Investigation of whole mitochondrial genome variation in normal tension glaucoma

Massively parallel sequencing of mitochondrial genome in primary open angle glaucoma identifies somatically acquired mitochondrial mutations in ocular tissue

Glaucoma is a sight threatening neurodegenerative condition of the optic nerve head associated with ageing and marked by the loss of retinal ganglion cells. Mitochondrial dysfunction plays a crucial role in the pathogenesis of neurodegeneration in the most prevalent type of glaucoma: primary open angle glaucoma (POAG). All previous mitochondrial genome sequencing studies in POAG analyzed mitochondrial DNA (mtDNA) isolated from peripheral blood leukocytes and have not evaluated cells derived from ocular tissue, which better represent the glaucomatous disease context. In this study, we evaluated mitochondrial genome variation and heteroplasmy using massively parallel sequencing of mtDNA in a cohort of patients with POAG, and in a subset assess the role of somatic mitochondrial genome mutations in disease pathogenesis using paired samples of peripheral blood leukocytes and ocular tissue (Tenon's ocular fibroblasts). An enrichment of potentially pathogenic nonsynonymous mtDNA variants was identified in Tenon's ocular fibroblasts from participants with POAG. The absence of oxidative DNA damage and predominance of transition variants support the concept that errors in mtDNA replication represent the predominant mutation mechanism in Tenon's ocular fibroblasts from patients with POAG. Pathogenic somatic mitochondrial genome mutations were observed in people with POAG. This supports the role of somatic mitochondrial genome variants in the etiology of glaucoma.

Association between glaucoma susceptibility with combined defects in mitochondrial oxidative phosphorylation and fatty acid beta oxidation

Glaucoma is one of the leading causes of visual impairment and blindness worldwide, and is characterized by the progressive damage of retinal ganglion cells (RGCs) and the atrophy of the optic nerve head (ONH). The exact cause of RGC loss and optic nerve damage in glaucoma is not fully understood. The high energy demands of these cells imply a higher sensitivity to mitochondrial defects. Moreover, it has been postulated that the optic nerve is vulnerable towards damage from oxidative stress and mitochondrial dysfunction. To investigate this further, we conducted a pooled analysis of mitochondrial variants related to energy production, specifically focusing on oxidative phosphorylation (OXPHOS) and fatty acid β-oxidation (FAO). Our findings revealed that patients carrying non-synonymous (NS) mitochondrial DNA (mtDNA) variants within the OXPHOS complexes had an almost two-fold increased risk of developing glaucoma. Regarding FAO, our results demonstrated that longer-chain acylcarnitines (AC) tended to decrease, while shorter-chain AC tended to increase in patients with glaucoma. Furthermore, we observed that the knocking down cpt1a (a key rate-limiting enzyme involved in FAO) in zebrafish induced a degenerative process in the optic nerve and RGC, which resembled the characteristics observed in glaucoma. In conclusion, our study provides evidence that genes encoding mitochondrial proteins involved in energy metabolisms, such as OXPHOS and FAO, are associated with glaucoma. These findings contribute to a better understanding of the molecular mechanisms underlying glaucoma pathogenesis and may offer potential targets for therapeutic interventions in the future.

Mitochondrial DNA D-loop variants correlate with a primary open-angle glaucoma subgroup

Introduction

Primary open-angle glaucoma (POAG) is a characteristic optic neuropathy, caused by degeneration of the optic nerve-forming neurons, the retinal ganglion cells (RGCs). High intraocular pressure (IOP) and aging have been identified as major risk factors; yet the POAG pathophysiology is not fully understood. Since RGCs have high energy requirements, mitochondrial dysfunction may put the survivability of RGCs at risk. We explored in buffy coat DNA whether mtDNA variants and their distribution throughout the mtDNA could be risk factors for POAG.

Methods

The mtDNA was sequenced from age- and sex-matched study groups, being high tension glaucoma (HTG, n=71), normal tension glaucoma patients (NTG, n=33), ocular hypertensive subjects (OH, n=7), and cataract controls (without glaucoma; n=30), all without remarkable comorbidities.

