Mitochondrial DNA Point Mutations Research Articles

Defective post-transcriptional modification of tRNA disrupts mitochondrial homeostasis in Leber’s hereditary optic neuropathy

Leber's Hereditary Optic Neuropathy (LHON) is a rare, maternally inherited eye disease, predominantly due to the degeneration of retinal ganglion cells (RGCs). It is associated with a mitochondrial DNA (mtDNA) point mutation. Our previous study identified that the m.15927G>A homoplasmic mutation damaged the highly conserved basepairing (28C-42G) in anticodon stem of tRNAThr, caused deficient t6A modification and significantly decreased efficiency in aminoacylation and steady-state levels of tRNAThr, and led to mitochondrial dysfunction. Meanwhile, mechanisms underlying mtDNA mutations regulate intracellular signaling related to the mitochondrial and cellular integrity are less explored. Here, we manifested that defective nucleotide modification induced by the m.15927G>A mutation interfered with the expression of nuclear genes involved in cytoplasmic proteins essential for oxidative phosphorylation system (OXPHOS), thereby impacting the assemble and integrity of OXPHOS complexes. As a result of these mitochondrial dysfunctions, there was an imbalance in mitochondrial dynamics, particularly distinguished by an increased occurrence of mitochondrial fission. Excessive fission compromised the autophagy process, including initiation phase, formation and maturation of autophagosome. Both Parkin-mediated mitophagy and receptor-dependent mitophagy were significantly impaired in cybrids haboring the m.15927G>A mutation. These changes facilitated intrinsic apoptosis, as indicated by increased cytochrome c release and elevated levels of apoptosis-associated proteins (e.g., BAK, BAX, cleaved caspase 9, cleaved caspase 3, and cleaved PARP) in the mutant cybrids. This study demonstrates that the m.15927G>A mutation contributes to LHON by dysregulating OXPHOS biogenesis, aberrant quality control, increased autophagy, inhibited mitophagy, and abnormal apoptosis.

Generation of iPSCs from identical twin, one affected by LHON and one unaffected, both carrying a combination of two mitochondrial variants: m.14484 T>C and m.10680G>A

Leber hereditary optic neuropathy (LHON) is one of the most common mitochondrial illness, causing retinal ganglion cell degeneration and central vision loss. It stems from point mutations in mitochondrial DNA (mtDNA), with key mutations being m.3460G > A, m.11778G > A, and m.14484 T > C. Fibroblasts from identical twins, sharing m.14484 T > C and m.10680G > A variants each with 70 % heteroplasmy, were used to generate iPSC lines. Remarkably, one twin, a LHON patient, displayed symptoms, while the other, a carrier, remained asymptomatic. These iPSCs offer a valuable tool for studying factors influencing disease penetrance and unravelling the role of m.10680G > A, which is still debated.

EMPLOYING CLINICALLY RELEVANT TRANSGENIC ANIMAL MODELS: MUSCULOSKELETAL REGENERATION IN THE POLGA MOUSE MODEL OF AGEING

Aging impairs the regenerative capacity of musculoskeletal tissues and is associated with poor healing outcomes. PolgAD257A/D257A (PolgA) mice present a premature aging phenotype due to the accumulation of mitochondrial DNA (mtDNA) point mutations at rates 3 – 5 fold higher compared to wild type mice. Consequently, PolgA mice exhibit the premature onset of clinically-relevant musculoskeletal aging characteristics including frailty, osteo-sarcopenia, and kyphosis. I will present our recent findings on the use of PolgA mice to investigate the effects of aging on the regenerative capacity of bone. In particular, I will focus on the mechano-sensitivity of the regenerative process in aged bone environments and the opportunities it presents for clinical translation of mechanical intervention therapies.

