Mutations In Different Genes Research Articles

OtoSeq Next‐Generation DNA Sequencing in the Evaluation of Congenital Sensorineural Hearing Loss

Objectives: Congenital sensorineural hearing loss (SNHL) is relatively common, occurring in 2 to 4 per 1000 infants, with genetic etiologies accounting for nearly 67% of cases. The clinical presentation of patients with syndromic and nonsyndromic SNHL is often indistinguishable. Establishing specific genetic causes is imperative for clinical management and genetic counseling. Recent advances in next-generation sequencing have allowed for facilitated multi-gene testing in genetically heterogeneous conditions such as SNHL. The present study evaluates the clinical utility of one such assay, OtoSeq, in genotyping pediatric patients with SNHL. Methods: Demographic, audiometric, imaging, and genetic data were retrospectively collected from 70 patients with prelingual hearing loss who underwent clinical genetic testing of 23 well-studied SNHL genes via OtoSeq, our next generation sequencing platform. The frequencies of pathogenic and likely pathogenic mutations were calculated and audiogram data were reviewed. Results: Of 70 patients studied, 15 patients (21%) were found to have an identifiable genetic etiology for their hearing loss, and 8 patients were found to have a previously undiagnosed genetic syndrome. Seven patients were diagnosed with nonsyndromic hearing loss. A total of 27 patients with mutations had adequate audiogram data available, of which 16 had mild to moderate hearing loss (59.3%) and 11 had severe to profound hearing loss (40.7%). Several unique combinations of deafness causing mutations in different genes were identified, including CDH23 and MYO7A, both Usher pathway of genes. Conclusions: This study demonstrates that OtoSeq is a valuable tool for determining genetic causes of SNHL in pediatric patients, which has direct implications for their clinical management.

Preliminary investigation of bottlenose dolphins (Tursiops truncatus) for hfe gene-related hemochromatosis.

Hemochromatosis (iron storage disease) has been reported in diverse mammals including bottlenose dolphins (Tursiops truncatus). The primary cause of excessive iron storage in humans is hereditary hemochromatosis. Most human hereditary hemochromatosis cases (up to 90%) are caused by a point mutation in the hfe gene, resulting in a C282Y substitution leading to iron accumulation. To evaluate the possibility of a hereditary hemochromatosis-like genetic predisposition in dolphins, we sequenced the bottlenose dolphin hfe gene, using reverse transcriptase-PCR and hfe primers designed from the dolphin genome, from liver of affected and healthy control dolphins. Sample size included two case animals and five control animals. Although isotype diversity was evident, no coding differences were identified in the hfe gene between any of the animals examined. Because our sample size was small, we cannot exclude the possibility that hemochromatosis in dolphins is due to a coding mutation in the hfe gene. Other potential causes of hemochromatosis, including mutations in different genes, diet, primary liver disease, and insulin resistance, should be evaluated.

Reproduction, smell, and neurodevelopmental disorders: genetic defects in different hypogonadotropic hypogonadal syndromes.

The neuroendocrine control of reproduction in mammals is governed by a neural hypothalamic network of nearly 1500 gonadotropin-releasing hormone (GnRH) secreting neurons that modulate the activity of the reproductive axis across life. Congenital hypogonadotropic hypogonadism (HH) is a clinical syndrome that is characterized by partial or complete pubertal failure. HH may result from inadequate hypothalamic GnRH axis activation, or a failure of pituitary gonadotropin secretion/effects. In man, several genes that participate in olfactory and GnRH neuronal migration are thought to interact during the embryonic life. A growing number of mutations in different genes are responsible for congenital HH. Based on the presence or absence of olfaction dysfunction, HH is divided in two syndromes: HH with olfactory alterations [Kallmann syndrome (KS)] and idiopathic hypogonadotropic hypogonadism (IHH) with normal smell (normosmic IHH). KS is a heterogeneous disorder affecting 1 in 5000 males, with a three to fivefold of males over females. KS is associated with mutations in KAL1, FGFR1/FGF8, FGF17, IL17RD, PROK2/PROKR2, NELF, CHD7, HS6ST1, FLRT3, SPRY4, DUSP6, SEMA3A, NELF, and WDR11 genes that are related to defects in neuronal migration. These reproductive and olfactory deficits include a variable non-reproductive phenotype, including sensorineural deafness, coloboma, bimanual synkinesis, craniofacial abnormalities, and/or renal agenesis. Interestingly, defects in PROKR2, FGFR1, FGF8, CHD7, DUSP6, and WDR11 genes are also associated with normosmic IHH, whereas mutations in KISS1/KISSR, TAC3/TACR3, GNRH1/GNRHR, LEP/LEPR, HESX1, FSHB, and LHB are only present in patients with normosmic IHH. In this paper, we summarize the reproductive, neurodevelopmental, and genetic aspects of HH in human pathology.