Results

No association was found between the number of mtDNA variants in genes encoding proteins, tRNAs, rRNAs, and in non-coding regions in the different study groups. Next, variants that controls shared with the other groups were discarded. A significantly higher number of exclusive variants was observed in the D-loop region for the HTG group (~1.23 variants/subject), in contrast to controls (~0.35 variants/subject). In the D-loop, specifically in the 7S DNA sub-region within the Hypervariable region 1 (HV1), we found that 42% of the HTG and 27% of the NTG subjects presented variants, while this was only 14% for the controls and OH subjects. As we have previously reported a reduction in mtDNA copy number in HTG, we analysed if specific D-loop variants could explain this. While the majority of glaucoma patients with the exclusive D-loop variants m.72T>C, m.16163 A>G, m.16186C>T, m.16298T>C, and m.16390G>A presented a mtDNA copy number below controls median, no significant association between these variants and low copy number was found and their possible negative role in mtDNA replication remains uncertain. Approximately 38% of the HTG patients with reduced copy number did not carry any exclusive D-loop or other mtDNA variants, which indicates that variants in nuclear-encoded mitochondrial genes, environmental factors, or aging might be involved in those cases.

Conclusion

In conclusion, we found that variants in the D-loop region may be a risk factor in a subgroup of POAG, possibly by affecting mtDNA replication.

Distinct Metabolic Profiles of Ocular Hypertensives in Response to Hypoxia

Glaucoma is a neurodegenerative disease that affects the retinal ganglion cells (RGCs). The main risk factor is elevated intraocular pressure (IOP), but the actual cause of the disease remains unknown. Emerging evidence indicates that metabolic dysfunction plays a central role. The aim of the current study was to determine and compare the effect of universal hypoxia on the metabolomic signature in plasma samples from healthy controls (n = 10), patients with normal-tension glaucoma (NTG, n = 10), and ocular hypertension (OHT, n = 10). By subjecting humans to universal hypoxia, we aim to mimic a state in which the mitochondria in the body are universally stressed. Participants were exposed to normobaric hypoxia for two hours, followed by a 30 min recovery period in normobaric normoxia. Blood samples were collected at baseline, during hypoxia, and in recovery. Plasma samples were analyzed using a non-targeted metabolomics approach based on liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS). Multivariate analyses were conducted using principal component analysis (PCA) and orthogonal partial least squares-discriminant analysis (OPLS-DA), and univariate analysis using the Wilcoxon signed-rank test and false discovery rate (FDR) correction. Unique metabolites involved in fatty acid biosynthesis and ketone body metabolism were upregulated, while metabolites of the kynurenine pathway were downregulated in OHT patients exposed to universal hypoxia. Differential affection of metabolic pathways may explain why patients with OHT initially do not suffer or are more resilient from optic nerve degeneration. The metabolomes of NTG and OHT patients are regulated differently from control subjects and show dysregulation of metabolites important for energy production. These dysregulated processes may potentially contribute to the elevation of IOP and, ultimately, cell death of the RGCs.

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.

Complete mitochondrial DNA profile in stroke: A geographical matched case-control study in Spanish population

INTRODUCTION

Stroke, the second leading cause of death worldwide, is a complex disease influenced by many risk factors among which we can find reactive oxygen species (ROS). Since mitochondria are the main producers of cellular ROS, nowadays studies are trying to elucidate the role of these organelles and its DNA (mtDNA) variation in stroke risk. The aim of the present study was to perform a comprehensive evaluation of the association between mtDNA mutations and mtDNA content and stroke risk.

MATERIAL AND METHODS

Homoplasmic and heteroplasmic mutations of the mtDNA were analysed in a case-controls study using 110 S cases and their corresponding control individuals. Mitochondrial DNA copy number (mtDNA-CN) was analysed in 73 of those case-control pairs.

RESULTS

Our results suggest that haplogroup V, specifically variants m.72C > T, m.4580G > A, m.15904C > T and m.16298 T > C have a protective role in relation to stroke risk. On the contrary, variants m.73A > G, m.11719G > A and m.14766C > T appear to be genetic risk factors for stroke. In this study, we found no statistically significant association between stroke risk and mitochondrial DNA copy number.

