Mitochondrial A3243G Mutation Research Articles

Clinical and molecular findings in a Chinese family with a de novo mitochondrial A1555G mutation

BackgroundThe mitochondrial 12S rRNA A1555G mutation is the most prevalent deafness-causing mitochondrial DNA (mtDNA) mutation and is inherited maternally. Studies have suggested that A1555G mutations have multiple origins, although there is no direct evidence of this. Here, we identified a family with a de novo A1555G mutation.MethodBased on detailed mtDNA analyses of the family members using next-generation sequencing with 1% sensitivity to mutated mtDNA, the level of heteroplasmy in terms of the A1555G mutation in blood DNA samples was quantified.ResultsAn individual harbored a heterogeneous A1555G mutation, at 28.68% heteroplasmy. The individual’s son was also a heterogeneous carrier, with 7.25% heteroplasmy. The individual’s brother and mother did not carry the A1555G mutation, and both had less than 1% mitochondrial 12S rRNA A1555G heteroplasmy.ConclusionThe A1555G mutation arose de novo in this family. This is the first report of a family with a de novo A1555G mutation, providing direct evidence of its multipoint origin. This is important for both diagnostic investigations and genetic counselling.

A linear five-ring pyrrole-imidazole polyamide-triphenylphosphonium conjugate targeting a mitochondrial DNA mutation efficiently induces apoptosis of HeLa cybrid cells carrying the mutation

Somatic mutations in mitochondrial DNA may provide a new avenue for cancer therapy due to their associations to a number of cancers and a tendency of homoplasmicity. In consideration of mitochondrial features and its relatively small genome size, a nucleotide-based targeting approach is a considerably more promising option. To explore the efficacy of short linear N-methylpyrrole-N-methylimidazole polyamide (PI polyamide), we synthesized a five-ring short PI polyamide that provided sequence-specific homing for the A3243G mitochondrial mutation upon conjugation with triphenylphosphonium cation (TPP). This PI polyamide-TPP was able to induce cytotoxicity in HeLamtA3243G cybrid cells, while preserving preferential binding for oligonucleotides containing the A3243G motif from melting temperature assays. The PI polyamide-TPP also localized in the mitochondria in HeLamtA3243G cells and induced mitochondrial reactive oxygen species production, mitophagy and apoptosis in a mutation-specific fashion compared to the wild-type HeLamtHeLa cybrids; normal human dermal fibroblasts were also relatively unaffected to suggest discriminating selectivity for the mutant mitochondria, offering a novel outlook for cancer therapy via mitochondrial homing of short linear PIP-TPPs.

High Prevalence of Mitochondrial tRNA A3243G Mutation in Invasive Breast Cancer

Background & Aim: Mitochondria play vital roles in various cellular activities, such as energy production, maintaining the redox balance of the cell, the regulation of cellular proliferation and differentiation, and programmed cell death. Mitochondrial tRNA mutations are associated with many pathological conditions and numerous diseases have been associated with them. Therefore, the objectives of this study were to evaluate the presence and the frequency of mutations in the selected tRNAs in breast cancer patients and to correlate these mutations with the clinicopathological characters. Materials & Methods: The is a cross sectional study, where seventy seven breast tumors and adjacent non-tumorous (normal) tissue samples were analyzed by PCR- RFLP, and direct DNA sequencing. In this study three mt-tRNAs wre selected, two of them are the most important disease associated mt-tRNAs i.e tRNALue (UUR), tRNALys and one of the least pathogenic associated tRNA which is tRNAarg. Statistical analysis was used to determine the relationship between the detected mutations and the clinicopathologhical characters. Results: The tRNAleu (UUR) A3243G mutation occurring at the highly conserved location was detected in 4 samples (5.2%) of both breast cancer and adjacent non-tumorous tissue except one detected only in tumor tissue. Another A8343G mutation was detected in tRNAlys. There was no significant association between these mutations and clinicopathological parameters (P. value > 0.05). Conclusion: The detection of high frequent A3243G mutations in patients with invasive breast cancer suggests role of this mutation in the carcinogenesis. This mutation affects complex I, reduces translation of its core subunits, which can contribute to the impairment of oxidative phosphorylation and increase ROS production, leading to cancer progression.

