Mitochondrial DNA mutations in multiple sclerosis

Analysis of the entire mitochondrial genome reveals Leber's hereditary optic neuropathy mitochondrial DNA mutations in an Arab cohort with multiple sclerosis

Several mitochondrial DNA (mtDNA) mutations of Leber's hereditary optic neuropathy (LHON) have been reported in patients with multiple sclerosis (MS) from different ethnicities. To further study the involvement of LHON mtDNA mutations in MS in the Arab population, we analyzed sequencing data of the entire mitochondrial genome from 47 unrelated Saudi individuals, 23 patients with relapse-remitting MS (RRMS) and 24 healthy controls. Ten LHON mutations/variants were detected in the patients but were absent in the controls. Of them, the common primary pathogenic mutation m.14484T>C and the rare mutation m.10237T>C were found in one patient, whereas the rare mutation m.9101T>C was found in another patient. The remaining were secondary single nucleotide variants (SNVs) found either in synergy with the primary/rare mutations or individually in other patients. Patients carrying LHON variants also exhibited distinct mtDNA variants throughout the mitochondrial genome, eight were previously reported in patients with LHON. Moreover, five other LHON-related SNVs differed significantly in their prevalence among patients and controls (P < 0.05). This study, the first to investigate LHON mtDNA mutations/variants in a Saudi cohort may suggest a role of these mutations/variants in the pathogenesis or genetic predisposition to MS, a possibility which needs to be explored further in a large-scale.

Detection of mitochondrial transfer RNA (mt-tRNA) gene mutations in patients with idiopathic pulmonary fibrosis and sarcoidosis

Mitochondrial reactive oxygen species production may lead to tissue injury associated with two respiratory disorders of unknown origin which are shared by common tissue fibrosis, IPF and sarcoidosis. Sequence analysis of 22 mt-tRNA genes and parts of their flanking genes revealed 32 and 45 mutations in 38/40 IPF and 69/85 sarcoidosis patients respectively. 4 novel mutations were identified. 15/32 and 25/45 mutations were exclusively expressed while 12/32 and 17/45 mutations predominantly occurred in IPF and sarcoidosis group respectively, compared to healthy controls. Novel mutation combinations were solely expressed in disease. Hence, a mitochondrial-mediated pathogenic pathway seems to underlie both entities.

Involvement of Mitochondria in Neurodegeneration in Multiple Sclerosis

Functional disruption and neuronal loss followed by progressive dysfunction of the nervous system underlies the pathogenesis of numerous disorders defined as "neurodegenerative diseases". Multiple sclerosis, a chronic inflammatory demyelinating disease of the central nervous system resulting in serious neurological dysfunctions and disability, is one of the most common neurodegenerative diseases. Recent studies suggest that disturbances in mitochondrial functioning are key factors leading to neurodegeneration. In this review, we consider data on mitochondrial dysfunctions in multiple sclerosis, which were obtained both with patients and with animal models. The contemporary data indicate that the axonal degeneration in multiple sclerosis largely results from the activation of Ca2+-dependent proteases and from misbalance of ion homeostasis caused by energy deficiency. The genetic studies analyzing association of mitochondrial DNA polymorphic variants in multiple sclerosis suggest the participation of mitochondrial genome variability in the development of this disease, although questions of the involvement of individual genomic variants are far from being resolved.

Mitochondrial DNA Double-Strand Breaks in Oligodendrocytes Cause Demyelination, Axonal Injury, and CNS Inflammation

Mitochondrial dysfunction has been implicated in the pathophysiology of neurodegenerative disorders, including multiple sclerosis (MS). To date, the investigation of mitochondrial dysfunction in MS has focused exclusively on neurons, with no studies exploring whether dysregulation of mitochondrial bioenergetics and/or genetics in oligodendrocytes might be associated with the etiopathogenesis of MS and other demyelinating syndromes. To address this question, we established a mouse model where mitochondrial DNA (mtDNA) double-strand breaks (DSBs) were specifically induced in myelinating oligodendrocytes (PLP:mtPstI mice) by expressing a mitochondrial-targeted endonuclease, mtPstI, starting at 3 weeks of age. In both female and male mice, DSBs of oligodendroglial mtDNA caused impairment of locomotor function, chronic demyelination, glial activation, and axonal degeneration, which became more severe with time of induction. In addition, after short transient induction of mtDNA DSBs, PLP:mtPstI mice showed an exacerbated response to experimental autoimmune encephalomyelitis. Together, our data demonstrate that mtDNA damage can cause primary oligodendropathy, which in turn triggers demyelination, proving PLP:mtPstI mice to be a useful tool to study the pathological consequences of mitochondrial dysfunction in oligodendrocytes. In addition, the demyelination and axonal loss displayed by PLP:mtPstI mice recapitulate some of the key features of chronic demyelinating syndromes, including progressive MS forms, which are not accurately reproduced in the models currently available. For this reason, the PLP:mtPstI mouse represents a unique and much needed platform for testing remyelinating therapies.SIGNIFICANCE STATEMENT In this study, we show that oligodendrocyte-specific mitochondrial DNA double-strand breaks in PLP:mtPstI mice cause oligodendrocyte death and demyelination associated with axonal damage and glial activation. Hence, PLP:mtPstI mice represent a unique tool to study the pathological consequences of mitochondrial dysfunction in oligodendrocytes, as well as an ideal platform to test remyelinating and neuroprotective agents.

