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Figure 1. 

Representative light microscopy images. A, Normal cytochrome c oxidase (COX) activity. B, Moderate COX deficiency (5-10 COX-deficient fibers per 100 fibers). C, Severe COX deficiency (>10 COX-deficient fibers per 100) (original magnification ×25).

Representative light microscopy images. A, Normal cytochrome c oxidase (COX) activity. B, Moderate COX deficiency (5-10 COX-deficient fibers per 100 fibers). C, Severe COX deficiency (>10 COX-deficient fibers per 100) (original magnification ×25).

Figure 2. 

Light microscopic image of sequential muscle biopsies from patient 6. Both the first biopsy (A) and the second (D) show a neurogenic pattern with small and angular muscle fibers. However, the first biopsy (B and C) shows many cytochrome c oxidase–deficient large fibers, while the second biopsy obtained 9 months later shows generalized cytochrome c oxidase deficiency (E and F) (original magnification ×25).

Light microscopic image of sequential muscle biopsies from patient 6. Both the first biopsy (A) and the second (D) show a neurogenic pattern with small and angular muscle fibers. However, the first biopsy (B and C) shows many cytochrome c oxidase–deficient large fibers, while the second biopsy obtained 9 months later shows generalized cytochrome c oxidase deficiency (E and F) (original magnification ×25).

