Multiple respiratory chain abnormalities associated with hypertrophic cardiomyopathy and 3-methylglutaconic aciduria

MEGDEL Syndrome in a Child From Palestine: Report of a Novel Mutation in SERAC1 Gene

We report the first Palestinian child manifesting with 3-methylglutaconic aciduria psychomotor delay, muscle hypotonia, sensori-neural deafness, and Leigh-like lesions on brain magnetic resonance imaging (MRI), a clinical phenotype that is characteristic of MEGDEL syndrome. MEGDEL syndrome was recently found to be caused by mutations in SERAC1, encoding a protein essential for mitochondrial function, phospholipid remodeling, and intracellular cholesterol trafficking. We identified a novel homozygous mutation in SERAC1 gene (c.1018delT) that generates frame shift and premature termination of protein translation. Plasma and cerebrospinal fluid lactate, plasma alanine, and respiratory chain complexes in fresh muscle were normal. This report further expands the genetic spectrum of MEGDEL syndrome and adds to the evidence that it is associated with variable patterns of respiratory chain abnormalities.

3-Methylglutaconyl-Coenzyme-A Hydratase Deficiency and the Development of Dilated Cardiomyopathy

A 25-year-old Canadian male with a history of 3-methylglutaconyl-coenzyme-A hydratase deficiency, also known as 3-methylglutaconic aciduria type I, a very rare inborn error of metabolism, presented with respiratory distress, nausea, vomiting and signs of multisystem organ failure due to a suspected underlying infectious process. An electrocardiogram revealed bilateral atrial enlargement and an elevated brain natriuretic peptide on the initial laboratory studies, which prompted a more thorough cardiac workup. The transthoracic echocardiogram revealed a dilated cardiomyopathy with severe systolic dysfunction. The deficient enzyme present in this patient is involved in the pathway of leucine catabolism and is particularly important in various tissues for energy production and sterol synthesis. The dilated cardiomyopathy in this patient possibly had a variety of potential mechanisms including: a mitochondrial myopathy due to the deficiency of this enzyme leading to a defect in energy production inside cardiac myocytes; or a direct toxicity from 3-methylglutaconic acid (3-MGA) and its toxic metabolites; or a cardiac dysfunction due to a variety of other potential mechanisms. In conclusion, this patient’s clinical presentation suggested that 3-methylglutaconyl-CoA hydratase deficiency could cause a severe dilated cardiomyopathy and heart failure.

Two novel compound heterozygous mutations in OPA3 in two siblings with OPA3-related 3-methylglutaconic aciduria

OPA3-related 3-methylglutaconic aciduria, or Costeff Optic Atrophy syndrome, is a neuro-ophthalmologic syndrome of early-onset bilateral optic atrophy and later-onset spasticity, and extrapyramidal dysfunction. Urinary excretion of 3-methylglutaconic acid and of 3-methylglutaric acid is markedly increased. OPA3-related 3-methylglutaconic aciduria is due to mutations in the OPA3 gene located at 19q13.2-13.3. Here we describe two siblings with novel compound heterozygous variants in OPA3: c.1A>G (p.1M>V) in the translation initiation codon in exon 1 and a second variant, c.142+5G>C in intron 1. On cDNA sequencing the c.1A>G appeared homozygous, indicating that the allele without the c.1A>G variant is degraded. This is likely due to an intronic variant; possibly the IVS1+5 splice site variant. The older female sibling initially presented with motor developmental delay and vertical nystagmus during her first year of life and was diagnosed subsequently with optic atrophy. Her brother presented with mildly increased hip muscle tone followed by vertical nystagmus within the first 6 months of life, and was found to have elevated urinary excretion of 3-methylglutaconic acid and 3-methylglutaric acid, and optic atrophy by 1.5 years of age. Currently, ages 16 and 7, both children exhibit ataxic gaits and dysarthric speech. Immunofluorescence studies on patient's cells showed fragmented mitochondrial morphology. Thus, though the exact function of OPA3 remains unknown, our experimental results and clinical summary provide evidence for the pathogenicity of the identified OPA3 variants and provide further evidence for a mitochondrial pathology in this disease.

The 3-methylglutaconic acidurias: what's new?

