Gliwice Scientific Meetings as a forum for discussion of research projects.Personal impressions.

The article has been written for the occasion of 25 Anniversary of Gliwice Scientific Meetings (GSN). For this reason, I am going to present scientific contacts of the Institute of Oncology at Gliwice with the Institute of Human Genetics of the Polish Academy of Sciences at Poznan not only at conference occasions but also in regular research manner.

Vitamin D in Head and Neck Cancer: a Systematic Review.

PURPOSE OF REVIEW: Observational studies have shown that serum 25-OH vitamin D [25(OH)D] is inversely associated with overall cancer risk in many malignancies. We performed a systematic literature review to determine whether vitamin D deficiency is related to head and neck cancer (HNC) etiology and outcome. RECENT FINDINGS: The search yielded five prospective studies reporting 25(OH)D levels prior to cancer diagnosis and their effect on the risk of HNC. Eight studies were cross-sectional or case-control studies, in which 25(OH)D levels were only measured after cancer diagnosis. Two studies found an inverse association between 25(OH)D level and HNC risk, while two other prospective cohort studies demonstrated no connection between 25(OH)D and HNC risk. Several studies reported cancer patients to have significantly lower 25(OH)D levels than controls. Associations between 25(OH)D and prognosis and mortality were variable. The link between vitamin D and HNC has so far only been investigated in a few observational, prospective, and case-control studies. Vitamin D deficiency may be more common in HNC patients than in the healthy population. There is no evidence for a causal relationship. Further studies are needed to evaluate whether low 25(OH)D concentrations play a role in the development or outcome of HNCs.

Molecular and health effects in the upper respiratory tract associated with tobacco smoking other than cigarettes.

The objective of the review was to compare molecular and health effects of tobacco smoking using cigars, cigarillos, pipe and water pipe in relation to the effects of cigarette smoking. In this review we will focus on the upper respiratory tract. Mechanisms of interaction of tobacco smoke constituents after products other than cigarettes are similar to these associated with cigarette smoking. Carcinogenic activity was demonstrated for any type of tobacco smoking, although the risk of developing head and neck squamous cell carcinoma (HNSCC) remains lower in users of cigars, traditional pipe and water pipe as compared to cigarette smoking. Nevertheless, there is no way of safe tobacco smoking.

Recurrent transcriptional loss of the PCDH17 tumor suppressor in laryngeal squamous cell carcinoma is partially mediated by aberrant promoter DNA methylation.

Protocadherins are cell-cell adhesion molecules encoded by a large family of genes. Recent reports demonstrate recurrent silencing of protocadherin genes in tumors and provide strong arguments for their tumor supresor functionality. Loss of protocadherins may contribute to cancer development not only by altering cell-cell adhesion, that is a hallmark of cancer, but also by enhancing proliferation and epithelial mesenchymal transition of cells via deregulation of the WNT signaling pathway. In this study we have further corroborated our previous findings on the involvement of PCDH17 in laryngeal squamous cell carcinoma (LSCC). We used bisulfite pyrosequencing to analyze a cohort of primary LSCC tumors for alterations in PCDH17 promoter DNA methylation as an alternative gene inactivation mechanism to the homozygous deletions reported earlier. Moreover, we analyzed primary LSCC samples by immunohistochemistry for PCDH17 protein loss. We identified recurrent elevation of PCDH17 promoter DNA methylation in 32/81 (40%) primary tumors (P < 0.001) and therein hypermethylation of 12 (15%) cases in contrast to no tumor controls (n = 24) that were all unmethylated. Importantly, DNA demethylation by decitabine has restored low level PCDH17 expression in LSCC cell lines. In conclusion, we provide a mechanistic explanation of recurrently observed PCDH17 silencing in LSCC by demonstrating the role of promoter methylation in this process. In light of these findings and recent reports showing that PCDH17 methylation is detectable in serum of cancer patients we suggest that testing PCDH17 DNA methylation might serve as a potential biomarker in LSCC.

Recurrent epigenetic silencing of the PTPRD tumor suppressor in laryngeal squamous cell carcinoma.