Table. 
Characteristics of Seven Patients With Amyotrophic Lateral Sclerosis and Severe Oxidative Defects
Characteristics of Seven Patients With Amyotrophic Lateral Sclerosis and Severe Oxidative Defects
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Magnus  TBeck  MGiess  RPuls  INaumann  MToyka  KV Disease progression in amyotrophic lateral sclerosis: predictors of survival.  Muscle Nerve 2002;25 (5) 709- 714PubMedGoogle ScholarCrossref
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Rosen  DRSiddique  TPatterson  D  et al.  Mutation in Cu/Zn superoxide dismutase gene are associated with familial amyotrophic lateral sclerosis.  Nature 1993;362 (6415) 59- 62PubMedGoogle ScholarCrossref
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Xu  ZJung  CHiggins  CLevine  JKong  J Mitochondrial degeneration in amyotrophic lateral sclerosis.  J Bioenerg Biomembr 2004;36 (4) 395- 399PubMedGoogle ScholarCrossref
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Mahoney  DJKaczor  JJBourgeois  JYasuda  NTarnopolsky  MA Oxidative stress and antioxidant enzyme upregulation in SOD1-G93A mouse skeletal muscle.  Muscle Nerve 2006;33 (6) 809- 816PubMedGoogle ScholarCrossref
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Chen  YZBennett  CLHuynh  HM  et al.  DNA/RNA helicase gene mutations in a form of juvenile amyotrophic lateral sclerosis (ALS4).  Am J Hum Genet 2004;74 (6) 1128- 1135PubMedGoogle ScholarCrossref
6.
Hadano  SHand  CKOsuga  H  et al.  A gene encoding a putative GTPase regulator is mutated in familial amyotrophic lateral sclerosis 2.  Nat Genet 2001;29 (2) 166- 173PubMedGoogle ScholarCrossref
7.
Yang  YHentati  ADeng  HX  et al.  The gene encoding alsin, a protein with three guanine-nucleotide exchange factor domains, is mutated in a form of recessive amyotrophic lateral sclerosis.  Nat Genet 2001;29 (2) 160- 165PubMedGoogle ScholarCrossref
8.
Puls  IJonnakuty  CLaMonte  BH  et al.  Mutant dynactin in motor neuron disease.  Nat Genet 2003;33 (4) 455- 456PubMedGoogle ScholarCrossref
9.
Greenway  MJAndersen  PMRuss  C  et al.  ANG mutations segregate with familial and ‘sporadic’ amyotrophic lateral sclerosis.  Nat Genet 2006;38 (4) 411- 413PubMedGoogle ScholarCrossref
10.
Nishimura  ALMitne-Neto  MSilva  HC  et al.  A mutation in the vesicle-trafficking protein VAPB causes late-onset spinal muscular atrophy and amyotrophic lateral sclerosis.  Am J Hum Genet 2004;75 (5) 822- 831PubMedGoogle ScholarCrossref
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Wiedemann  FRManfredi  GMawrin  CBeal  MFSchon  EA Mitochondrial DNA and respiratory chain function in spinal cords of ALS patients.  J Neurochem 2002;80 (4) 616- 625PubMedGoogle ScholarCrossref
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Gitcho  MABaloh  RHChakraverty  S  et al.  TDP-43 A315T mutation in familial motor neuron disease.  Ann Neurol 2008;63 (4) 535- 538PubMedGoogle ScholarCrossref
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Corrado  LRatti  AGellera  C  et al.  High frequency of TARDBP gene mutations in Italian patients with amyotrophic lateral sclerosis.  Hum Mutat 2009;30 (4) 688- 694PubMedGoogle ScholarCrossref
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Sreedharan  JBlair  IPTripathi  VB  et al.  TDP-43 mutations in familial and sporadic amyotrophic lateral sclerosis.  Science 2008;319 (5870) 1668- 1672PubMedGoogle ScholarCrossref
15.
Kwiatkowski  TJ  JrBosco  DALeClerc  AL  et al.  Mutations in the FUS/TLS gene on chromosome 16 cause familial amyotrophic lateral sclerosis.  Science 2009;323 (5918) 1205- 1208PubMedGoogle ScholarCrossref
16.
Vance  CRogelj  BHortobágyi  T  et al.  Mutations in FUS, an RNA processing protein, cause familial amyotrophic lateral sclerosis type 6.  Science 2009;323 (5918) 1208- 1211PubMedGoogle ScholarCrossref
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Corcia  PMayeux-Portas  VKhoris  J  et al. French ALS Research Group. Amyotrophic Lateral Sclerosis, Abnormal SMN1 gene copy number is a susceptibility factor for amyotrophic lateral sclerosis.  Ann Neurol 2002;51 (2) 243- 246PubMedGoogle ScholarCrossref
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Lacomblez  LDoppler  VBeucler  I  et al.  APOE: a potential marker of disease progression in ALS.  Neurology 2002;58 (7) 1112- 1114PubMedGoogle ScholarCrossref
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Andersen  PM Genetics of sporadic ALS.  Amyotroph Lateral Scler Other Motor Neuron Disord 2001;2 ((suppl 1)) S37- S41PubMedGoogle ScholarCrossref
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Rizzardini  MMangolini  ALupi  MUbezio  PBendotti  CCantoni  L Low levels of ALS-linked Cu/Zn superoxide dismutase increase the production of reactive oxygen species and cause mitochondrial damage and death in motor neuron-like cells.  J Neurol Sci 2005;232 (1-2) 95- 103PubMedGoogle ScholarCrossref
21.
Bendotti  CCalvaresi  NChiveri  L  et al.  Early vacuolation and mitochondrial damage in motor neurons of FALS mice are not associated with apoptosis or with changes in cytochrome oxidase histochemical reactivity.  J Neurol Sci 2001;191 (1-2) 25- 33PubMedGoogle ScholarCrossref
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Simpson  EPYen  AAAppel  SH Oxidative stress: a common denominator in the pathogenesis of amyotrophic lateral sclerosis.  Curr Opin Rheumatol 2003;15 (6) 730- 736PubMedGoogle ScholarCrossref
23.