In Aspergillus nidulans the suppressors suaA and suaC code for release factors eRF1 and eRF3 and suaD codes for a glutamine tRNA.

In Aspergillus nidulans, after extensive mutagenesis, a collection of mutants was obtained and four suppressor loci were identified genetically that could suppress mutations in putative chain termination mutations in different genes. Suppressor mutations in suaB and suaD have a similar restricted spectrum of suppression and suaB111 was previously shown to be an alteration in the anticodon of a gln tRNA. We have shown that like suaB, a suaD suppressor has a mutation in the anticodon of another gln tRNA allowing suppression of UAG mutations. Mutations in suaA and suaC had a broad spectrum of suppression. Four suaA mutations result in alterations in the coding region of the eukaryotic release factor, eRF1, and another suaA mutation has a mutation in the upstream region of eRF1 that prevents splicing of the first intron within the 5′UTR. Epitope tagging of eRF1 in this mutant results in 20% of the level of eRF1 compared to the wild-type. Two mutations in suaC result in alterations in the eukaryotic release factor, eRF3. This is the first description in Aspergillus nidulans of an alteration in eRF3 leading to suppression of chain termination mutations.

Combined newborn screening for familial hemophagocytic lymphohistiocytosis and severe T- and B-cell immunodeficiencies

Combined newborn screening for familial hemophagocytic lymphohistiocytosis and severe T- and B-cell immunodeficiencies

Rapid and cost effective screening of breast and ovarian cancer genes using novel sequence capture method in clinical samples.

BRCA1 and BRCA2 are two well-known genes in the background of hereditary breast and ovarian cancer. There is also evidence that several other genes play an important role in the pathogenesis of these two malignancies. Latest population-scaled studies showed that certain mutations in different genes could cause similar risk elevation like BRCA2 mutations. In this study we present a new method to analyse the risk assessment of women to breast and ovarian cancer. Using Haloplex, a novel sequence capture method combined with next-generation sequencing we were able to perform rapid and cost-effective screening of 16 genes that could be associated with an increased risk of breast and ovarian cancer. The rapid and cost effective analysis of this 16-gene cohort can reveal the genetic background of approximately 30 % of hereditary and familiar cases of breast and ovarian cancers. Thus, it opens up a new and high-throughput approach with fast turnaround time to the genetic diagnostics of these disorders and may be helpful to investigate other familial genetic disorders as well.

Genetic basis of the variability of nitrate reduction trait in Yersinia pestis strains

The genetic basis of the varying ability to reduce nitrate in strains belonging to different biovars and subspecies of plague-causing microbe has been investigated and the inability to reduce nitrate observed in different intraspecies groups of Yersinia pestis has been shown to stem from mutations in different genes involved in the expression of this trait. The absence of denitrifying activity in strains of altaica and hissarica subspecies was not due to a mutation at position 613 of the periplasmic reductase napA observed in the strains of the biovar medievalis of the main subspecies, but rather was due to a mutation in the sequence encoding the nitrate-binding domain of the ABC transporter protein SsuA; a thymine insertion (+T) was detected at position 302 from the start of the ssuA gene. Five strains of biovar antiqua isolated at different times in Mongolia, China, and Africa were shown to lack the ability to reduce nitrate. A PCR test targeting two chromosomal regions containing deletions of 19 and 24 bp in size has been developed for the identification of strains of the biovar medievalis. This test can be combined with the test for the marker mutation in the napA gene for a more reliable detection of Y. pestis strains belonging to this biovar.

Update on primary hypobetalipoproteinemia.

