Mitochondrial disease and stroke

BACKGROUND AND PURPOSE

It is well known that some mitochondrial disorders are responsible for ischemic cerebral infarction in young patients. Our purpose was to determine, in this prospective ongoing study, whether ischemic stroke is the only manifestation of a mitochondrial disorder in young patients.

METHODS

Patients aged </=50 years, admitted to the Stroke Unit from January 1999 to May 2000 with a diagnosis of ischemic stroke of unknown origin, were included in the study. All of them had full biochemical and hematologic tests, neuroimaging studies, transesophageal echocardiography, and extracranial and transcranial Doppler sonography. Patent foramen ovale was ruled out. Lactic acid concentrations were measured after anaerobic exercise of the forearm, and a morphological, biochemical, and molecular study after biceps muscle biopsy was performed.

RESULTS

Of the 18 patients so far included, 3 (17%) presented lactic acid hyperproduction after physical exercise, and 6 (33%) showed deficit of the mitochondrial respiratory chain complexes. The molecular analyses have confirmed mitochondrial mutations at base pairs 3243 (characteristic of mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes [MELAS]), 4216, and 15 928.

CONCLUSIONS

These results suggest that ischemic stroke may be the only manifestation or the initial manifestation of a mitochondrial disorder.

Congenital hydranencephalic-hydrocephalic syndrome with proliferative vasculopathy: a possible relation with mitochondrial dysfunction

We report the case of a fetus aborted at gestation week 20 because of hydranencephalic-hydrocephalic syndrome. The fetus was the third pregnancy of a nonconsanguineous couple whose first child exhibited congenital hydranencephalic-hydrocephalic syndrome associated with muscle histology findings consistent with mitochondrial cytopathy and deficiency of complexes III and IV of the respiratory chain and whose second pregnancy had terminated in an elective abortion on detection of progressive hydrocephalus at gestation week 19. The third pregnancy had a normal course according to obstetric and ultrasonography examinations performed at gestation weeks 5, 10, and 15, and negative results were obtained in standard serologic and polymerase chain reaction (PCR) tests for prenatal infections of the mother. However, the ultrasonography examination at gestation week 18 revealed hydrocephalus, in response to which the parents requested an abortion, which was performed at gestation week 20; the fetus was male and with no evident external malformations. Histopathologic studies of the brain and medulla oblongata revealed proliferative vasculopathy (glomeruloid vessels, intracytoplasmic inclusions, and microcalcifications) and intracytoplasmic inclusions in the voluntary muscle. Microbiologic and PCR tests of hepatic and spleen tissue were negative for prenatal infections. In view of the precedent of a sister with mitochondrial dysfunction, these findings raise the pos sibility that at least some cases of familial syndrome of congenital hydranencephalic-hydrocephalic syndrome with proliferative vasculopathy can be attributed to alterations in the mitochondrial respiratory chain.

Molecular heterogeneity of myophosphorylase deficiency (McArdle's disease): a genotype-phenotype correlation study

We report on 54 Spanish patients with McArdle's disease from 40 unrelated families. Molecular analysis revealed that the most common R49X mutation was present in 70% of patients and 55% of alleles. The G204S mutation was less frequent and found in 14.8% of patients and 9% of mutant alleles. The W797R mutation was observed in 16.5% of patients, accounting for 13.7% of mutant alleles. Moreover, 78% of mutant alleles among Spanish patients can be identified by using polymerase chain reaction-restriction fragment length polymorphism analysis for the R49X, G204S, and W797R mutations, which makes noninvasive diagnosis possible through molecular genetic analysis of blood DNA. Six novel mutations were found. Three were missense mutations, E348K, R601W, and A703V; two nonsense mutations, E124X and Q754X; and one single base pair deletion, 533 delA. No clear genotype-phenotype correlation emerges from our study. Most of the mutations of uncharged and solvent inaccessible residues and the truncations must disrupt the basic structure of the protein. The mutations of charged residues would be expected to interfere with internal hydrogen bonding networks, introducing severe incompatible partnering that is caused by poor packing or electrostatic repulsions.

Mitochondrial dysfunction associated with a mutation in the Notch3 gene in a CADASIL family

BACKGROUND

Cerebral autosomal arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is characterized by recurrent subcortical ischemic strokes and dementia caused by mutations in the Notch3 gene. In Drosophila melanogaster, Notch signaling has a pleiotropic effect, affecting most tissues of the organism during development.

OBJECTIVE

To characterize a potential mitochondrial dysfunction associated with mutations in the Notch3 gene.

METHODS

Biochemical, histochemical, molecular, and genetic analyses were performed on muscle biopsy specimens and fibroblasts obtained from patients of a Spanish family with CADASIL. Additional biochemical and molecular analyses of the N(55e11) mutant of D. melanogaster were performed.