LHON spectrum disorder: Phenotype and genes

Leber hereditary optic neuropathy (LHON) is an inherited optic neuropathy primarily affecting young male with subacute bilateral visual loss. Clinically it is characterized by central scotoma, discromatopsia, and usually permanent central visual loss.This disease has a typical optic disc appearance at fundus examination of pseudoedema and microangiopathy which characterize the asymptomatic and subacute phases of the disease. Optic disc atrophy follows in the chronic phase.When the disease manifests, the preferential involvement of papillomacular fibres and macular retinal ganglion cell (RGC) damage are evident. These clinical features combined with the ophthalmoscopic pattern create the framework that make the disease unique.Primary point mutations of mitochondrial DNA (mtDNA) have been described as the genetic cause of the disease in about 90% of cases. Recently, new autosomal recessive DNA mutations have been reported in patients affected by subacute visual loss associated with a clinical picture resembling LHON.We herein describe the phenotype of 6 patients in which whole‐exome sequencing identified variants in the MECR gene in 2 probands of the same pedigree, in the NDUFAF4 gene in one patient, and mutation in the nuclear gene DNAJC30 in 3 patients. The 3 male probands with DNAJC30 mutation presented the typical LHON clinical picture with subacute loss of vision at an adult age in 2 cases and at a childhood age in one case. The pattern of visual loss with central scotoma and discromatopsia was associated with pseudoedema and microangiopathy at fundus appearance. Optical coherence tomography (OCT) analysis showed in both acute and asymptomatic family members the swelling of fibres while in the dynamic and chronic stages a progressive thinning of fibres. Visual recovery was detected in the younger patient and, partially, in one of adult patient.The 3 other patients carrying the MECR and NDUFAF4 gene variants showed a particular course of the disease characterized by a childhood onset of visual loss followed by a recurrence of visual loss at an adult age. The childhood onset was insidious in one case and subacute in the other 2 cases (about 6 years of age).OCT analysis demonstrated in the insidious case the temporal thinning of fibres and the macular RGC atrophy followed by swelling of fibres during the recurrence.In the differential diagnosis of inherited optic neuropathies with clinical presentation resembling LHON we should take into consideration the recessive form with mutations in the DNAJC30 gene which appears to overlap the mtDNA LHON disease. Moreover, clinical patterns resembling LHON with recurrence of visual loss represent another form of LHON with unique clinical presentation associated with variants in the MECR and the NDUFAF4 genes. These new clinical and genetic patterns enlarge the spectrum of LHON disease.

Management of LHON ‐ An update

Leber hereditary optic neuropathy (LHON) is a devastating cause of blindness that predominantly affects young adult men. Over 90% of patients harbour one of three mitochondrial DNA point mutations, namely, m.3460G>A (MT‐ND1), m.11778G>A (MT‐ND4) and m.144484T>C (MT‐ND6). Idebenone is the only approved treatment for LHON. New evidence has refined the management guidelines for idebenone, in particular the duration of treatment and the therapeutic window of opportunity. Gene therapy using allotopic expression is an attractive strategy for LHON as it corrects the underlying mitochondrial DNA defect. Promising results have been obtained for the m.1178G>A (MT‐ND4) mutation for patients treated within 1 year of disease onset with an intravitreal injection of a modified adeno‐associated viral vector carrying the replacement gene.

DNAJC30 Gene Variants Are a Frequent Cause of a Rare Disease: Leber Hereditary Optic Neuropathy in Polish Patients.

Leber hereditary optic neuropathy (LHON) is a rare disorder causing a sudden painless loss of visual acuity in one or both eyes, affecting young males in their second to third decade of life. The molecular background of the LHON is up to 90%, genetically defined by a point mutation in mitochondrial DNA. Recently, an autosomal recessive form of LHON (LHONAR1, arLHON) has been discovered, caused by biallelic variants in the DNAJC30 gene. This study provides the results of the DNAJC30 gene analysis in a large group of 46 Polish patients diagnosed with LHON, together with the clinical characterization of the disease. The c.152A>G (p.Tyr51Cys) substitution in the DNAJC30 gene was detected in all the patients as homozygote or compound heterozygote. Moreover, we identified one novel variant, c.293A>G, p.(Tyr98Cys), as well as two ultra-rare DNAJC30 variants: c.293A>C, p.(Tyr98Ser), identified to date only in one individual affected with LHONAR1, and c.130_131delTC (p.Ser44ValfsTer8), previously described only in two patients with Leigh syndrome. The patients presented here represent the largest group of subjects with DNAJC30 gene mutations described to date. Based on our data, the autosomal recessive form of LHON caused by DNAJC30 gene mutations is more frequent than the mitochondrial form in Polish patients. The results of our study suggest that Sanger sequencing of the single-exon DNAJC30 gene should be a method of choice applied to identify a molecular background of clinically confirmed LHON in Polish patients. This approach will help to reduce the costs of molecular testing.

