Domain landscapes of somatic NF1 mutations in pheochromocytoma and paraganglioma.

Pheochromocytoma and paraganglioma (PPGL), are rare neuroendocrine tumors arising from the adrenal medulla and extra-adrenal paraganglia, respectively. Up to about 60% are explained by germline or somatic mutations in one of the major known susceptibility genes e.g., inNF1,RET,VHL, SDHx,MAXandHRAS. Targeted Next Generation Sequencing was performed in 14 sporadic tumors using a panel including 26 susceptibility genes to characterize the mutation profile. A total of 6 germline and 8 somatic variants were identified. The most frequent somatic mutations were found in NF1(36%), four have not been reported earlier in PCC or PGL. Gene expression profile analysis showed that NF1 mutated tumors are classified into RTK3 subtype, cluster 2, with a high expression of genes associated with chromaffin cell differentiation, and into a RTK2 subtype, cluster 2, as well with overexpression of genes associated with cortisol biosynthesis. On the other hand, by analyzing the entire probe set on the array and TCGA data, ALDOC was found as the most significantly down regulated gene in NF1-mutated tumors compared to NF1-wild-type. Differential gene expression analysis showed a significant difference between Nt - and Ct-NF1 domains in mutated tumors probably engaging different cellular pathways. Notably, we had a metastatic PCC with a Ct-NF1 frameshift mutation and when performing protein docking analysis, Ct-NF1 showed an interaction with Nt-FAK suggesting their involvement in cell adhesion and cell growth. These results show that depending on the location of the NF1-mutation different pathways are activated in PPGLs. Further studies are required to clarify their clinical significance.

Nuclear and mitochondrial DNA alterations in pheochromocytomas and paragangliomas, and their potential treatment.

Mitochondrial DNA (mtDNA) alterations have been reported in different types of cancers and are suggested to play important roles in cancer development and metastasis. However, there is little information about its involvement in pheochromocytomas and paragangliomas (PCCs/PGLs) formation. PCCs and PGLs are rare endocrine tumors of the chromaffin cells in the adrenal medulla and extra-adrenal paraganglia that can synthesize and secrete catecholamines. Over the last 3 decades, the genetic background of about 60% of PCCs/PGLs involving nuclear DNA alterations has been determined. Recently, a study showed that mitochondrial alterations can be found in around 17% of the remaining PCCs/PGLs. In this review, we summarize recent knowledge regarding both nuclear and mitochondrial alterations and their involvement in PCCs/PGLs. We also provide brief insights into the genetics and the molecular pathways associated with PCCs/PGLs and potential therapeutical targets.

Case report: Two sisters with a germline CHEK2 variant and distinct endocrine neoplasias.

Genetic testing has become the standard of care for many disease states. As a result, physicians treating patients who have tumors often rely on germline genetic testing results for making clinical decisions. Cases of two sisters carrying a germline CHEK2 variant are highlighted whereby possible other genetic drivers were discovered on tumor analysis. CHEK2 (also referred to as CHK2) loss of function has been firmly associated with breast cancer development. In this case report, two siblings with a germline CHEK2 mutation also had distinct endocrine tumors. Pituitary adenoma and pancreatic neuroendocrine tumor (PNET) was found in the first sibling and pheochromocytoma (PCC) discovered in the second sibling. Although pituitary adenomas, PNETs, and PCC have been associated with NF1 gene mutations, the second sister with a PCC did have proven germline CHEK2 with a pathogenic somatic NF1 mutation. We highlight the clinical point that unless the tumor is sequenced, the real driver mutation that is causing the patient's tumor may remain unknown.

Novel combined UGT1A1 mutations in Crigler Najjar Syndrome type I.

