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

Gene Therapy with Single-Subunit Yeast NADH-Ubiquinone Oxidoreductase (NDI1) Improves the Visual Function in Experimental Autoimmune Encephalomyelitis (EAE) Mice Model of Multiple Sclerosis (MS)

Mitochondrial dysfunction mediated loss of respiration, oxidative stress, and loss of cellular homeostasis contributes to the neuronal and axonal degenerations permanent loss of function in experimental autoimmune encephalomyelitis model (EAE) of multiple sclerosis (MS). To address the mitochondrial dysfunction mediated visual loss in EAE mice, self-complementary adeno-associated virus (scAAV) containing the NADH-dehydrogenase type-2 (NDI1) complex I gene was intravitreally injected into the mice after the onset of visual defects. Visual function assessed by pattern electroretinogram (PERGs) showed progressive loss of function in EAE mice were improved significantly in NDI1 gene therapy-treated mice. Serial optical coherence tomography (OCT) revealed that progressive thinning of inner retinal layers in EAE mice was prevented upon NDI1 expression. The 45% optic nerve axonal and 33% retinal ganglion cell (RGC) loss contributed to the permanent loss of visual function in EAE mice were ameliorated by NDI1-mediated prevention of mitochondrial cristae dissolution and improved mitochondrial homeostasis. In conclusion, targeting the dysfunctional complex I using NDI1 gene can be an approach to address axonal and neuronal loss responsible for permanent disability in MS that is unaltered by current disease modifying drugs.

mtDNA polymorphism and metabolic inhibition affect sperm performance in conplastic mice

Whereas a broad link exists between nucleotide substitutions in the mitochondrial genome (mtDNA) and a range of metabolic pathologies, exploration of the effect of specific mtDNA genotypes is on-going. Mitochondrial DNA mutations are of particular relevance for reproductive traits, since they are expected to have profound effects on male specific processes as a result of the strict maternal inheritance of mtDNA. Sperm motility is crucially dependent on ATP in most systems studied. However, the importance of mitochondrial function in the production of the ATP necessary for sperm function remains uncertain. In this study, we test the effect of mtDNA polymorphisms upon mouse sperm performance and bioenergetics by using five conplastic inbred strains that share the same nuclear background while differing in their mitochondrial genomes. We found that, while genetic polymorphisms across distinct mtDNA haplotypes are associated with modification in sperm progressive velocity, this effect is not related to ATP production. Furthermore, there is no association between the number of mtDNA polymorphisms and either (a) the magnitude of sperm performance decrease, or (b) performance response to specific inhibition of the main sperm metabolic pathways. The observed variability between strains may be explained in terms of additive effects of single nucleotide substitutions on mtDNA coding sequences, which have been stabilized through genetic drift in the different laboratory strains. Alternatively, the decreased sperm performance might have arisen from the disruption of the nuclear DNA/mtDNA interactions that have coevolved during the radiation of Mus musculus subspecies.

Excitotoxins, Mitochondrial and Redox Disturbances in Multiple Sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS). There is increasing evidence that MS is not only characterized by immune mediated inflammatory reactions, but also by neurodegenerative processes. There is cumulating evidence that neurodegenerative processes, for example mitochondrial dysfunction, oxidative stress, and glutamate (Glu) excitotoxicity, seem to play an important role in the pathogenesis of MS. The alteration of mitochondrial homeostasis leads to the formation of excitotoxins and redox disturbances. Mitochondrial dysfunction (energy disposal failure, apoptosis, etc.), redox disturbances (oxidative stress and enhanced reactive oxygen and nitrogen species production), and excitotoxicity (Glu mediated toxicity) may play an important role in the progression of the disease, causing axonal and neuronal damage. This review focuses on the mechanisms of mitochondrial dysfunction (including mitochondrial DNA (mtDNA) defects and mitochondrial structural/functional changes), oxidative stress (including reactive oxygen and nitric species), and excitotoxicity that are involved in MS and also discusses the potential targets and tools for therapeutic approaches in the future.