Appel  SH Is ALS a systemic disorder? evidence from muscle mitochondria.  Exp Neurol 2006;198 (1) 1- 3PubMedGoogle ScholarCrossref
24.
Dupuis  LGonzalez de Aguilar  JLEchaniz-Laguna  A  et al.  Muscle mitochondrial uncoupling dismantles neuromuscular junction and triggers distal degeneration of motor neurons.  PLoS One 2009;4 (4) e5390PubMedGoogle ScholarCrossref
25.
Echaniz-Laguna  AZoll  JRibera  F  et al.  Mitochondrial respiratory chain function in skeletal muscle of ALS patients.  Ann Neurol 2002;52 (5) 623- 627PubMedGoogle ScholarCrossref
26.
Krasnianski  ADeschauer  MNeudecker  S  et al.  Mitochondrial changes in skeletal muscle in amyotrophic lateral sclerosis and other neurogenic atrophies.  Brain 2005;128 (pt 8) 1870- 1876PubMedGoogle ScholarCrossref
27.
Siklós  LEngelhardt  JHarati  YSmith  RGJoó  FAppel  SH Ultrastructural evidence for altered calcium in motor nerve terminals in amyotrophic lateral sclerosis.  Ann Neurol 1996;39 (2) 203- 216PubMedGoogle ScholarCrossref
28.
Przedborski  S Programmed cell death in amyotrophic lateral sclerosis: a mechanism of pathogenic and therapeutic importance.  Neurologist 2004;10 (1) 1- 7PubMedGoogle ScholarCrossref
29.
Atsumi  T The ultrastucture of intramuscular nerves in amyotrophic lateral sclerosis.  Acta Neuropathol 1981;55 (3) 193- 198PubMedGoogle ScholarCrossref
30.
Sasaki  SIwata  M Ultrastructural study of synapses in the anterior neurons of patients with amyotrophic lateral sclerosis.  Neurosci Lett 1996;204 (1-2) 53- 56PubMedGoogle ScholarCrossref
31.
Afifi  AKAleu  FPGoodgold  JMacKay  B Ultrastructure of atrophic muscle in amyotrophic lateral sclerosis.  Neurology 1966;16 (5) 475- 481PubMedGoogle ScholarCrossref
32.
Sasaki  SIwata  M Mitochondrial alterations in the spinal cord of patients with sporadic amyotrophic lateral sclerosis.  J Neuropathol Exp Neurol 2007;66 (1) 10- 16PubMedGoogle ScholarCrossref
33.
Comi  GPBordoni  ASalani  S  et al.  Cytochrome c oxidase subunit I microdeletion in a patient with motor neuron disease.  Ann Neurol 1998;43 (1) 110- 116PubMedGoogle ScholarCrossref
34.
Hirano  MAngelini  CMontagna  P  et al.  Amyotrophic lateral sclerosis with ragged red fibres.  Arch Neurol 2008;65 (3) 403- 406PubMedGoogle ScholarCrossref
35.
Brooks  BR El Escorial World Federation of Neurology criteria for the diagnosis of amyotrophic lateral sclerosis: Subcommittee on Motor Neuron Diseases/Amyotrophic Lateral Sclerosis of the World Federation of Neurology Research Group on Neuromuscular Diseases and the El Escorial Clinical Limits of Amyotrophic Lateral Sclerosis workshop contributors.  J Neurol Sci 1994;124 ((suppl)) 96- 107PubMedGoogle ScholarCrossref
36.
Dubowitz  V Muscle Biopsy: A Practical Approach. 2nd ed. London, England Bailliere Tindal1985;
37.
Sciacco  MPrelle  AComi  GP  et al.  Retrospective study of a large population of patients affected with mitochondrial disorders: clinical, morphological and molecular genetic evaluation.  J Neurol 2001;248 (9) 778- 788PubMedGoogle ScholarCrossref
38.
Rustin  PChretien  DBourgeron  T  et al.  Biochemical and molecular investigations in respiratory chain deficiencies.  Clin Chim Acta 1994;228 (1) 35- 51PubMedGoogle ScholarCrossref
39.
Andersen  PMSims  KBXin  WW  et al.  Sixteen novel mutations in the Cu/Zn superoxide dismutase gene in amyotrophic lateral sclerosis: a decade of discoveries, defects and disputes.  Amyotroph Lateral Scler Other Motor Neuron Disord 2003;4 (2) 62- 73PubMedGoogle ScholarCrossref
40.
Strong  MJVolkening  KHammond  R  et al.  TDP43 is a human low molecular weight neurofilament (hNFL) mRNA-binding protein.  Mol Cell Neurosci 2007;35 (2) 320- 327PubMedGoogle ScholarCrossref
41.
Corti  SDonadoni  CRonchi  D  et al.  Amyotrophic lateral sclerosis linked to a novel SOD1 mutation with muscle mitochondrial dysfunction.  J Neurol Sci 2009;276 (1-2) 170- 174PubMedGoogle ScholarCrossref
42.
Rubio-Gozalbo  MESmeitink  JARuitenbeek  W  et al.  Spinal muscular atrophy-like picture, cardiomyopathy and cytochrome c oxidase deficiency.  Neurology 1999;52 (2) 383- 386PubMedGoogle ScholarCrossref
43.
Finsterer  J Mitochondriopathy mimicking amyotrophic lateral sclerosis.  Neurologist 2003;9 (1) 45- 48PubMedGoogle ScholarCrossref
44.
Fetoni  VBriem  ECarrara  FMora  MZeviani  M Monomelic amyotrophy associated with the 7472insC mutation in the mtDNA tRNA ser(UCN) gene.  Neuromuscul Disord 2004;14 (11) 723- 726PubMedGoogle ScholarCrossref
45.
Borthwick  GMTaylor  RWWalls  TJ  et al.  Motoneuron disease in a patient with a mitochondrial tRNA ile mutation.  Ann Neurol 2006;59 (3) 570- 574PubMedGoogle ScholarCrossref
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Johnston  WKarpati  GCarpenter  SArnold  DShoubridge  EA Late-onset mitochondrial myopathy.  Ann Neurol 1995;37 (1) 16- 23PubMedGoogle ScholarCrossref
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Virgilio  RRonchi  DHadjigeorgiou  GM  et al.  Novel Twinkle (PEO1) gene mutations in mendelian progressive external ophthalmoplegia.  J Neurol 2008;255 (9) 1384- 1391PubMedGoogle ScholarCrossref
48.
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Echaniz-Laguna  AZoll  JPonsot  E  et al.  Muscular mitochondrial function in amyotrophic lateral sclerosis is progressively altered as the disease develops: a temporal study in man.  Exp Neurol 2006;198 (1) 25- 30PubMedGoogle ScholarCrossref
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Original Contribution
July 2010