CONCLUSIONS

These results demonstrate the possible role of mtDNA genetics on the pathogenesis of stroke, probably through alterations in mitochondrial ROS production.

Mitochondrial Genome Variation in Polish Elite Athletes

Energy efficiency is one of the fundamental athletic performance-affecting features of the cell and the organism as a whole. Mitochondrial DNA (mtDNA) variants and haplogroups have been linked to the successful practice of various sports, but despite numerous studies, understanding of the correlation is far from being comprehensive. In this study, the mtDNA sequence and copy number were determined for 99 outstanding Polish male athletes performing in power (n = 52) or endurance sports (n = 47) and 100 controls. The distribution of haplogroups, single nucleotide variant association, heteroplasmy, and mtDNA copy number were analyzed in the blood and saliva. We found no correlation between any haplogroup, single nucleotide variant, especially rare or non-synonymous ones, and athletic performance. Interestingly, heteroplasmy was less frequent in the study group, especially in endurance athletes. We observed a lower mtDNA copy number in both power and endurance athletes compared to controls. This could result from an inactivity of compensatory mechanisms activated by disadvantageous variants present in the general population and indicates a favorable genetic makeup of the athletes. The results emphasize a need for a more comprehensive analysis of the involvement of the mitochondrial genome in physical performance, combining nucleotide and copy number analysis in the context of nuclear gene variants.

Pharmaceutical Approaches to Normal Tension Glaucoma

Normal tension glaucoma (NTG) is defined as a subtype of primary open-angle glaucoma (POAG) in which the intraocular pressure (IOP) values are constantly within the statistically normal range without treatment and represents approximately the 30-40% of all glaucomatous cases. The pathophysiology of this condition is multifactorial and is still not completely well known. Several theories have been proposed to explain the onset and progression of this disease, which can be divided into IOP-dependent and IOP-independent factors, suggesting different therapeutic strategies. The current literature strongly supports the fundamental role of IOP in NTG. The gold standard treatment for NTG tends to be based on the lowering IOP even if "statistically normal". Numerous studies have shown, however, that the IOP reduction alone is not enough to slow down or stop the disease progression in all cases, suggesting that other IOP-independent risk factors may contribute to the NTG pathogenesis. In addition to IOP-lowering strategies, several different therapeutic approaches for NTG have been proposed, based on vaso-active, antioxidant, anti-inflammatory and/or neuroprotective substances. To date, unfortunately, there are no standardized or proven treatment alternatives for NTG when compared to traditional IOP reduction treatment regimes. The efficacy of the IOP-independent strategies in decreasing the risk or treating NTG still remains inconclusive. The aim of this review is to highlight strategies reported in the current literature to treat NTG. The paper also describes the challenges in finding appropriate and pertinent treatments for this potentially vision-threatening disease. Further comprehension of NTG pathophysiology can help clinicians determine when to use IOP-lowering treatments alone and when to consider additional or alternatively individualized therapies focused on particular risk factors, on a case-by-case basis.

The Differences in the Pattern of OCT and OCTA Examinations between Early Normal- and High-Tension Pseudoexfoliative Glaucoma

Purpose. The aim of this study was to compare the results of optical coherence tomography angiography (OCTA) and optical coherence tomography (OCT) examinations in patients with normal-tension glaucoma (NTG) in comparison to high-tension pseudoexfoliative glaucoma (HTG) patients at the early stage of glaucoma. Material and methods. The studied groups consisted of patients in the early stage of NTG (70 eyes) and the early stage of HTG (71 eyes). In NTG and HTG groups, a detailed ophthalmic examination was performed. Optic disc OCT with peripapillary RNFL measurements and OCTA examination with the evaluation of the macula and optic disc were performed for all participants using Zeiss Cirrus 5000. Results. NTG and HTG groups were statistically similar as far as the MD was concerned, and both groups had early glaucoma. When evaluating the RNFL thickness, the only statistical difference between early NTG and HTG was observed in the thicknesses in the temporal sector of peripapillary RNFL, with thinner values in the NTG group (53.94 vs. 59.94, p = 0.0071). When the OCTA results of the macula and optic disc were evaluated, there were no statistical differences between early NTG and HTG. Conclusions. The vascular density and flow parameters assessed in OCTA were equal between early NTG and HTG, and therefore the involvement of vascular factors in NTG pathogenesis could not be confirmed. Our results confirm the preponderance of more frequent temporal RNFL involvement in early NTG.