"Primary hypobetalipoproteinemia" refers to an eclectic group of inherited lipoprotein disorders characterized by low concentrations of or absence of low-density lipoprotein cholesterol and apolipoprotein B in plasma. Abetalipoproteinemia and homozygous familial hypobetalipoproteinemia, although caused by mutations in different genes, are clinically indistinguishable. A framework for the clinical follow-up and management of these two disorders has been proposed recently, focusing on monitoring of growth in children and preventing complications by providing specialized dietary advice and fat-soluble vitamin therapeutic regimens. Other recent publications on familial combined hypolipidemia suggest that although a reduction of angiopoietin-like 3 activity may improve insulin sensitivity, complete deficiency also reduces serum cholesterol efflux capacity and increases the risk of early vascular atherosclerotic changes, despite low low-density lipoprotein cholesterol levels. Specialist laboratories offer exon-by-exon sequence analysis for the molecular diagnosis of primary hypobetalipoproteinemia. In the future, massively parallel sequencing of panels of genes involved in dyslipidemia may play a greater role in the diagnosis of these conditions.

Molecular diagnosis of putative Stargardt disease by capture next generation sequencing.

Stargardt Disease (STGD) is the commonest genetic form of juvenile or early adult onset macular degeneration, which is a genetically heterogeneous disease. Molecular diagnosis of STGD remains a challenge in a significant proportion of cases. To address this, seven patients from five putative STGD families were recruited. We performed capture next generation sequencing (CNGS) of the probands and searched for potentially disease-causing genetic variants in previously identified retinal or macular dystrophy genes. Seven disease-causing mutations in ABCA4 and two in PROM1 were identified by CNGS, which provides a confident genetic diagnosis in these five families. We also provided a genetic basis to explain the differences among putative STGD due to various mutations in different genes. Meanwhile, we show for the first time that compound heterozygous mutations in PROM1 gene could cause cone-rod dystrophy. Our findings support the enormous potential of CNGS in putative STGD molecular diagnosis.

M.3635G>A mutation as a cause of Leber hereditary optic neuropathy

Over 90% of Leber's hereditary optic neuropathy (LHON) is caused by one of three mtDNA mutations (m.11778A>G, m.3460G>A, m.14484T>C). The remaining cases are due to rare mutations in different genes...

Paternal germline mosaicism of a SCN2A mutation results in Ohtahara syndrome in half siblings

Ohtahara syndrome is a devastating early infantile epileptic encephalopathy caused by mutations in different genes. We describe a patient with Ohtahara syndrome who presented on the first day of life with refractory tonic seizures and a suppression-burst pattern on EEG. The patient developed severe microcephaly, and never achieved any developmental milestones. He died at the age of 5 years. A de novo missense mutation (c. 4007C>A, p.S1336Y) in SCN2A was found. Interestingly, the father has another son with Ohtahara syndrome from a different mother. The half brother carries the same SCN2A mutation, strongly suggesting paternal gonadal mosaicism of the mutation. The broad clinical spectrum of SCN2A mutations now includes Ohtahara syndrome. This is the first report of familial Ohtahara syndrome due to a germline mosaic SCN2A mutation. Somatic mosaicism, including germline, has been described in several epileptic encephalopathies such as Dravet syndrome, KCNQ2 neonatal epileptic encephalopathy, SCN8A epileptic encephalopathy and STXBP1 related Ohtahara syndrome. Mosaicism should be considered as one of the important inheritance patterns when counseling parents with a child with these devastating diseases.