Cellular processes like differentiation, mitotic cycle, and cell growth are regulated by tyrosine kinases with known oncogenic potential and tyrosine phosphatases that downmodulate the first. Therefore, tyrosine phosphatases are recurrent targets of gene alterations in human carcinomas. We and others suggested recently a tumor suppressor function of the PTPRD tyrosine phosphatase and reported homozygous deletions of the PTPRD locus in laryngeal squamous cell carcinoma. In this study, we investigated other gene-inactivating mechanisms potentially targeting PTPRD, including loss-of-function mutations and also epigenetic alterations like promoter DNA hypermethylation. We sequenced the PTPRD gene in eight laryngeal squamous cell carcinoma cell lines but did not identify any inactivating mutations. In contrast, by bisulfite pyrosequencing of the gene promoter region, we identified significantly higher levels of methylation (p = 0.001 and p = 0.0002, respectively) in 9/14 (64%) laryngeal squamous cell carcinoma cell lines and 37/79 (47%) of primary laryngeal squamous cell carcinoma tumors as compared to normal epithelium of the upper aerodigestive tract. There was also a strong correlation (p = 0.0001) between methylation and transcriptional silencing for the PTPRD gene observed in a cohort of 497 head and neck tumors from The Cancer Genome Atlas dataset suggesting that DNA methylation is the main mechanism of PTPRD silencing in these tumors. In summary, our data provide further evidence of the high incidence of PTPRD inactivation in laryngeal squamous cell carcinoma. We suggest that deletions and loss-of-function mutations are responsible for PTPRD loss only in a fraction of cases, whereas DNA methylation is the dominating mechanism of PTPRD inactivation.

Proteomic profiling identifies the inorganic pyrophosphatase (PPA1) protein as a potential biomarker of metastasis in laryngeal squamous cell carcinoma.

Relapse and metastasis are the main causes of unfavorable outcome in head and neck cancers. Whereas, understanding of the molecular background of these processes is far from being complete. Therefore, in this study we aimed to identify potential biomarker candidates of relapse and metastasis in laryngeal squamous cell carcinoma (LSCC) by combining the 2D electrophoresis based protein screen and immunohistochemical analysis of candidate proteins. We screened three groups of LSCC cell lines derived from primary tumors, recurrent tumors and metastases and identified seven proteins that differed significantly in relative abundance between the analyzed groups. Among the identified proteins were the heat shock proteins HSP60 and HSP70 that were significantly downregulated both in recurrences- and metastases-derived cell lines but not in primary tumor-derived cell lines. Moreover, we identified significant upregulation of the annexin V, calreticulin and the inorganic pyrophosphatase (PPA1) exclusively in the metastases-derived cell lines. As these upregulated proteins could potentially become novel biomarkers of metastasis, we have compared their abundance in primary tumor LSCC N(0) cases, primary tumor LSCC N(+) cases as well as in LSCC metastases N(+). Our results show an intense increase of cytoplasmic PPA1 abundance in the N(+) (p = 0.000042) compared to the N(0) group. In summary, we show a group of proteins deregulated in recurrences and metastases of LSCC. Moreover, we suggest the PPA1 protein as a potential new biomarker for metastasis in this cancer.

Metal concentrations in hair of patients with various head and neck cancers as a diagnostic aid.

Head and neck cancers are one of the most frequent cancers worldwide. This paper attempts to evaluate disturbances of homeostasis of the necessary elements (calcium, magnesium, zinc, copper, iron, manganese) and changes in the levels of toxic metals (lead, cadmium, cobalt, chromium VI) in hair of patients with head and neck cancers, as well as people without a diagnosed neoplastic disease. In order to quantify the necessary elements and toxic metals, a method using ICP-MS and ICP-OES techniques had been developed and validated. The studies have shown that patients with head and neck cancer used to drink alcohol and smoked much more frequently than healthy individuals, both in the past and presently. Statistically significant differences in concentrations of average metal content in the group of patients with head and neck cancers compared to the control group were confirmed. Significant differences in metal content between the group of patients with head and neck cancers and healthy individuals were found which enabled distinguishing between the study groups. To this end, a more advanced statistical tool, i.e. chemometrics, was used. The conducted research analyses and the use of advanced statistical techniques confirm the benefits of using alternative material to distinguish the patients with head and neck cancers from the healthy individuals.

Frequent chromosomal aberrations and candidate genes in head and neck squamous cell carcinoma.

The knowledge of the biology of head and neck squamous cell carcinoma (HNSCC) has had relatively little impact on the improvement in oncologic outcome up to date. However, the identification of oncogenes and tumor suppressor genes (TSGs) involved in cancer progression contributes to the understanding of the molecular pathways involved in oncogenesis and could contribute to individual risk assessment and provide tools for improvement of treatment and targets for therapy based on the alterations in these pathways. The aim of this article is to review the chromosomal aberrations commonly found in HNSCC, to identify the genes in these chromosomal regions suggested to act as (candidate) oncogenes or TSGs, and to discuss the molecular mechanisms modulating their expression.