Stressed cybrids model demyelinated axons in multiple sclerosis

Multiple sclerosis is likely caused by a complex interaction of multiple genes and environmental factors. The contribution of mitochondrial DNA genetic backgrounds has been frequently reported. To evaluate the effect of mitochondrial DNA haplogroups in the same genetic and environmental circumstances, we have built human transmitochondrial cell lines and simulated the effect of axon demyelination, one of the hallmarks of multiple sclerosis pathology, by altering the ionic gradients through the plasmalemma and increasing ATP consumption. In this model, mitochondrial biogenesis is observed. This process is larger in Uk cybrids, which mirrors their lower oxidative phosphorylation capacity in basal conditions. This model replicates a process occurring in both patients suffering from multiple sclerosis and several animal models of axon demyelination. Therefore, it can be used to analyze the contribution of various mitochondrial DNA genotypes to multiple sclerosis. In this sense, a longer or stronger energy stress, such as that associated with demyelinated axons in multiple sclerosis, could make Uk individuals more susceptible to this pathology. Finally, pharmacologic compounds targeted to mitochondrial biogenesis could be a potential therapy for multiple sclerosis.

Mitochondria as oxidative signaling organelles in T-cell activation: physiological role and pathological implications

Early scientific reports limited the cell biological role of reactive oxygen species (ROS) to the cause of pathological damage. However, extensive research performed over the last decade led to a wide recognition of intracellular oxidative/redox signaling as a crucial mechanism of homeostatic regulation. Amongst different cellular processes known to be influenced by redox signaling, T-cell activation is one of the most established. Numerous studies reported an indispensible role for ROS as modulators of T-cell receptor-induced transcription. Nevertheless, mechanistic details regarding signaling pathways triggered by ROS are far from being delineated. The nature and interplay between enzymatic sources involved in the generation of "oxidative signals" are also a matter of ongoing research. In particular, active participation of the mitochondrial respiratory chain as ROS producer constitutes an intriguing issue with various implications for bioenergetics of activated T cells as well as for T-cell-mediated pathologies. The aim of the current review is to address these interesting concepts.

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.

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.

Is multiple sclerosis a mitochondrial disease?

Multiple sclerosis (MS) is a relatively common and etiologically unknown disease with no cure. It is the leading cause of neurological disability in young adults, affecting over two million people worldwide. Traditionally, MS has been considered a chronic, inflammatory disorder of the central white matter in which ensuing demyelination results in physical disability. Recently, MS has become increasingly viewed as a neurodegenerative disorder in which axonal injury, neuronal loss, and atrophy of the central nervous system leads to permanent neurological and clinical disability. In this article, we discuss the latest developments on MS research, including etiology, pathology, genetic association, EAE animal models, mechanisms of neuronal injury and axonal transport, and therapeutics. In this article, we also focus on the mechanisms of mitochondrial dysfunction that are involved in MS, including mitochondrial DNA defects, and mitochondrial structural/functional changes.

Multiple sclerosis: clinical features, pathophysiology, neuroimaging and future therapies

Multiple sclerosis (MS) is a common immune-mediated progressive neurodegenerative disease of the CNS that typically manifests with periods of disease activity followed by intervals of remission. The etiology of MS remains unknown; however, existing evidence indicates that MS is a ‘whole-brain disease’ that is driven by a potent immune response against CNS antigen(s), particularly myelin peptide antigens. The immunopathogenesis of MS includes both the cell- and humorally-mediated arms of the immune system. Genetic and environmental factors play important roles in the development of MS. Application of various neuroimaging techniques to the world of MS have expanded our knowledge concerning its pathogenesis and assist us in the more accurate diagnosis of MS versus its imitators. Current treatments target acute attacks and aim to reduce future clinical relapses. A summary of the potential future therapies for MS is presented.