RESULTS

In muscle biopsy specimens, a significant decrease was found in the activity of complex I (NADH [reduced form of nicotinamide adenine dinucleotide] dehydrogenase), and in one patient, histochemical analysis showed the presence of ragged-red fibers with abnormal cytochrome c oxidase staining. Reduced fibroblast activity of complex V (ATP synthase) was found. Supporting data on patients with CADASIL, it was found that the mutation N(55e11) in Drosophila decreases the activity of mitochondrial respiratory complexes I and V.

CONCLUSIONS

Mitochondrial respiratory chain activity responds, directly or indirectly, to the Notch signaling pathway. Mitochondrial dysfunction in patients with CADASIL may be an epiphenomenon, but results of this study suggest that the pathophysiology of the disease could include a defect in oxidative phosphorylation.

Early-onset multisystem mitochondrial disorder caused by a nonsense mutation in the mitochondrial DNA cytochrome C oxidase II gene

We report the first nonsense mutation (G7896A) in the mtDNA gene for subunit II of cytochrome c oxidase (COX) in a patient with early-onset multisystem disease and COX deficiency in muscle. The mutation was heteroplasmic in muscle, blood, and fibroblasts from the patient and abundantly present in COX-deficient fibers, but less abundant in COX-positive fibers; it was not found in blood samples from the patient's asymptomatic maternal relatives. Immunoblot analysis showed a reduced concentration of both COX II and COX I polypeptides, suggesting impaired assembly of COX holoenzyme.

[MELAS syndrome masquerading as herpes encephalitis: genetic diagnosis]

INTRODUCTION

MELAS syndrome (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke like episodes) is a mitochondrial disease related to the mitochondrial DNA mutation. The tRNALeu(UUR) mutation at the base pair 3234 is associated to 80% of cases of MELAS syndrome. The onset with the stroke like episodes is often before the age 40. Herpes simplex encephalitis (HSE) presents as acute episodes of focal neurologic deficit that are often related to the temporal lobe. Occasionally MELAS syndrome and HSE may have a similar clinical presentation.

CLINICAL CASE

A 33-year-old woman presented with seizures and a right parietotemporal syndrome of acute onset. The differential diagnosis between HSE and MELAS syndrome was established. MELAS syndrome was suspected based on her phenotype. The diagnosis of MELAS syndrome was confirmed by the presence of the mitochondrial tRNALeu(UUR) mutation at the base pair 3243.

CONCLUSION

The clinical presentation of the MELAS syndrome may mimic that of the HSE, and antiviral treatment should be given until the diagnosis of MELAS syndrome is definitive. The study of the mitochondrial DNA helps diagnosing in a non invasive way many patients with MELAS syndrome.

A new mtDNA mutation in the tRNA(Leu(UUR)) gene associated with ocular myopathy

We studied a patient with ptosis, ophthalmoparesis, and exercise intolerance who showed in her muscle biopsy ragged-red fibers and combined defects of the complexes I and IV of the mitochondrial respiratory chain. Molecular analysis revealed a T3273C transition in the mitochondrial DNA tRNA(Leu(UUR)) gene. The mutation was heteroplasmic and very abundant in muscle from the proposita, less abundant in her other tissues studied, and still less abundant in blood from her maternal relatives. Single muscle fiber analysis showed significantly higher levels of mutant genomes in ragged-red fibers than in normal fibers. The T3273C mutation affects a strictly conserved base pair in the anticodon stem and was not found in controls, thus satisfying the accepted criteria for pathogenicity.

[Multiple symmetrical lipomatosis with familial polineuropathy]

INTRODUCTION

Multiple symmetrical lipomatosis (LSM) is characterized by the development of symmetrical lipomas and is often associated with axonal polyneuropathy (PNP). Presentation is usually sporadic. Familial cases have been reported infrequently, with variable modes of inheritance. The pathogenesis is unknown. It has been related to mitochondrial cytopathy and alterations in lipid metabolism.

OBJECTIVES

To establish clinico pathological correlation in our cases of familial presentation. Patients and methods. We report seven patients, from three families, teetotalers with LSM. Clinical assessment included lipidogram, neurophysiological study of nerve and muscle, sural nerve biopsy in two of them and muscle biopsy in one member of each family for morphological assessment, respiratory chain biochemistry and study of molecular genetics.

RESULTS

LSM was associated with axonal PNP and hyperlipidemia in the seven members of the three families, with an apparent pattern of autosomal recessive inheritance. No conclusive data of mitochondrial cytopathy, in the form of significant morphological changes, biochemistry of the mitochondrial respiratory chain or micochondrial DNA were found.

CONCLUSION

Although mitochondrial cytopathy has been described as part of the syndromes in which LSM occurs, there may be other undefined aspects, such as disorders of lipid metabolism which form part of the pathogenesis.

