Mitochondrial cytopathy with lactic acidosis, carnitine deficiency and DeToni-Fanconi-Debré syndrome

Methylmalonic acidemia: a megamitochondrial disorder affecting the kidney

BACKGROUND

Classical (or isolated) methylmalonic acidemia (MMA) is a heterogeneous inborn error of metabolism most typically caused by mutations in the vitamin B12-dependent enzyme methylmalonyl-CoA mutase (MUT). With the improved survival of individuals with MMA, chronic kidney disease has become recognized as part of the disorder. The precise description of renal pathology in MMA remains uncertain.

METHODS

Light microscopy, histochemical, and ultrastructural studies were performed on the native kidney obtained from a 19-year-old patient with mut MMA who developed end stage renal disease and underwent a combined liver-kidney transplantation.

RESULTS

The light microscopy study of the renal parenchyma in the MMA kidney revealed extensive interstitial fibrosis, chronic inflammation, and tubular atrophy. Intact proximal tubules were distinguished by the widespread formation of large, circular, pale mitochondria with diminished cristae. Histochemical preparations showed a reduction of cytochrome c oxidase and NADH activities, and the electron microscopy analysis demonstrated loss of cytochrome c enzyme activity in these enlarged mitochondria.

CONCLUSIONS

Our results demonstrate that the renal pathology of MMA is characterized by megamitochondria formation in the proximal tubules in concert with electron transport chain dysfunction. Our findings suggest therapies that target mitochondrial function as a treatment for the chronic kidney disease of MMA.

De Toni-Debré-Fanconi syndrome in a patient with Kearns-Sayre syndrome: a case report

Introduction

Kearns-Sayre syndrome is a mitochondrial myopathy that demonstrates chronic progressive ophthalmoplegia with onset before the age of 20 and pigmentary degeneration of the retina.

Case presentation

We report the case of an 18-year-old Romanian man with short stature, external ophthalmoplegia, palpebral ptosis, myopathy, sensorineural hearing impairment, cerebellar ataxia, cardiac conduction defect, diabetes mellitus, hypoparathyroidism and hyperaldosteronism. The patient's evolution showed progressive insufficiency of the renal tubule: hyperphosphaturia, hyperaminoaciduria and, later, glucosuria (de Toni-Debré-Fanconi syndrome), a syndrome, to date, rarely diagnosed in association with complete Kearns-Sayre syndrome. The final diagnosis was delayed for several years and was only established when he developed diabetes mellitus. Southern blot analysis and polymerase chain reaction amplification revealed the presence of a deletion in the mitochondrial DNA.

Conclusion

Despite the rarity of this syndrome, the diagnosis was easily made due to the presence of the classic triad: external ophthalmoplegia, pigmentary retinopathy and onset in a patient younger than 20 years old. In our opinion, a search for Kearns-Sayre syndrome in all patients with de Toni-Debré-Fanconi syndrome is a valuable medical routine.

A secondary respiratory chain defect in a patient with Fanconi-Bickel syndrome

A North African boy, the son of consanguineous parents, presented at 8 years of age with hypophosphataemic rickets due to De Toni-Debré-Fanconi syndrome. Hepatomegaly and abnormalities of carbohydrate metabolism were suggestive of Fanconi-Bickel syndrome. This was confirmed by the detection of a mutation within GLUT2, the gene encoding the liver-type facilitative glucose transporter. The study of the respiratory chain revealed a deficiency of complexes I, III and IV in muscle. Mechanisms responsible for an impairment ofmitochondrial function, which we interpret as a secondary phenomenon, are discussed.

Renal manifestations of congenital lactic acidosis

Congenital lactic acidoses (CLAs) constitute a group of rare inborn errors of mitochondrial metabolism in which cellular energy failure is the defining biochemical abnormality. We report the principal manifestations of renal dysfunction in 35 children with CLA caused by defects in either the pyruvate dehydrogenase multienzyme complex or one or more components of the respiratory chain. The most prominent renal abnormalities included bicarbonaturia, phosphaturia, hypercalciuria, complete Fanconi's syndrome, proteinuria, and decreased glomerular filtration rate. These data were compared with those from 79 previously published cases. Clinical manifestations of renal dysfunction in CLA are common and may be the first presenting sign of the disease. The glomerulus and proximal renal tubule appear to be the anatomic sites most vulnerable to abnormal mitochondrial energy transduction. We propose that the primary defect in mitochondrial energy metabolism, together with the consequent intracellular accumulation of lactate and hydrogen ions, precipitates a state of tissue injury that, unless interrupted, becomes self-perpetuating and ultimately leads to renal cell death.