Familial hemiplegic migraine: A model for the genetic studies of migraine

FHM3 is a rare subtype of familial hemiplegic migraine (FHM) caused by mutations in the neuronal sodium channel gene SCN1A (1). Only five FHM3 mutations have been described in a few families since the identification of SCN1A as the third FHM gene in 2005 (1–4). In the present issue of Cephalalgia, Weller et al. (5) report the identification of two novel SCN1A FHM3 mutations in two families with pure FHM. This study is important for clinicians managing patients with FHM, and should also encourage geneticists to consider or reconsider FHM as one of the major targets in the continuing quest for migraine genes. Despite extensive studies, migraine genes remain difficult to identify (6). The common migraines (migraine without aura and migraine with aura) are characterized by high prevalence in the general population, high phenotypic variability, absence of any objective diagnosis marker and polygenic inheritance. Therefore, a successful approach in the search for migraine genes has been the study of FHM, a rare autosomal dominant subform of migraine with aura characterized by the presence of a motor weakness during the aura phase. However, studies of FHM have shown that being monogenic does not imply being a ‘‘simple’’ model. Indeed, FHM is genetically heterogeneous, i.e. mutations in different genes can cause the same phenotype of recurrent migraine attacks with complex aura. From 1996 to 2005, three FHM genes have been identified that all encode ion transporters: a neuronal calcium channel (CACNA1A, FHM1) (7), a glial sodium/potassium pump (ATP1A2, FHM2) (8) and a neuronal sodium channel (SCN1A, FHM3) (1). In 2012, the proline-rich transmembrane protein 2 gene (PRRT2), encoding a protein associated with the exocytosis complex, was proposed as the fourth FHM gene (9,10). Mutations in CACNA1A, ATP1A2 and PRRT2 have also been found in patients with sporadic hemiplegic migraine (SHM) and are often de novo mutations (9,11–13). Study of cellular and murine models have shown that FHM mutations in CACNA1A and ATP1A2 facilitated the initiation of cortical spreading depression waves, the mechanism underlying the migraine aura, and increased neuronal excitability with an excess of glutamatergic neurotransmission (11,13). A proportion of cases with FHM or SHM do not harbor a mutation in the four known genes, indicating that other FHM genes are still to be discovered. Furthermore, genotype-phenotype correlations studies have described the wide clinical spectrum of FHM and the high clinical variability among patients with the same mutation (13). While most cases have so-called ‘‘pure’’ hemiplegic migraine, a small subset of familial and sporadic cases have associated manifestations including permanent cerebellar signs (nystagmus and/ or ataxia), epilepsy, cognitive impairment, elicited repetitive daily blindness and paroxysmal dyskinesia. Some patients can present with early-onset severe attacks with coma, prolonged hemiplegia, fever and brain edema (13). Moreover, different mutations in FHM genes induce other monogenic neurological disorders. CACNA1A mutations can cause episodic ataxia type 2 and spinocerebellar ataxia type 6 (7,13). PRRT2 mutations are associated with benign familial infantile convulsions, infantile convulsions with choreoathetosis, and paroxysmal dyskinesias (10). SCN1A was already known as an epilepsy gene previous to its identification as the FHM3 gene (1). Diagnosing HM might be a challenge. The first step relies on a detailed description of the aura (13). Apart from the presence of a motor weakness during the aura and the frequency of prolonged auras, most HM attacks are similar to attacks of migraine with typical or with brain stem aura. Single cases are diagnosed as sporadic HM, while at least two affected firstand/or

Massively Parallel DNA Sequencing Facilitates Diagnosis of Patients with Usher Syndrome Type 1

Usher syndrome is an autosomal recessive disorder manifesting hearing loss, retinitis pigmentosa and vestibular dysfunction, and having three clinical subtypes. Usher syndrome type 1 is the most severe subtype due to its profound hearing loss, lack of vestibular responses, and retinitis pigmentosa that appears in prepuberty. Six of the corresponding genes have been identified, making early diagnosis through DNA testing possible, with many immediate and several long-term advantages for patients and their families. However, the conventional genetic techniques, such as direct sequence analysis, are both time-consuming and expensive. Targeted exon sequencing of selected genes using the massively parallel DNA sequencing technology will potentially enable us to systematically tackle previously intractable monogenic disorders and improve molecular diagnosis.Using this technique combined with direct sequence analysis, we screened 17 unrelated Usher syndrome type 1 patients and detected probable pathogenic variants in the 16 of them (94.1%) who carried at least one mutation. Seven patients had the MYO7A mutation (41.2%), which is the most common type in Japanese. Most of the mutations were detected by only the massively parallel DNA sequencing. We report here four patients, who had probable pathogenic mutations in two different Usher syndrome type 1 genes, and one case of MYO7A/PCDH15 digenic inheritance.This is the first report of Usher syndrome mutation analysis using massively parallel DNA sequencing and the frequency of Usher syndrome type 1 genes in Japanese. Mutation screening using this technique has the power to quickly identify mutations of many causative genes while maintaining cost-benefit performance. In addition, the simultaneous mutation analysis of large numbers of genes is useful for detecting mutations in different genes that are possibly disease modifiers or of digenic inheritance.