Lack of mitochondrial DNA deletions in lesions of multiple sclerosis

OBJECTIVE

To test if mitochondrial (mt)DNA deletions accumulate in brains of patients with multiple sclerosis (MS).

BACKGROUND

Previous studies demonstrated an accumulation of oxidative damage to mtDNA and decreased activity of mitochondrial enzymes in lesions of MS, where activated immune cells produce increased amounts of reactive oxygen species and nitric oxide. The unknown link between oxidative damage and decreased activity of mitochondrial enzymes may be the accumulation of deletions in mtDNA molecules. mtDNA deletions in the brain have been associated with neurodegeneration and aging.

METHODS

mtDNA deletions were quantified by using real-time PCR in laser-dissected, COX-positive and COX-negative single neuronal and glial cells from frozen postmortem brain tissue specimens including normal appearing gray (NAGM) and white matter (NAWM) regions and chronic active plaques of MS patients, and gray matter (GM) and white matter (WM) regions of age-matched controls. Three patients with advance Alzheimer's and Parkinson's diseases were included as positive controls. The proportion of deleted mtDNA molecules was correlated with pathology and age.

RESULTS

We detected no pathology-related accumulation of mtDNA deletions when comparisons were made among NAGM, NAWM, and plaque of MS brains, or between NAGM-GM and NAWM-WM of patients and age-matched controls. However, an accumulation of mtDNA deletions was noted in non-neurological controls beyond 60 years of age and in patients with Alzheimer's and Parkinson's diseases. As expected, the rate of mtDNA deletions was higher in COX- than in COX+ cells.

CONCLUSION

While aging and neurodegeneration in PD and AD are associated with accumulation of COX- cells and mtDNA deletions, the pathology of MS is not.

Dissecting the effects of mtDNA variations on complex traits using mouse conplastic strains

Previous reports have demonstrated that the mtDNA of mouse common inbred strains (CIS) originated from a single female ancestor and that mtDNA mutations occurred during CIS establishment. This situation provides a unique opportunity to investigate the impact of individual mtDNA variations on complex traits in mammals. In this study, we compiled the complete mtDNA sequences of 52 mouse CIS. Phylogenetic analysis demonstrated that 50 of the 52 CIS descended from a single female Mus musculus domesticus mouse, and mtDNA mutations have accumulated in 26 of the CIS. We then generated conplastic strains on the C57BL/6J background for 12 mtDNA variants with one to three functional mtDNA mutations. We also generated conplastic strains for mtDNA variants of the four M. musculus subspecies, each of which contains hundreds of mtDNA variations. In total, a panel of conplastic strains was generated for 16 mtDNA variants. Phenotypic analysis of the conplastic strains demonstrated that mtDNA variations affect susceptibility to experimental autoimmune encephalomyelitis and anxiety-related behavior, which confirms that mtDNA variations affect complex traits. Thus, we have developed a unique genetic resource that will facilitate exploration of the biochemical and physiological roles of mitochondria in complex traits.

Human mitochondrial variants influence on oxygen consumption

This work investigates if human mitochondrial variants influence on maximal oxygen consumption (VO(2max)). With this purpose we recruited, as a uniform population in term of nutritional habits and life style, 114 healthy male Spanish subjects that practiced fitness exercises 3-4 times a week. Once mtDNA haplogroups were determined, we found that J presents with lower VO(2max) (P=0.02) than nonJ variants. J has been related with a lower efficiency of electron transport chain (ETC), diminished ATP and ROS production. Thus, the difficult to compensate the mitochondrial energetic deficiency could explain the accumulation of J haplogroup in LHON and multiple sclerosis. Furthermore, the lower ROS production associated to J could also account for the accrual of this variant in elderly people consequent to a decreased oxidative damage.

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.