Adrenocorticotropic hormone versus methylprednisolone added to interferon β in patients with multiple sclerosis experiencing breakthrough disease: a randomized, rater-blinded trial

BACKGROUND

The objective of this study was to evaluate monthly intramuscular adrenocorticotropic hormone (ACTH) gel versus intravenous methylprednisolone (IVMP) add-on therapy to interferon β for breakthrough disease in patients with relapsing forms of multiple sclerosis.

METHODS

This was a prospective, open-label, examiner-blinded, 15-month pilot study evaluating patients with Expanded Disability Status Scale (EDSS) score 3.0-6.5 and at least one clinical relapse or new T2 or gadolinium-enhanced lesion in the previous year. Twenty-three patients were randomized to ACTH (n = 12) or IVMP (n = 11) and completed the study. The primary outcome measure was the cumulative number of relapses. Secondary outcomes included EDSS, Mental Health Inventory (MHI), plasma cytokines, MS Functional Composite (MSFC), Quality-of-Life (MS-QOL) score, bone mineral density (BMD), and new or worsened psychiatric symptoms per month. Brain magnetic resonance imaging was analyzed post hoc. This was a preliminary and small-scale study.

RESULTS

Relapse rates differed significantly [ACTH 0.08, 95% confidence interval (CI) 0.01-0.54 versus IVMP 0.80, 95% CI 0.36-1.75; rate ratio, IVMP versus ACTH: 9.56, 95% CI 1.23-74.6; p = 0.03]. ACTH improved (p = 0.03) MHI (slope 0.95 ± 0.38 points/month; p = 0.02 versus slope -0.38 ± 0.43 points/month; p = 0.39). On-study decreases (all p < 0.05) in eight cytokine levels occurred only in the ACTH group. However, on-study EDSS, MSFC, MS-QOL, BMD, and MRI lesion changes were not significant between groups. Psychiatric symptoms per patient were greater with IVMP than ACTH (0.55, 95% CI 0.12-2.6 versus 0; p < 0.0001). Other common adverse events were insomnia and urinary tract infections (IVMP, seven events each) and fatigue or flu symptoms (ACTH, five events each).

CONCLUSIONS

This study provided class II evidence that ACTH produced better examiner-assessed cumulative rates of relapses per patient than IVMP in the adjunctive treatment of breakthrough disease in multiple sclerosis.

MtDNA T4216C variation in multiple sclerosis: a systematic review and meta-analysis

MtDNA T4216C variation has frequently been investigated in Multiple Sclerosis (MS) patients; nonetheless, controversy has existed about the evidence of association of this variation with susceptibility to MS. The present systematic review and meta-analysis converge the results of the preceding publications, pertaining to association of mtDNA T4216C variation with susceptibility to MS, into a common conclusion. A computerized literature search in English was carried out to retrieve relevant publications from which required data were extracted. Using a fixed effect model, pooled odds ratio (OR), 95 % confidence interval (95 % CI), and P value were calculated for association of mtDNA T4216C variation with susceptibility to MS. The pooled results showed that there was a significant association between mtDNA T4216C variation and MS (OR = 1.38, 95 % CI = 1.13-1.67, P = 0.001). The present systematic review and meta-analysis suggest that mtDNA T4216C variation is a contributory factor in susceptibility to MS.

Mitochondrial reactive oxygen species and inflammation: Molecular mechanisms, diseases and promising therapies

Over the last few decades, many different groups have been engaged in studies of new roles for mitochondria, particularly the coupling of alterations in the redox pathway with the inflammatory responses involved in different diseases, including Alzheimer's disease, Parkinson's disease, atherosclerosis, cerebral cavernous malformations, cystic fibrosis and cancer. Mitochondrial dysfunction is important in these pathological conditions, suggesting a pivotal role for mitochondria in the coordination of pro-inflammatory signaling from the cytosol and signaling from other subcellular organelles. In this regard, mitochondrial reactive oxygen species are emerging as perfect liaisons that can trigger the assembly and successive activation of large caspase-1- activating complexes known as inflammasomes. This review offers a glimpse into the mechanisms by which inflammasomes are activated by mitochondrial mechanisms, including reactive oxygen species production and mitochondrial Ca²⁺ uptake, and the roles they can play in several inflammatory pathologies.

Clinical features of MS associated with Leber hereditary optic neuropathy mtDNA mutations

Objective:

To determine whether the association between multiple sclerosis (MS) and Leber hereditary optic neuropathy (LHON) (known as “Harding disease”) is a chance finding, or the 2 disorders are mechanistically linked.

Methods:

We performed a United Kingdom–wide prospective cohort study of prevalent cases of MS with LHON mitochondrial DNA (mtDNA) mutations. The new cases were compared with published cases, enabling a comprehensive clinical description. We also performed a meta-analysis of studies screening patients with MS for LHON mtDNA mutations to find evidence of a genetic association.

Results:

Twelve new patients were identified from 11 pedigrees, and 44 cases were identified in the literature. The combined cohort had the following characteristics: multiple episodes of visual loss, predominance for women, and lengthy time interval before the fellow eye is affected (average 1.66 years), which is very atypical of LHON; conversely, most patients presented without eye pain and had a poor visual prognosis, which is unusual for optic neuritis associated with MS. The number of UK cases of LHON-MS fell well within the range predicted by the chance occurrence of MS and the mtDNA mutations known to cause LHON. There was no association between LHON mtDNA mutations and MS in a meta-analysis of the published data.