Narrowing the localization of the region breakpoint in most frequent Robertsonian translocations.

Despite that Robertsonian translocations (ROBs) are the most common chromosomal rearrangements in humans (1/1000 individuals), an exact breakpoint and the molecular mechanisms leading to their formation are still not well known. This is partly due to the fact that Human Genome Project did not provide any map or sequence for the acrocentric short arms. The main aim of our studies was to narrow the breakpoints in de novo arising and in familial cases of the most frequently occurring ROBs, using eight, previously not tested clones derived from 21p. Our results from PCR and FISH analysis showed that only the clones CR382285, CR382287, and a small fragment of CR382332 are retained in the examined ROBs. Moreover, interphase FISH on monochromosomal hybrids verified the orientation of studied clones in relation to centromeres of chromosomes 14 and 21. Given our results, we propose localization of the breakpoints in or nearby to clone CR382332. Summarizing, our results allowed to narrow the region where the breakpoints are localized and demonstrated that their position could be the same in all common ROBs.

The rationale for HPV-related oropharyngeal cancer de-escalation treatment strategies.

The treatment paradigms for head and neck squamous cell cancer (HNSCC) are changing due to the emergence of human papillomavirus-associated tumors (HPV-related), possessing distinct molecular profiles and responses to therapy. Retrospective studies have suggested that HPV-related HNSCCs are more frequently cured than those caused by tobacco. Current clinical trials focus on the reduction of treatment-related toxicity and the development of HPV-targeted therapies. New treatment strategies include: 1) dose reduction of radiotherapy, 2) the use of cetuximab instead of cisplatin for chemo-radiation 3) less invasive surgical options, i.e. trans-oral robotic surgery and trans-oral laser microlaryngoscopy, and 4) more specific treatment attempts, including immunotherapeutic strategies, thanks to increasing comprehension of the molecular background of HPV-related HNSCC. Whereas recently published data shed light on immune mechanisms, other studies have focused on specific vaccination against HPV-related HNSCC. A crucial problem is patient selection to the chosen bias. Truly HPV-related cancers (p16-positive and HPV DNA-positive) with biomarkers for good response to therapy could be included in randomized trials aiming for less severe and better tailored therapy.

Prognostic factors in oral and oropharyngeal cancer based on ultrastructural analysis and DNA methylation of the tumor and surgical margin.

Oral and oropharyngeal cancers are characterized by relatively low 5- year survival rates due to many factors, including local recurrence. The identification of new molecular markers may serve for the estimation of prognosis and thus augment treatment decisions and affect therapy outcome. The aim of this study was to describe the morphological characteristics and the DNA methylation status of the CDKN2A,CDH1, ATM, FHIT and RAR- genes in the central and peripheral part of the tumor and the surgical margin and evaluate their prognostic significance. 53 patients with oral and oropharyngeal cancer were enrolled to the prospective study, and had been primarily treated surgically. Correlations between morphological data, hypermethylation status and clinicopathological data, as well as prognosis, were assessed. Nuclei polymorphism highly correlated with T stage (p < 0.0001), N stage (p < 0.046), and metastases to the lymph nodes pN (p < 0.004 ). Also, the number of cells in irregular mitosis correlated with T stage (p < 0.004), and highly with pN (p < 0.009). The significance of CDKN2A hypermethylation as a good prognostic factor was also established in the Kaplan-Meir test. The ultrastructural analysis showed that none of the examined tumors had homogenous texture and that resection margin specimens clean in HE stained tissue samples frequently contained single tumor cells or few cells in groups surrounded by connective tissue. This indicates the superiority of electron microscopy over standard histopathological analysis. Thus, a combination of such morphological examination with epigenetic parameters described herein could result in the discovery of promising new prognostic markers of the disease.

Heterogeneity of 11q13 region rearrangements in laryngeal squamous cell carcinoma analyzed by microarray platforms and fluorescence in situ hybridization.

