Fatal infantile mitochondrial cardiomyopathy and myopathy with heterogeneous tissue expression of combined respiratory chain deficiencies

Clinical manifestations and enzymatic activities of mitochondrial respiratory chain complexes in Pearson marrow-pancreas syndrome with 3-methylglutaconic aciduria: a case report and literature review

Pearson marrow-pancreas syndrome (PS) is a rare mitochondrial disorder. Impaired mitochondrial respiratory chain complexes (MRCC) differ among individuals and organs, which accounts for variable clinical pictures. A subset of PS patients develop 3-methylglutaconic aciduria (3-MGA-uria), but the characteristic symptoms and impaired MRCC remain unknown. Our patient, a girl, developed pancytopenia, hyperlactatemia, steatorrhea, insulin-dependent diabetes mellitus, liver dysfunction, Fanconi syndrome, and 3-MGA-uria. She died from cerebral hemorrhage at 3 years of age. We identified a novel 5.4-kbp deletion of mitochondrial DNA. The enzymatic activities of MRCC I and IV were markedly reduced in the liver and muscle and mildly reduced in skin fibroblasts and the heart. To date, urine organic acid analysis has been performed on 29 PS patients, including our case. Eight patients had 3-MGA-uria, while only one patient did not. The remaining 20 patients were not reported to have 3-MGA-uria. In this paper, we included these 20 patients as PS patients without 3-MGA-uria. PS patients with and without 3-MGA-uria have similar manifestations. Only a few studies have examined the enzymatic activities of MRCC.

CONCLUSION

No clinical characteristics distinguish between PS patients with and without 3-MGA-uria. The correlation between 3-MGA-uria and the enzymatic activities of MRCC remains to be elucidated.

WHAT IS KNOWN

• The clinical characteristics of patients with Pearson marrow-pancreas syndrome and 3-methylglutaconic aciduria remain unknown.

WHAT IS NEW

• No clinical characteristics distinguish between Pearson marrow-pancreas syndrome patients with and without 3-methylglutaconic aciduria.

Association of 3-methylglutaconic aciduria with sensori-neural deafness, encephalopathy, and Leigh-like syndrome (MEGDEL association) in four patients with a disorder of the oxidative phosphorylation

In this paper, we describe a distinct clinical subtype of 3-methylglutaconic aciduria. 3-Methylglutaconic aciduria is a group of different metabolic disorders biochemically characterized by increased urinary excretion of 3-methylglutaconic acid. We performed biochemical and genetic investigations, including urine organic acid analysis, NMR spectroscopy, measurement of 3-methylglutaconyl-CoA hydratase activity, cardiolipin levels, OPA3 gene analysis and measurement of the oxidative phosphorylation in four female patients with 3-methylglutaconic aciduria. 3-Methylglutaconic aciduria type I, Barth syndrome, and Costeff syndrome were excluded as the activity of 3-methylglutaconyl-CoA hydratase, the cardiolipin levels, and molecular analysis of the OPA3 gene, respectively, showed no abnormalities. The children presented with characteristic association of hearing loss and the neuro-radiological evidence of Leigh disease. They also had neonatal hypotonia, recurrent lactic acidemia, episodes with hypoglycemia and severe recurrent infections, feeding difficulties, failure to thrive, developmental delay, and progressive spasticity with extrapyramidal symptoms. Our patients were further biochemically characterized by a mitochondrial dysfunction and persistent urinary excretion of 3-methylglutaconic acid.

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.

Type IV 3-methylglutaconic (3-MGC) aciduria: a new case presenting with hepatic dysfunction

We describe a new patient with type IV 3-methylglutaconic aciduria who presented with a clinical picture simulating a primary hepatic disorder subsequently followed with progressive neurologic impairment and an magnetic resonance imaging picture of Leigh syndrome.