Resolution of a mispaired secondary structure intermediate could account for a novel micro-insertion/deletion (387 insA/del 8 bp) in the PYGM gene causing McArdle's disease

We report two siblings with McArdle's disease who are both compound heterozygotes for two non-identical frameshift mutations in the PYGM gene; a previously reported 753 delA in exon 18 and a novel 387 insA/del 8 bp in exon 10. The novel mutation is predicted to result in premature termination of translation 33 amino acids downstream of the site of mutation, potentially encoding a severely truncated protein of 419 amino acids instead of 841 amino acids. The complete lack of myophosphorylase activity observed in muscle derived from one sibling suggests that this mutation has deleterious functional consequences. The underlying mechanism of mutagenesis may have been slipped mispairing mediated by the formation of a Moebius loop-like secondary intermediate.

Myocardial carnitine and carnitine palmitoyltransferase deficiencies in patients with severe heart failure

We studied myocardial tissue from 25 cardiac transplant recipients, who had end-stage congestive heart failure (CHF), and from 21 control donor hearts. Concentrations of total carnitine (TC), free carnitine (FC), short-chain acylcarnitines, long-chain acylcarnitines (LCAC) as well as carnitine palmitoyltransferase (CPT) activities were measured in myocardial tissue homogenates and referred to the concentration of non-collagen protein. Compared to controls, the concentrations of TC and FC as well as total CPT activities were significantly lower in patients. LCAC levels and the LCAC to FC ratio values were significantly greater in patients than in controls. While the malonyl-CoA sensitive fraction of CPT, which represents CPT I activity, was similar in patients and controls, the residual CPT activity after inhibition by malonyl-CoA, representing CPT II activity, was significantly reduced in patients compared to controls. Moreover, the activity of CPT in the presence of Triton X-100, which also represents the activity of CPT II, was significantly lower in patients than in controls. Malonyl-CoA concentrations required for half-maximal inhibition of CPT activity were significantly greater in patients than in controls. There was a linear relationship between ejection fraction (EF) values and concentrations of TC, FC, or total CPT activities. Values for LCAC and the LCAC to FC ratio were inversely related to EF values. We conclude that failing heart shows decreased total CPT and CPT II activities and carnitine deficiency that may be related to ventricle function.

[Benign congenital myopathy associated with a partial deficiency of complexes I and III of the mitochondrial respiratory chain]]

INTRODUCTION

Isolated or combined enzyme deficiencies of the mitochondrial respiratory chain results in a number of clinical heterogeneous conditions. When presented in the neonatal period or early in the infancy the course is usually severe, although isolated cases with benign evolution have also been described.

OBJECTIVE

To describe the clinical and biochemical characteristics of a child with a benign form of mitochondrial myopathy due to a combined deficiency of the complexes I and III of the respiratory chain.

CLINICAL CASE

A 40 days-old male, the second son of a young non-consanguineous couple, presented with axial congenital hypotonia, asymmetrical macrocephaly, mild enlargement of the liver, mild coarsening of facial features, increased CK serum values, persistently elevation of serum lactate and lactate/pyruvate ratio and external hydrocephalus. Electromyogram and histological muscle examination were normal but analysis of the respiratory chain disclosed a deficiency of the complexes I and III. From 13 months-age onwards clinical detailed abnormalities progressively ameliorated and also did it serum CK, lactate and external hydrocephalus.

CONCLUSION

We think that on clinical, basic biochemical and histological grounds there are some similarities between this case of congenital unspecific myopathy and benign reversible form of mitochondrial myopathy, arguing in favor of a possible relationship between both conditions.

A mitochondrial tRNA(Lys) gene mutation (T8316C) in a patient with mitochondrial myopathy, lactic acidosis, and stroke-like episodes

We studied a patient with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes who had morphologically and biochemically abnormal muscle mitochondria. Molecular analysis revealed a T8316C transition in the mitochondrial DNA tRNA(Lys) gene. The mutation was homoplasmic in muscle from the proposita, heteroplasmic in her blood, and still less abundant in blood from her asymptomatic maternal relatives. The T8316C mutation affects a highly conserved base pair and was not found in controls, thus satisfying the accepted criteria for pathogenicity. Our data document the genetic heterogeneity in mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes syndrome, underlining that the same syndrome may be associated with mutations of different genes.

[Mitochondrial encephalopathies]

OBJECTIVE

We carry out a review of the current basic genetic, biochemical, clinical, diagnostic and therapeutic aspects of mitochondrial cytopathies due to deficiencies in the mitochondrial respiratory chain complexes, which appear clinically during childhood and/or adolescence.

DEVELOPMENT

The clinical description has been divided into two groups: mitochondrial cytopathies secondary to alterations of mitochondrial DNA (mtDNA) and mitochondrial cytopathies secondary to alterations of the nuclear DNA (nDNA); we also consider about the importance of such conditions at this age.