BACKGROUND: Uridine diphosphate-glucuronosyl transferase 1A1 (UGT1A1), which is the major UGT1 gene product, is located on chromosome 2q37. The expression of UGT1A1 is relatively managed by a polymorphic dinucleotide repeat inside the promoter TATA box consisting of 5-8 copies of a TA repeat. A (TA) 6TAA is considered as the wild type. The A (TA) 7TAA allele has been identified as the most frequent allele in the Caucasian populations while A (TA) 8TAA allele remains the rarest allele worldwide in North Africa, including the Arab populations. METHODS: The spectrum of UGT1A1 genetic mutations in seventeen Tunisian children affected by persistent unconjugated hyperbilirubinemias is represented in addition to their relatives, notably parents, sisters, and brothers. Tunisian children, from 16 unrelated families as well as a 17th family without CN1 affected child, were originated from the West Center of Tunisia. The promoter region and coding exons of the UGT1A1 were PCR amplified, subsequently subjected to Sanger sequencing. RESULTS: The frequencies of genotypes in CN1 patients were as follows (TA) (7/7) (12/17: 70.6%) and (TA) (8/8) (5/17: 29.4%). All patients harbored the c.1070A>G mutation of exon 3 (UGT1A1*16) in the homozygous state. Among relatives of our patients (n = 16), who were all heterozygotes for UGT1A1*16, 13/16 (81.25%) had a heterozygous state for UGT1A1∗1/UGT1A1∗28 or (TA) (6/7) and, 18.75% (3/16) were heterozygous for UGT1A1∗28/UGT1A1∗37 or (TA) (7/8) of the promoter polymorphisms. CONCLUSION: UGT1A1*16 accompanied with UGT1A1*28 or UGT1A1*37 had a specific geographic and ethnic distribution for CN pathogenesis in this Tunisian cohort.

Genetic Alterations in Mitochondrial DNA Are Complementary to Nuclear DNA Mutations in Pheochromocytomas.

BACKGROUND: Somatic mutations, copy-number variations, and genome instability of mitochondrial DNA (mtDNA) have been reported in different types of cancers and are suggested to play important roles in cancer development and metastasis. However, there is scarce information about pheochromocytomas and paragangliomas (PCCs/PGLs) formation. MATERIAL: To determine the potential roles of mtDNA alterations in sporadic PCCs/PGLs, we analyzed a panel of 26 nuclear susceptibility genes and the entire mtDNA sequence of seventy-seven human tumors, using next-generation sequencing, and compared the results with normal adrenal medulla tissues. We also performed an analysis of copy-number alterations, large mtDNA deletion, and gene and protein expression. RESULTS: Our results revealed that 53.2% of the tumors harbor a mutation in at least one of the targeted susceptibility genes, and 16.9% harbor complementary mitochondrial mutations. More than 50% of the mitochondrial mutations were novel and predicted pathogenic, affecting mitochondrial oxidative phosphorylation. Large deletions were found in 26% of tumors, and depletion of mtDNA occurred in more than 87% of PCCs/PGLs. The reduction of the mitochondrial number was accompanied by a reduced expression of the regulators that promote mitochondrial biogenesis (PCG1α, NRF1, and TFAM). Further, P62 and LC3a gene expression suggested increased mitophagy, which is linked to mitochondrial dysfunction. CONCLUSION: The pathogenic role of these finding remains to be shown, but we suggest a complementarity and a potential contributing role in PCCs/PGLs tumorigenesis.

Loss of SDHB Induces a Metabolic Switch in the hPheo1 Cell Line toward Enhanced OXPHOS.