The heterogeneous group of 3-methylglutaconic aciduria (3-MGA-uria) syndromes includes several inborn errors of metabolism biochemically characterized by increased urinary excretion of 3-methylglutaconic acid. Five distinct types have been recognized: 3-methylglutaconic aciduria type I is an inborn error of leucine catabolism; the additional four types all affect mitochondrial function through different pathomechanisms. We provide an overview of the expanding clinical spectrum of the 3-MGA-uria types and provide the newest insights into the underlying pathomechanisms. A diagnostic approach to the patient with 3-MGA-uria is presented, and we search for the connection between urinary 3-MGA excretion and mitochondrial dysfunction.

OPA3, mutated in 3-methylglutaconic aciduria type III, encodes two transcripts targeted primarily to mitochondria

3-Methylglutaconic aciduria type III (3-MGCA type III), caused by recessive mutations in the 2-exon gene OPA3, is characterized by early-onset bilateral optic atrophy, later-onset extrapyramidal dysfunction, and increased urinary excretion of 3-methylglutaconic acid and 3-methylglutaric acid. Here we report the identification of a novel third OPA3 coding exon, the apparent product of a segmental duplication event, resulting in two gene transcripts, OPA3A and OPA3B. OPA3A deficiency (as in optic atrophy type 3) causes up-regulation of OPA3B. OPA3 protein function remains unknown, but it contains a putative mitochondrial leader sequence, mitochondrial sorting signal and a peroxisomal sorting signal. Our green fluorescent protein tagged OPA3 expression studies found its localization to be predominantly mitochondrial. These findings thus place the cellular metabolic defect of 3-MGCA type III in the mitochondrion rather than the peroxisome and implicate loss of OPA3A rather than gain of OPA3B in disease etiology.

Induction of oxidative stress by the metabolites accumulating in 3-methylglutaconic aciduria in cerebral cortex of young rats

3-methylglutaconic (MGT), 3-methylglutaric (MGA) and occasionally 3-hydroxyisovaleric (OHIVA) acids accumulate in a group of diseases known as 3-methylglutaconic aciduria (MGTA). Although the clinical presentation of MGTA is mainly characterized by neurological symptoms, the mechanisms of brain damage in this disease are poorly known. In the present study we investigated the in vitro effect of MGT, MGA and OHIVA on various parameters of oxidative stress in cerebral cortex from young rats. Thiobarbituric acid-reactive substances (TBA-RS) and chemiluminescence were significantly increased by MGT, MGA and OHIVA, indicating that these metabolites induce lipid oxidative damage. Furthermore, the addition of melatonin, alpha-tocopherol and superoxide dismutase plus catalase fully prevented MGT-induced increase on TBA-RS, suggesting that free radicals were involved in this effect. These metabolites also provoked protein oxidative damage determined by increased carbonyl formation and sulfhydryl oxidation, but did not induce superoxide generation in submitochondrial particles. It was also verified that MGA and MGT significantly decreased the non-enzymatic antioxidant defenses in cerebral cortex supernatants and that melatonin and alpha-tocopherol totally blocked MGA-induced GSH reduction. The data indicate that the metabolites accumulating in MGTA elicit oxidative stress in vitro in the cerebral cortex. It is therefore presumed that this pathomechanism may be involved in the brain damage observed in patients affected by MGTA.

3-methyglutaconic aciduria in a Chinese patient with glycogen storage disease Ib

We report elevated urinary excretion of 3-methylglutaconic (3MGC) and 3-methylglutaric acids (3MGR) in a patient with glycogen storage disease Ib. Combined excretion was 10-fold elevated in comparison to control during inadequate glucose maintenance, and still elevated following dietary improvement. 3MGC acid excretion correlated with plasma lactate and glucose. We speculate that imbalanced gluconeogenesis and de novo cholesterol synthesis result in secondarily increased 3MGC/3MGR production.

Neonatal presentation of ventricular tachycardia and a Reye-like syndrome episode associated with disturbed mitochondrial energy metabolism

BACKGROUND

Hyperammonemia, hypoglycemia, hepatopathy, and ventricular tachycardia are common presenting features of carnitine-acylcarnitine translocase deficiency (Mendelian Inheritance in Man database: *212138), a mitochondrial fatty acid oxidation disorder with a lethal prognosis. These features have not been identified as the presenting features of mitochondrial cytopathy in the neonatal period.

CASE PRESENTATION

We describe an atypical presentation of mitochondrial cytopathy in a 2 day-old neonate. She presented with a Reye-like syndrome episode, premature ventricular contractions and ventricular tachycardia. Initial laboratory evaluation exhibited a large amount of 3-methylglutaconic acid on urine organic acid analysis, mild orotic aciduria and a nonspecific abnormal acylcarnitine profile. The evaluation for carnitine-acylcarnitine translocase deficiency and other fatty acid oxidation disorders was negative. The patient later developed a hypertrophic cardiomyopathy and continued to be affected by recurrent Reye-like syndrome episodes triggered by infections. A muscle biopsy exhibited signs of a mitochondrial cytopathy. During the course of her disease, her Reye-like syndrome episodes have subsided; however, cardiomyopathy has persisted along with fatigue and exercise intolerance.