Renal involvement in mitochondrial cytopathies

Mitochondrial cytopathies have long been regarded as neuromuscular diseases. However, an oxidative phosphorylation disorder may give rise to various symptoms in other organs or tissues which are dependent upon mitochondrial energy supply. A broad spectrum of clinical symptoms have been described in these patients, including renal symptoms. The most frequent is proximal tubular dysfunction with a more or less complete de Toni-Debré-Fanconi syndrome. A few patients have been reported with tubular acidosis, Bartter syndrome, chronic tubulointerstitial nephritis, or nephrotic syndrome. The diagnosis of a respiratory chain deficiency is difficult when only renal symptoms are present but should be easier when another seemingly unrelated symptom is observed. Metabolic screening for abnormal oxidoreduction status in plasma, including lactate/pyruvate and ketone body molar ratios, can help to identify patients for further investigations. These include the measurement of oxygen consumption by mitochondria, the assessment of mitochondrial respiratory enzyme activities by spectrophotometric studies, and, when possible, the molecular analysis of mitochondrial DNA. Any mode of inheritance can be observed: sporadic, autosomal dominant or recessive, or maternal inheritance. No satisfactory therapy is presently available for mitochondrial disorders.

Renal amino acid transport in adults with oxidative phosphorylation diseases

The clinical manifestations of mitochondrial DNA (mtDNA) mutations depend on a variety of factors including ratios of normal to abnormal mtDNA and tissue-specific differences in ATP production by oxidative phosphorylation (OXPHOS). In order to investigate the effects of OXPHOS defects on renal tubule function, we characterized sodium-coupled transport processes in six individuals with OXPHOS diseases. Pathogenic mtDNA mutations were identified in five of these individuals. Sodium coupled transport processes were evaluated by determining fractional excretions of amino acids, glucose, lactate, urate, and phosphate in patients and controls. Four of the six individuals had high fractional excretions of neutral amino acids, indicating abnormal renal tubule reabsorbtion of these amino acids. Abnormalities in fractional excretions of lactate, glucose, urate, and phosphate were less pronounced. These results demonstrate that sodium-coupled transport processes in the kidney are sensitive to OXPHOS impairment. When abnormalities in these processes are encountered, an OXPHOS disease should be included in the differential diagnosis.

Mitochondrial DNA deletion: a cause of chronic tubulointerstitial nephropathy

We report the first case of a mitochondrial DNA (mtDNA) deletion diagnosed by renal biopsy. An eight-year-old girl with megaloblastic anemia and severe growth retardation developed progressive renal insufficiency accompanied by partial Fanconi syndrome. Histologic examination of the renal biopsy disclosed nonspecific chronic tubulointerstitial disease characterized by tubular atrophy and interstitial fibrosis. On ultrastructural examination, tubular cell mitochondria were extremely dysmorphic with prominent size variation, abnormal arborization, disorientation of the cristae and osmiophilic electron-dense inclusions. Functional histochemical stains for mitochondrial enzymes performed on cryostat renal sections revealed focal tubular absence of cytochrome C oxidase (COX), a respiratory chain enzyme partially encoded by mtDNA, with preservation of succinate dehydrogenase (SDH), a respiratory chain enzyme entirely encoded by nuclear DNA (nDNA). Immunoreactivity for COX subunit 2 (encoded by mtDNA) was weak to undetectable in most tubular cells, whereas reactivity for subunit 4 (encoded by nDNA) was intense in all cells. Molecular analysis of the mtDNA of kidney and peripheral blood leukocytes was performed using Southern blot and PCR. Both techniques disclosed a 2.7 kb mtDNA deletion located between nucleotide (nt) 9700 and nt 13700, a common site for mtDNA deletions associated with encephalomyopathies. Mitochondrial DNA deletions may be an under-recognized cause of idiopathic tubulointerstitial nephropathy in children lacking neurologic or myopathic manifestations.