BACKGROUND: Enzymes of tricarboxylic acid (TCA) have recently been recognized as tumor suppressors. Mutations in the SDHB subunit of succinate dehydrogenase (SDH) cause pheochromocytomas and paragangliomas (PCCs/PGLs) and predispose patients to malignant disease with poor prognosis. METHODS: Using the human pheochromocytoma cell line (hPheo1), we knocked down SDHB gene expression using CRISPR-cas9 technology. RESULTS: Microarray gene expression analysis showed that >500 differentially expressed gene targets, about 54%, were upregulated in response to SDHB knock down. Notably, genes involved in glycolysis, hypoxia, cell proliferation, and cell differentiation were up regulated, whereas genes involved in oxidative phosphorylation (OXPHOS) were downregulated. In vitro studies show that hPheo1 proliferation is not affected negatively and the cells that survive by shifting their metabolism to the use of glutamine as an alternative energy source and promote OXPHOS activity. Knock down of SDHB expression results in a significant increase in GLUD1 expression in hPheo1 cells cultured as monolayer or as 3D culture. Analysis of TCGA data confirms the enhancement of GLUD1 in SDHB mutated/low expressed PCCs/PGLs. CONCLUSIONS: Our data suggest that the downregulation of SDHB in PCCs/PGLs results in increased GLUD1 expression and may represent a potential biomarker and therapeutic target in SDHB mutated tumors and SDHB loss of activity-dependent diseases.

The first concurrent detection of mitochondrial DNA m.3243A>G mutation, deletion, and depletion in a family with mitochondrial diabetes.

BACKGROUND: Mitochondrial diabetes (MD) is a rare monogenic form of diabetes and divided into type l and type 2. It is characterized by a strong familial clustering of diabetes with the presence of maternal transmission in conjunction with bilateral hearing impairment in most of the carriers. The most common form of MD is associated with the m.3243A>G mutation in the mitochondrial MT-TL1, but there are also association with a range of other point mutations, deletion, and depletion in mtDNA. METHODS: The mitochondrial genome anomalies were investigated in a family with clinical features of MD, which includes a proband presenting severe MD conditions including cardiomyopathy, retinopathy, and psychomotor retardation. RESULTS: By investigating the patient's blood leukocytes and skeletal muscle, we identified the m.3243A>G mutation in heteroplasmic state. This mutation was absent in the rest of the family members. In addition, our analysis revealed in the proband a large mtDNA heteroplasmic deletion (~1 kb) and a reduction in mtDNA copy number. CONCLUSION: Our study points out, for the first time, a severe phenotypic expression of the m.3243A>G point mutation in association with mtDNA deletion and depletion in MD.

Hypoxia Signaling and Circadian Disruption in and by Pheochromocytoma.

Disruption of the daily (i.e., circadian) rhythms of cell metabolism, proliferation and blood perfusion is a hallmark of many cancer types, perhaps most clearly exemplified by the rare but detrimental pheochromocytomas. These tumors arise from genetic disruption of genes critical for hypoxia signaling, such as von Hippel-Lindau and hypoxia-inducible factor-2 or cellular metabolism, such as succinate dehydrogenase, which in turn impacts on the cellular circadian clock function by interfering with the Bmal1 and/or Clock transcription factors. While pheochromocytomas are often non-malignant, the resulting changes in cellular physiology are coupled to de-regulated production of catecholamines, which in turn disrupt circadian blood pressure variation and therefore circadian entrainment of other tissues. In this review we thoroughly discuss the molecular and physiological interplay between hypoxia signaling and the circadian clock in pheochromocytoma, and how this underlies endocrine disruption leading to loss of circadian blood pressure variation in the affected patients. We furthermore discuss potential avenues for targeting these tumor-specific pathophysiological mechanisms therapeutically in the future.

Potential dysfunctional effects of synonymous variants: Insights from an exhaustive in silico analysis of the ABCB4 gene.