Extranuclear DNA Variations in the Susceptibility of Glaucoma

Glaucoma is a leading cause of irreversible blindness worldwide which affects all age groups. It is often identified by high intraocular pressure, characteristic optic neuropathy, and vision loss. Due to multifactorial nature of glaucoma pathogenesis, the molecular events responsible for its precipitation are currently poorly understood. Mitochondrial DNA (mtDNA) variations which are inherited maternally are being closely studied in recent times to elucidate the effect on glaucoma. Mitochondrial genetic studies till date have found a possible link between Leber hereditary optic neuropathy loci and glaucoma but with conflicting views. Furthermore, whole mtDNA studies in glaucoma points at the involvement of oxidative phosphorylation complex I and specifically the NADH dehydrogenase 5 gene in glaucoma. This review focuses on identifying the potential genes and variations in the maternally inherited mtDNA which might be involved in glaucoma pathogenesis.

Mitochondrial DNA variants spectrum and the association with chronic Tic disorders

BACKGROUND

Tic disorders (TD) are childhood-onset neuropsychiatric disorders characterized by single or multiple sudden, rapid, recurrent, and motor tics and/or vocal tics. Several nuclear genes that involved in mitochondrial functions suggest potential role of mitochondria in tic deficit.

METHODS

To evaluate the association of mitochondrial DNA (mtDNA) variants with Tic disorders, we screened the whole mitochondrial genomes in 493 TD patients and 109 age- and sex matched healthy controls using next-generation sequencing technology.

RESULTS

A total of 1918 mtDNA variants including 1220 variants in patients only, 154 variants in controls only, and 544 variants shared by both cases and controls were identified. We found higher number of overall mtDNA variants in TD patients (P =0.00028). The variant density in MT-ATP6/8 and MT-CYB coding regions had significant difference between TD patients and controls (P=0.0025 and P=0.003, respectively). Furthermore, we observed a significant association of 15 common variants with TD based on additive model, including m.14766C>T, m.14783T>C, m.14905G>A, and m.15301G>A in MT-CYB; m.4769A>G, m.10398A>G, m.12705C>T, and m.12850A>G in MT-ND genes; m.7028C>T in MT-CO1; m.8701A>G in MT-ATP6; two noncoding variants with m.16223C>T, m.5580T>C; and three rRNA variants with m.1438A>G and m.750A>G in RNR1, and m.2352T>C in RNR2.

CONCLUSIONS

Our data provide the evidence of mtDNA variants associated with tic disorders. The accumulation of the heteroplasmic levels may increase the risk of TD. Replication studies with larger samples are necessary to understand the pathogenesis of TD.

Yield of investigations in patients with questionable nonglaucomatous optic neuropathy

OBJECTIVE

Nonglaucomatous optic neuropathy (NGON) may often be mistaken for normal-tension glaucoma. The distinction between these two entities is important in determining treatment, prognosis, and need for further investigations. We report characteristics of a cohort of patients referred for neuro-ophthalmologic consultation to distinguish between glaucomatous (GON) and NGON.

METHODS

Retrospective chart review of patients presenting to a tertiary neuro-ophthalmology practice investigated for GON versus NGON between 2018 and 2020. Patients were classified as GON or NGON based on presence of optic disc pallor, degree of cupping, central visual acuity, and/or when investigations yielded a cause of NGON.