Arrythmogenic right ventricular cardiomyopathy

<h3>Key points</h3> 1. A cause of arrhythmias and sudden death. 2. Usually in young males during exertion. 3. Transmural fat macroscopically with thinning and scarring in both ventricles. 4. Heart may be macroscopically normal. 5. Microscopically transmural fat and fibrosis with focal inflammation usually on epicardial surface of right and left ventricle. Fat infiltration alone is not pathological. 6. Histological changes may be focal in the right ventricular outflow tract. 7. Be wary and do not diagnose in obesity, coronary artery disease and in the elderly. The classification of cardiomyopathies is now based more on genetic and pathogenetic mechanisms. Gene mutations distinguish cytoskeleton (cytoskeletalopathies, e.g. DCM or ARVC), sarco-meric (sarcomyopathies as in HCM and RCM) and ion channel (channelopathies, e.g., long or short QT syndrome and Brugada's syndrome) cardiomyopathies. Cardiomyopathies, previously considered single entities, are the result of mutations in different genes. Different mutations in the same gene may be the cause of different clinical entities. Large phenotypic and genetic heterogeneity exists. Arrhythmogenic cardiomyopathy (ARVC) was the last cardiomyopathy to be described back in the 1990 s and its pathogenesis remains controversial both pathologically and genetically. Both the right and left ventricle can be involved with transmural fat infiltration and fibrosis.

Syndromic and non-syndromic forms of retinitis pigmentosa: a comprehensive Italian clinical and molecular study reveals new mutations.

Mutations in more than 60 different genes have been associated with non-syndromic and syndromic retinitis pigmentosa (RP), a heterogeneous group of inherited retinal dystrophies. To increase the understanding of the molecular epidemiology of the disease in Italy, we analyzed 56 patients with syndromic and non-syndromic forms of RP attending the Retinitis Pigmentosa Center of San Paolo Hospital (Milan, Italy). Patients underwent detailed clinical examination. Genomic DNA isolated from peripheral blood samples was screened for mutations in different genes according to RP form by direct sequencing analysis. The impact of novel missense mutations on protein functions was predicted by in silico analysis and protein sequence alignment. Cosegregation analysis was performed between available family members. Forty-one of the 56 probands analyzed had non-syndromic and 15 had syndromic RP forms. Putative disease-causing mutations were identified in 19 of 56 unrelated RP probands. Mutation screening identified a total of 22 different heterozygous variants. Notably, 12 of these putative pathogenic mutations have not been previously reported. New variants were found to be located on the USH2A, RPGR, EYS, and RHO genes. All 3 new variants detected in X-linked RP probands were confirmed in other affected family members. We found a positivity rate of 24.4% and 60% for probands with non-syndromic and syndromic RP, respectively. This is the first report of RPGR X-linked RP proband-ORF15 mutations in Italian patients with X-linked (XL)-RP. In addition, this is the first report of data regarding the association between EYS mutations and non-syndromic RP forms in the Italian population.

Hereditary hypomelanocytoses: the role of PAX3, SOX10, MITF, SNAI2, KIT, EDN3 and EDNRB genes

Hypo- and hyperpigmentation disorders are the most severe dermatological diseases observed in patients from all over the world. These disorders can be divided into melanoses connected with disorders of melanocyte function and melanocytoses connected with melanocyte development. The article presents some hereditary hypomelanocytoses, which are caused by abnormal melanoblast development, migration and proliferation as well as by abnormal melanocyte viability and proliferation. These disorders are represented by Waardenburg syndrome, piebaldism and Tietz syndrome, and are caused by different mutations of various or the same genes. The types of mutations comprise missense and nonsense mutations, frameshifts (in-frame insertions or deletions), truncating variations, splice alterations and non-stop mutations. It has been demonstrated that mutations of the same gene may cause different hypopigmentation syndromes that may have similar phenotypes. For example, mutations of the MITF gene cause Waardenburg syndrome type 2A as well as Tietz syndrome. It has also been demonstrated that mutations of different genes may cause an identical syndrome. For example, mutations of MITF, SNAI2 and SOX10 genes are observed in Waardenburg syndrome type II and mutations of EDNRB, EDN3 and SOX10 genes are responsible for Waardenburg syndrome type IV. In turn, mutation of the KIT gene and/or heterozygous deletion of the SNAI2 gene result in piebaldism disease. The knowledge of the exact mechanisms of pigmentary disorders may be useful in the development of new therapeutic approaches to their treatment.