CONCLUSIONS

This case illustrates that, in the neonatal period, hyperammonemia and ventricular tachycardia may be the presenting features of a lethal carnitine-acylcarnitine translocase deficiency or of a mitochondrial cytopathy, associated with a milder clinical course. This association broadens the spectrum of presenting phenotypes observed in patients with disturbed mitochondrial energy metabolism. Also, the presence of 3-methylglutaconic aciduria suggests mitochondrial dysfunction and mild orotic aciduria could potentially be used as a marker of mitochondrial disease.

Defects in mitochondrial respiratory complexes III and IV, and human pathologies

Here, relationships between alterations in tissue-specific content, protein structure, activity, and/or assembly of respiratory complexes III and IV induced by mutations in corresponding genes and various human pathologies are reviewed. Cytochrome bc(1) complex and cytochrome c oxidase (COX) deficiencies have been detected in a heterogeneous group of neuromuscular and non-neuromuscular diseases in childhood and adulthood, presenting a number of clinical phenotypes of variable severity. Such disorders can be caused by mutations located either in mitochondrial genes or in nuclear genes encoding structural subunits of the complexes or corresponding assembly factors/chaperones. Of the defects in mitochondrial DNA genes, mutations in cytochrome b subunit of complex III, and in structural subunits I-III of COX have been described to date. As to defects in nuclear DNA genes, mutations in genes encoding the complexes assembly factors such as the BCS1L protein for complex III; and SURF-1, SCO1, SCO2, and COX10 for complex IV have been identified so far.

Type III 3-methylglutaconic aciduria (optic atrophy plus syndrome, or Costeff optic atrophy syndrome): identification of the OPA3 gene and its founder mutation in Iraqi Jews

Type III 3-methylglutaconic aciduria (MGA) (MIM 258501) is a neuro-ophthalmologic syndrome that consists of early-onset bilateral optic atrophy and later-onset spasticity, extrapyramidal dysfunction, and cognitive deficit. Urinary excretion of 3-methylglutaconic acid and of 3-methylglutaric acid is increased. The disorder has been reported in approximately 40 patients of Iraqi Jewish origin, allowing the mapping of the disease to chromosome 19q13.2-q13.3, by linkage analysis. To isolate the causative gene, OPA3, we sequenced four genes within the critical interval and identified, in the intronic sequence of a gene corresponding to cDNA clone FLJ22187, a point mutation that segregated with the type III MGA phenotype. The FLJ22187-cDNA clone, which we identified as the OPA3 gene, consists of two exons and encodes a peptide of 179 amino acid residues. Northern blot analysis revealed a primary transcript of approximately 5.0 kb that was ubiquitously expressed, most prominently in skeletal muscle and kidney. Within the brain, the cerebral cortex, the medulla, the cerebellum, and the frontal lobe, compared to other parts of the brain, had slightly increased expression. The intronic G-->C mutation abolished mRNA expression in fibroblasts from affected patients and was detected in 8 of 85 anonymous Israeli individuals of Iraqi Jewish origin. Milder mutations in OPA3 should be sought in patients with optic atrophy with later onset, even in the absence of additional neurological abnormalities.

Barth's syndrome-like disorder: a new phenotype with a maternally inherited A3243G substitution of mitochondrial DNA (MELAS mutation)