Mitochondrial Respiratory Chain Dysfunction in Muscle From Patients With Amyotrophic Lateral Sclerosis

Author Affiliations

Author Affiliations: Department of Neurological Sciences, “Dino Ferrari” Center, Università degli Studi di Milano, Scientific Institute for Research and Treatment (IRCCS) Foundation Ospedale Maggiore Policlinico, Mangiagalli and Regina Elena (Drs Crugnola, Lamperti, Lucchini, Ronchi, Peverelli, Prelle, Sciacco, Fassone, Corti, Bresolin, Comi, and Moggio; Ms Bordoni; and Mr Fortunato); and Department of Neurology and Laboratory of Neuroscience, “Dino Ferrari” Center, Università degli Studi di Milano, IRCCS Istituto Auxologico Italiano (Dr Silani), Milan, Italy; and Department of Neurology, Columbia University Medical Center, New York, New York (Dr Di Mauro).

Arch Neurol. 2010;67(7):849-854. doi:10.1001/archneurol.2010.128
Abstract

Background  Amyotrophic lateral sclerosis (ALS) is a major cause of neurological disability and its pathogenesis remains elusive despite a multitude of studies. Although defects of the mitochondrial respiratory chain have been described in several ALS patients, their pathogenic significance is unclear.

Objective  To review systematically the muscle biopsy specimens from patients with typical sporadic ALS to search for possible mitochondrial oxidative impairment.

Design  Retrospective histochemical, biochemical, and molecular studies of muscle specimens.

Setting  Tertiary care university.

Subjects  Fifty patients with typical sporadic ALS (mean age, 55 years).

Main Outcome Measure  Number of patients showing a clear muscle mitochondrial dysfunction assessed through histochemical and biochemical muscle analysis.

Results  Histochemical data showed cytochrome c oxidase (COX)–negative fibers in 46% patients. Based on COX histochemical activity, patients fell into 4 groups: 27 had normal COX activity; and 8 had mild (2-4 COX-negative fibers of 100 fibers), 8 had moderate (5-10 COX-negative fibers of 100), and 7 had severe (>10 COX-negative fibers of 100) COX deficiency. Spectrophotometric measurement of respiratory chain activities showed that 3 patients with severe histochemical COX deficiency also showed combined enzyme defects. In 1 patient, COX deficiency worsened in a second biopsy taken 9 months after the first. Among the patients with severe COX deficiency, one had a new mutation in the SOD1 gene, another a mutation in the TARDBP gene, and a third patient with biochemically confirmed COX deficiency had multiple mitochondrial DNA deletions detectable by Southern blot analysis.