Mitochondrial Diabetes: More Than Just Hyperglycemia.

Juvenile-onset diabetes is often branded as type 1 diabetes when a clear family history is absent. A high degree of suspicion regarding other forms of diabetes should be kept in mind when systems not known to be affected by hyperglycemia or associated with type 1 diabetes are involved. Such a scenario is often complicated by the slow evolution of symptomatology and the absence of diabetes in family members. Here, we report on a genetically proven mitochondrial A3243G mutation–related syndromic diabetes in a young patient whose mitochondrial disease–related multisystem symptomatology slowly evolved over the course of a decade. Our association with the patient started from his childhood (Figure 1). His first visit to our hospital was for short stature at the age of 9 years. Systemic work-up and growth hormone studies were normal. Familial factors were thought to be responsible. He was noted to have an IQ of 75, with poor performance in school. FIGURE 1. Chronology of symptoms in the patient. At the age of 16 years, he presented to us with diabetes without ketosis or a family history of diabetes. Tests for GAD65 and IA2 antibodies were negative at this stage. Although a trial of oral hypoglycemic agents was instituted, he was soon shifted to insulin therapy because of his poor response. Two years later, he presented with gastrointestinal symptoms in the form of intermittent diarrhea. Work-up for celiac disease and pancreatic insufficiency, including upper and lower endoscopies with biopsies, was normal. Fortunately, the diarrhea subsided, which was attributed by the family to dietary manipulation, especially restriction of wheat products. At around this time, sensorineural hearing loss was documented. The combination of these symptoms led to a consideration of mitochondrial diabetes. However, fundus evaluation for characteristic pigmentary changes was normal. Also around this …

Analysis of mitochondrial A1555G mutation in infants with hearing impairment.

Mutations in the mitochondrial 12S ribosomal RNA gene have been identified to be associated with deafness. Among these, the A to G transition at position 1555 is one of the most common pathogenic mutations associated with hearing loss. In order to evaluate the allele frequency of this mutation in infants with hearing loss, the A1555G mutation was screened in 300 deaf children and 100 age- and sex-matched healthy subjects. Consequently, 5 patients with this mutation were identified, whereas the mutation was absent in healthy controls. Among the patients with the mutation, only one had an obvious family history of hearing impairment. Notably, this pedigree manifested a high penetrance of deafness. In particular, the penetrance of deafness was 80 and 40%, when the aminoglycoside antibiotics (AmAn) was included or excluded, respectively. Clinical evaluation of this family exhibited a wide degree of hearing loss. Furthermore, screening for the complete mitochondrial genes revealed the occurrence of A1555G and transfer (t)RNAThr T15943C mutations, together with other genetic variations belonging to East Asian haplogroup C. Notably, the T15943C mutation, located at the T arm of tRNAThr, could disrupt the 63T-55A base-pairing and impair tRNA metabolism. Therefore, it was hypothesized that the combination of A1555G and T15943C mutations may result in mitochondrial dysfunction that is responsible for deafness. Screening for A1555G, as well as other potential pathogenic mutations in the mitochondrial genome, is critical for clinical diagnosis and prevention of hearing impairment.

Analysis of mitochondrial function in human induced pluripotent stem cells from patients with mitochondrial diabetes due to the A3243G mutation

We previously established human induced pluripotent stem (iPS) cells in two diabetic patients from different families with the mitochondrial A3243G mutation and isolated isogenic iPS cell clones with either undetectable or high levels of the mutation in both patients. In the present study, we analyzed the mitochondrial functions of two mutation-undetectable and two mutation-high clones in each patient through four methods to assess complex I activity, mitochondrial membrane potential, mitochondrial respiration, and mitochondrial ATP production. In the first patient, complex I activity, mitochondrial respiration, and mitochondrial ATP production were decreased in the mutation-high clones compared with the mutation-undetectable clones, and mitochondrial membrane potential was decreased in a mutation-high clone compared with a mutation-undetectable clone. In the second patient, complex I activity was decreased in one mutation-high clone compared with the other clones. The other parameters showed no differences in any clones. In addition, the complex I activity and mitochondrial respiration of the mutation-undetectable clones from both patients were located in the range of those of iPS cells from healthy subjects. The present study suggests that the mitochondrial function of the mutation-undetectable iPS cell clones obtained from two patients with the A3243G mutation is comparable to the control iPS cells.