Leber Optic Neuropathy and Low Vision Rehabilitation: A Case Report

Leber’s Hereditary Optic Neuropathy (LHON) is a maternally inherited mitochondrial disease, characterized by point mutations in mitochondrial DNA and subsequent mitochondrial dysfunction; which leads to a bilateral and painless loss of central vision. Unfortunately at this time, there is no proven treatment to prevent or reverse this optic neuropathy. Therefore, individualized low vision rehabilitation services and assistive devices are essential to help people with LHON regain their independence and quality of life. We highlight through a case study the importance of psychic support as well as the impact of low vision rehabilitation on a young man with LHON.

Mitochondrial disorders: Understanding mitochondrial DNA point mutations and deletion syndromes.

Mitochondrial disorders arise from DNA mutations in either the mitochondrial DNA (mtDNA) or nuclear DNA genomes. This article focuses on a mtDNA base-pair mutation associated with neuropathy, ataxia, and retinitis pigmentosa and Leigh syndrome and the large-scale mtDNA deletion associated with Kearns-Sayre syndrome. Disease sequelae and management strategies are reviewed, along with implications for the nurse practitioner in primary or specialty care.

Absence of lenadogene nolparvovec DNA in a brain tumor biopsy from a patient in the REVERSE clinical study, a case report

BackgroundLeber Hereditary Optic Neuropathy (LHON) is a rare, maternally-inherited mitochondrial disease that primarily affects retinal ganglion cells (RGCs) and their axons in the optic nerve, leading to irreversible, bilateral severe vision loss. Lenadogene nolparvovec gene therapy was developed as a treatment for patients with vision loss from LHON caused by the most prevalent m.11778G > A mitochondrial DNA point mutation in the MT-ND4 gene. Lenadogene nolparvovec is a replication-defective recombinant adeno-associated virus vector 2 serotype 2 (AAV2/2), encoding the human wild-type MT-ND4 protein. Lenadogene nolparvovec was administered by intravitreal injection (IVT) in LHON patients harboring the m.11778G > A ND4 mutation in a clinical development program including one phase 1/2 study (REVEAL), three phase 3 pivotal studies (REVERSE, RESCUE, REFLECT), and one long-term follow-up study (RESTORE, the follow-up of REVERSE and RESCUE patients).Case presentationA 67-year-old woman with MT-ND4 LHON, included in the REVERSE clinical study, received a unilateral IVT of lenadogene nolparvovec in the right eye and a sham injection in the left eye in May 2016, 11.4 months and 8.8 months after vision loss in her right and left eyes, respectively. The patient had a normal brain magnetic resonance imaging with contrast at the time of diagnosis of LHON. Two years after treatment administration, BCVA had improved in both eyes. The product was well tolerated with mild and resolutive anterior chamber inflammation in the treated eye. In May 2019, the patient was diagnosed with a right temporal lobe glioblastoma, IDH-wildtype, World Health Organization grade 4, based on histological analysis of a tumor excision. The brain tumor was assessed for the presence of vector DNA by using a sensitive validated qPCR assay targeting the ND4 sequence of the vector.ConclusionND4 DNA was not detected (below 15.625 copies/μg of genomic DNA) in DNA extracted from the brain tumor, while a housekeeping gene DNA was detected at high levels. Taken together, this data shows the absence of detection of lenadogene nolparvovec in a brain tumor (glioblastoma) of a treated patient in the REVERSE clinical trial 3 years after gene therapy administration, supporting the long-term favorable safety of lenadogene nolparvovec.

Mitochondrial DNA Variation Correlated With the High Altitude Intolerance in Chinese Young Han Males.