The multiple drug resistance 3 (MDR3) protein is a canalicular phospholipid translocator involved in the bile secretion and encoded by the ABCB4 gene. Its deficiency is related to a large spectrum of liver diseases. Taking into account the increased evidence about the involvement of synonymous variants in inherited diseases, this study aims to explore the putative effects of silent genetic variants on the ABCB4 expression. We performed an exhaustive computational approach using ESE finder, RegRNA 2.0, MFOLD, SNPfold, and %MinMax software added to the measurement of the Relative Synonymous Codon Usage. This analysis included 216 synonymous variants distributed throughout the ABCB4 gene. Results have shown that 11 synonymous coding SNPs decrease the ESE activity, while 8 of them change the codon frequency. Besides, the c.24C>T variation, located 21 nucleotides downstream the start A (Adenine) U (Uracil) G (Glutamine) AUG causes an increase in the local stability. Moreover, the computational analysis of the 3'UTR region showed that six of the eight variants located in this region affected the Wild Type (WT) pattern of the miRNA targets sites and/or their proper display. The 26 sSNPs retained as putatively functional possessed a very low allele frequency, supporting their pathogenicity. In conclusion, the obtained results suggest that some synonymous SNPs in the ABCB4 gene, considered up to now as neutral, may be involved in the MDR3 deficiency.

A novel TBX1 missense mutation in patients with syndromic congenital heart defects.

Congenital heart defects represent a characteristic part of several genetic syndromes associated with chromosomal abnormalities such as 22q11.2 deletion syndrome; many genes located in this locus, mainly TBX1, are candidate genes for congenital heart defects. In our cohort of 27 subjects with congenital heart defect, both karyotype analysis and Fluorescence in situ hybridization (FISH) were performed. The TBX1 gene was sequenced in patients lacking chromosomal abnormalities. FISH analysis showed a de novo 22q11.2 deletion in two patients. The screening of TBX1 coding sequence identified a novel missense mutation c.569C > A (p.P190Q) in six unrelated patients and detected two associated known single nucleotide polymorphisms; the c.664C > T (rs2301558) in three patients and the c.420T > C (p.Phe140 Phe) (rs41298814) in one patient. Bioinformatic tools show that the novel missense mutation c.569C > A could modify the function and the stability of the TBX1 protein. The c.569C > A mutation was not found in 50 healthy controls. Ours results suggest a deleterious role of the c.569C > A mutation and strengthen the hypothesis that this mutation might be responsible for the same phenotype spectrum as the 22q11.2 deletion syndrome.

First description of a novel mitochondrial mutation in the MT-TI gene associated with multiple mitochondrial DNA deletion and depletion in family with severe dilated mitochondrial cardiomyopathy.

Mitochondria are essential for early cardiac development and impaired mitochondrial function was described associated with heart diseases such as hypertrophic or dilated mitochondrial cardiomyopathy. In this study, we report a family including two individuals with severe dilated mitochondrial cardiomyopathy. The whole mitochondrial genome screening showed the presence of several variations and a novel homoplasmic mutation m.4318-4322delC in the MT-TI gene shared by the two patients and their mother and leading to a disruption of the tRNAIle secondary structure. In addition, a mitochondrial depletion was present in blood leucocyte of the two affected brother whereas a de novo heteroplasmic multiple deletion in the major arc of mtDNA was present in blood leucocyte and mucosa of only one of them. These deletions in the major arc of the mtDNA resulted to the loss of several protein-encoding genes and also some tRNA genes. The mtDNA deletion and depletion could result to an impairment of the oxidative phosphorylation and energy metabolism in the respiratory chain in the studied patients. Our report is the first description of a family with severe lethal dilated mitochondrial cardiomyopathy and presenting several mtDNA abnormalities including punctual mutation, deletion and depletion.

Association study of apoptosis gene polymorphisms in mitochondrial diabetes: A potential role in the pathogenicity of MD.