Detection of a new case harboring mitochondrial A3243G mutation of MELAS syndrome

Mitochondrial genome A3243G mutation in the tRNALeu(UUR) encodinggene (MTTL)is the main cause of mitochondrial encephalopathy, lactic acidosis and stroke-like episodes (MELAS). This mutation exists in heteroplasmic form and severity of the disease is affected by many factors including heteroplasmy level.
 In this study, a pediatric proband (female, 8 years old) was found to carry A3243G mutation at 77.6% of heteroplasmy by using PCR-RFLP in combination with real-time PCR. The results of the A3243G mutation analysis of the proband’s family showed that her mother without any symptoms of encephalopathyalso carried the mutation at 7.9% of heteroplasmy whereas the mutation was not found in the proband’s healthy father and healthy sister, indicating that the proband received the A3243G mutation from her mother and the expression of MELAS syndromes depended on the level of heteroplasmy.

Identification of a mitochondrial 12S rRNA A1555G mutation causing aminoglycoside-induced deafness in a large Thai family

Abstract Background Hearing loss is among the most frequent sensory disorders. Preventable causes include medications given to genetically susceptible individuals. Several families around the world with an A1555G mitochondrial mutation who became profoundly deaf after receiving aminoglycosides have been described. However, none has been reported in Thailand. Objectives To identify the cause of hearing loss of a large Thai family with 11 members who reportedly turned deaf after receiving antibiotics. Methods We obtained blood samples from 5 members; 4 of whom had hearing loss. Mutation analyses were performed using molecular techniques including polymerase chain reaction, Sanger sequencing, and restriction fragment length polymorphism. Results All 4 affected members were found to harbor the same A1555G mitochondrial mutation, while the unaffected had only the wild-type A. Conclusions We have identified the mitochondrial mutation leading to aminoglycoside-induced hearing loss in a Thai population. Raising awareness for medical practitioners of this genetic susceptibility in Thailand is warranted. Avoidance of certain medications in these individuals would prevent this acquired permanent hearing loss.

Identification and Clinical Characterization of Adult Patients with Multigenerational Diabetes Mellitus.

BackgroundSome patients diagnosed as having type 2 diabetes mellitus (T2DM) are, instead, affected by multigenerational diabetes whose clinical characteristics are mostly undefined.Objective1. To identify among patients who had been previously defined as affected by T2DM those, in fact, affected by multigenerational diabetes; 2. After excluding patients carrying the most common MODY genes and mitochondrial mutations, we compared clinical features of remaining patients with those of patients with T2DM.MethodsAmong 2,583 consecutive adult patients who had been defined as affected by T2DM, we looked for those with diabetes in ≥3 consecutive generations. All probands were screened for mutations in six MODY genes (HNF4A, GCK, HNF1A, PDX1, HNF1B and NeuroD1) and for the A3243G mitochondrial mutation. After excluding patients with mutations in one of such genes, we compared clinical features of the remaining 67 patients (2.6% of the whole initial sample) affected by multigenerational “familial diabetes of the adulthood” (FDA) and of their diabetic relatives (n = 63) to those with T2DM (n = 1,028) by generalized hierarchical linear models followed by pairwise comparisons.ResultsAge, age at diagnosis, proportion of hypertension (all p<0.001), and waist circumference (p<0.05) were lower in FDA than T2DM. Nonetheless, the two groups had similar age-adjusted incidence rate of all-cause mortality.ConclusionsBeside younger age at diagnosis, FDA patients show lower waist circumference and reduced proportion of hypertension as compared to those with T2DM; despite such reduced potential cardiovascular risk factors, FDA patients did not show a reduced mortality risk than patients with T2DM.