Mitochondrial myopathy in Senna occidentalis-seed-fed chicken

Plants of the genus Senna (formerly Cassia) have been recognized as the cause of a natural and experimental syndrome of muscle degeneration frequently leading to death in animals. Histologically, it demonstrated skeletal and cardiac muscle necrosis, with floccular degeneration and proliferation of sarcolemmal nuclei. Recently, it was described as an experimental model of mitochondrial myopathy in hens chronically treated with Senna occidentalis. Currently, skeletal muscles of chicks intoxicated with seeds of the poisonous plant S. occidentalis were studied by histochemistry and electron microscopy. Since birth, the birds were fed ground dried seeds of this plant with a regular chicken ration at a dose of 4% for 11 days. Microscopic examination revealed, besides muscle-fiber atrophy, lipid storage in most fibers and a moderate amount of cytochrome oxidase-negative fibers. By electron microscopy, enlarged mitochondria with disrupted or excessively branched cristae were seen. This picture was characteristic of mitochondrial myopathy. These findings have hitherto remained unnoticed in skeletal muscle of young birds treated with S. occidentalis.

Subunit specific monoclonal antibodies show different steady-state levels of various cytochrome-c oxidase subunits in chronic progressive external ophthalmoplegia

Monoclonal antibodies recognizing the mitochondrially encoded subunits I and II, and the nuclear-encoded subunits IV, Va, Vb and VIc of human cytochrome-c oxidase were generated. These antibodies are highly specific and allow the assessment of subunit steady-state levels in crude cell extracts and tissue sections. In the experimental human cell line 143B206, which is devoid of mitochondrial DNA, immunovisualization with the antibodies revealed that the nuclear-encoded subunits IV and Va were present in amounts close to that of the parental cell line despite the absence of the mitochondrially encoded subunits. In contrast, the nuclear-encoded subunits Vb and VIc were severely reduced in cell line 143B206, suggesting that unassembled nuclear-encoded subunits are degraded at different rates. In skeletal muscle sections of a patient with chronic progressive external ophthalmoplegia known to harbor the 'common deletion' in a subpopulation of her mitochondrial DNA, most cytochrome-c oxidase activity negative fibers had greatly reduced levels of subunits I, II, Va, Vb and VIc of cytochrome-c oxidase. The steady-state level of subunit IV, however, was less affected. This was particularly evident in cytochrome-c oxidase activity negative fibers with accumulated mitochondria ('ragged-red' fibers) where immunodetection with anti-subunit IV resulted in intense staining. The data presented in this paper demonstrate that the battery of monoclonal antibodies can be employed for diagnostic purposes to analyze steady-state levels of mitochondrially and nuclear-encoded subunits of cytochrome-c oxidase.

Dilated cardiomyopathy and neonatal lethality in mutant mice lacking manganese superoxide dismutase

The Sod2 gene for Mn-superoxide dismutase (MnSOD), an intramitochondrial free radical scavenging enzyme that is the first line of defense against superoxide produced as a byproduct of oxidative phosphorylation, was inactivated by homologous recombination. Homozygous mutant mice die within the first 10 days of life with a dilated cardiomyopathy, accumulation of lipid in liver and skeletal muscle, and metabolic acidosis. Cytochemical analysis revealed a severe reduction in succinate dehydrogenase (complex II) and aconitase (a TCA cycle enzyme) activities in the heart and, to a lesser extent, in other organs. These findings indicate that MnSOD is required for normal biological function of tissues by maintaining the integrity of mitochondrial enzymes susceptible to direct inactivation by superoxide.

Cardiomyopathy in respiratory chain disorders

Disorders of mitochondrial oxidative phosphorylation may disturb cardiac energy metabolism and cause cardiomyopathy. Twenty one cases from the literature and one further patient with cardiomyopathy due to biochemically defined respiratory chain defects were reviewed for clinical course, morphology, and pathophysiological mechanisms of the cardiomyopathy. All cases showed concentric hypertrophy of the myocardium without an outflow tract obstruction. In most patients the cardiomyopathy was diagnosed early in infancy and showed rapid deterioration with death before the age of 2 years. Hypertrophy of the myocardium appears to result from swelling of the cardiomyocytes caused by accumulation of mitochondria and by morphologically abnormal megamitochondria.