Mitochondrial diabetes (MD) is a heterogeneous disorder characterized by a chronic hyperglycemia and is maternally transmitted. Syndromic MD is a subgroup of MD including diabetic microangiopathy and macroangiopathy, in addition to extrapancreatic disorder. MD is caused by genetic mutations and deletions affecting mitochondrial DNA. This mitochondrial damage initiates apoptosis. In this study, we hypothesized that functional polymorphisms in genes involved in apoptotic pathway could be associated with the development of apoptosis in MD disease and increased its risk. Detection of apoptosis was confirmed on muscle biopsies taken from MD patients using the TUNEL method and the Cytochrome c protein expression level. We genotyped then 11 published SNPs from intrinsic and extrinsic apoptotic pathway and assessed the signification of these polymorphisms in 43 MD patients and 100 healthy controls. We found 10 selected polymorphisms (p53 (rs1042522 and rs17878362), BCL2 (rs2279115), BAX (rs1805419), BAK1 (rs210132 and rs2227925), CASP3 (rs1405937), CASP7 (rs2227310), CASP8 (rs1045485) and CASP10 (rs13006529)) with a potential apoptosis effect in MD patients compared to control population. Specifically, SNPs involved in the intrinsic pathway (p53, BCL2, BAK1 and CASP3) presented the highest risk of apoptosis. Our result proved that apoptosis initiated by mtDNA mutations, can be emphasized by a functional apoptotic polymorphisms associated with high expression of cytochrome c protein and more myofibers with apoptosis in syndromic MD subgroup compared with non-syndromic MD subgroup.

Oxidative stress and glutathione S-transferase genetic polymorphisms in medical staff professionally exposed to ionizing radiation.

PURPOSE: Ionizing radiation (IR) is considered as a diagnostic and therapeutic tool in medicine. However, chronic occupational exposure of medical staff to IR may affect the antioxidant status and, as a result, DNA damage and cancers as well. The objective of our study was to evaluate the oxidative stress profile caused by IR in 29 Tunisian medical staff from radiology and radiotherapy departments, and to find an association between the GSTM1 null, GSTT1 null, and GSTP1 Ile105Val polymorphisms and oxidative stress biomarkers. MATERIALS AND METHODS: The oxidant biomarkers malondialdehyde (MDA) and advanced oxidation protein product (AOPP) and the activities of the antioxidant superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT) enzymes were spectrophotometrically determined in erythrocytes hemolysates. The analysis of GSTT1 null, GSTM1 null, and GSTP1 Ile105Val polymorphisms was determined for each participant using PCR methods. RESULTS: A significant increase of white blood cell (WBC) numbers (p < .05) and a significant decrease by 11% of hemoglobin (Hb) (p < .01) were noted in the exposed subjects in our study. Moreover, we report a significant increase of MDA level and the activities of SOD and CAT enzymes of the IR-exposed group compared to controls (p < .001). Interestingly, a close association was noted between the genotypes GSTP1 low active, GSTT1 null, GSTM1 null, and both GSTT1/GSTM1 null and oxidative stress biomarkers, especially with MDA level, SOD, and CAT activities. CONCLUSIONS: Our findings indicate that the medical staff exposed to low IR levels were under risk of significant oxidative stress that was enhanced by their glutathione S-transferase (GST) polymorphisms.

Co segregation of the m.1555A>G mutation in the MT-RNR1 gene and mutations in MT-ATP6 gene in a family with dilated mitochondrial cardiomyopathy and hearing loss: A whole mitochondrial genome screening.

Mitochondrial disease refers to a heterogeneous group of disorders resulting in defective cellular energy production due to dysfunction of the mitochondrial respiratory chain, which is responsible for the generation of most cellular energy. Because cardiac muscles are one of the high energy demanding tissues, mitochondrial cardiomyopathies is one of the most frequent mitochondria disorders. Mitochondrial cardiomyopathy has been associated with several point mutations of mtDNA in both genes encoded mitochondrial proteins and mitochondrial tRNA and rRNA. We reported here the first description of mutations in MT-ATP6 gene in two patients with clinical features of dilated mitochondrial cardiomyopathy. The mutational analysis of the whole mitochondrial DNA revealed the presence of m.1555A>G mutation in MT-RNR1 gene associated to the m.8527A>G (p.M>V) and the m.8392C>T (p.136P>S) variations in the mitochondrial MT-ATP6 gene in patient1 and his family members with variable phenotype including hearing impairment. The second patient with isolated mitochondrial cardiomyopathy presented the m.8605C>T (p.27P>S) mutation in the MT-ATP6 gene. The three mutations p.M1V, p.P27S and p.P136S detected in MT-ATP6 affected well conserved residues of the mitochondrial protein ATPase 6. In addition, the substitution of proline residue at position 27 and 136 effect hydrophobicity and structure flexibility conformation of the protein.