ObjectiveAcute exposure to hypobaric hypoxia can trigger acute mountain sickness (AMS), while the exact mechanism has not been fully revealed. The role of genetic factors in the susceptibility of various high-altitude diseases has also gained much interest. Previous studies have provided evidence for the link between AMS and certain nuclear genes or mitochondrial haplogroup. The correlation between point mutations of mitochondrial DNA (mtDNA) and AMS was further explored in the present study.MethodsA total of 84 young Han males residing at low altitude were taken to an elevation of 4,000 m within 40 h. We collected data of their heart rate, blood pressure, peripheral oxygen saturation (SaO2), and obtained blood samples, at sea level and at high altitude. AMS was diagnosed using the revised version of the Lake Louise Questionnaire Score. Sequencing was utilized to identify the association between mtDNA alleles and the occurrence of AMS. We also assessed the association between the presence of AMS and physiological variables, and provided a preliminary discussion of the association between genotypic and phenotypic variation.ResultsThe percentage of neutrophils [Odds ratio (OR): 1.06, 95% confidence interval (CI): 1.01–1.12, P = 0.034) and SaO2 level (OR: 0.87, 95% CI: 0.79–0.95, P = 0.004) were independently associated with the development of AMS. A4576G was a risk factor for AMS (OR: 6.27, 95% CI: 1.2–32.7). T11613C (OR: 0.10, 95% CI: 0.01–0.83), A8923G (OR: 0.15, 95% CI: 0.03–0.76), and T5543C (OR: 0.19, 95% CI: 0.04–0.95) were protective factors for AMS. The level of SaO2 was significantly lower in the individual with A4576G mutation as compared with the individual without A4576G mutation (68.1 ± 7.9 vs. 75.8 ± 6.1, P = 0.001). The level of serum sodium was significantly higher in the individual with A8923G mutation as compared to the individual without A8923G mutation (144.6 ± 1.9 vs. 143.2 ± 1.9, P = 0.027).ConclusionsThe increase in neutrophils and the disability to preserve oxygen saturation may be associated with the high altitude intolerance in young Chinese Han males. A4576G is the risk factor for AMS. T11613C, A8923G, and T5543C are protective factors for AMS. The role of A8923G mutation may correlate with the sodium and water balance and the role of the A4576G mutation may be related to the disability to maintain blood oxygen level after quickly entering the plateau.

Clinicopathologic Features of Mitochondrial Nephropathy

IntroductionThe clinicopathologic characteristics of nephropathy associated with mitochondrial disease (MD) remain unknown. We retrospectively analyzed a cohort of patients with proteinuria, decreased glomerular filtration rate, or Fanconi syndrome who had a genetic mutation confirmed as the cause of MD, defined as mitochondrial nephropathy.MethodsThis nationwide survey included 757 nephrology sections throughout Japan, and consequently, data on 81 cases of mitochondrial nephropathy were collected.ResultsThe most common renal manifestation observed during the disease course was proteinuria. Hearing loss was the most common comorbidity; a renal-limited phenotype was observed only in mitochondrial DNA (mtDNA) point mutation and COQ8B mutation cases. We found a median time delay of 6.0 years from onset of renal manifestations to diagnosis. Focal segmental glomerular sclerosis (FSGS) was the most common pathologic diagnosis. We then focused on 63 cases with the m.3243A>G mutation. The rate of cases with diabetes was significantly higher among adult-onset cases than among childhood-onset cases. Pathologic diagnoses were more variable in adult-onset cases, including diabetic nephropathy, nephrosclerosis, tubulointerstitial nephropathy, and minor glomerular abnormalities. During the median observation period of 11.0 years from the first onset of renal manifestations in patients with m.3243A>G, renal replacement therapy (RRT) was initiated in 50.8% of patients. Death occurred in 25.4% of the patients during the median observation period of 12.0 years. The median estimated glomerular filtration rate (eGFR) decline was 5.4 ml/min per 1.73 m2/yr in the cases, especially 8.3 ml/min per 1.73 m2/yr in FSGS cases, with m.3243A>G.ConclusionHere, we described the clinicopathologic features and prognosis of mitochondrial nephropathy using large-scale data.