Renal tubular involvement mimicking Bartter syndrome in a patient with Kearns-Sayre syndrome

A 10-year-old boy had short stature, external ophthalmoplegia, atypical retinal pigmentary degeneration, and sensorineural hearing loss (Kearns-Sayre syndrome). In addition to ragged-red fibers observed on modified Gomori trichrome staining, there were scattered fibers exhibiting no cytochrome c oxidase activity, indicating a focal deficiency. Cytochrome c oxidase and other respiratory chain enzyme activities were normal biochemically. The patient also had renal tubular dysfunction, including isosthenuria, decreased urine-concentrating ability, and excessive excretion of potassium and magnesium. In addition, he had hyperreninemia and hyperaldosteronism but no hypertension. The renal dysfunction was thought to have resulted from a primary defect in the thick ascending limb of the loop of Henle, mimicking Bartter syndrome. In contrast to previously described cases of cytochrome c oxidase deficiency with de Toni-Fanconi Debré syndrome, the patient had less intensive muscle abnormalities. A renal biopsy specimen showed ultrastructural changes in mitochondria that were similar to those seen in biopsy specimens of muscle. A large-scale deletion (8.8 kilobases) in mitochondrial DNA was found in biopsy specimens of muscle and kidney.

Glycogen storage disease, Fanconi nephropathy, abnormal galactose metabolism and mitochondrial myopathy

We present a 4-year-old male suffering from profound muscular weakness, enzymatically undefined glycogen storage disease. Fanconi nephropathy and impaired galactose utilization. Distorted mitochondria, intramitochondrial fat droplets and partial deficiencies of pyruvate dehydrogenase complex, succinate: cytochrome c oxidoreductase, and cytochrome c oxidase have been found in muscle tissue. The causal relationship between mitochondrial myopathy, glycogen storage disease, Fanconi nephropathy and impaired utilization of galactose is discussed.

Mitochondria-related encephalomyopathies

Owing to advances in morphological and biochemical techniques, the mitochondria-related myopathies and encephalomyopathies have emerged as a still rapidly growing group of primary and secondary metabolic disorders, which may extend from infancy to late adulthood. Impairment of the biochemically diversified mitochondria is reflected in an enormous number of deficiencies, often affecting several mitochondrial enzymes in the same patient; morphologically abnormal mitochondria are common and are thus not specific to individual mitochondrial enzyme deficiencies. Skeletal muscle biopsies have provided a wealth of data through histological and histochemical studies and from isolated mitochondria. As a similar abundance of biochemical and morphological findings has not been obtained from brain tissue in mitochondrial encephalomyopathies, investigation of these disorders is still in its infancy; interpretation of these conditions and their encephalopathic components has largely been based on comparison of data not derived from brain tissues. Therefore, it has been, and still is, largely the link between an encephalopathy and an associated mitochondrial myopathy that identifies the brain lesions as clinical and morphological expressions of a mitochondrial defect. As enzyme histochemical and electron microscopic investigations of mitochondrial encephalopathies have not yielded a comparable rich spectrum of morphological findings, it is conceivable that the spectrum of mitochondrial encephalopathies may be much larger than defined by the hitherto identified encephalomyopathies. This may be especially so when the myopathic component is of minor nosological significance.

Disorders of the mitochondrial respiratory chain: clinical manifestations and diagnostic approach

The clinical identification of patients with defects in the mitochondrial respiratory chain is almost impossible. We describe screening tests that should be performed in order to select those patients in whom a skeletal muscle biopsy should be carried out for more specific biochemical assays. The importance of performing in vivo function tests is stressed. The biochemical diagnosis in disorders of the respiratory chain is presented and the application of immunological methods discussed.

Mitochondrial myopathy with lactic acidaemia, Fanconi-De Toni-Debré syndrome and a disturbed succinate: cytochrome c oxidoreductase activity

A patient with severe muscular hypotonia, failure to thrive, a metabolic acidosis and a renal tubular dysfunction is presented. The disease followed a fatal course. Blood lactate and pyruvate levels as well as lactate/pyruvate ratios were strongly elevated. There were a massive excretion of lactate in urine, a generalized hyperaminoaciduria, a proteinuria and a mellituria. The carnitine concentration was diminished in blood and muscle tissue. Biochemical investigations of skeletal muscle and liver tissue revealed a defect in the respiratory chain at the level of succinate: cytochrome c oxidoreductase. The defect could not be demonstrated in cultured fibroblasts.