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.

Infantile histiocytoid cardiomyopathy: three cases and literature review

A review is presented of the clinical and cardiac morphologic findings in 50 previously reported and 3 new patients with histiocytoid cardiomyopathy. This disorder occurs in infants and small children and is characterized clinically by severe and often fatal arrhythmias and morphologically by focal collections of altered myocytes that are roundshaped and resemble histiocytes. Sixteen patients had yellowish nodules on the endocardium, epicardium, and/or valves; the other 37 had foci of abnormal myocytes throughout the myocardium. These cells were remarkably similar in all patients and had poorly developed or absent intercellular junctions, few or no contractile elements, and markedly increased numbers of mitochondria, which imparted a granular or vacuolated appearance to the cytoplasm. There was a high prevalence of anomalies involving the nervous system and eyes and of oncocytic cells in various glands. Evidence is presented to exclude the possibilities that the disorder represents a developmental anomaly of the atrioventricular conduction system, a multifocal tumor of Purkinje cells, a developmental arrest of cardiac myocytes, and a diffuse type of mitochondrial cardiomyopathy. Histiocytoid cardiomyopathy is considered to be the result of hamartoma-like aggregations of cardiac myocytes with features similar to those of oncocytes. This syndrome is likely caused by prenatal myocardial or systemic (viral?) injury. Surgical excision of nodules of histiocytoid cells can result in clinical remission.

3-Methylglutaconic aciduria in the Iraqi-Jewish 'optic atrophy plus' (Costeff) syndrome

Eleven new patients of Iraqi-Jewish origin with bilateral optic atrophy, neurological abnormalities ('optic atrophy plus' syndrome) and 3-methylglutaconic aciduria (type III) are described. Clinical abnormalities in decreasing order of frequency were bilateral optic atrophy, extrapyramidal signs, spasticity, ataxia, dysarthria and cognitive deficit. An association with age was found only for spasticity. Spasticity, extrapyramidal signs and optic atrophy frequently led to major disability, in contrast to ataxia, dysarthria and cognitive deficit. The combined excretion of 3-methylglutaconic and 3-methylglutaric acid ranged between 9 and 187 mmol/mol creatinine. The primary enzymatic defect possibly may reside in the mitochondrial respiratory chain.

A new mtDNA mutation in the tRNA(Leu(UUR)) gene associated with maternally inherited cardiomyopathy

We report a new mutation, a C to T transition at nt 3303 of mtDNA, in seven members of a family with cardiomyopathy and myopathy: the proband and two siblings had fatal infantile cardiomyopathy, whereas in three maternal relatives the disease manifested later in life as sudden cardiac death or as mitochondrial myopathy with cardiomyopathy. The mutation was homoplasmic in all tissues (including blood) from the proband and her brother, but heteroplasmic in blood from five oligosymptomatic or asymptomatic maternal relatives. This mutation disrupts a conserved base pair in the aminoacyl stem of the tRNA(Leu(UUR)). None of 70 controls carried the mutation. Our data indicate that this mutation is the genetic cause of the disorder in this family, and confirm that the tRNA(Leu(UUR)) is a "hot spot" for mutations in mtDNA.

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

In a 4.5-month-old boy presenting with marked muscular hypotonia in the neonatal period, hepatomegaly, cardiac hypertrophy, recurrent hypoglycemia, metabolic acidosis, and secondary carnitine deficiency, there was a considerable urinary excretion of 3-methylglutaconic and 3-methylglutaric acid. Estimation of 3-methylglutaconyl-CoA hydratase, 3-hydroxy-3-methylglutaryl-CoA lyase and initial enzymatic steps of cholesterol biosynthesis in cultured fibroblasts and in different tissues postmortem revealed no enzyme deficiency. Analyses of the respiratory chain in postmortem tissues demonstrated severe impairment of complex I (NADH ubiquinone oxidoreductase) and complex IV (cytochrome c oxidase) activities in skeletal muscle and reduced complex IV activity in heart.