Molecular analysis of Spanish patients with AMP deaminase deficiency

We found six patients with AMPD deficiency in muscle who were homozygous for the most common mutation, Q12X in the AMPD gene (AMPD1), associated with this disease. Three patients had AMPD deficiency alone, showing a mild clinical phenotype. Two patients showed a defect of PPL in muscle, and were homozygous for the most common mutation associated with McArdle's disease, R49X in the muscle PPL gene (PYGM). In one of these patients, the clinical phenotype was more severe than usually seen in patients with McArdle's disease. The remaining patient harbored the mtDNA A3243G mutation, showing one of the usual clinical patterns associated with this mutation. We conclude that the Q12X mutation in AMPD1 may result in a mild clinical effect; that it is frequent in the Spanish population, and therefore frequently associated with other metabolic diseases; and that the effect of the association of AMPD and PPL deficiencies seems to be neutral.

A homozygous missense mutation (A659D) in the myophosphorylase gene in a Spanish patient with McArdle's disease

We identified a novel missense mutation in the myophosphorylase gene (PYGM) in a Spanish patient with McArdle's disease. This homozygous C-to-A mutation results in the replacement of a highly conserved alanine at amino acid position 659 with an aspartic acid in the C-terminal domain of the myophosphorylase gene protein, near binding sites for pyridoxal phosphate and glucose. Our data further expand the genetic heterogeneity in patients with McArdle's disease.

The pathogenic role of point mutations affecting the translational initiation codon of mitochondrial genes

The mutation T3308C results in a Met --> Thr change at the highly conserved amino acid position 1 of the mtDNA ND1 gene (M1T). To study its potential pathogenic effect we have carried out a combination of mitochondrial protein synthesis and Northern and Western analyses. Our data demonstrate that M1T mutation does not affect the efficiency of the synthesis of the ND1 polypeptide and suggest that any codon specifying methionine located close to the 5' end of mitochondrial mRNAs may be used as translational initiator.

Identification of novel mutations in Spanish patients with muscle carnitine palmitoyltransferase II deficiency

Carnitine palmitoyltransferase II (CPT II) deficiency is the most common recessively inherited disorder of lipid metabolism affecting skeletal muscle and the most frequent cause of hereditary myoglobinuria. We studied 5 Spanish patients with CPT II deficiency from four unrelated families. Four patients had the typical clinical phenotype of muscle CPT II deficiency with recurrent episodes of myoglobinuria, triggered by prolonged exercise, fasting, or fever, and marked elevation of creatine kinase values during metabolic crisis. One patient had exercise-related myalgia, cramps and moderate elevation of serum CK values, but had never had myoglobinuria. Molecular analysis showed that three patients were heterozygous for the S113L mutation and one patient heterozygous for the P50H substitution. To identify the mutations in the other alleles of our patients we amplified and sequenced genomic DNA fragments encompassing the entire coding region and intron/exon boundaries of the CPT2 gene. We found the recently reported 178 insT/del 25 bp in one patient. Three novel mutations were identified: a Y120C substitution that leads to a nonconservative amino acid replacement; a 36-38 insGC mutation that results in premature termination of the translation; and an I502T substitution that affects a conserved amino acid residue in the CPT II protein. Our data confirm the molecular heterogeneity of patients with CPT II deficiency, and suggest that the ethnic origin has to be taken into account before performing mutation analysis in these patients.

Lipomatosis, proximal myopathy, and the mitochondrial 8344 mutation. A lipid storage myopathy?

Multiple symmetric lipomatosis (MSL) has been related in some cases to the 8344 point mutation of the tRNA-lysine gene of the mitochondrial DNA, mainly in the context of families with classic myoclonic epilepsy with ragged-red fibers (MERRF) and exceptionally in patients with proximal myopathy as the only manifestation of mitochondrial disease. We report on two families harboring the 8344 mutation. The patients presented with MSL and myopathy, expressed as limb girdle weakness in index cases and as exercise intolerance in the others. All muscle biopsies performed showed lipid storage apart from RRF and respiratory chain complexes deficiency. A possible explanation for both adipose proliferation and lipid storage myopathy in these cases is a disturbance in intermediary lipid metabolism secondary to mitochondrial respiratory chain deficiency that could be related via carnitine deficiency.