Whole Mitochondrial Genome Analysis in Turkish Patients with Mitochondrial Diseases

Background:Mitochondrial diseases are a clinically heterogeneous group of rare hereditary disorders that are defined by a genetic defect predominantly affecting mitochondrial oxidative phosphorylation. Mitochondrial diseases are caused by mutations of genes encoded by either nuclear DNA or mitochondrial DNA. Hundreds of different mitochondrial DNA point mutations and large-scale mitochondrial DNA rearrangements have been shown to cause mitochondrial diseases including Kearns–Sayre syndrome, Leber’s hereditary optic neuropathy, Leigh syndrome, myoclonic epilepsy with ragged-red fibers, mitochondrial encephalopathy lactic acidosis stroke.Aims:To investigate new variants that could be associated with mitochondrial diseases and to determine the effect of mitochondrial DNA mutations on the clinical spectrum.Study Design:Cross-sectional study.Methods:We screened whole mitochondrial DNA genome using next-generation sequencing in 16 patients who are considered to have mitochondrial disease. CentoGene and Mikrogen Genetic Diseases Diagnostic Center’s database were used to investigate sequence variants. Detected variants were evaluated in bioinformatic databases to determine pathogenicity and were classified as class 1 (pathogenic), class 2 (likely pathogenic), and class 3 (variant of uncertain significance) according to CentoGene-ACMG database.Results:As a result of the study, 2 patients were diagnosed with Leigh syndrome as previously reported class 1 mutations in MT-ATP6 and MT-ND5 genes. Four variants were identified for the first time in literature and 2 variants, previously reported but with uncertain pathogenic effect, are thought to be associated with mitochondrial disease.Conclusion:Mitochondrial DNA screening should be among the primary clinical tests in patients with suspected mitochondrial disease to rule out DNA-associated mutations.

Circulating Cell-Free Mitochondrial DNA in Cerebrospinal Fluid as a Biomarker for Mitochondrial Diseases.

Mitochondrial diseases (MD) are genetic metabolic disorders that impair normal mitochondrial structure or function. The aim of this study was to investigate the status of circulating cell-free mitochondrial DNA (ccfmtDNA) in cerebrospinal fluid (CSF), together with other biomarkers (growth differentiation factor-15 [GDF-15], alanine, and lactate), in a cohort of 25 patients with a molecular diagnosis of MD. Measurement of ccfmtDNA was performed by using droplet digital PCR. The mean copy number of ccfmtDNA was approximately 6 times higher in the MD cohort compared to the control group; patients with mitochondrial deletion and depletion syndromes (MDD) had the higher levels. We also detected the presence of both wild-type mtDNA and mtDNA deletions in CSF samples of patients with single deletions. Patients with MDD with single deletions had significantly higher concentrations of GDF-15 in CSF than controls, whereas patients with point mutations in mitochondrial DNA presented no statistically significant differences. Additionally, we found a significant positive correlation between ccfmtDNA levels and GDF-15 concentrations (r = 0.59, P = 0.016). CSF ccfmtDNA levels are significantly higher in patients with MD in comparison to controls and, thus, they can be used as a novel biomarker for MD research. Our results could also be valuable to support the clinical outcome assessment of MD patients.

Long-term prognosis and genetic background of cardiomyopathy in 223 pediatric mitochondrial disease patients

BackgroundCardiomyopathy is a risk factor for poor prognosis in pediatric patients with mitochondrial disease. However, other risk factors including genetic factors related to poor prognosis in mitochondrial disease has yet to be fully elucidated. Methods and resultsBetween January 2004 and September 2019, we enrolled 223 consecutive pediatric mitochondrial disease patients aged <18 years with a confirmed genetic diagnosis, including 114 with nuclear gene mutations, 89 patients with mitochondrial DNA (mtDNA) point mutations, 11 with mtDNA single large-scale deletions and 9 with chromosomal aberrations. Cardiomyopathy at baseline was observed in 46 patients (21%). Hazard ratios (HR) and 95% confidence intervals (CI) were calculated for all-cause mortality. Over a median follow-up of 36 months (12–77), there were 85 deaths (38%). The overall survival rate was significantly lower in patients with cardiomyopathy than in those without (p < 0.001, log-rank test). By multivariable analysis, left ventricular (LV) hypertrophy (HR = 4.6; 95% CI: 2.8–7.3), neonatal onset (HR = 2.9; 95% CI: 1.8–4.5) and chromosomal aberrations (HR = 2.9; 95% CI: 1.3–6.5) were independent predictors of all-cause mortality. Patients with LV hypertrophy with neonatal onset and/or chromosomal aberrations had higher mortality (100% in 21 patients) than those with LV hypertrophy alone (71% in 14 patients). ConclusionIn pediatric patients with mitochondrial disease, cardiomyopathy was common (21%) and was associated with increased mortality. LV hypertrophy, neonatal onset and chromosomal aberrations were independent predictors of all-cause mortality. Prognosis is particularly unfavorable if LV hypertrophy is combined with neonatal onset and/or chromosomal aberrations.