Conclusions:

Although the co-occurrence of MS and LHON mtDNA mutations is likely to be due to chance, the resulting disorder has a distinct phenotype, implicating a mechanistic interaction. Patients with LHON-MS have a more aggressive course, and prognostication and treatment should be guarded.

Multiple sclerosis and mitochondrial gene variations: a review

Multiple sclerosis (MS) is a debilitating disease of the central nervous system. Its etiology is still an unanswered enigma; its symptoms are varied and unpredictable; and there is no cure for it. Genetics has been introduced as a contributing factor to MS. Not only may MS stem from nuclear gene variations/mutations, but also it may arise from mitochondrial gene variations/mutations. The association of mitochondrial DNA variations/mutations with the pathogenesis of MS has, so far, been analyzed by several studies. This paper reviews the literature with regard to MS and corresponding mitochondrial DNA variations.

Role of gender in multiple sclerosis: clinical effects and potential molecular mechanisms

Multiple sclerosis (MS) is more prevalent in females than males, and this female predominance is increasing as time goes by. Additionally, gender appears to play critical roles in development, progression and treatment of MS, and is therefore an aspect that should always be considered in the design and interpretation of research and clinical trials for MS. In this review, factors that could potentially explain the gender-biased observations in MS are discussed. These include sex-specific differences between the male and female immune systems and nervous systems, genetic and epigenetic or environmental-related effects, the effects of gonadal hormones, and materno-fetal interactions.

Mitochondrial DNA haplogroups and mutations in children with acquired central demyelination

OBJECTIVE

We investigated mitochondrial DNA (mtDNA) variants in children with a first episode of acquired demyelinating syndromes (PD-ADS) of the CNS and their relationship to disease phenotype, including subsequent diagnosis of multiple sclerosis (MS).

METHODS

This exploratory analysis included the initial 213 children with PD-ADS in the prospective Canadian Pediatric Demyelinating Study and 166 matched healthy sibling controls from the Canadian Autism Genome Project. A total of 31 single nucleotide polymorphisms (SNPs) were analyzed, including haplogroup-defining SNPs and mtDNA variants previously reported to be associated with MS.

RESULTS

Primary Leber hereditary optic neuropathy (LHON) mutations and other known pathogenic mtDNA mutations were absent in both patients with pediatric acquired demyelinating syndromes and controls. The 13708A haplogroup J-associated variant, previously linked to adult MS, was more frequent among subjects with PD-ADS (13.0%) compared to controls (6.2%; odds ratio [OR] 2.27; 95% confidence interval [CI] 1.06 to 4.83) and haplogroup M was associated with an earlier age at onset of PD-ADS (-1.74 years; 95% CI -3.33 to -0.07). In contrast, the haplogroup cluster UKJT, as well as 3 other SNPs, were each associated with a lower risk of PD-ADS. A total of 33 subjects with PD-ADS were diagnosed with MS during a mean follow-up period of 3.11 ± 1.14 (SD) years. No single SNP was associated with the risk of subsequent diagnosis of MS. However, haplogroup H was associated with an increased risk of MS (OR 2.60; 95% CI 1.21 to 5.55).

CONCLUSION

These data suggest an association between mtDNA variants and the risk of PD-ADS and of a subsequent MS diagnosis. Replication of these findings in an independent population of subjects with PD-ADS is required.

Multiple sclerosis associated with Leber's Hereditary Optic Neuropathy

The cause of multiple sclerosis is unknown although it is recognised to involve an inflammatory process associated with demyelinating plaques and more widespread neurodegeneration. It appears to have become progressively more common in females which is further discussed in this issue, and genetic factors, as identified to date, appear to play only a moderate role. One curious observation is that Leber's Hereditary Optic Neuropathy (LHON), a rare genetic syndrome, presents clinically overwhelmingly in males, but can be associated with an MS-like illness and when it does it occurs mainly in females. It is interesting to examine this further to assess if this could give us any clues as to the pathogenesis of MS.

Association of UCP2 -866 G/A polymorphism with chronic inflammatory diseases

We reported earlier that two mitochondrial gene polymorphisms, UCP2 -866 G/A (rs659366) and mtDNA nt13708 G/A (rs28359178), are associated with multiple sclerosis (MS). Here we aim to investigate whether these functional polymorphisms contribute to other eight chronic inflammatory diseases, including rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), Wegener' granulomatosis (WG), Churg-Strauss syndrome (CSS), Crohn's disease (CD), ulcerative colitis (UC), primary sclerosing cholangitis (PSC) and psoriasis. Compared with individual control panels, the UCP2 -866 G/A polymorphism was associated with RA and SLE, and the mtDNA nt13708 G/A polymorphism with RA. Compared with combined controls, the UCP2 -866 G/A polymorphism was associated with SLE, WG, CD and UC. When all eight disease panels and the original MS panel were combined in a meta-analysis, the UCP2 was associated with chronic inflammatory diseases in terms of either alleles (odds ratio (OR)=0.91, 95% confidence interval (95% CI): 0.86-0.96), P=0.0003) or genotypes (OR=0.88, (95% CI: 0.82-0.95), P=0.0008), with the -866A allele associated with a decreased risk to diseases. As the -866A allele increases gene expression, our findings suggest a protective role of the UCP2 protein in chronic inflammatory diseases.

