Salvatore Di Mauro

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

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.

Two cases of prenatal analysis for the pathogenic T to G substitution at nucleotide 8993 in mitochondrial DNA

We report the outcome of two prenatal analyses for the T to G mutation at nucleotide 8993 in the mitochondrial DNA. This mutation is associated with neurogenic muscle weakness, ataxia and retinitis pigmentosa (NARP) and the neurodegenerative condition, Leigh syndrome. One prospective mother was the sister of a severely affected individual, and had previously had an unaffected child and a stillborn child. The second prospective mother had two unaffected children and two affected children. The mutation was not detected in the chorionic villus sample from one fetus nor in the amniocytes from the other fetus. Both pregnancies were continued, and the resulting children were healthy at two years and five years of age. Prenatal diagnosis of this mitochondrial DNA mutation is an option likely to be acceptable to some families to prevent the birth of a child at high risk for neurological disease. Copyright

Hepatocerebral Form of Mitochondrial DNA Depletion Syndrome: Novel MPV17 Mutations

BACKGROUND Autosomal recessive mutations in MPV17 (OMIM *137960) have been identified in the hepatocerebral form of mitochondrial DNA depletion syndrome (MDS). OBJECTIVE To describe the clinical, morphologic, and genetic findings in 3 children with MPV17-related MDS from 2 unrelated families. DESIGN Case report. SETTING Academic research. MAIN OUTCOME MEASURES We identified 3 novel pathogenic mutations in 3 children. RESULTS Two children were homozygous for nonsense mutation p.W120X. A third child was compound heterozygous for missense mutation p.G24W and for a macrodeletion spanning MPV17 exon 8. All patients demonstrated lactic acidosis, hypoglycemia, hepatomegaly, and progressive liver failure. Neurologic symptoms manifested at a later stage of the disease. Death occurred within the first year of life in all 3 patients. CONCLUSIONS These data confirm that MPV17 mutations are associated with a 2-stage syndrome. The first symptoms are metabolic and rapidly progress to hepatic failure. This stage is followed by neurologic involvement affecting the central and peripheral systems.

Ultrastructural mitochondrial abnormalities in patients with sporadic amyotrophic lateral sclerosis

A large number of neurodegenerative diseases are caused by impairment of mitochondrial function. Mutations in genes that encode proteins responsible for the shape and dynamics of mitochondria have been associated with some genetic neurodegenerative diseases, which implies that mitochondrial shape plays an important role in the health of neurons and muscle. Neurons are highly dependent on mitochondria because they have high energy demands and are unable to switch to glycolysis when mitochondrial oxidative phosphorylation is impaired. An ultrastructural hallmark of the synapse is the abundance of mitochondria, which are essential to maintaining calcium homeostasis and adequate levels of adenosine triphosphate (critical for nerve transmission). Neurons have extraordinarily long cellular processes, and tight control of mitochondrial dynamics facilitates the distribution of active mitochondria to dendrites and axon terminals. Higgins et al described vacuolated mitochondria in the early phases of motor neuron degeneration in transgenic mice with familial amyotrophic lateral sclerosis (ALS) and the SOD1 gene; they found that mutant SOD1 extends the outer mitochondrial membrane and expands the intermembrane space. Much less is known about the involvement of mitochondria in muscle of patients with ALS. Defects of the mitochondrial respiratory chain have been described in several patients with ALS. Comi and colleagues described a patient with early-onset and rapidly progressive motor neuron disease who harbored a heteroplasmic microdeletion of the mitochondrial DNA (mtDNA)– encoded subunit I of cytochrome-c oxidase (COX). Finsterer described a mother and 2 daughters with symptoms compatible with ALS. All 3 patients showed COXnegative muscle fibers, ultrastructurally abnormal mitochondria, and no mutations in SOD1, but they all harbored 3 mtDNA mutations, one in the transfer RNA gene, one in the cytochrome b gene, and one in the adenosine triphosphatase 6 gene. Recently, we reviewed the muscle biopsy specimens from 50 patients with typical sporadic ALS. Histochemical data showed variably severe COX deficiency in 23 of the 50 patients (46%). Of these 23 patients, 7 (30%) showed severe deficiency ( 10 COX-negative fibers of 100), and in these 7 patients, the biochemical defect of respiratory chain enzymes paralleled the histochemical defect.