Two homozygous mutations (R193W and 794/795 delAA) in the myophosphorylase gene in a patient with McArdle's disease

We report two novel homozygous mutations in the myophosphorylase gene (PYGM) in a patient with McArdle's disease. A C-to-T transition that changed an arginine to tryptophan at codon 193 (R193W) in exon 5, and a deletion of two adenine base pairs in exon 20 at codon 794/795 (794/795 delAA) were identified. Several lines of evidence suggest the pathogenicity of both mutations: (i) they were the only nucleotide alteration in the coding region and adjacent exon/intron boundaries of the PYGM gene; (ii) the R193W mutation leads to the replacement of a highly conserved amino acid residue involved in glucose-6-P binding, and the 794/795 delAA mutation predicts a frameshift and premature termination of the protein; (iii) 60 normal controls and 20 disease controls did not have the mutations in their 160 alleles. Hum Mutat 15:294, 2000.

[The use of cardiopulmonary exercise test in patients with mitochondrial myopathies]

BACKGROUND

Exercise tests has been used in the diagnosis of metabolic myopathies. If there is an abnormal response pattern in mild mitochondrial myopathy (MM) and her role in the initial suspect diagnostic is unknown.

SUBJECTS AND METHODS

Prospective study of 26 patients with mitochondrial myopathy (15 men, 11 women) and a control group of 14 sedentary volunteers (9 men, 5 woman) with similar antropometric characteristics. We have made pulmonary function tests and treadmill exercise with serial venous sampling of blood lactate, piruvate, ketone bodies, free fatty acids and creatinkinase.

RESULTS

Patients with MM showed exercise limitation with lower maximal power (MM = 143 [47] vatts, C = 187 [40] vatts, p = 0.006), maximal oxygen uptake (MM = 27 [8] ml/min/kg, C = 40 [7] ml/min/kg, p = 0.001) and maximal oxygen pulse (MM = 11 [3] ml/beat, C = 14 [3] ml/beat, p = 0.006). For the same oxygen uptake the heart rate was higher and the anaerobic threshold was earlier in MM patients (MM = 48% [14], C = 62% [12], p = 0.01). We found a considerable slower maximal oxygen uptake in patients with lipid increase in muscle biopsy (n = 15). Acetoacetate curves, beta-hydroxybutyrate, free fatty acids and creatinkinase were similar in both groups. The exercise test was pathologic in 17/26 of the patients. The sensitivity of the exercise test for maximal oxygen uptake was 0.65.

CONCLUSIONS

The cardiopulmonary exercise test is a useful test in the suspect initial diagnostic of patients with mild mitochondrial myopathy because the majority of patients show a pathologic test.

A missense mutation T487N in the myophosphorylase gene in a Spanish patient with McArdle's disease

A heterozygous C-to-A substitution at codon 487, changing a highly conserved threonine to an asparagine (T487N) was identified in two siblings with McArdle's disease who were also heterozygous for the nonsense mutation at codon 49 (R49X). Our data further expand the genetic heterogeneity in patients with McArdle's disease.

Single large-scale mitochondrial DNA deletion in a patient with encephalopathy, cardiomyopathy, and prominent intestinal pseudo-obstruction

We studied a 62 year-old woman with a clinical phenotype characterized by encephalopathy, restrictive cardiomyopathy, and prominent intestinal pseudo-obstruction. Muscle morphology showed ragged red fibres with ultrastructurally abnormal mitochondrial whereas muscle respiratory chain was normal. Molecular genetics revealed the 'common deletion' in mtDNA, which represented 40% of total mtDNA. These data expand and confirm the wide clinical spectrum of mitochondrial disorders associated with single large-scale mtDNA deletions.

A missense mutation W797R in the myophosphorylase gene in a Spanish patient with McArdle's disease

We identified a novel missense mutation in the myophosphorylase gene (PYGM) in a Spanish patient with McArdle's disease. This homozygous T-to-C transition results in the replacement of a highly conserved tryptophan at amino acid position (aa) 797 with an arginine in the C-terminal domain of the PYGM protein. The lack of enzyme activity in the proband's muscle is consistent with a crucial role of the aa 797 in the normal function of the PYGM protein. Our data further expand the genetic heterogeneity in patients with McArdle's disease.

[Early mitochondrial encephalomyopathy due to complex IV deficiency consistent with Alpers-Huttenlocher syndrome: report of two cases]

INTRODUCTION

Complex IV or cytochrome c oxidase (COX) deficiency is the most common disorder involving complexes of the respiratory chain in the pediatric age. Exceptionally, it has been reported in association with Alpers syndrome or Alpers disease, and with its variant named progressive neuronal degeneration with liver disease or Alpers-Huttenlocher syndrome.

OBJECTIVE

To report the cases of two infants with mitochondrial encephalomyopathy due to COX deficiency in whom the clinical, biochemical, neurophysiologic and neuroimaging characterization suggested an associated Alpers-Huttenlocher syndrome.

