mt DNA mutations in our families with NSHL. The presented data is the first report about mt DNA and it will improve the genetic counseling of hearing impaired in Syrian families.

A reverse dot blot assay for the screening of twenty mutations in four genes associated with NSHL in a Chinese population

Background

Congenital deafness is one of the most distressing disorders affecting humanity and exhibits a high incidence worldwide. Most cases of congenital deafness in the Chinese population are caused by defects in a limited number of genes. A convenient and reliable method for detecting common deafness-related gene mutations in the Chinese population is required.

Methods

We developed a PCR-reverse dot blot (RDB) assay for screening 20 hotspot mutations of GJB2, GJB3, SLC26A4, and MT-RNR1, which are common non-syndromic hearing loss (NSHL)–associated genes in the Chinese population. The PCR-RDB assay consists of multiplex PCR amplifications of 10 fragments in the target sequence of the four above-mentioned genes in wild-type and mutant genomic DNA samples followed by hybridization to a test strip containing allele-specific oligonucleotide probes. We applied our method to a set of 225 neonates with deafness gene mutations and 30 normal neonates.

Results

The test was validated through direct sequencing in a blinded study with 100% concordance.

Conclusions

The results demonstrated that our reverse dot blot assay is a reliable and effective genetic screening method for identifying carriers and individuals with NSHL among the Chinese population.