Whole mitochondrial genome screening of a family with maternally inherited diabetes and deafness (MIDD) associated with retinopathy: A putative haplotype associated to MIDD and a novel MT-CO2 m.8241T>G mutation.

Mitochondrial diseases are a clinically heterogeneous group of disorders that arise as a result of dysfunction of the mitochondrial respiratory chain. They can be caused by mutations in both nuclear and mitochondrial DNA. In fact, mitochondrial DNA (mtDNA) defects are known to be associated with a large spectrum of human diseases and patients might present wide range of clinical features with various combinations. Our study reported a Tunisian family with clinical features of maternally inherited diabetes and deafness (MIDD). Accordingly, we performed a whole mitochondrial genome mutational analysis, results revealed a haplotype composed by "A750G, A1438G, G8860A, T12705, T14766C and T16519C", in homoplasmic state, in the mother and transmitted to her daughter and her son. The patient with MIDD2 and retinopathy presented, in addition to this haplotype associated to the MIDD, two de novo variations including a novel one m.8241T>G (p. F219C) in MT-CO2 gene and a known one m.13276G>A (p. M314V) in MT-ND5 gene. The coexistence of these two mutations could explain the retinopathy observed in this patient.

A de-novo large deletion of 2.8 kb produced in the ABCD1 gene causing adrenoleukodystrophy disease.

X-linked adrenoleukodystrophy (X-ALD) is a neurodegenerative disorder caused by mutations in the ABCD1 gene, which encodes an ATP-binding cassette transporter protein, ALDP. The disease is characterized by increased concentrations of very long chain fatty acids (VLCFAs) in plasma, adrenal, testicular, and nerve tissues. For this study, our objective was to conduct clinical, molecular, and genetic studies of a Tunisian patient with X-ALD. The diagnosis was based on clinical indications, biochemical analyses, typical brain-scan patterns, and molecular biology; the molecular analyses were based on PCR, long-range PCR, and sequencing. The molecular analysis by long-range PCR and direct sequencing of the ABCD1 gene showed the presence of a de-novo 2794 bp deletion covering the whole of exon 2. Using bioinformatics tools, we demonstrate that the large deletion is located in a region rich with Alu sequences. Furthermore, we suggest that the AluJb sequence could be the cause of the large deletion of intron 1, exon 2, and intron 2, and the creation of a premature stop codon within exon 3. This report is the first report in which we demonstrate the breakpoints and the size of a large deletion in a Tunisian with X-ALD.

Mutational screening in patients with profound sensorineural hearing loss and neurodevelopmental delay: Description of a novel m.3861A > C mitochondrial mutation in the MT-ND1 gene.

Mitochondrial diseases caused by mitochondrial dysfunction are a clinically and genetically, heterogeneous group of disorders involving multiple organs, particularly tissues with high-energy demand. Hearing loss is a recognized symptom of a number of mitochondrial diseases and can result from neuronal or cochlear dysfunction. The tissue affected in this pathology is most probably the cochlear hair cells, which are essential for hearing function since they are responsible for maintaining the ionic gradients necessary for sound signal transduction. Several mitochondrial DNA mutations have been associated with hearing loss and since mitochondria are crucial for the cellular energy supply in many tissues, most of these mtDNA mutations affect several tissues and will cause syndromic hearing loss. In the present study, we described 2 patients with sensorineural hearing loss and neurodevelopmental delay in whom we tested mitochondrial genes described to be associated with syndromic hearing loss. One of these patients showed a novel heteroplasmic mitochondrial mutation m.3861A > C (W185C) which lead to a loss of stability of the ND1 protein since it created a new hydrogen bund between the unique created cystein C185 and the A182 residue. In the second patient, we detected two novel heteroplasmic variations m.12350C > A (T5N) and m.14351T > C (E108G) respectively in the MT-ND5 and the MT-ND6 genes. The TopPred II prediction for the E108G variation revealed a decrease of the hydrophobicity in the mutated MT-ND6.