Mitochondrial DNA sequence variation and neurodegeneration

Mitochondria, the powerhouse of the cell, play a critical role in several metabolic processes and apoptotic pathways. Many lines of evidence suggest that mitochondria have a central role in ageing-related neurodegenerative diseases. Moreover, there is a long history of investigations on mitochondria aimed at identifying genetic markers relating to ageing and neurodegenerative diseases. In this review, some of the major neurodegenerative disorders are highlighted and the role of mitochondrial haplogroups in the pathogenetic cascade leading to these diseases is discussed.

Mitochondrial mutation in Iranian patients with multiple sclerosis, correlation between haplogroups H, A and clinical manifestations

As multiple sclerosis (MS) has long been known to be associated with Leber, hereditary optic neuropathy (LHON), a disease caused by mitochondrial (mtDNA) mutations, in this study we assessed possible involvement of mtDNA point mutation in MS patients. Fifty-two MS patients whose disease was confirmed with revised McDonald criteria and referred to Iranian Center of Neurological Research of Imam Khomeini hospital during 2006-2007 entered the study. Secondary mtDNA mutations, age, gender, clinical disability according to expanded disability status scale (EDSS), course of the disease, and presenting symptoms were the variables investigated in this study. DNA purification was performed by Diatom DNA Extraction Kit. Analysis of data was done by SPSS V11.5. The prevalent mutations with frequency of 19.2% were J, L, and T haplogroups. Haplotype A was more prevalent in patients with younger age of onset (P-value = 0.012) and high proportion of haplogroup H was associated with optic nerve involvement (P-value = 0.015). No motor symptoms were seen in haplogroup H patients. There is no significant relationship between duration of the disease and EDSS in different mutation of mtDNA.

Cerebrospinal fluid evidence of increased extra-mitochondrial glucose metabolism implicates mitochondrial dysfunction in multiple sclerosis disease progression

In contrast to relapse, the mechanisms of multiple sclerosis (MS) disease progression are less understood and appear not to be exclusively inflammatory in nature. In this pilot study we investigated the relationship between disturbed CNS energy metabolism and MS disease progression. We tested the hypothesis that cerebrospinal fluid (CSF) concentrations of sorbitol, fructose, and lactate, all metabolites of extra-mitochondrial glucose metabolism, would be elevated in secondary progressive (SP) MS patients and would be associated with worsening neurologic disability. We measured metabolite concentrations by gas chromatographic/mass spectrometric and enzymatic methods in archived CSF samples from 85 MS patients [31 relapsing-remitting (RR) and 54 SP patients] and 18 healthy controls. We found that concentrations of all three metabolites, but not concentrations of glucose or myoinositol, were significantly increased in CSF from SP and, to a lesser degree, RR patients, compared to controls. Furthermore, CSF concentrations of sorbitol and fructose (polyol pathway metabolites), but not lactate (anaerobic glycolysis metabolite), correlated positively and significantly with Expanded Disability Status Scale (EDSS) score, an index of neurologic disability in MS patients. We conclude that extra-mitochondrial glucose metabolism is increased in MS patients and is associated with disease progression evidenced by increasing EDSS score. As extra-mitochondrial glucose metabolism increases with impaired mitochondrial metabolism of glucose, these findings implicate mitochondrial dysfunction in the pathogenesis of MS disease progression. CSF metabolic profiling may be useful in clarifying the role of mitochondrial pathology in progression and in targeting and monitoring therapies for disease progression that aim to preserve or boost mitochondrial glucose metabolism.

Investigation of the role of mitochondrial DNA in multiple sclerosis susceptibility

Several lines of evidence suggest that mitochondrial genetic factors may influence susceptibility to multiple sclerosis. To explore this hypothesis further, we re-sequenced the mitochondrial genome (mtDNA) from 159 patients with multiple sclerosis and completed a haplogroup analysis including a further 835 patients and 1,506 controls. A trend towards over-representation of super-haplogroup U was the only evidence for association with mtDNA that we identified in these samples. In a parallel analysis of nuclear encoded mitochondrial genes, we also found a trend towards association with the complex I gene, NDUFS2. These results add to the evidence suggesting that variation in mtDNA and nuclear encoded mitochondrial genes may contribute to disease susceptibility in multiple sclerosis.

mtDNA nt13708A variant increases the risk of multiple sclerosis

Background

Mitochondrial DNA (mtDNA) polymorphism is a possible factor contributing to the maternal parent-of-origin effect in multiple sclerosis (MS) susceptibility.

Methods and Findings

In order to investigate the role of mtDNA variations in MS, we investigated six European MS case-control cohorts comprising >5,000 individuals. Three well matched cohorts were genotyped with seven common, potentially functional mtDNA single nucleotide polymorphisms (SNPs). A SNP, nt13708 G/A, was significantly associated with MS susceptibility in all three cohorts. The nt13708A allele was associated with an increased risk of MS (OR = 1.71, 95% CI 1.28–2.26, P = 0.0002). Subsequent sequencing of the mtDNA of 50 individuals revealed that the nt13708 itself, rather than SNPs linked to it, was responsible for the association. However, the association of nt13708 G/A with MS was not significant in MS cohorts which were not well case-control matched, indicating that the significance of association was affected by the population structure of controls.