We reinvestigated rearrangements occurring in region q13 of chromosome 11 aiming to: (i) describe heterogeneity of the observed structural alterations, (ii) estimate amplicon size and (iii) identify of oncogenes involved in laryngeal cancer progression as potential targets for therapy. The study included 17 cell lines derived from laryngeal cancers and 34 specimens from primary laryngeal tumors. The region 11q13 was analyzed by fluorescence in situ hybridization (FISH), array comparative genomic hybridization (aCGH) and gene expression microarray. Next, quantitative real time PCR was used for chosen genes to confirm results from aCGH and gene expression microarray. The observed pattern of aberrations allows to distinguish three ways, in which gain and amplification involving 11q13 region may occur: formation of a homogeneously staining region; breakpoints in/near 11q13, which lead to the three to sevenfold increase of the copy number of 11q13 region; the presence of additional copies of the whole chromosome 11. The minimal altered region of gain and/or amplification was limited to ~1.8 Mb (chr.11:69,395,184-71,209,568) and comprised mostly 11q13.3 band which contain 12 genes. Five, out of these genes (CCND1, ORAOV1, FADD, PPFIA1, CTTN) had higher expression levels in comparison to healthy controls. Apart from CCND1 gene, which has an established role in pathogenesis of head and neck cancers, CTTN, ORAOV1 and FADD genes appear to be oncogene-candidates in laryngeal cancers, while a function of PPFIA1 requires further studies.

Simple technique for RNA purification from mouse inner ear hair cells.

Obtaining a good quality of RNA from small population of cells remain an issue. Isolation for a special anatomic location such as inner ear placed in the temporal bone become a challenge, especially in terms of time needed for isolation of living tissue from the bone, which is a key factor to preserve the RNA. Due to limited accessibility to the technologies such as laser dissection, we present a simplified procedure for isolation of good quality of RNA from the inner ear for further studies.

High resolution ArrayCGH and expression profiling identifies PTPRD and PCDH17/PCH68 as tumor suppressor gene candidates in laryngeal squamous cell carcinoma.

Many classical tumor suppressor genes (TSG) were identified by delineation of bi-allelic losses called homozygous deletions. To identify systematically homozygous deletions in laryngeal squamous cell carcinoma (LSCC) and to unravel novel putative tumor suppressor genes, we screened 10 LSCC cell lines using high resolution array comparative genomic hybridization (arrayCGH) and array based expression analysis. ArrayCGH identified altogether 113 regions harboring protein coding genes that showed strong reduction in copy number indicating a potential homozygous deletion. Out of the 113 candidate regions, 22 novel homozygous deletions that affected the coding sequences of 15 genes were confirmed by multiplexPCR. Three genes were homozygously lost in two cell lines: PCDH17/PCH68, PRR20, and PTPRD. For the 15 homozygously deleted genes, four showed statistically significant downregulation of expression in LSCC cell lines as compared with normal human laryngeal controls. These were ATG7 (1/10 cell line), ZMYND11 (BS69) (1/10 cell line), PCDH17/PCH68 (9/10 cell lines), and PTPRD (7/10 cell lines). Quantitative real-time PCR was used to confirm the downregulation of the candidate genes in 10 expression array-studied cell lines and an additional cohort of cell lines; statistical significant downregulation of PCDH17/PCH68 and PTPRD was observed. In line with this also Western blot analyses demonstrated a complete absence of the PCDH17 and PTPRD proteins. Thus, expression profiling confirmed recurrent alterations of two genes identified primarily by delineation of homozygous deletions. These were PCDH17/PCH68, the protocadherin gene, and the STAT3 inhibiting receptor protein tyrosine phosphatase gene PTPRD. These genes are good candidates for novel TSG in LSCC.

[Head and neck cancer--history]. / Nowotwory glowy i szyi--historia.

According to epidemiological data head and neck cancers constitute for 12% of all malignancies in the world. It is estimated that a total of 400 000 cases of the mouth and throat and of 160 000 cases of laryngeal cancer, 300 000 people die each year. History of head and neck cancers developed and underwent many changes at the turn of the century. Treatment, pathogenesis and possessed state of knowledge on the subject has changed. Starting from the ancient times there were texts on how to treat and examine patients. The Edwin Smith and Ebers Papyrus are two of the oldest medical documents describing the treatment of cancer patients. Hippocrates was the first person who used the word "cancer" and probably he was the first who divided the tumors into benign and malignant. In a document known as the Doctrine of Hippocrates he described skin cancer and cancer treatments. Over the next centuries, medical science did not develop because of religious concerns about autopsy and surgical procedures. The 17th century is a period in which there were a lot of new information about how to treat such oral cancer. Cancer of the tongue was removed by cauterization, which in the 18th century was replaced by the use of surgical instruments. In the same age glossectomy has been accepted as the treatment of choice performed in the treatment of cancer. The 19th century brought a major breakthrough in the treatment of surgical, diagnostic, anesthetic techniques and understanding of the pathological mechanisms. Histological evaluation of tumors has become mandatory and standard practice in the assessment of cancer. Laryngectomy and neck lymph nodes removal has become commonplace. Modified Radical Neck Dissection (MRND), became popularized as another cancer treatment technique. Describing ways to treat cancer, radiotherapy can not be ignored - there are several new techniques such as Intensity Modulated Radiotherapy (IMRT) and hypofractionation currently used. Chemotherapy and the introduction of many new drugs have changed the outlook for patients suffering from cancer. Recently there are expectations about the targeted therapy, especially in medicaments blocking epidermal growth factor receptor (EGFR).