Sensitive quantification of mitochondrial mutation using new Taqman probes

Abstract The A3243G mitochondrial mutation is the major cause of mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS). The severity of the disease is correlated with the heteroplasmy level of the mutation. Here we describe for the first time the validation of a real-time polymerase chain reaction (PCR) assay with Taqman locked nucleic acid (LNA) fluorescent (FAM for mutant, HEX for wild type) probes for quantification of heteroplasmy levels in a total of 18 family members from 5 Vietnamese MELAS patients carrying A3243G. Almost no background of FAM signals was detected in normal samples, indicating that the probes were allele-specific. Standard curves indicate sensitive detection at 0.1% mutants and high reliability with R2 &gt; 0.985. The correlation line between measured % mutant and expected % mutant was highly reliable, with a slope of 0.993 and R2 of 0.998. All positive A3243G mutant samples pre-screened by PCR-restriction fragment length polymorphism (RFLP) were confirmed, and their heteroplasmy levels quantified to be from 3.68 to 80.85%. The heteroplasmy levels in patients were higher than in their family members and generally correlated well with the severity of their clinical symptoms. Overall, this work is the first demonstration of the application of LNA probes for sensitive and highly reliable quantification of heteroplasmy levels in human mitochondria.

Expression and significance of respiratory chain enzyme of cells in urine sediment in MELAS syndrome

To explore the expression and significance of respiratory chain enzyme of cells in urine sediment in mitochondrial encephalopathy myopathy, lactic acidosis and stroke-like episodes (MELAS) syndrome. Through enzyme histochemistry, the authors analyzed the changes of respiratory chain enzyme in urine sediment in 20 MELAS patients due to mitochondrial A3243G mutation (MELAS group) and 20 health peoples (control group). And the impact on the expression of protein encoded by nuclear DNA (A21347) and mitochondrial DNA (A6404) was detected by immunochemistry. Image pro Plus 6.0 software was used for analysis of absorbance (A) of staining images as staining intensity. The data were expressed as M (Q1, Q3) and analyzed through statistical software. The staining intensity of complexes Iin the MELAS group was lower than that in the control group (0.06(0.01, 0.12) vs 0.12(0.01, 0.62), P = 0.010). The intergroup staining intensity of complex II showed no marked difference. Increased density of blue particle and cytoplasmic gathering was found in 13 cased (65%) of the MELAS group under light microscope. The staining intensity of complexes IV was expressed at a low level in the MELAS group (0.14(0.03, 0.32) vs 0.23(0.06, 0.43), P = 0.038). The expression of protein encoded by nuclear DNA (A21347) was lower than that in the control group (0.05(0.02, 0.45) vs 0.17(0.03, 0.70), P = 0.000). The expression of protein encoded by mitochondrial DNA (A6404) was also lower than that in the control group (0.03(0.01, 0.07) vs 0.15 (0.09, 0.23), P = 0.000). Abnormal change of respiratory chain enzyme in urine sediment in MELAS due to mitochondrial A3243G mutation and a low expression of proteins encoded by two kinds of DNA in complexes IV can help to confirm the genetic diagnosis of mitochondrial encephalomyopathies so that different subtypes may be classified and its pathogenesis elucidated.

A case of mitochondrial A3243G mutation accompanied by ossicular malformation

A case of mitochondrial A3243G mutation accompanied by ossicular malformation

Frequency of the mitochondrial A1555G mutation in Iranian patients with non- syndromic hearing impairment

Mitochondrial 12S rRNA gene mutations account for non-syndromic hearing impairment (NSHI). The A1555G substitution is the most common mitochondrial DNA mutation and is associated with both aminoglycoside-induced HI and NSHI. Its frequency is variable among populations of different ethnic background. The purpose of the present survey was to determine the frequency of the A1555G mutation in the Iranian probands with NSHI. We have screened 152 unrelated Iranian probands with NSHI with childhood onset and 548 normal hearing controls for the occurrence of the A1555G mutation using PCR-RFLP method. Totally, 2 patients carrying the homoplasmic A1555G mutation were identified with a total frequency of 1.3% in Iran. Mutation A1555G had a variable frequency among subpopulations of different ethnic origins in Iran: Azeri Turkish (4.16%), Lure (0.0%), Fars (0.0%) and Bushehri (2.86%). The A1555G mutation was not found in any member of the controls. Our study shows that the frequency of the A1555G mutation in Azeri Turkish and Bushehri hearing impaired patients is compatible with that reported for Caucasian populations.