Conclusions  Our data confirm that the histochemical finding of COX-negative fibers is common in skeletal muscle from patients with sporadic ALS. We did not find a correlation between severity of the oxidative defect and age of the patients or duration of the disease. However, the only patient who underwent a second muscle biopsy did show a correlation between severity of symptoms and worsening of the respiratory chain defect. In 7 patients, the oxidative defect was severe enough to support the hypothesis that mitochondrial dysfunction must play a role in the pathogenesis of the disease.

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder characterized by loss of motor neurons in the anterior horns of the spinal cord, brainstem motor nuclei, and cerebral cortex. The disease usually starts in the fourth or fifth decade of life. Presentation is heterogeneous, and weakness may initially be limited to 1 limb or even to 1 muscle group. As a rule, the disease progresses rapidly and causes widespread paralysis and spasticity.1,2

The prevalence of ALS is approximately 1 to 2 in 100 000 individuals. About 10% of ALS cases are familial, of which 20% are caused by dominant mutations in copper/zinc superoxide dismutase (SOD1), which is encoded by a gene on chromosome 21. Cases of SOD1-associated ALS are due to a toxic gain of function of the enzyme that leads to increased oxidative stress.3 Mice expressing mutant Sod1 develop motor neuron degeneration despite increased SOD1 activity.4

Other genes that are mutated in rarer forms of ALS are involved in DNA repair,5-7 axonal transport,8-10 mitochondrial respiration,11 or gene expression and splicing.12,13 Mutations in the TARDBP gene have been detected in approximately 1% to 5% of patients with familial ALS and approximately 1% of patients with sporadic ALS.14 Recently, mutations in another RNA-binding protein, fused in sarcoma/translated in liposarcoma (FUS/TLS), have been described in familial ALS patients.15,16 It is likely that additional genetic factors predispose individuals to the disease17 or modify its onset and progression.18,19 Oxidative stress results from mitochondrial dysfunction and may play a role in the pathogenesis of ALS by worsening or even initiating the motor neuron injury.20-22 In fact, several reports describe mitochondrial alterations in ALS.23 Transgenic mice with muscular overexpression of uncoupling protein 1, a potent mitochondrial uncoupler, displayed age-dependent deterioration of the neuromuscular junction correlated with progressive signs of denervation and a mild late-onset motor neuron pathology.24 On the other hand, some authors are still questioning the presence of mitochondrial dysfunction.25,26

Motor neuron death might also be caused by calcium-mediated excitotoxicity or by activation of the intrinsic apoptotic pathway.27 Paradoxically, both decreased mitochondrial number and increased mitochondrial mass (with increased intramitochondrial calcium concentrations) have been reported in intramuscular nerves, spinal cord, and skeletal muscles of patients with sporadic ALS.28-30 Abnormal mitochondria were also seen by electron microscopy in muscle31 and in the anterior horn cells of the spinal cord.32

One patient with motor neuron degeneration had severe muscle cytochrome c oxidase (COX) deficiency due to a mutation in the mitochondrial DNA (mtDNA)–encoded subunit I of COX.33 Hirano et al34 have recently reviewed several articles documenting how respiratory chain defects can mimic ALS or spinal muscular atrophy. To assess the importance of mitochondria respiratory chain defects in ALS, we have studied muscle biopsies from a cohort of 50 typical patients.

Methods
Subjects

We studied biceps brachii muscle biopsy specimens from 50 patients (14 women and 36 men ranging in age from 24 to 78 years; mean age, 55 years) with sporadic ALS defined according to El Escorial35 criteria who were admitted to our clinic from 2000 to 2008. Of these specimens, 29 were biopsied within 1 year and 20 within 2 years from onset of the disease. In 1 patient, the first symptoms had appeared 4 years before the muscle biopsy.