Impaired complex I repair causes recessive Leber's hereditary optic neuropathy.

Leber’s hereditary optic neuropathy (LHON) is the most frequent mitochondrial disease and was the first to be genetically defined by a point mutation in mitochondrial DNA (mtDNA). A molecular diagnosis is achieved in up to 95% of cases, the vast majority of which are accounted for by 3 mutations within mitochondrial complex I subunit–encoding genes in the mtDNA (mtLHON). Here, we resolve the enigma of LHON in the absence of pathogenic mtDNA mutations. We describe biallelic mutations in a nuclear encoded gene, DNAJC30, in 33 unsolved patients from 29 families and establish an autosomal recessive mode of inheritance for LHON (arLHON), which to date has been a prime example of a maternally inherited disorder. Remarkably, all hallmarks of mtLHON were recapitulated, including incomplete penetrance, male predominance, and significant idebenone responsivity. Moreover, by tracking protein turnover in patient-derived cell lines and a DNAJC30-knockout cellular model, we measured reduced turnover of specific complex I N-module subunits and a resultant impairment of complex I function. These results demonstrate that DNAJC30 is a chaperone protein needed for the efficient exchange of complex I subunits exposed to reactive oxygen species and integral to a mitochondrial complex I repair mechanism, thereby providing the first example to our knowledge of a disease resulting from impaired exchange of assembled respiratory chain subunits.

Leber’s hereditary optic neuropathy

Leber’s hereditary optic neuropathy (LHON) is a maternally inherited mitochondrial disease caused by several point mutations in mitochondrial DNA. We present the case of a healthy 12-year-old Chinese boy who presented with bilateral, painless, subacute loss of central vision (more severe in the left eye the than right eye) for 1 week. No abnormalities were detected on magnetic resonance imaging of the brain and orbit. Serial Humphrey visual field tests initially showed a centrocaecal scotoma that worsened progressively. Cerebrospinal fluid samples and blood investigations showed normal results. A trial of steroid therapy was commenced with not much improvement in the patient’s vision. A blood sample was then sent for LHON genetic testing and a mitochondrial DNA (mtDNA) G11778A pathogenic mutation was detected. The same mutation was also present in the patient’s mother.

Elimination of Mutant mtDNA by an Optimized mpTALEN Restores Differentiation Capacities of Heteroplasmic MELAS-iPSCs

Various mitochondrial diseases, including mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), are associated with heteroplasmic mutations in mitochondrial DNA (mtDNA). Herein, we refined a previously generated G13513A mtDNA-targeted platinum transcription activator-like effector nuclease (G13513A-mpTALEN) to more efficiently manipulate mtDNA heteroplasmy in MELAS-induced pluripotent stem cells (iPSCs). Introduction of a nonconventional TALE array at position 6 in the mpTALEN monomer, which recognizes the sequence around the m.13513G>A position, improved the mpTALEN effect on the heteroplasmic shift. Furthermore, the reduced expression of the new Lv-mpTALEN(PKLB)/R-mpTALEN(PKR6C) pair by modifying codons in their expression vectors could suppress the reduction in the mtDNA copy number, which contributed to the rapid recovery of mtDNA in mpTALEN-applied iPSCs during subsequent culturing. Moreover, MELAS-iPSCs with a high proportion of G13513A mutant mtDNA showed unusual properties of spontaneous, embryoid body-mediated differentiation in vitro, which was relieved by decreasing the heteroplasmy level with G13513A-mpTALEN. Additionally, drug-inducible, myogenic differentiation 1 (MYOD)-transfected MELAS-iPSCs (MyoD-iPSCs) efficiently differentiated into myosin heavy chain-positive myocytes, with or without mutant mtDNA. Hence, heteroplasmic MyoD-iPSCs controlled by fine-tuned mpTALENs may contribute to a detailed analysis of the relationship between mutation load and cellular phenotypes in disease modeling.