RESULTS

Eighty-three patients were enrolled. Seventy-one patients (86%) were deemed to have possible NGON after initial evaluation and having undergone neuroimaging. Of these, 14 patients (19.7%) were determined to have NGON and 7 patients (9.9%) both GON and NGON. The most common causes of NGON were undetermined (8), previous optic neuritis (4), and neurovascular conflict (2). The yield of neuroimaging was low, with abnormalities seen in only 4 of 71 patients (5.6%). No patients with bilateral cupping and no relative afferent pupillary defect (RAPD) had abnormalities on imaging, and no patients with positive imaging required intervention. Patients with NGON had lower intraocular pressure and cup-to-disc ratio and usually had optic disc pallor (86%). Nerve fibre bundle defects were most common in both GON and NGON, with more nasal defects seen in GON.

CONCLUSIONS

When NGON resembles GON, the underlying cause is often undetermined, and the yield of neuroimaging is low. The yield of investigating patients with bilateral cupping and no RAPD for NGON is especially low.

Insight of the mitochondrial genomes of the Orang Asli and Malays: The heterogeneity and the disease-associated variants

Orang Asli are the oldest inhabitants in Peninsular Malaysia that forms as a national minority while the Malays are the majority. The study aimed to screen the mitochondrial genomes of the Orang Asli and the Malays to discover the disease-associated variants. A total of 99 Orang Asli from six tribes (Bateq, Cheq Wong, Orang Kanaq, Kensiu, Lanoh, and Semai) were recruited. Mitochondrial genome sequencing was conducted using a next-generation sequencing platform. Furthermore, we retrieved mitochondrial DNA sequences from the Malays for comparison. The clinical significance, pathogenicity prediction and frequency of variants were determined using online tools. Variants associated with mitochondrial diseases were detected in the 2 populations. A high frequency of variants associated with mitochondrial diseases, breast cancer, prostate cancer, and cervical cancer were detected in the Orang Asli and modern Malays. As medicine evolves to adopt prediction and prevention of diseases, this study highlights the need for intervention to adopt genomics medicine to strategise better healthcare management as a way forward for Precision Health.

Neuroinflammatory Mechanisms of Mitochondrial Dysfunction and Neurodegeneration in Glaucoma

The exact mechanism of retinal ganglion cell loss in the pathogenesis of glaucoma is yet to be understood. Mitochondrial damage-associated molecular patterns (DAMPs) resulting from mitochondrial dysfunction have been linked to Leber's hereditary optic neuropathy and autosomal dominant optic atrophy, as well as to brain neurodegenerative diseases. Recent evidence shows that, in conditions where mitochondria are damaged, a sustained inflammatory response and downstream pathological inflammation may ensue. Mitochondrial damage has been linked to the accumulation of age-related mitochondrial DNA mutations and mitochondrial dysfunction, possibly through aberrant reactive oxygen species production and defective mitophagy. The present review focuses on how mitochondrial dysfunction may overwhelm the ability of neurons and glial cells to adequately maintain homeostasis and how mitochondria-derived DAMPs trigger the immune system and induce neurodegeneration.

To Be a Champion of the 24-h Ultramarathon Race. If Not the Heart ... Mosaic Theory?

This comprehensive case analysis aimed to identify the features enabling a runner to achieve championship in 24-h ultramarathon (UM) races. A 36-year-old, multiple medalist of the World Championships in 24-h running, was assessed before, one and 10 days after a 24-h run. Results of his extensive laboratory and cardiological diagnostics with transthoracic echocardiography (TTE) and a one-time cardiopulmonary exercise test (CPET) were analyzed. After 12 h of running (approximately 130 km), the athlete experienced an increasing pain in the right knee. His baseline clinical data were within the normal range. High physical efficiency in CPET (VO₂max 63 mL/kg/min) was similar to the average achieved by other ultramarathoners who had significantly worse results. Thus, we also performed genetic tests and assessed his psychological profile, body composition, and markers of physical and mental stress (serotonin, cortisol, epinephrine, prolactin, testosterone, and luteinizing hormone). The athlete had a mtDNA haplogroup H (HV0a1 subgroup, belonging to the HV cluster), characteristic of athletes with the highest endurance. Psychological studies have shown high and very high intensity of the properties of individual scales of the tools used mental resilience (62–100% depending on the scale), openness to experience (10th sten), coherence (10th sten), positive perfectionism (100%) and overall hope for success score (10th sten). The athlete himself considers the commitment and mental support of his team to be a significant factor of his success. Body composition assessment (%fat 13.9) and the level of stress markers were unremarkable. The tested athlete showed a number of features of the champions of ultramarathon runs, such as: inborn predispositions, mental traits, level of training, and resistance to pain. However, none of these features are reserved exclusively for “champions”. Team support’s participation cannot be underestimated. The factors that guarantee the success of this elite 24-h UM runner go far beyond physiological and psychological explanations. Further studies are needed to identify individual elements of the putative “mosaic theory of being a champion”.