For controls, we used biceps brachii muscle biopsy specimens from 8 normal, healthy controls, 10 biopsies from patients with peripheral neuropathy, and 10 biopsies from patients with nonmitochondrial metabolic diseases (5 carnitine palmitoyltransferase II deficiencies, 2 myoadenylate deaminase deficiencies, and 3 glycogenoses). Control muscle samples came from individuals of similar ages as the ALS patients. All specimens were obtained from the DNA, Muscle and Nerve Tissue Bank of the Neurological Unit, Fondazione Ospedale Maggiore, University of Milan, Milan, Italy, with informed consent according to a protocol approved by the institutional review board of Foundation IRCCS Ospedale Maggiore Policlinico, Mangiagalli and Regina Elena, Milan, in compliance with Italian and European Union laws.

Muscle biopsy

Muscle biopsy specimens from the left biceps brachii were frozen in isopentane-cooled liquid nitrogen, and cryostat cross sections were processed according to standard histological techniques.36 Histochemistry for COX, succinic dehydrogenase (SDH), and combined COX/SDH stains were performed as previously described.37

Biochemistry

Mitochondrial respiratory chain enzyme and citrate synthase activities were measured spectrophotometrically in all patients with histochemical evidence of COX deficiency by described assays.38 The specific activity of each complex was normalized to that of citrate synthase.

Molecular genetics

In the 7 patients with severe COX deficiency, we sequenced both the SOD1 gene (OMIM 147450) and mtDNA. We also performed Southern blot analysis of muscle mtDNA.39 Molecular examination for TARDBP (OMIM 605078) was also performed.40 Quantitation of mtDNA was performed using Southern blot analysis as described.

Genomic DNA was extracted from peripheral blood of all patients and used as a template for polymerase chain reaction (PCR) amplification of each of the 5 exons of SOD1. Mitochondrial DNA was PCR-amplified using the VariantSEQr Resequencing System (Applied Biosystem, Foster City, California). All PCR products were purified and directly sequenced using the BigDye Terminator protocol on an automated 3100 ABI Prism Genetic Analyzer (Applied Biosystem). The following nuclear genes were analyzed in patient 7: PEO1, POLG1, POLG2, ANT1, and OPA1.

Results
Clinical and muscle biopsy findings

In all patients, histopathologic examination showed a chronic neurogenic pattern, with small groups of atrophic fibers and fiber-type grouping. Histochemically, COX-negative fibers were observed in 23 patients (46%). The oxidative defect was mild in 8 patients (2-4 COX-negative fibers per 100 fibers), moderate in 8 (5-10 COX-negative fibers per 100), and severe in 7 (>10 COX-negative fibers per 100) (Figure 1). In patient 6, a second muscle biopsy performed 9 months after the first one documented further decreasing of the COX activity (almost all muscle fibers lacked COX activity) (Figure 2). The clinical, morphological and biochemical features of the 7 patients with severe oxidative defects are presented in the Table.

All patients were men; age at onset ranged from 31 to 75 years; and two-thirds of patients were younger than 50 years. At onset, all patients had predominantly lower motor neuron involvement and variable disease severity.

Biochemistry

Respiratory chain enzyme activities were normal in all patients but patients 3, 6, and 7. The enzyme activities were normal in all patients with scattered (<10) COX-negative muscle fibers. In the more severe group, as defined by the presence of more than 10 histochemically deficient COX fibers, the degree of respiratory chain deficiency paralleled the histochemical defect. For example, patients 1, 2, 4, and 5, who had borderline histochemical COX defects, had either normal respiratory chain activities (patients 1, 4, and 5) or showed moderate complex III deficiency (patient 2). On the other hand, patients 3, 6, and 7 showed severe combined deficiencies involving all respiratory chain complexes, but more markedly COX activity (Table). Respiratory complex activities were normal in muscle biopsy from patients with peripheral neuropathy.

Molecular genetics

Besides having severe muscle COX deficiency, patient 2 also harbored a missense mutation (c.65A>G, p.Q22R) in SOD1,41 and patient 4 had an A382T mutation in TARDBP.13 To rule out the presence of rearrangements in mtDNA, we performed a Southern blot analysis and a specific PCR assay on muscle-derived DNA in all patients. Patient 7 showed multiple mtDNA deletions detectable by Southern blot analysis. In this same patient, there were no mutations in PEO1, POLG, POLG2, ANT1, or OPA1. Sequence analysis of the entire mtDNA was performed in all patients belonging to the group with severe histochemical COX deficiency. The nucleotide variations that were found had been reported in the probands' ethnic groups as polymorphisms and are not likely to explain the observed COX deficiency. The Table summarizes the genetic findings in the 7 patients with severe COX deficiency.