Frequency of the mitochondrial A1555G mutation in Iranian patients with nonsyndromic hearing impairment

Frequency of the mitochondrial A1555G mutation in Iranian patients with nonsyndromic hearing impairment

Molecular and Clinical Characterization of the Variable Phenotype in Korean Families with Hearing Loss Associated with the Mitochondrial A1555G Mutation

Hearing loss, which is genetically heterogeneous, can be caused by mutations in the mitochondrial DNA (mtDNA). The A1555G mutation of the 12S ribosomal RNA (rRNA) gene in the mtDNA has been associated with both aminoglycoside-induced and non-syndromic hearing loss in many ethnic populations. Here, we report for the first time the clinical and genetic characterization of nine Korean pedigrees with aminoglycoside-induced and non-syndromic hearing loss. These Korean families carry in the A1555G mutation of 12S rRNA gene and exhibit variable penetrance and expressivity of hearing loss. Specifically, the penetrance of hearing loss in these families ranged between 28.6% and 75%, with an average of 60.8%. These results were higher than the 29.8% penetrance that was previously reported in a Chinese population but similar to the 65.4% and 54.1% penetrance observed in a large Arab-Israeli population and nineteen Spanish pedigrees, respectively. The mutational analysis of the complete mtDNA genome in these families showed that the haplogroups of the Korean population, which belongs to the eastern Asian population, were similar to those of the Chinese population but different from the Spanish population, which belongs to the European-Caucasian population. The mtDNA variants that may act as modifier factors were also found to be similar to the Chinese population. Although the mtDNA haplogroups and variants were similar to the eastern Asian population, we did find some differing phenotypes, although some subjects had the same variants. This result suggests that both the ethnic background and environmental factors lead to a variable phenotype of the A1555G mutation.

A case of mitochondrial cardiomyopathy with restrictive transmitral filling pattern

A 61-year-old diabetic woman with a mitochondrial A3243G mutation was hospitalized for evaluation of breathlessness, general fatigue, and leg edema. Chest radiography revealed cardiomegaly with massive pleural effusion. Serum lactate, pyruvate, and brain natriuretic peptide concentrations were elevated. Transthoracic echocardiography revealed a restrictive pattern of transmitral flow, although systolic function of the left ventricle was only mildly impaired. Based on these findings and her clinical course, the patient was diagnosed with right-sided heart failure caused by mitochondrial cardiomyopathy associated with a restrictive transmitral filling pattern. Treatment with furosemide, enalapril, and eplerenone was effective, and improvement in her symptoms was associated with amelioration of transthoracic echocardiographic findings and a reduction in serum brain natriuretic peptide levels. Previous reports have indicated heterogeneity in the clinical features of mitochondrial cardiomyopathy in patients carrying the A3243G mutation; the present case highlights the substantial variability in the clinical features of this disease.

Mitochondrial A3243G Mutation With Manifestation of Acute Dilated Cardiomyopathy

A 35-year-old woman (body mass index, 16 kg/m2; height, 140 cm) presented to the emergency ward with severe dyspnea of acute onset. The medical history was noteworthy for bilateral hypacusis treated with a hearing aid. On admission, the laboratory results revealed an N-terminal prohormone of brain natriuretic peptide level of 10 219 ng/L (normal <200 ng/L). Thoracic CT scan excluded pulmonary embolism but showed cardiomegaly with pericardial and bilateral pleural effusion suggesting the presence of acute heart failure. Cardiac MRI (CMR) demonstrated a severely reduced left ventricular ejection fraction (LVEF, 13%) and severe right ventricular dysfunction (Figure 1A and 1B, baseline); LV mass index was normal. Late gadolinium enhancement images demonstrated extensive subepicardial lesions in inferior and lateral LV segments (Figure 1C, baseline). The angiogram excluded a coronary pathology, and myocardial histology …