An Argentine male child died at 4.5 years of age of a lethal mitochondrial disease associated with a MELAS mutation and a Barth syndrome-like presentation. The child had severe failure to thrive from the early months and for approximately two years thereafter. In addition, the patient had severely delayed gross motor milestones, marked muscle weakness, and dilated cardiomyopathy that progressed to congestive heart failure. He also had persistently elevated urinary levels of 3-methylglutaconic and 2-ethylhydracrylic acids and low blood levels of cholesterol. Detailed histopathologic evaluation of the skeletal muscle biopsy showed high activity of succinate dehydrogenase, a generalized decrease of COX activity, and abundant ragged-red fibers. Electron microscopic studies revealed multiple mitochondrial abnormalities in lymphocytes and monocytes, in the striated muscle, and in the postmortem samples (muscle, heart, liver, and brain). Biochemical analysis showed a pronounced and constant lactic acidosis, and abnormal urinary organic acid excretion (unchanged in the fasting and postprandial states). In addition, in CSF there was a marked increase of lactate and beta-hydroxybutyrate (beta-HOB) and also a high systemic ratio beta-HOB/acetoacetate. Enzymatic assay of the respiratory chain in biopsied muscle showed 10% of complex I activity and 24% of complex IV activity compared with controls. Molecular studies of the mitochondrial genome revealed an A to G mutation at nucleotide pair 3243 in mitochondrial DNA, a well-known pathogenetic mutation (MELAS mutation) in all the patient's tissues and also in the blood specimens of the probands mother and sibs (4 of 5). The diagnosis of MELAS mutation was reinforced by the absence of an identifiable mutation in the X-linked G4.5 gene of the propositus. The present observation gives additional evidence of the variable clinical expression of mtDNA mutations in humans and demonstrates that all clinical variants deserve adequate investigation to establish a primary defect. It also suggests adding Barth-like syndrome to the list of phenotypes with the MELAS mutation.

X-linked cardioskeletal myopathy and neutropenia (Barth syndrome) (MIM 302060)

X-linked cardioskeletal myopathy, neutropenia and abnormal mitochondria (MIM 302060) (synonyms: Barth syndrome, 3-methylglutaconic acid-uria type II, endocardial fibroelastosis type 2) has been reported in patients and families from Europe, North America and Australia. Previous studies characterized the main components of the disease: dilated cardiomyopathy, skeletal myopathy, neutropenia, 3-methylglutaconic aciduria and diminished statural growth. Respiratory chain impairments have been found in several studies, without pinpointing a single enzyme complex. 3-Methylglutaconic aciduria is shared with several other disorders that affect the respiratory chain. Previous studies excluded a block in the major pathway of leucine catabolism. We performed leucine loading, accompanied by fasting, in patients and observed a significant rise of 3-methylglutaconic acid and 3-methylglutaric acid. Taken together with the absence of an enzymatic block in the major leucine catabolic route, the possibility remains that the increased basal excretion of 3-methylglutaconic acid and other products of branched-chain amino acids is the result of overload of this pathway or--more likely--mitochondrial leakage. Linkage studies have localized the gene to the Xq28 region. The associated tafazzin gene (TAZ), has been fully characterized recently, and mutations located in conserved regions have been reported. Carrier detection and prenatal diagnosis have now become possible through mutation analysis. Sequence homology of the TAZ gene to a highly conserved superclass of acyltransferases (Neuwald's hypothesis) predicts a glycerophospholipid as the missing end product. This points to the (lipid) structure of the inner mitochondrial membrane as a promising new area of research.

Mitochondrial disease in superoxide dismutase 2 mutant mice

Oxidative stress has been implicated in many diseases. The chief source of reactive oxygen species within the cell is the mitochondrion. We have characterized a variety of the biochemical and metabolic effects of inactivation of the mouse gene for the mitochondrial superoxide dismutase (CD1-Sod2(tm1Cje)). The Sod2 mutant mice exhibit a tissue-specific inhibition of the respiratory chain enzymes NADH-dehydrogenase (complex I) and succinate dehydrogenase (complex II), inactivation of the tricarboxylic acid cycle enzyme aconitase, development of a urine organic aciduria in conjunction with a partial defect in 3-hydroxy-3-methylglutaryl-CoA lyase, and accumulation of oxidative DNA damage. These results indicate that the increase in mitochondrial reactive oxygen species can result in biochemical aberrations with features reminiscent of mitochondrial myopathy, Friedreich ataxia, and 3-hydroxy-3-methylglutaryl-CoA lyase deficiency.

18Fluoro-2-deoxyglucose (18FDG) PET scan of the brain in type IV 3-methylglutaconic aciduria: clinical and MRI correlations

The clinical, 18fluorodeoxyglucose positron emission tomography (18FDG PET) and the magnetic resonance imaging (MRI) brain scan characteristics of four patients diagnosed to have 3-methylglutaconic aciduria were reviewed retrospectively. The disease has a characteristic clinical pattern. The initial presentations were developmental delay, hypotonia, and severe failure to thrive. Later, progressive encephalopathy with rigidity and quadriparesis were observed, followed by severe dystonia and choreoathetosis. Finally, the patients became severely demented and bedridden. The 18FDG PET scans showed progressive disease, explaining the neurological status. It could be classified into three stages. Stage I: absent 18FDG uptake in the heads of the caudate, mild decreased thalamic and cerebellar metabolism. Stage II: absent uptake in the anterior half and posterior quarter of the putamina, mild-moderate decreased uptake in the cerebral cortex more prominently in the parieto-temporal lobes. Progressive decreased thalamic and cerebellar uptake. Stage III: absent uptake in the putamina and severe decreased cortical uptake consistent with brain atrophy and further decrease uptake in the cerebellum. The presence of both structural and functional changes in the brain, demonstrated by the combined use of MRI and 18FDG PET scan, with good clinical correlation, make the two techniques complementary in the imaging evaluation of 3-methylglutaconic aciduria.