Comment

Amyotrophic lateral sclerosis is a major cause of neurological disability and its pathogenesis remains elusive despite a multitude of studies. Because the diagnosis is based on clinical and neurophysiologic criteria, few patients undergo muscle biopsy.

Although defects of the mitochondrial respiratory chain have been described in several ALS patients, their pathogenic significance is unclear. Comi and colleagues33 described a patient with early onset and rapidly progressive motor neuron disease who harbored a heteroplasmic microdeletion of the mtDNA-encoded subunit I of COX. Rubio-Gozalbo et al42 reported on a child with spinal muscular atrophy, cardiomyopathy, and reduced COX activity in muscle and fibroblasts; the absence of mutations in SMN1 and the presence of cardiomyopathy suggest that this child might have had mutations in the COX assembly gene SCO2. Finsterer43 described a mother and 2 daughters with symptoms compatible with ALS. All 3 patients showed COX-negative muscle fibers, ultrastructurally abnormal mitochondria, and no mutations in SOD1, but harbored 3 mtDNA mutations, one in the transfer RNAIle gene, a second in the cytochrome b gene, and the third in the adenosine triphosphatase 6 gene. Fetoni et al44 described a man with monomelic amyotrophy, diabetes mellitus, and COX-negative ragged red fibers in the muscle biopsy. Other family members had maternally inherited hearing loss. A mutation in the transfer RNASer(UCN) gene of mtDNA was found in the patient and in a maternal niece. Borthwick et al45 described a patient with clinical features suggestive of ALS, diabetes mellitus, and cardiac arrhythmia who died of cardiac arrest during the study. Autopsy results showed a normal cortex and corticospinal tracts but numerous COX-deficient motor neurons. Sequencing of mtDNA showed a heteroplasmic mitochondrial transfer RNAIle mutation different from that reported by Finsterer.43 Recently, Hirano and colleagues34 reported on a 65-year-old man with typical ALS in whom muscle biopsy specimens showed 10% ragged red fibers, which were unexpectedly abundant even at his age and suggested mitochondrial dysfunction.

Given the provocative but still anecdotal evidence of mitochondrial involvement in muscle of patients with ALS, we decided to review systematically the remarkable collection of muscle biopsy specimens from patients with typical ALS in our possession. Our histochemical data in 50 patients showed variably severe but unequivocal COX deficiency in 46% of patients, an unexpectedly high proportion. Patients can be divided into 4 groups according to COX histochemical activity: 27 had normal COX activity; and 8 had mild, 8 had moderate, and 7 had severe COX deficiency. When respiratory chain enzyme activities were measured spectrophotometrically in whole muscle extracts, only 3 patients showed combined enzyme defects (Table, patients 3, 6, and 7). In patient 6, COX activity worsened in a second biopsy taken 9 months after the first. The fact that respiratory enzyme analyses in 4 of 7 patients with severe histochemical COX deficiency were normal is not surprising because biochemistry does not accurately reflect the extent of histochemical changes, which are nonetheless significant.34

Notably, among the patients with severe COX deficiency, 1 (patient 2) had a mutation in SOD1 (c.65A>G, p.Q22R),41 another (patient 4) had a mutation in TARDBP,13 whereas another patient (patient 7) with biochemically confirmed COX deficiency had multiple mtDNA deletions detectable by Southern blot analysis, though sequencing all the known nuclear genes associated with multiple mtDNA deletions failed to show any pathogenic mutation. The patient's advanced age may explain this finding, at least in part46; however, a substantial proportion of mtDNA multiple deletion syndromes is not assigned to any known gene.47 Therefore, the possibility of a mutation in a yet unidentified gene cannot be ruled out. Vielhaber et al48 described multiple deletions of mtDNA in 1 patient with sporadic ALS and attributed the mtDNA alteration to the decreased activity of membrane-associated mitochondrial Mn-superoxide dismutase activity, but did not study nuclear genes associated with multiple mtDNA deletions.