CLINICAL CASES

Two no-related males, one with noncontributory family history and the other with third-grade consanguineous parents developed refractory seizures from age 20 and 60 days, respectively. Additionally, myoclonic fits accounted on evolution of the condition. In the first case, serial EEG recordings showed low amplitude polyspikes, polyspike waves and very slow waves of high amplitude alternating with a trace of burst-suppression activity. In the second case, a right preponderant but also bilateral low amplitude polyspikes, polyspike waves and occasional desynchronization of basal trace were recorded. In both, a rapidly progressive cerebral atrophy, neurological deterioration with pyramidal signs, and tendency to microcephaly, ensued. Accompanying to this clinical picture, minor hepatic dysfunction, elevated protein levels in the CSF, lactic acidosis and COX deficiency in muscle homogenate were demonstrated. In the first case, moreover, cortical blindness and severe hepatic failure occurred while receiving valproate, in spite of concomitant L-carnitine therapy.

CONCLUSIONS

We believe that the reported cases are consisted with Alpers-Huttenlocher syndrome associated with mitochondrial encephalomyopathy due to COX deficiency. Nevertheless, early myoclonic encephalopathy, a condition related in same cases with poliodistrophy, must be keep in mind as a possible diagnosis in case 1.

[Mitochondrial encephalomyopathy of late presentation with progressive ophthalmoplegia, tremor and diffuse leukoencephalopathy]

A 60-year-old woman had developed ptosis, progressive external ophthalmoplegia and action tremor over the last ten years. Physical examination also revealed short stature and retinal pigmentation. Anaerobic forearm exercise test showed increase of basal lactate and rise of lactate/piruvate index. Biceps biopsy displayed numerous ragged red fibers. Respiratory chain studies were consistent with complex I deficiency. Point mutations or deletions in mitochondrial DNA were not found. MR identified a diffuse leukoencephalopathy over both cerebral hemispheres, mesencephalon, pons and cerebellum. The late and sporadic onset of a progressive external ophthalmoplegia outlining a Kearns-Sayre syndrome is striking. A leukoencephalopathy associated with mitochondrial encephalomyopathy is an infrequent finding. The action tremor of this patient could be symptomatic of her mitochondrial disfunction.

Muscle dysfunction in elderly individuals with hip fracture

OBJECTIVE

To investigate muscle metabolism in elderly people with hip fracture.

METHODS

Free carnitine, carnitine esters, and respiratory chain enzyme activity were measured in muscle tissue from 54 patients over 65 years who underwent surgery for hip fracture, and from 40 healthy controls.

RESULTS

Eighty-five percent of patients older than 85 have either abnormal carnitine distribution or defects in the respiratory chain.

CONCLUSION

Elderly patients with hip fracture have muscle metabolic alterations that may contribute to neuromuscular impairment and be amenable to therapy.

Molecular analysis in Spanish patients with muscle carnitine palmitoyltransferase deficiency

The most common mutation in muscle carnitine palmitoyltransferase II (CPT II) deficiency is a missense mutation that replaces a leucine for a serine residue at amino acid position 113 of the CPT II protein (S113L). We performed molecular analysis in a group of 14 Spanish patients with CPT II deficiency from ten unrelated families. The S113L mutation was observed in 8 of the 14 patients studied. Seven patients were homozygous for the mutation, 1 patient was heterozygous, and 6 patients did not carry the mutation on either allele. Seven healthy relatives belonging to three different families carried the mutation on one allele. One patient carried the missense mutation that replaces a tyrosine for a serine at amino acid position 628 on one allele. Our data indicate that the S113L is also the most common mutation in Spanish patients with CPT II deficiency in muscle, and that further pathogenic mutations remain to be identified.

McArdle's disease associated with homozygosity for the missense mutation Gly204Ser of the myophosphorylase gene in a Spanish patient

We studied a pateint whose clinical, morphological and biochemical findings were consistent with McArdle's disease. Molecular genetic studies revealed that the patient did not harbor the common Arg49Stop mutation and was homozygous for the Gly204Ser mutation. Until now, no patient having the missense mutation in the two alleles has been documented.

Congenital hydranencephalic-hydrocephalic syndrome associated with mitochondrial dysfunction

We report the case of a 3-year-old girl, the only child of a nonconsanguineous couple without relevant antecedents, who was born with hydranencephalic-hydrocephalic syndrome diagnosed by ultrasonography at gestation week 28, and who was treated during the neonatal period by implantation of a ventriculoperitoneal shunt. She showed severe mental retardation, and died at age 4 years following an acute respiratory infection. Due to persistently high lactic acid levels in blood, muscle and skin biopsies were taken. Analysis of muscle biopsies revealed microscopic and ultrastructural alterations typical of mitochondrial disorders, and low levels of complexes III and IV of the mitochondrial respiratory chain. The enzymes of the pyruvate dehydrogenase complex showed normal activities in cultured skin fibroblasts. These findings raise the possibility that at least some cases of congenital hydranencephalic-hydrocephalic syndrome may be due to alterations in the mitochondrial respiratory chain.