Mutation characterization and genotype-phenotype correlation in Barth syndrome

Barth syndrome is an X-linked cardiomyopathy with neutropenia and 3-methylglutaconic aciduria. Recently, mutations in the G4.5 gene, located in Xq28, have been described in four probands with Barth syndrome. We have now evaluated 14 Barth syndrome pedigrees for mutations in G4.5 and have identified unique mutations in all, including four splice-site mutations, three deletions, one insertion, five missense mutations, and one nonsense mutation. Nine of the 14 mutations are predicted to significantly disrupt the protein products of G4.5. The occurrence of missense mutations in exons 3 and 8 suggests that these exons encode essential portions of the G4. 5 proteins, whose functions remain unknown. We found no correlation between the location or type of mutation and any of the clinical or laboratory abnormalities of Barth syndrome, which suggests that additional factors modify the expression of the Barth phenotype. The characterization of mutations of the G4.5 gene will be useful for carrier detection, genetic counseling, and the identification of patients with Barth syndrome who do not manifest all of the cardinal features of this disorder.

A new case of multiple mitochondrial enzyme deficiencies with decreased amount of heat shock protein 60

Heat shock protein 60 (hsp60) is a mitochondrial matrix protein involved in the folding and correct assembly of polypeptides into complex mitochondrial enzymes. Its deficiency has recently been described as the most likely primary cause of congenital lactic acidaemia with multiple mitochondrial enzyme deficiencies in a female patient. We describe a new case of a girl with a substantially decreased amount of hsp60 in cultured fibroblasts. She presented from birth with hypotonia, unusual facial features, feeding difficulties and failure to thrive. Death occurred at age 4.5 years. Biochemical findings included metabolic acidosis with lactic acidaemia, hyperammonaemia and intermittent ketosis. In contrast to the previously reported case, organic acid analysis showed an altered profile throughout her life. In agreement with this profile, various mitochondrial enzyme activities were deficient in cultured fibroblasts, including enzymes of the respiratory chain and the Krebs cycle, the pyruvate dehydrogenase complex and the mitochondrial biotindependent carboxylases. Fibroblast mitochondria showed ultrastructural abnormalities, were swollen, and were mainly localized around the nucleus. The description of a second case of multiple mitochondrial enzyme deficiencies with reduced amount of hsp60 supports the idea that hsp60 deficiency might be a more common cause of mitochondrial disease. This opens new possibilities for the diagnosis and understanding of congenital lactic acidaemia.

A microdeletion in cytochrome c oxidase (COX) subunit III associated with COX deficiency and recurrent myoglobinuria

We have identified a 15-bp microdeletion in a highly conserved region of the mitochondrially encoded gene for cytochrome c oxidase (COX) subunit III in a patient with severe isolated COX deficiency and recurrent myoglobinuria. The mutant mitochondrial DNA (mtDNA) comprised 92% of the mtDNA in muscle and 0.7% in leukocytes. Immunoblots and immunocytochemistry suggested a lack of assembly or instability of the complex. Microdissected muscle fibres revealed significantly higher portions of mutant mtDNA in COX-negative than in COX-positive fibres. This represents the first case of isolated COX deficiency to be defined at the molecular level.

Organic acidurias and related abnormalities

Organic acid analysis is a powerful technique in the diagnosis of inborn errors of metabolism. Since the development of the technique over twenty-five years ago, it has evolved into a sophisticated and powerful method and is an essential tool in the diagnosis of the organic acidurias. The chemistry and biochemistry of organic acids, as well as sample preparation, instrumentation, and many aspects of the more commonly used methods for the analysis of these compounds, are reviewed. The biochemical and clinical characteristics of each of the primary organic acidurias are described. In addition, the various noninherited causes of secondary organic acidurias that lead to the excretion of abnormal organic acids are also described, and ways of differentiating primary from secondary causes are discussed.