GJB2 and GJB6 genes and the A1555G mitochondrial mutation are only minor causes of nonsyndromic hearing loss in the Qatari population

Objective: This study reports results from the first survey of the genetic causes of nonsyndromic sensorineural hearing loss (NSHHL) in the Qatari population. Design and Study samples: Data were collected from 126 Qatari patients (58 males and 68 females) belonging to inbred families (56%), showing an autosomal recessive pattern of inheritance (96%). Fifty-three patients were less than 10 years old, 55 in the age range of 10 to 20 years, while 18 were aged between 20 and 30 years. All subjects had moderate to severe sensorineural hearing loss and were screened for GJB2 mutations, GJB6 deletion, and for A1555G mitochondrial mutation. Results: Four patients were homozygous and one was heterozygous for c.35delG; five were homozygous for the IVS1 + 1G < A, and two were heterozygous for c.229 T > C. Only 8.3% of the pathogenic alleles were detected. No patients were positive for GJB6 deletion or for A1555G . Conclusions: These findings: (1) demonstrate that GJB2, GJB6 deletion and A1555G mutation account for a minor proportion of NSHHL in the Qatari population, (2) further strengthen the need to search for causative genes, (3) clearly contribute to establishing preventive strategies for NSHHL in Qatar and in the Gulf area.

The mitochondrial A3243G mutation involves the peripheral vestibule as well as the cochlea

To evaluate vestibular function in patients with the mitochondrial A3243G mutation. Data from patients with the A3243G mutation attending an academic tertiary referral center were prospectively recorded. The clinical histories of 13 unrelated patients with the mitochondrial A3243G mutation (six mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes; and seven maternally inherited diabetes and deafness) were recorded, in particular their history of vestibular symptoms. Vestibular examinations including caloric testing and vestibular evoked myogenic potentials in response to air-conducted sound (ACS-VEMPs) were performed. In seven patients who showed abnormal ACS-VEMP, VEMP in response to galvanic stimuli (galvanic-VEMP) were also recorded. Eleven of the 13 patients had vestibular symptoms. The age of onset of vestibular symptoms was significantly later than the ages of onset of hearing loss and diabetes mellitus (P < .05). Ten of the 13 patients showed abnormal caloric responses, whereas 12 patients showed abnormal ACS-VEMPs on one or both sides. All of the seven patients who underwent galvanic-VEMP testing showed normal responses. The A3243G mutation is associated with vestibular dysfunction involving both the superior and inferior vestibular nerve systems. Furthermore, our results from galvanic-VEMP testing suggests that a labyrinthine lesion is primarily responsible for the symptoms of vestibular dysfunction.

Prevalence of A1555G mitochondrial mutation in Chinese newborns and the correlation with neonatal hearing screening

ObjectiveTo investigate the feasibility of genetic screening for deafness causative genes in the process of newborn hearing screening in China. MethodsTotal 865 newborn babies between November 2009 and March 2010 were enrolled for the simultaneous hearing and deafness causative gene screening in Tongji Hospital, Wuhan, China. Hearing screening followed a two-stage strategy with transient evoked otoacoustic emissions. Infants referred after the second-stage screening were tested by diagnostic auditory brainstem response (ABR). Genomic DNA was extracted from heel blood of newborns, and the mitochondrial 12S rRNA A1555G mutation was detected by polymerase chain reaction (PCR) based restriction fragment length polymorphism and confirmed by DNA sequencing. ResultsIn hearing screening, 134 out of the 865 newborns (15.5%) were referred after the first-stage screening and 86.6% (116/134) of them returned for the second stage. After the second-stage screening, 15 who were still referred were tested by diagnostic ABR and 3 of them failed the test. On the other hand, gene screening identified 6 of the 865 newborns (0.7%) harbored homoplasmic 12S rRNA A1555G mutation although they passed the hearing screening. ConclusionIt might be practical and effective to complement routine hearing screening in newborns with gene screening for the purpose of early diagnosis and discovery of the late-onset hearing loss.