A double mutation (A8296G and G8363A) in the mitochondrial DNA tRNA (Lys) gene associated with myoclonus epilepsy with ragged-red fibers

OBJECTIVE

To define potential pathogenic mitochondrial DNA (mtDNA) point mutations in a patient with myoclonus epilepsy with ragged-red fibers (MERRF) syndrome.

BACKGROUND

MERRF syndrome is typically associated with point mutations in the mtDNA tRNALys gene.

METHODS

We performed morphologic, biochemical, and genetic analysis of muscle samples from the patient and four relatives. Molecular genetic studies included sequencing, PCR, and restriction enzyme analysis on whole muscle, blood, and single muscle fibers.

RESULTS

Muscle biopsy showed cytochrome c oxidase (COX), negative ragged-red fibers (RRF), and a defect of complex I of the mitochondrial respiratory chain. We found an A8296G transition and a G8363A mutation in the mtDNA tRNALYs gene. The A8296G was almost homoplasmic in muscle and blood from the propositus and his oligosymptomatic maternal relatives. The G8363A mutation was heteroplasmic and more abundant in muscle than in blood, and its proportion correlated with clinical severity. Single muscle fiber analysis showed significantly higher levels of G8363A genomes in COX-negative than in normal fibers, and almost homoplasmic levels of mutant A8296G mtDNA in both COX-negative and normal fibers. The two mutations affect highly conserved nucleotides and were not found in controls.

CONCLUSIONS

The G8363A mutation is pathogenic; the co-occurrence of the A8296G mutation is of unclear significance and is likely to be a rare polymorphism.

Myophosphorylase deficiency associated with a defect in complex I of the mitochondrial respiratory chain

We studied a 21-year-old patient with clinical, biochemical and histochemical evidence of myophosphorylase deficiency and unusual repetitive episodes of pigmenturia. His muscle biopsy also revealed morphological signs of mitochondrial proliferation and a defect of complex I of the respiratory chain. His mother had exercise intolerance without myoglobinuria and no histochemical evidence of myophosphorylase deficiency. In muscle, the mother showed some ragged-red fibers, normal respiratory chain levels and a significant residual phosphorylase activity. Molecular genetic analysis revealed that the proband was homozygous for the mutation commonly found in McArdle's disease. The mother, father, and the five siblings were all heterozygous for the same mutation. Mitochondrial DNA analysis of the proband's muscle failed to demonstrate known mutations associated with his clinical pattern. Moreover, we sequenced his tRNA(Leu(UUR)) gene, a hot spot for mutations, showing no abnormality.

Biological roles of L-carnitine in perinatal metabolism

Carnitine performs a crucial role in the energy supply of tissues during fetal life and in the neonatal period by controlling the influx of fatty acids into mitochondria. Carnitine also facilitates the oxidation of pyruvate and branched chain amino acids, and contributes to the protection of cells from the deleterious actions of acyl CoAs. Carnitine further acts as a secondary antioxidant, favouring fatty acid replacement within previously oxidatively damaged membrane phospholipids. Availability of L-carnitine is essential in the developing fetus for processes underlying fetal maturation. L-carnitine is also essential for development of hepatic ketone synthesis, a central pathway for neonatal energy metabolism. Ketone bodies inhibit the oxidation of both glucose and lactate, sparing these metabolic substrates for biosynthetic functions.

Clinical heterogeneity associated with mitochondrial DNA depletion in muscle

We studied 10 patients with a variable degree of mtDNA depletion in muscle. Seven patients showed a clear-cut myopathic pattern, while the three remaining had brain involvement. There was no relationship between age at onset and relative mtDNA copy number in muscle, but we found an apparent correlation between clinical severity and degree of muscle mtDNA depletion. Muscle morphology showed that mtDNA depletion was associated with mitochondrial proliferation and cytochrome c oxidase negative fibers. Biochemical studies revealed single or combined defects of mtDNA-dependent respiratory chain complexes. Our data indicate that patients with mtDNA depletion may have a more variable age at onset and clinical evolution and wider phenotype than previously thought. The diagnosis of this condition, so far regarded as rare, may have been overlooked to some extent.

[Enzyme complex defects of the mitochondrial respiratory chain]

The mitochondrial respiratory chain is the final step in oxidative metabolism and plays an essential part in the mechanisms of energy production. It is composed of five enzymatic complexes under the dual control of nuclear and mitochondrial genomes. The disorders caused by respiratory chain defects are heterogeneous, mainly affecting organs and tissues which are functionally dependent on oxidative metabolism, such as brain, muscle, myocardium, kidney and liver. The activity of the enzymatic complexes may be measured in any tissue or organ, but skeletal muscle is usually used since it is post-mitotic and permits correlation with morphological studies. Defects in the electron transport chain may affect one or more complexes. Monoenzymopathies are characteristic of nuclear alterations, particularly if there is phenotype histo-specificity. However, mutations of the structural genes of the mitochondrial DNA (mtDNA) may also produce specific defects. Combined defects are characteristic of mtDNA alterations due to reduced synthesis of mitochondrial proteins.