Multiple syndromes of 3-methylglutaconic aciduria

The most common clinical syndromes associated with 3-methylglutaconic aciduria are presented. In some patients these syndromes are multisystemic, progressive disorders of unknown etiology. Tissues deriving significant energy through oxidative metabolism (notably brain and cardiac muscle) are most often affected and in some the primary defect may reside within the mitochondrial respiratory chain. Although increasing biochemical evidence suggests that 3-methylglutaconic aciduria may correlate with deranged mitochondrial energy metabolism, the biochemical origin of 3-methylglutaconic acid and the significance of its increased excretion remain unknown. This review describes these syndromes and illustrates the necessity of urinary organic acid analysis to assist in the differential diagnosis.

3-Methylglutaconic aciduria associated with Pearson syndrome and respiratory chain defects

3-Methylglutaconic aciduria was detected in four patients with Pearson syndrome, a multitissue disorder with hematologic abnormalities, lactic acidosis resulting from defective oxidative phosphorylation, and deletions in the mitochondrial genome. 3-Methylglutaconic acid may be an additional useful marker for Pearson syndrome and may be a more specific marker than other organic acids identified in this disorder.

In situ hybridization of mitochondrial DNA in the heart of a patient with Kearns-Sayre syndrome and dilatative cardiomyopathy

Previous studies have revealed cytochrome-c-oxidase-deficient cardiomyocytes and the 4,977 base pair deletion ("common deletion") of mitochondrial DNA (position 8,482-13,459) in the heart of a patient with dilatative cardiomyopathy and Kearns-Sayre syndrome. In the present investigation the co-localization of the enzymatic and genomic defects was studied. In situ hybridization of mitochondrial DNA (mtDNA) revealed different hybridization patterns in the cytochrome-c-oxidase-deficient cells: (1) a selective reduction of the hybridization signal with an mtDNA probe recognizing the common deletion, indicating predominance of the deleted over the nondeleted mtDNA molecules in the cytochrome-c-oxidase-deficient cells; (2) a reduced hybridization signal with different mtDNA probes, indicating depletion of mtDNA; and (3) normal hybridization signals with different probes in single cytochrome-c-oxidase-deficient cardiomyocytes. These results indicate that different mechanisms may co-exist in Kearns-Sayre syndrome and may lead to defective respiratory chain function. The question of the pathogenetic interrelationship is discussed.

Progressive loss of cytochrome c oxidase in the human extraocular muscles in ageing--a cytochemical-immunohistochemical study

Cytochrome c oxidase (complex IV of the respiratory chain) was studied histochemically in autoptic human extraocular muscles (n = 135), revealing randomly distributed single fibers without enzyme activity. The enzyme defect was expressed in all the mitochondria of an involved fiber as evidenced by ultracytochemistry. Succinate dehydrogenase showed normal histochemical reactivity. The defects occurred already in the second decade and were regularly seen from the third decade on. The defect density (defects/mm2) increased from approx. 1/mm2 below the fifth decade to about 4/mm2 in advanced age (P = 0.000). The highest defect density was observed in the levator palpebrae muscle. On the whole, the defect density was about 5-6 times higher in the extraocular muscles than in the limb muscle, diaphragm and heart (Müller-Höcker, 1989, 1990). Immunocytochemical detection of cytochrome c oxidase showed that loss of cytochrome c oxidase activity was due to an almost complete absence of both nuclear and mitochondria subunits of the enzyme. The results document different organ and heterogenic cellular sensitivity to the age-related loss of cytochrome c oxidase. The loss of both mitochondrial and nuclear subunits indicates that nuclear factors are most probably involved in the decline of the respiratory chain function in senescence.