Conclusions

Taken together, our finding identified the nt13708A variant as a susceptibility allele to MS, which could contribute to defining the role of the mitochondrial genome in MS pathogenesis.

Mitochondrial DNA variants in Bulgarian patients affected by multiple sclerosis

The occurrence of multiple sclerosis (MS) in subjects clustering to a particular mitochondrial DNA (mtDNA) haplogroup/haplotype or carrying mtDNA mutations associated with Leber's hereditary optic neuropathy (LHON) has suggested that mitochondrial genome may contribute to susceptibility to MS. In the present study, 58 unrelated Bulgarian patients with relapsing remitting form of MS and 104 randomly selected healthy individuals were analysed for the presence of 14 mtDNA polymorphisms determining major European haplogroups as well as three (4216, 14 798, 13 708) secondary LHON mutations. Restriction enzyme analysis used to screen patients and controls for the common haplogroup-associated polymorphisms showed that each of these changes was present in MS patients at a similar frequency to control subjects. However, 21 of the 58 patients (36.2%) were positive for T4 216C mutation, while only 11.3% of the controls carried this secondary LHON base change (P < 0.01; OR = 4.38). Our finding indicated that 4216C base substitution could be considered as a predisposing marker for MS and supported the hypothesis that particular mtDNA variants could contribute to genetic susceptibility of MS, and merits further investigation.

Multiplex primer extension analysis for rapid detection of major European mitochondrial haplogroups

The evolution of the human mitochondrial genome is reflected in the existence of ethnically distinct lineages or haplogroups. Alterations of mitochondrial DNA (mtDNA) have been instrumental in studies of human phylogeny, in population genetics, and in molecular medicine to link pathological mutations to a variety of human diseases of complex etiology. For each of these applications, rapid and cost effective assays for mtDNA haplogrouping are invaluable. Here we describe a hierarchical system for mtDNA haplogrouping that combines multiplex PCR amplifications, multiplex single-base primer extensions, and CE for analyzing ten haplogroup-diagnostic mitochondrial single nucleotide polymorphisms. Using this rapid and cost-effective mtDNA genotyping method, we were able to show that within a large, randomly selected cohort of healthy Austrians (n = 1172), mtDNAs could be assigned to all nine major European haplogroups. Forty-four percent belonged to haplogroup H, the most frequent haplogroup in European Caucasian populations. The other major haplogroups identified were U (15.4%), J (11.8%), T (8.2%) and K (5.1%). The frequencies of haplogroups in Austria is within the range observed for other European countries. Our method may be suitable for mitochondrial genotyping of samples from large-scale epidemiology studies and for identifying markers of genetic susceptibility.

The European-specific mitochondrial cluster J/T could confer an increased risk of insulin-resistance and type 2 diabetes: an analysis of the m.4216T > C and m.4917A > G variants

The aims of this study were to investigate the contributions of the mitochondrial DNA m.4216T > C and m.4917A > G variants, and also of the European-specific mitochondrial cluster J/T, to the development of type 2 diabetes mellitus in Caucasian-Brazilian patients from Southern Brazil. We analyzed 347 type 2 diabetes patients and 350 control subjects. Variant frequencies in patients and control subjects were compared using chi2 tests or odds ratio. We also compared clinical and laboratory characteristics among patients with and without the variants. We found that the frequencies of the m.4216T > C and m.4917A > G variants are higher in diabetic patients than in control subjects. Moreover, haplogroups J (partially defined by the presence of the m.4216T > C variant only) and T (partially defined by the presence of both m.4216T > C and m.4917A > G variants) are more frequent in the type 2 diabetic group than in the control group. Patients belonging to the cluster J/T are more insulin resistant than patients of other haplogroups. In conclusion, our results indicate the association of the cluster J/T (as suggested by analyses of the m.4216T > C and m.4917A > G variants) with insulin resistance and type 2 diabetes.

Role of mitochondria in multiple sclerosis

This review presents inherited and acquired forms of mitochondrial dysfunction associated with oligodendrocytopathy and neurodegeneration in order to better understand the degenerative features of inflammatory demyelination. The recognition that various mitochondrial mechanisms are involved in the pathogenesis of multiple sclerosis leads to therapeutic considerations, re-emphasizing the importance of early neuroprotection in combination with the approved means of immune modulation.

North American white mitochondrial haplogroups in prostate and renal cancer

PURPOSE

While the mitochondrion is known to be a key mediator of apoptosis, there has been little inquiry into the inheritance pattern of mitochondria in patients with cancer. We compared the mtDNA haplotype in patients with prostate and renal cancer to that in controls to determine if there is an association between mitochondrial genotype and cancer.

MATERIALS AND METHODS

Haplotyping was performed using polymerase chain reaction/digest identification of key polymorphic sites in the mitochondrial genome. A total of 121 and 221 white men with renal and prostate cancer, respectively, were identified following pathological confirmation of cancer, while 246 white controls were selected randomly from a bank of cadaveric organ donor DNA. Statistical analysis was performed and ORs were calculated.