[The HPV infection as an alternative to tobacco smoking way of head and neck tumors development--what are the implications for patients?]. / Infekcja HPV jako alternatywna wobec palenia tytoniu droga rozwoju nowotworów glowy i szyi--jakie ma znaczenie dla pacjenta?

It was established, that HPV virus (Human Papilloma Virus) is responsible for tumor induction in some anatomical regions of head and neck, mainly in palatine tonsils. The characteristics of HPV-related tumors as well as the course of the disease are definitely different compared to tobacco-smoking related tumors; patients HPV-positve have better prognosis - less patients develops recurrences and dies from the disease. There is no full compliance about patients' characteristics, although most indications concern "young adults" with their intensive sexual life. Because the course of HPV-related tumors is milder, there is a need to distinguish the cause of disease to carry on the therapy adjusted to the causative factor. This approach might help to select HPV-negative patients with severe course of disease to apply more aggressive chemotherapy.

[Physiological metals in the serum, hair and nails of patients with head and neck cancer]. / Metale fizjologiczne w surowicy, we wlosach i paznokciach pacjentów z nowotworami w obrebie glowy i szyi.

Cigarette smoking and excessive alcohol drinking result in the rise of numbers of patients suffering from the head and neck cancer. Addiction to any of these stimulants carry a risk of developing a cancerogenesis process. Using them simultaniously lead not to a summary of each of those risks but multiplies them. Scientific research also indicates the important difference in the incidence of cancer in people who have never smoked cigarettes or drunk alcohol in comparison to those, whose exposure to these stimulatns was longterm - in such case, the former group had a lower percentage of developing the disease. Human body burdened with the ongoing cancer shows disturbances on various levels of the system. One of such disturbances is change of the concetration levels of physiological metals, such as calcium, magnesium, iron, copper, zinc or mangenese. They play key roles in maintaing the hormonal and ionic stability, they act as cofactors in many enzymes in metabolic processes. Diagnostic research of any deviations in levels of those essential elements enables a full estimation of a patient condition. The aim of this study was physiological metal levels evaluation in different kinds of biological material in patients with tumors of larynx, salivary glands and oral cavity and tongue. Hair and nail samples were used as examples of alternative material, beside the serum samples, which is a standard material and often used. Subjects were patients of Otolaryngology and Laryngological Oncology Clinic of Poznan University of Medical Sciences (Samodzielny Publiczny Szpital Kliniczny nr 2 im. Heliodora Swiecickiego Uniwersytetu Medycznego im. Karola Marcinkowskiego w Poznaniu) and The Head and Neck Surgery Ward of The Greater Poland Cancer Centre in Poznan. Subjects were 41 men and 18 women with tumors of larynx, salivary glands and oral cavity and tongue. The control group consisted of patients from the Otolaryngology and Laryngological Oncology Clinic of Poznan University of Medical Sciences (Samodzielny Publiczny Szpital Kliniczny nr 2 im. Heliodora Swiecickiego Uniwersytetu Medycznego im. Karola Marcinkowskiego w Poznaniu), The Head and Neck Surgery Ward of The Greater Poland Cancer Centre in Poznan and patients of Department of Endocrinology, Metabolism and Internal Medicine of Poznan University of Medical Sciences (Samodzielny Publiczny Szpital Kliniczny nr 2 im. Heliodora Swiecickiego Uniwersytetu Medycznego im. Karola Marcinkowskiego w Poznaniu) and Department of Conservative Dentistry and Periodontology Poznan University of Medical Sciences. They gave answers to the questionnaire concerning smoking habits, alcohol consumption and dietary habits, Then the samples of their serum, hair and nails were collected. After careful preparations the biological material has underwent the process of digestion, and then calcium, magnesium, iron, copper, zinc, mangenese were determined quantitatively using the method of ICP-MS. Profile of the patients who took part in the research displayed a strong correlation between tobacco smoking with alcohol drinking and appearance of larynx, salivary gland and oral cavity and tongue cancer as well as between exclusively tobacco smoking and appearance of these types of cancer. There is a higher incidence of larynx, salivary gland and oral cavity and tongue cancer when there is a deficiency of grain products or fibre in everyday diet. A higher level of calcium, magnesium, iron and manganese was found in patients' hair and nails who suffered from salivary gland cancer. According to applied Chemometric Analysis of Principal Component 1 - concentrations of iron, copper and manganese with magnesium and zinc in patients' nail samples showed strong correlation between measured variables. In patiens' hair samples measured correlation between variables was decreased - concentrations of calcium and magnesium as well as of iron and manganese were highlighted as two groups of variables which showed some correlation in this type of biological material. Further research is required to indicate which of alternative biological materials - hair or nail samples - in relation to serum, would provide a better evaluation of physiological metal levels.