Our data confirm that varyingly severe histochemical COX deficiency is a common finding in skeletal muscle from ALS patients and does not correlate with age. In fact, it is noteworthy that most patients with severe COX deficiency by histochemistry (group 4) were in their 30s, 1 was aged 40 years, another was in his 60s, and only 1 was aged 75 years. Paradoxically, the patient with the most severe histochemical COX deficiency was one of the youngest in our cohort (32 years of age at disease onset).

We failed to detect a general correlation between severity of the oxidative defect and duration of the disease. Most patients underwent muscle biopsy within 1 year from the onset of symptoms. However, in the only patient who underwent a second muscle biopsy, we did find a correlation between worsening of the respiratory chain defect and severity of symptoms. Echaniz-Laguna et al49 twice performed biopsies in 7 patients with sporadic ALS and showed worsening of complex IV deficiency in the later biopsies.

In 7 patients, the oxidative defect was severe enough to support the hypothesis that, at least in some cases, mitochondrial dysfunction plays a role in the pathogenesis of the disease. Although aging can cause mitochondrial changes50,51 and onset is typically late in ALS, it is important to note that most of our ALS patients were still young and that the changes we observed were much more pronounced than those described in healthy elderly individuals and were not present in age-matched controls.

The partial oxidative defect in patients with pathogenic mutations in SOD1 (patient 2) and TARDBP (patient 4) further suggests that the COX deficiency may be secondary to identifiable genetic defects. This concept is reinforced by the molecular findings in the single patient with muscle multiple mtDNA deletions, though we could not identify the nuclear gene responsible for this defect of intergenomic signaling.

Correspondence: Maurizio Moggio, MD, Department of Neurological Sciences, Università degli Studi di Milano, IRCCS Foundation Ospedale Maggiore Policlinico, Mangiagalli and Regina Elena, Padiglione Ponti, Via Francesco Sforza 35, 20122 Milan, Italy (maurizio.moggio@unimi.it).

Accepted for Publication: December 18, 2009.

Author Contributions:Study concept and design: Crugnola, Silani, Bresolin, and Moggio. Acquisition of data: Lamperti, Lucchini, Ronchi, Peverelli, Prelle, Sciacco, Bordoni, Fassone, Fortunato, Corti, Silani, Bresolin, and Comi. Analysis and interpretation of data: Lamperti, Ronchi, Prelle, Sciacco, Bordoni, Fortunato, Corti, Silani, Bresolin, Di Mauro, and Comi. Drafting of the manuscript: Lamperti, Ronchi, Prelle, Sciacco, Bordoni, Fortunato, Corti, and Comi. Critical revision of the manuscript for important intellectual content: Crugnola, Lamperti, Lucchini, Peverelli, Prelle, Sciacco, Fassone, Corti, Silani, Bresolin, Di Mauro, Comi, and Moggio. Administrative, technical, and material support: Lucchini, Ronchi, Peverelli, Bordoni, Fassone, Fortunato, Silani, and Bresolin. Study supervision: Crugnola, Lamperti, Prelle, Sciacco, Corti, Silani, Bresolin, Di Mauro, Comi, and Moggio.

Financial Disclosure: None reported.

Funding/Support: This research received support from Associazione Amici del Centro Dino Ferrari. Dr Comi received funding from research grant Progetti Ricerca Interesse Nazionale (PRIN) 2006 2006069034 from the Italian Ministry of University and Research for the project entitled “An Integrated Approach to the Study of the Etiopathogenesis of Mitochondrial Disorders.” Dr Comi was also funded by the Italian Ministry of Health for the 2009 project entitled “Mitochondrial Disorders: From Medical Genetics to Molecular Mechanisms, Toward the Development of Therapeutic Strategies.” The Telethon Network of Genetics Biobanks (Genetic Telethon Biobank No. 07001E) was the source of muscle, DNA, and cells used in this study. EuroBioBank project QLTR-2001-02769 is also gratefully acknowledged.

Additional Contributions: We wish to thank the patients and their families for their support and collaboration.

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