RESULTS

Mitochondrial haplogroup U was a highly significant risk factor for prostate and renal cancer vs controls (16.74% and 20.66% vs 9.35%, Fisher's exact test p = 0.019 and 0.005, respectively). The association remained statistically significant in renal cancer even after Bonferroni adjustment for multiple comparisons. Haplogroup U carried an OR of 1.95 for prostate cancer and an OR of 2.52 for renal cancer.

CONCLUSIONS

The inheritance of mitochondrial haplogroup U is associated with an approximately 2-fold increased risk of prostate cancer and 2.5-fold increased risk of renal cancer in white North American individuals. Therefore, individuals with this mitochondrial haplotype are in a high risk group. Because mitochondrial haplogroup U is found in 9.35% of the white United States population, there are more than 20 million individuals in this high risk group.

Genetic variants of Complex I in multiple sclerosis

HYPOTHESIS

A mitochondrial mechanism contributes to neurodegeneration in multiple sclerosis (MS). Genetic variants of Complex I genes may influence the nature of tissue response to inflammation in the central nervous system (CNS).

BACKGROUND

Complex I is encoded by seven mitochondrial and 38 nuclear genes. Many of the nuclear genes colocalize with regions where full genome scans detected linkage in MS. Previous studies revealed an association between variants of mitochondrial (mt)DNA encoded subunits of Complex I and MS. Biochemical studies suggested a functional involvement of Complex I in the degenerative processes downstream to inflammatory injury in the CNS.

METHODS

Patients with all MS phenotypes were included. DNA specimens of affected sib pair, trio and multiplex families were studied. Single nucleotide polymorphisms (SNP) were determined by using the Taqman assay. The association of MS with nuclear DNA encoded alleles and haplotypes of Complex I was tested by the pedigree disequilibrium test (PDT) and by the transmit program in the families. Haplotypes were further investigated by using ldmax (GOLD). The association of mtDNA encoded variants with MS was tested by the Fisher's Exact Test.

RESULTS

The previously identified MS-associated mtDNA variants and haplotypes were not increased in mothers as compared to fathers in these families. However, an association of all clinical phenotypes with haplotypes within NDUFS5 (1p34.2-p33), NDUFS7 (19p13) and NDUFA7 (19p13) was detected. The inclusion of families with primary progressive (PP)-MS phenotype did not modify the outcome and, as a subgroup alone, did not have a sufficient size to draw conclusion regarding phenotype specific associations.

CONCLUSIONS

SNP haplotypes within Complex I genes are associated with MS. Further studies are needed to refine the identification of disease relevant variants nearby or within these haplotypes. Molecular and functional properties of Complex I subunits may offer novel explanations to better understand the relationship between inflammation and neurodegeneration.

Familial multiple sclerosis and other inherited disorders of the white matter

BACKGROUND

An objective demonstration of lesions disseminated in time and space remains the core of the last revision of diagnostic criteria for multiple sclerosis (MS), but this update is now empowered by a weighted use of magnetic resonance imaging (MRI), which results in an earlier and more unambiguous diagnosis ("MS," "not MS," or "possible MS"). Nevertheless, the exclusion of other entities still remains an integral element of the diagnostic process.

REVIEW SUMMARY

Exclusion of genetic disorders can be challenging in some cases with familial recurrence of MS, particularly when the transmission is mimicking a mendelian or a maternal pattern of inheritance. Vice versa, many forms of mendelian leukodystrophies and leukoencephalopathies present with juvenile or adult onset, progressive or relapsing-remitting courses, intrafamilial phenotypic heterogeneity and MRI signs of multifocal white matter (WM) pathology, features potentially leading to a temporary confusion with MS. With the recent availability of disease modifying medications in MS, the development of specific molecular therapies in inherited WM disorders, and the general recognition of the effectiveness of early treatments, the accuracy of initial diagnostic assessment has become critical.

CONCLUSION

Considering the importance of disease specific treatments, here we review the major characteristics of familial MS and some of the inheritable diseases of the WM. Although no direct genetic link between MS and these WM abnormalities is known, molecular data from the field of rare genetic disorders may also provide some experimental paradigms to a further exploration of MS.

Leber's hereditary optic neuropathy--case report and literature review

CONTEXT

Leber's hereditary optic neuropathy is an important cause of progressive painless visual loss among young male patients.

OBJECTIVE

To report on a case of a young patient with a clinical and neurophysiological condition suggestive of Leber's hereditary optic neuropathy, confirmed by genetic testing.

CASE REPORT

We describe a 17-year-old male with progressive bilateral visual loss. Two maternal uncles had had similar patterns of visual loss. The patient had a history of smoking and alcohol abuse. Neuro-ophthalmological examination revealed visual acuity of 20/800 in both eyes, with decreased direct and consensual pupillary light reflexes. Fundus examination demonstrated pale optic discs. The visual evoked potential test showed signs of conduction disturbances in both optic nerves and campimetric study showed complete visual loss in all fields of both eyes. A diagnosis of bilateral optic neuropathy with a clinical suspicion of Leber's hereditary optic neuropathy was made. A blood sample was submitted to genetic analysis in relation to the principal mutations of this disorder, and homoplasmic mutation in 11778 was detected, thereby confirming the diagnosis of Leber's hereditary optic neuropathy.