[Comparison of different deafening strategies based on ototoxic drugs on mouse animals model]. / Porównanie skutecznosci ogluszania mysiego modelu zwierzecego w oparciu o protokoly wykorzystujace leki ototoksyczne.

AIM OF THE STUDY: To compare safety, reliability and usefulness of two deafening protocols on animal mouse model, based on aminoglycosides exposure MATERIAL AND METHOD: Adults mice, Bulb/C, deafened with kanamycine 14 days treatment (group I), single kanamycin injection followed by etacrinic acid administration (group II) and control group. Hearing evaluation performed with ABR recordings on 6th day after drug exposure RESULTS: Both protocols were not able to guarantee complete ablation of the inner ear in tested animals. Although short deafening strategy was more effective (83.33% deaf mice) it was combined with high rate of mortality during general anesthesia for hearing evaluation. CONCLUSIONS: Variable outcomes in deafening mouse animal model implies the necessity of hearing evaluation every time prior to the pathophysiological as well as molecular studies. Mice exposed to severe oto- and nephrotoxic insult do not recover after anesthetic drug administration, thus harvesting inner ear tissues especially as the source of RNA should be performed immediately after ABR recordings.

Congenital amusia-pathology of musical disorder.

Amusia also known as tone deafness affects roughly 1.5% population. Congenital amusia appears from birth and lasts over life span. Usually, it is not associated with other diseases. Its link to hearing impairment has been definitively excluded. Neurobiological studies point to asymmetrical processing of musical signals in auditory cortex of left and right brain hemispheres. The finding was supported by discovering microlesions in the right-side gray matter. Because of its connection with asymmetry, amusia has been classified to disconnection syndromes. Alternatively to the neurobiological explanation of amusia background, an attention was turned to the significance of genetic factors. The studies done on relatives and twins indicated familial aggregation of amusia. Molecular genetic investigations linked amusia with deletion of 22q11.2 chromosome region. Until now no specific genes responsible for development of amusia were found.

The contribution of the mitochondrial COI/tRNA(Ser(UCN)) gene mutations to non-syndromic and aminoglycoside-induced hearing loss in Polish patients.

Mutations in mitochondrial DNA have been implicated in both, non-syndromic and aminoglycoside-induced hearing loss. In the present study, we have performed the systematic mutation screening of the COI/tRNA(Ser(UCN)) genes in 250 unrelated Polish subjects with hearing impairment. Three different homoplasmic sequence variants were identified, including one common polymorphism m.7476 C>T in tRNA(Ser(UCN)) and two mutations, m.7444 G>A and m.7445 A>G localized in the COI/precursor of tRNA(Ser(UCN)). The incidence of m.7444 G>A substitution was estimated at 1.6% (4/250), however variable penetrance of hearing loss, age of onset and hearing thresholds among m.7444 G>A carriers was observed. Two subjects had the positive history of aminoglycoside exposure and one of them harbored both m.7444 G>A and 12S rRNA m.1555 A>G mutations. Those suggest that m.7444 G>A itself is not sufficient to produce a clinical phenotype and additional modifier factors are required for pathogenic manifestation of m.7444 G>A substitution. Moreover, we have described the first Polish family with non-syndromic hearing loss, harboring m.7445 A>G mutation. The penetrance of hearing loss in this pedigree was 58% when aminoglycoside-induced hearing impairment was included, and 8% when ototoxic effect was excluded. This finding strongly suggests the possible role of m.7445 A>G in susceptibility to aminoglycoside induced-hearing loss.