Neuroimaging of mitochondrial disease

Mitochondrial disease represents a heterogeneous group of genetic disorders that require a variety of diagnostic tests for proper determination. Neuroimaging may play a significant role in diagnosis. The various modalities of nuclear magnetic resonance imaging (MRI) allow for multiple independent detection procedures that can give important anatomical and metabolic clues for diagnosis. The non-invasive nature of neuroimaging also allows for longitudinal studies. To date, no pathonmonic correlation between specific genetic defect and neuroimaging findings have been described. However, certain neuroimaging results can give important clues that a patient may have a mitochondrial disease. Conventional MRI may show deep gray structural abnormalities or stroke-like lesions that do not respect vascular territories. Chemical techniques such as proton magnetic resonance spectroscopy (MRS) may demonstrate high levels of lactate or succinate. When found, these results are suggestive of a mitochondrial disease. MRI and MRS studies may also show non-specific findings such as delayed myelination or non-specific leukodystrophy picture. However, in the context of other biochemical, structural, and clinical findings, even non-specific findings may support further diagnostic testing for potential mitochondrial disease. Once a diagnosis has been established, these non-invasive tools can also aid in following disease progression and evaluate the effects of therapeutic interventions.

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.

Investigation on Mitochondrial tRNALeu/Lys, NDI and ATPase 6/8 in Iranian Multiple Sclerosis Patients

As with chromosomal DNA, the mitochondrial DNA (mtDNA) can contain mutations that are highly pathogenic . In fact, many diseases of the central nervous system are known to be caused by mutations in mtDNA. Dysfunction of the mitochondrial Respiratory Chain (RC) has been shown in patients with neurological disease including Alzheimer's disease (AD), Parkinson's disease (PD) and Multiple sclerosis (MS). MS is a demyelinating disease of central nervous system characterized by morphological hallmarks of inflammation, demyelination and axonal loss. Considering this importance, we decided to investigate several highly mutative parts of mtDNA for point mutations as MT-LTI (tRNA(Leucine1(UUA/G))), MT-NDI (NADH Dehydrogenase subunit 1), MT-COII (Cytochrome c oxidase subunit II), MT-TK (tRNA(Lysine)), MT-ATP8 (ATP synthase subunit F0 8) and MT-ATP6 (ATP synthase subunit F0 6) in 20 Iranian MS patients and 80 age-matched control subjects by PCR and automated DNA sequencing to evaluate any probable point mutations. Our results revealed that 15 (75%) out of 20 MS patients had point mutations. Some of point mutations were newly found in this study. This study suggested that point mutation occurred in mtDNA might be involved in pathogenesis of MS.

Novel role for mitochondria: protein kinase Ctheta-dependent oxidative signaling organelles in activation-induced T-cell death

Reactive oxygen species (ROS) play a key role in regulation of activation-induced T-cell death (AICD) by induction of CD95L expression. However, the molecular source and the signaling steps necessary for ROS production are largely unknown. Here, we show that the proximal T-cell receptor-signaling machinery, including ZAP70 (zeta chain-associated protein kinase 70), LAT (linker of activated T cells), SLP76 (SH2 domain-containing leukocyte protein of 76 kDa), PLCgamma1 (phospholipase Cgamma1), and PKCtheta (protein kinase Ctheta), are crucial for ROS production. PKCtheta is translocated to the mitochondria. By using cells depleted of mitochondrial DNA, we identified the mitochondria as the source of activation-induced ROS. Inhibition of mitochondrial electron transport complex I assembly by small interfering RNA (siRNA)-mediated knockdown of the chaperone NDUFAF1 resulted in a block of ROS production. Complex I-derived ROS are converted into a hydrogen peroxide signal by the mitochondrial superoxide dismutase. This signal is essential for CD95L expression, as inhibition of complex I assembly by NDUFAF1-specific siRNA prevents AICD. Similar results were obtained when metformin, an antidiabetic drug and mild complex I inhibitor, was used. Thus, we demonstrate for the first time that PKCtheta-dependent ROS generation by mitochondrial complex I is essential for AICD.