Ingested type I interferon: a potential treatment for autoimmunity

We have proposed a unifying hypothesis of the etiopathogenesis of autoimmunity that defines autoimmunity as a type I interferon (IFN) immunodeficiency syndrome. We have examined toxicity and potential efficacy in three phase I (type 1 diabetes, rheumatoid arthritis, multiple sclerosis) and one phase II clinical trials in multiple sclerosis (MS). In a phase I open-label trial in type 1 diabetes, ingested IFN-alpha preserved residual beta cell function in recent onset patients. In a second phase I trial, treatment of rheumatoid arthritis (RA) with ingested IFN-alpha reduced the secretion of interleukin-1 (IL-1), a proinflammatory cytokine. In a third phase I trial in MS, there was a significant decrease in peripheral blood mononuclear cell (PBMC) IL-2 and IFN-gamma production after ingesting IFN-alpha. In a phase II randomized, placebo-controlled, double-blind trial in MS, 10,000 IU ingested IFN-alpha significantly decreased gadolinium enhancements compared with the placebo group at month 5. Tumor necrosis factor-alpha (TNF-alpha) and IFN-gamma cytokine secretion in the 10,000 IU group at month 5 showed a significant decrease that corresponded with the effect of ingested IFN-alpha on decreasing gadolinium enhancements. Ingested IFN-alpha was not toxic in any of these clinical trials. These studies suggest that ingested IFN-alpha may have a potential role in the treatment of autoimmunity.

Mitochondria, aging and longevity--a new perspective

A new perspective is emerging indicating that mitochondria play a critical role in aging not only because they are the major source and the most proximal target of reactive oxygen species, but also because they regulate stress response and apoptosis. Recent literature indicates that, in response to stress, a variety of molecules translocate to and localise in mitochondria. These molecules are likely to interact with each other, in order to mediate mitochondria/nucleus cross-talk and to regulate apoptosis. We surmise that an integration of signals in multimolecular complexes occurs at mitochondrial level. These phenomena can be of critical importance for human aging and longevity.

Human mtDNA haplogroups associated with high or reduced spermatozoa motility

A variety of mtDNA mutations responsible for human diseases have been associated with molecular defects in the OXPHOS system. It has been proposed that mtDNA genetic alterations can also be responsible for sperm dysfunction. In addition, it was suggested that if sperm dysfunction is the main phenotypic consequence, these mutations could be fixed as stable mtDNA variants, because mtDNA is maternally inherited. To test this possibility, we have performed an extensive analysis of the distribution of mtDNA haplogroups in white men having fertility problems. We have found that asthenozoospermia, but not oligozoospermia, is associated with mtDNA haplogroups in whites. Thus, haplogroups H and T are significantly more abundant in nonasthenozoospermic and asthenozoospermic populations, respectively, and show significant differences in their OXPHOS performance.

The genetics of multiple sclerosis

Classical genetic studies involving the analysis of pedigrees and recurrence risk within families have defined the extent to which genetic factors contribute to the aetiology of multiple sclerosis. Limited progress has been made in identifying the number and topography of genetic loci contributing to susceptibility through molecular investigation either of candidate genes or the whole genome using microsatellite and single nucleotide polymorphisms.

The genetic epidemiology of multiple sclerosis

Epidemiological studies have implicated an interplay between genetic and environmental factors in the aetiology of multiple sclerosis (MS). There is a familial recurrence rate of approximately 15%. Meta-analysis of the recurrence risk shows that the rate is highest overall for siblings, then parents and children, with lower rates in second- and third-degree relatives. Recurrence is highest for monozygotic twins. Conversely, the frequency in adoptees is similar to the population lifetime risk. The age-adjusted risk for half siblings is also less than for full siblings. Recurrence is higher in the children of conjugal pairs with MS than the offspring of single affected. These classical genetic observations suggest that MS is a complex trait in which susceptibility is determined by several genes acting independently or epistatically. Comparisons between co-affected sibling pairs provide no evidence for correlation with age or year at onset and mode of presentation or disability. Thus far, the identification of susceptibility genes has proved elusive but genetic strategies are now in place which should illuminate the problem. The main dividend will be an improved understanding of the pathogenesis. To date, population studies have demonstrated an association between the class II major histocompatibility complex (MHC) alleles DR15 and DQ6 and their corresponding genotypes. An association with DR4, with or without the primary DR15 link, is seen in some Mediterranean populations. Candidate gene approaches have otherwise proved unrewarding. Four groups of investigators have undertaken a systematic search of the genome. In common with most other complex traits, no major susceptibility gene has been identified but regions of interest have been provisionally identified. These genetic analyses are predicated on the assumption that MS is one disease. Genotypic and phenotypic analyses are beginning to question this assumption. A major part of future studies in the genetics of MS will be to resolve the question of disease heterogeneity.