Genetics of Parkinson's disease – state of the art, 2013

In the past 15 years there has been substantial progress in our understanding of the genetics of Parkinson's disease (PD). Highly-penetrant mutations in different genes (SNCA, LRRK2, VPS35, Parkin, PINK1, and DJ-1) are known to cause rare monogenic forms of the disease. Furthermore, different variants with incomplete penetrance in the LRRK2 and the GBA gene are strong risk factors for PD, and are especially prevalent in some populations. Last, common variants of small effect size, modulating the risk for PD, have been identified by genome-wide association studies in more than 20 chromosomal loci. Here, I first outline the evolution of the research strategies to find PD-related genes, and then focus on recent advances in the field of the monogenic forms, including VPS35 mutations in autosomal dominant PD, and DNAJC6 and SYNJ1 mutations in recessive forms of juvenile parkinsonism. Additional genetic determinants of PD likely remain to be identified, as the currently known mutations and variants only explain a minor fraction of the disease burden. There is great expectation that the new DNA sequencing technologies (exome and whole-genome sequencing) will bring us closer to the full resolution of the genetic landscape of PD.

A comparative survey of functional footprints of EGFR pathway mutations in human cancers

Genes functioning in epidermal growth factor receptor (EGFR) signaling pathways are among the most frequently activated oncogenes in human cancers. We have conducted a comparative analysis of functional footprints (that is, effect on signaling and transcriptional landscapes in cells) associated with oncogenic and tumor suppressor mutations in EGFR pathway genes in human cancers. We have found that mutations in the EGFR pathway differentially have an impact on signaling and metabolic pathways in cancer cells in a mutation- and tissue-selective manner. For example, although signaling and metabolic profiles of breast tumors with PIK3CA or AKT1 mutations are, as expected, highly similar, they display markedly different, sometimes even opposite, profiles to those with ERBB2 or EGFR amplifications. On the other hand, although low-grade gliomas and glioblastomas, both brain cancers, driven by EGFR amplifications are highly functionally similar, their functional footprints are significantly different from lung and breast tumors driven by EGFR or ERBB2. Overall, these observations argue that, contrary to expectations, the mechanisms of tumorigenicity associated with mutations in different genes along the same pathway, or in the same gene across different tissues, may be highly different. We present evidence that oncogenic functional footprints in cancer cell lines have significantly diverged from those in tumor tissues, which potentially explains the discrepancy of our findings with the current knowledge. Nevertheless, our analyses reveal a common inflammatory response signature in EGFR-driven human cancers of different tissue origins. Our results may have implications in the design of therapeutic strategies in cancers driven by these oncogenes.

A Review of Current Knowledge of Resistance Aspects for the Next-Generation Succinate Dehydrogenase Inhibitor Fungicides

The new broad-spectrum fungicides from the succinate dehydrogenase inhibitor (SDHI) class have been quickly adopted by the market, which may lead to a high selection pressure on various pathogens. Cases of resistance have been observed in 14 fungal pathogens to date and are caused by different mutations in genes encoding the molecular target of SDHIs, which is the mitochondrial succinate dehydrogenase (SDH) enzyme. All of the 17 marketed SDHI fungicides bind to the same ubiquinone binding site of the SDH enzyme. Their primary biochemical mode of action is the blockage of the TCA cycle at the level of succinate to fumarate oxidation, leading to an inhibition of respiration. Homology models and docking simulations explain binding behaviors and some peculiarities of the cross-resistance profiles displayed by different members of this class of fungicides. Furthermore, cross-resistance patterns among SDHIs is complex because many mutations confer full cross resistance while others do not. The nature of the mutations found in pathogen populations varies with species and the selection compound used but cross resistance between all SDHIs has to be assumed at the population level. In most of the cases where resistance has been reported, the frequency is still too low to impact field performance. However, the Fungicide Resistance Action Committee has developed resistance management recommendations for pathogens of different crops in order to reduce the risk for resistance development to this class of fungicides. These recommendations include preventative usage, mixture with partner fungicides active against the current pathogen population, alternation in the mode of action of products used in a spray program, and limitations in the total number of applications per season or per crop.

Association between idiopathic hearing loss and mitochondrial DNA mutations: A study on 169 hearing-impaired subjects

Mutations in mitochondrial DNA (mtDNA) have been shown to be an important cause of sensorineural hearing loss (SNHL). In this study, we performed a clinical and genetic analysis of 169 hearing-impaired patients and some of their relatives suffering from idiopathic SNHL, both familial and sporadic. The analysis of four fragments of their mtDNA identified several polymorphisms, the well known pathogenic mutation, A1555G, and some novel mutations in different genes, implying changes in the aminoacidic sequence. A novel sporadic mutation in 12S rRNA (MT-RNR1), not previously reported in the literature, was found in a case of possible aminoglycoside-induced progressive deafness.