Mitochondrial genome variation in male LHON patients with the m.11778G > A mutation

Leber hereditary optic neuropathy (LHON) is a mitochondrial disorder with symptoms limited to a single tissue, optic nerve, resulting in vision loss. In the majority of cases it is caused by one of three point mutations in mitochondrial DNA (mtDNA) but their presence is not sufficient for disease development, since ~50% of men and ~10% women who carry them are affected. Thus additional modifying factors must exist. In this study, we use next generation sequencing to investigate the role of whole mtDNA variation in male Polish patients with LHON and m.11778G > A, the most frequent LHON mutation. We present a possible association between mtDNA haplogroup K and variants in its background, a combination of m.3480A > G, m.9055G > A, m.11299 T > C and m.14167C > T, and LHON mutation. These variants may have a negative effect on m.11778G > A increasing its penetrance and the risk of LHON in the Polish population. Surprisingly, we did not observe associations previously reported for m.11778G > A and LHON in European populations, particularly for haplogroup J as a risk factor, implying that mtDNA variation is much more complex. Our results indicate possible contribution of novel combination of mtDNA genetic factors to the LHON phenotype.

Cell Autonomous Neuroprotection by the Mitochondrial Uncoupling Protein 2 in a Mouse Model of Glaucoma

Glaucoma is a group of disorders associated with retinal ganglion cell (RGC) degeneration and death. There is a clear contribution of mitochondrial dysfunction and oxidative stress toward glaucomatous RGC death. Mitochondrial uncoupling protein 2 (Ucp2) is a well-known regulator of oxidative stress that increases cell survival in acute models of oxidative damage. The impact of Ucp2 on cell survival during sub-acute and chronic neurodegenerative conditions, however, is not yet clear. Herein, we test the hypothesis that increased Ucp2 expression will improve RGC survival in a mouse model of glaucoma. We show that increasing RGC but not glial Ucp2 expression in transgenic animals decreases glaucomatous RGC death, but also that the PPAR-γ agonist rosiglitazone (RSG), an endogenous transcriptional activator of Ucp2, does not significantly alter RGC loss during glaucoma. Together, these data support a model whereby increased Ucp2 expression mediates neuroprotection during a long-term oxidative stressor, but that transcriptional activation alone is insufficient to elicit a neuroprotective effect, motivating further research in to the post-transcriptional regulation of Ucp2.

New mtDNA Association Model, MutPred Variant Load, Suggests Individuals With Multiple Mildly Deleterious mtDNA Variants Are More Likely to Suffer From Atherosclerosis

The etiology of common complex diseases is multifactorial, involving both genetic, and environmental factors. A role for mitochondrial dysfunction and mitochondrial DNA (mtDNA) variation has been suggested in the pathogenesis of common complex traits. The aim of this study was to investigate a potential role of mtDNA variants in the development of obesity, diabetes, and atherosclerosis in the Polish population. Whole mtDNA sequences from 415 Polish individuals representing three disease cohorts and a control group were obtained using high-throughput sequencing. Two approaches for the assessment of mtDNA variation were applied, traditional mitochondrial haplogroup association analysis and the mutational or variant load model using the MutPred pathogenicity prediction algorithm for amino acid substitutions in humans. We present a possible association between mildly deleterious mtDNA variant load and atherosclerosis that might be due to having more than one likely mildly deleterious non-synonymous substitution. Moreover, it seems largely dependent upon a few common haplogroup associated variants with MutPred score above 0.5.