The genetics of multiple sclerosis. A review

Multiple sclerosis (MS) is characterized by chronic inflammation and demyelination in the central nervous system (CNS). Although the etiology of MS is unknown, both genetic and environmental contributions to the pathogenesis are inferred from epidemiologic studies. Geographic distributions and epidemics of MS and data from migration studies provide evidence for some, thus far unidentified, environmental effects. The co-occurrence of MS with high and low frequencies in ethnic groups often sharing an environment, the increased recurrence rate in families, and the high concordance rate among identical twins point to inheritable determinants of susceptibility. Based on the autoimmune hypothesis of demyelination, genetic studies sought associations between MS and polymorphic alleles of candidate genes which regulate either the immune response or myelin production. The most consistent finding in case-control studies was the association with the major histocompatibility complex (MHC) (also called human leukocyte antigen--HLA) class II, DR15, DQ6, Dw2 haplotype. Studies on other gene products encoded within or close to the MHC complex on chromosome 6p21.3 (e.g., HLA DP, complement components, transporter proteins, tumor necrosis factor, and myelin-oligodendrocyte glycoprotein) resulted in conflicting observations in different patient populations. The potential contribution of polymorphic alleles within the genes of the T-cell receptor alpha beta chains, immunoglobulins, cytokines, and oligodendrocyte growth factors or their receptors to MS susceptibility either remains equivocal or is rejected. Studies on families with multiple affected members have revealed that MS is a complex trait, that the contribution of individual genes to susceptibility is probably small, and that differences are possible between familial and sporadic forms. The development of molecular and computer technologies have facilitated the performance of comprehensive genomic scans in multiplex families, which have confirmed the possible linkage of multiple loci to susceptibility, each with a minor contribution. Several provisional sites were reported, but only 6p21 (MHC complex), 5p14, and 17q22 were positive in more than one study. The British update demonstrated segregation among regions of interest depending on DR15 sharing, and excluded a gene of major effect from 95%, and one with a moderate effect from 65% of the genome. The extended study by the US collaboration group revealed that the MHC linkage was limited to families segregating HLA DR2 alleles, which suggested that linkage to the MHC is related to the HLA DR2 association, and that sporadic and familial MS share at least one common susceptibility marker. Further identification of MS susceptibility loci may involve additional family sets, more polymorphic markers, and the exploration of telomeric chromosomal regions. Data from these studies may further elucidate pathogenic mechanisms of MS.

Large scale screening of the mitochondrial DNA reveals no pathogenic mutations but a haplotype associated with multiple sclerosis in Caucasians

We report the first large-scale screening of mitochondrial (mt) DNA in 77 Caucasian patients with relapsing-remitting or secondary progressive form of multiple sclerosis (MS) and in 84 Caucasian controls by using the method of restriction site polymorphism and haplotype analysis. No pathogenic mtDNA mutation was found in association with MS. However, mtDNA haplotypes K* and J* defined by the simultaneous presence of Ddel restriction sites at nucleotides 10,394 and 14,798 of the mtDNA in haplogroups K and J showed association with MS at a P-value of 0.001. A relative increase of MS patients compared to controls either with the J* or with the K* haplotype (+10,394Ddel/+14,798Ddel in haplogroup J or K) also was detected (each with a P<0.05). No distinct phenotypic characteristics of MS were observed when clinical data of patients with haplotypes K* or J* were analyzed. In addition to previous complete sequencing in several MS patients, the population screening of mtDNA presented here suggests that mtDNA point mutations are not likely to be involved in the pathogenesis of typical forms of MS. However, the mitochondrial genetic background (haplotype K* and J*) may moderately contribute to MS susceptibility. The reported association between MS and Leber's hereditary optic nerve atrophy, a disease caused by mtDNA point mutations preferentially occurring in haplogroup J, may be at least in part related to the overlapping mitochondrial genetic background of the two diseases.

Inheritance of susceptibility to multiple sclerosis

In recent years, epidemiological evidence supporting the genetic basis of multiple sclerosis has been extended and whole-genome linkage screening has advanced the mapping of the involved genes. Understanding of the known HLA associations has also improved and many candidate genes have been studied.

Is the mitochondrial DNA involved in determining susceptibility to multiple sclerosis?

An increasing number of case reports on Leber's hereditary optic neuropathy (LHON) associated mitochondrial (mt)DNA point mutations in patients with multiple sclerosis (MS) raised the possibility that mitochondrial determinants may contribute to genetic susceptibility to MS. These observations prompted many laboratories including ours to perform comprehensive sequencing or large scale screening of the mtDNA in MS patients. Here we review the available data arguing for or against a mitochondrial hypothesis for MS. We conclude that pathogenic mtDNA point mutations are not associated with typical forms of this disease. A very small subgroup of MS patients, usually with prominent optic neuritis (PON), may carry pathogenic LHON mutations. This partial overlap between the two diseases may be related to the association of MS with a mtDNA haplotype (a set of mtDNA polymorphisms) within which pathogenic LHON mutations preferentially occur.

The genetic analysis of multiple sclerosis

Although monogenic diseases often show extreme clinical phenotypes, the major burden of genetic ill health lies in the more prevalent polygenic disorders, such as diabetes, hypertension and multiple sclerosis. These conditions affect many thousands of individuals and their management consumes vast amounts of health care resources: in the UK some 80,000 people have multiple sclerosis; the estimated financial cost to society of introducing treatments, such as beta interferon, could be as high as 250 million pounds per year. Knowledge on the genetics of these common diseases is poor, but has potentially received a considerable boost with the arrival of whole genome screening. The genome screen in insulin-dependent diabetes mellitus (IDDM) reported in 1994 was the first in a human polygenic disease. Since this publication, whole genome screening has been performed in a variety of human polygenic diseases, including schizophrenia, bipolar affective disorder, non-insulin-dependent diabetes mellitus (NIDDM), inflammatory bowel disease, asthma and multiple sclerosis.