Primary mitochondrial myopathy: Clinical features and outcome measures in 118 cases from Italy.

ObjectiveTo determine whether a set of functional tests, clinical scales, patient-reported questionnaires, and specific biomarkers can be considered reliable outcome measures in patients with primary mitochondrial myopathy (PMM), we analyzed a cohort of Italian patients.MethodsBaseline data were collected from 118 patients with PMM, followed by centers of the Italian network for mitochondrial diseases. We used the 6-Minute Walk Test (6MWT), Timed Up-and-Go Test (x3) (3TUG), Five-Times Sit-To-Stand Test (5XSST), Timed Water Swallow Test (TWST), and Test of Masticating and Swallowing Solids (TOMASS) as functional outcome measures; the Fatigue Severity Scale and West Haven-Yale Multidimensional Pain Inventory as patient-reported outcome measures; and FGF21, GDF15, lactate, and creatine kinase (CK) as biomarkers.ResultsA total of 118 PMM cases were included. Functional outcome measures (6MWT, 3TUG, 5XSST, TWST, and TOMASS) and biomarkers significantly differed from healthy reference values and controls. Moreover, functional measures correlated with patients' perceived fatigue and pain severity. Patients with either mitochondrial or nuclear DNA point mutations performed worse in functional measures than patients harboring single deletion, even if the latter had an earlier age at onset but similar disease duration. Both the biomarkers FGF21 and GDF15 were significantly higher in the patients compared with a matched control population; however, there was no relation with severity of disease.ConclusionsWe characterized a large cohort of PMM by evaluating baseline mitochondrial biomarkers and functional scales that represent potential outcome measures to monitor the efficacy of treatment in clinical trials; these outcome measures will be further reinvestigated longitudinally to define the natural history of PMM.

Age-induced mitochondrial DNA point mutations are inadequate to alter metabolic homeostasis in response to nutrient challenge.

Mitochondrial dysfunction is frequently associated with impairment in metabolic homeostasis and insulin action, and is thought to underlie cellular aging. However, it is unclear whether mitochondrial dysfunction is a cause or consequence of insulin resistance in humans. To determine the impact of intrinsic mitochondrial dysfunction on metabolism and insulin action, we performed comprehensive metabolic phenotyping of the polymerase gamma (PolG) D257A “mutator” mouse, a model known to accumulate supraphysiological mitochondrial DNA (mtDNA) point mutations. We utilized the heterozygous PolG mutator mouse (PolG+/mut) because it accumulates mtDNA point mutations ~ 500‐fold > wild‐type mice (WT), but fails to develop an overt progeria phenotype, unlike PolGmut/mut animals. To determine whether mtDNA point mutations induce metabolic dysfunction, we examined male PolG+/mut mice at 6 and 12 months of age during normal chow feeding, after 24‐hr starvation, and following high‐fat diet (HFD) feeding. No marked differences were observed in glucose homeostasis, adiposity, protein/gene markers of metabolism, or oxygen consumption in muscle between WT and PolG+/mut mice during any of the conditions or ages studied. However, proteomic analyses performed on isolated mitochondria from 12‐month‐old PolG+/mut mouse muscle revealed alterations in the expression of mitochondrial ribosomal proteins, electron transport chain components, and oxidative stress‐related factors compared with WT. These findings suggest that mtDNA point mutations at levels observed in mammalian aging are insufficient to disrupt metabolic homeostasis and insulin action in male mice.

Nuclear DNA Mutation Causing a Phenotypic Leber Hereditary Optic Neuropathy Plus

Leber hereditary optic neuropathy (LHON) is a mitochondrial disorder characterized by acute or subacute, bilateral, sequential, or simultaneous painless vision loss.1 It is generally nonsyndromic; however, dystonia, ataxia, and multiple sclerosis have been associated. Leber hereditary optic neuropathy is a maternally inherited disorder due to point mutations in mitochondrial (mt) DNA.1 Mutations of complex 1 in positions 11778 of the ND4 subunit, 3460 of the ND1 subunit, and 14484 of the ND6 subunit are responsible for 90% to 95% of all cases.