Mitochondrial DNA triplication and punctual mutations in patients with mitochondrial neuromuscular disorders.

Mitochondrial diseases are a heterogeneous group of disorders caused by the impairment of the mitochondrial oxidative phosphorylation system which have been associated with various mutations of the mitochondrial DNA (mtDNA) and nuclear gene mutations. The clinical phenotypes are very diverse and the spectrum is still expanding. As brain and muscle are highly dependent on OXPHOS, consequently, neurological disorders and myopathy are common features of mtDNA mutations. Mutations in mtDNA can be classified into three categories: large-scale rearrangements, point mutations in tRNA or rRNA genes and point mutations in protein coding genes. In the present report, we screened mitochondrial genes of complex I, III, IV and V in 2 patients with mitochondrial neuromuscular disorders. The results showed the presence the pathogenic heteroplasmic m.9157G>A variation (A211T) in the MT-ATP6 gene in the first patient. We also reported the first case of triplication of 9 bp in the mitochondrial NC7 region in Africa and Tunisia, in association with the novel m.14924T>C in the MT-CYB gene in the second patient with mitochondrial neuromuscular disorder.

Mutational analysis in patients with neuromuscular disorders: Detection of mitochondrial deletion and double mutations in the MT-ATP6 gene.

Mitochondrial diseases encompass a wide variety of pathologies characterized by a dysfunction of the mitochondrial respiratory chain resulting in an energy deficiency. The respiratory chain consists of five multi-protein complexes providing coupling between nutrient oxidation and phosphorylation of ADP to ATP. In the present report, we studied mitochondrial genes of complex I, III, IV and V in 2 Tunisian patients with mitochondrial neuromuscular disorders. In the first patient, we detected the m.8392C>T variation (P136S) in the mitochondrial ATPase6 gene and the m.8527A>G transition at the junction MT-ATP6/MT-ATP8 which change the initiation codon AUG to GUG. The presence of these two variations in such an important gene could probably affect the ATP synthesis in the studied patient. In the second patient, we detected several known variations in addition to a mitochondrial deletion in the major arc of the mtDNA eliminating tRNA and respiratory chain protein genes. This deletion could be responsible of an inefficient translation leading to an inefficient mitochondrial protein synthesis in P2.

Whole mitochondrial genome analysis in two families with dilated mitochondrial cardiomyopathy: detection of mutations in MT-ND2 and MT-TL1 genes.

Pathogenic mitochondrial DNA (mtDNA) mutations leading to mitochondrial dysfunction can cause cardiomyopathy and heart failure. These mutations were described in the mt-tRNA genes and in the mitochondrial protein-coding genes. The aim of this study was to identify the genetic defect in two patients belonging to two families with cardiac dysfunction associated to a wide spectrum of clinical phenotypes. The sequencing analysis of the whole mitochondrial DNA in the two patients and their parents revealed the presence of known polymorphisms associated to cardiomyopathy and two pathogenic mutations in DNA extracted from blood leucocytes: the heteroplasmic m.3243A > G mutation in the MT-TL1 gene in patient A; and the homoplasmic m.5182C > T mutation in the ND2 gene in patient B. Secondary structure analysis of the ND2 protein further supported the deleterious role of the m.5182C > T mutation, as it was found to be involved an extended imbalance in its hydrophobicity and affect its function. In addition, the mitochondrial variants identified in patients A and B classify both of them in the same haplogroup H2a2a1.