Complex I deficiency in Persian multiple sclerosis patients

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system characterized by the morphological hallmarks of inflammation, demyelination and axonal loss. Until now, little attention has been paid to the contribution of mitochondrial respiratory chain enzyme activities to MS. In this study, kinetic analysis of mitochondrial respiratory chain complex I enzyme (measured as NADH-ferricyanide reductase) was performed on intact mitochondria isolated from fresh skeletal muscle in MS patients (n = 10) and control subjects (n = 11). Mitochondrial DNA common deletion and deletions were also tested in MS patients. Our findings showed that complex I activities were significantly reduced (P = 0.007) in patients compared with control. However, we could not find deletion in mtDNA of patients with MS. The presupposition of relationship between MS and mitochondrial disorders is due to predominant maternal transmission of MS in affected parent-child pairs, pathoaetiological role of respiratory chain dysfunction in multisystem disorders and important role of it in neurodegenerative disorders, a number of patients such as LHON or other mtDNA abnormality with developed neurological symptoms indistinguishable from MS and similarity of clinical symptoms in mitochondrial disorders to those of MS. This study suggested that a biochemical defect in complex I activity may be involved in pathogenesis of MS.

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.

White matter involvement in mitochondrial diseases

White matter involvement is recently being realized as a common finding in mitochondrial disorders. It is considered an inherent part of the classical mitochondrial syndromes which are usually associated with alterations in the mitochondrial DNA such as: Leigh disease, Kearns-Sayre syndrome, mitochondrial encephalomyopathy lactic acidosis, and stroke like episodes, mitochondrial neuro-gastro-intestinal encephalomyopathy and Leber's hereditary optic neuropathy. White matter involvement is also described in mitochondrial disorders due to mutations in the nuclear DNA which are transmitted in an autosomal pattern. MRI findings suggestive of a mitochondrial disease are: small cyst-like lesions in abnormal white matter, involvement of both cerebral and cerebellar white matter, and a combination of a leukoencephalopathy with bilateral basal ganglia lesions. The clinical manifestations may be disproportionate to the extent of white matter involvement. Other organs may frequently be involved. The onset is often in infancy with a neurodegenerative course. The finding of a leukoencephalopathy in a patient with a complex neurologic picture and multisystem involvement should prompt a thorough mitochondrial evaluation.

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.

Visual recovery in a man with the rare combination of mtDNA 11778 LHON mutation and a MS-like disease after mitoxantrone therapy

We describe a young man with prognostic unfavourable homoplasmatic mitochondrial DNA(mt DNA) 11778 Leber's hereditary optic neuropathy (LHON) point mutation and confirmed multiple sclerosis (MS). This combination of LHON and MS-like disease is rare in both sexes, and in men has been described in only a few case reports. In a 4-year follow-up during immunosuppressive therapy with mitoxantrone, we found a remarkable time delayed visual recovery 12 months after acute onset of rapid sequential bilateral subtotal visual loss followed by episodes of isolated acute demyelinative optic neuropathy. Visual recovery to such extent after this latency is uncommon in both mtDNA 11778 LHON mutation and optic neuritis (ON) in MS. Relapses in visual deterioration must be considered as extremely rare in LHON. This case might support the hypothesis of an immunological pathogenetic factor in combined LHON and MS, and possibly in LHON alone. We suggest a search for the LHON mutation in MS patients with predominant visual impairment, independent of patients' gender.

Susceptibility to multiple sclerosis: interplay between genes and environment

Multiple sclerosis is a complex trait of unknown etiology. Epidemiological data have shown that susceptibility to multiple sclerosis is determined by both genetic and environmental factors. It is unknown whether the clinical subcategories of multiple sclerosis are separate diseases with separate etiologies and causes. Recent theories of the pathogenesis of multiple sclerosis and candidate genes are discussed. Other potential nonchromosomal factors involved in multiple sclerosis susceptibility such as mitochondrial DNA and viral factors such as Chlamydia pneumoniae are reviewed.

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.