Congenital ocular motor apraxia associated with myopathy, external hydrocephalus and NADH dehydrogenase deficiency

Congenital ocular motor apraxia (COMA), first described by Cogan [Trans Am Acad Ophthalmol Otolaryngol 1952;56:853-862], is a rare disorder characterized by impairment of voluntary and optically induced horizontal eye movements and compensatory head thrust. The causes and pathogenesis of COMA are poorly understood. It frequently occurs in association with other neurologic abnormalities including non-progressive congenital disorders of the central nervous system (CNS), various systemic diseases and chromosomal alterations. Here, we report the case of a 6-month-old girl with psychomotor retardation, myopathy and clinical features of COMA, associated with external hydrocephalus and mitochondrial dysfunction (partial deficiency of the respiratory-chain enzyme NADH dehydrogenase). In view of this finding, we recommend that tests to characterize patients with COMA should include determination of blood levels of lactic and pyruvic acid.

[Molecular genetics of alterations in the mitochondrial respiratory chain]

Mitochondrial biogenesis is the result of the coordinated action of two genomes, nuclear (nDNA) and mitochondrial (mtDNA). Therefore respiratory chain defects are divided into alterations of mtDNA and of nDNA. The former may be due to sporadic isolated deletions and specific duplications and mutations, which are both transmitted maternally. The nDNA disorders are inherited following a mendelian pattern and may affect genes which codify enzymes, genes which take part in the process of importing proteins, or genes involved in intergenomic communication. In the latter case, the alterations are seen in the mtDNA as multiple deletions or depletion. The characteristics of mitochondrial genetics are maternal inheritance, polyplasmia, heteroplasmia, mitotic segregation and threshold effect and largely explain the characteristic phenotype behaviour specific to these changes.

Cerebrospinal fluid carnitine levels in patients with Alzheimer's disease

We assessed free carnitine (FC) and acylcarnitine esters (AC) in both cerebrospinal fluid (CSF) and plasma from 24 patients with diagnostic criteria for Alzheimer's disease (AD), and from 28 healthy matched-controls. We found no significant correlation between FC and AC levels in CSF. FC and AC levels in CSF did not differ significantly between AD patients and controls, but plasma FC levels were significantly lower in AD patients. CSF and plasma FC and AC levels did not correlate with age, age at onset of AD, duration of AD, and scores of the Minimental State Examination of Folstein. Although these results suggest that CSF carnitine levels are apparently unrelated with the risk for AD, the trend of the FC/AC ratio to be higher in AD patients might suggest the possibility of a lower carnitine acetyltransferase activity in AD, as previously reported in some brain areas.

Effects of L-carnitine on erythrocyte acyl-CoA, free CoA, and glycerophospholipid acyltransferase in uremia

We studied the effects of L-carnitine treatment in the acyl flux of erythrocyte membranes from uremic patients. We found a significantly lower relative proportion of long-chain acyl-CoA (LCCoA) to free CoA (FCoA) in patients than in control subjects. In addition, patients had reduced activities of both carnitine palmitoyltransferase (CPT) and glycerophospholipid acyltransferase (LAT; CoA dependent), and increased ratios of long-chain acylcarnitine (LCAC) to free carnitine in their erythrocytes. These data support the hypothesis that acyl-trafficking is altered in erythrocytes in uremia. After treatment with L-carnitine, we observed a significant increase in CPT and LAT activities as well as in the LCCoA-FCoA ratio, and a significant decrease in the ratio of LCAC to free carnitine. These results support the conclusion that L-carnitine supplementation improves erythrocyte flux in uremic patients.

Complex I defect in muscle from patients with Huntington's disease

We found a variable defect of complex I of the mitochondrial respiratory chain, ranging in severity from 25% to 63% of control values, in muscle of patients with Huntington's disease (HD). The most severe defect was observed in the patient with the greatest expansion of CAG triplets. Muscle morphology showed myopathic changes such as moth-eaten fibers, angulated fibers, increased subsarcolemmal oxidative activities, or an increased number of enlarged mitochondria with abnormal cristae. Multiple mitochondrial DNA deletions were found by polymerase chain reaction (PCR) analysis in muscle of the patient with the most severe defect of complex I. Our data further support the involvement of energetic defects and oxidative damage in muscle of patients with HD.

Mitochondrial gene expression and respiratory enzyme activities in cardiac diseases

Respiratory enzyme activities and steady-state level of two mitochondrial-encoded transcripts were quantified in heart muscle biopsies from patients suffering various types of cardiomyopathies unrelated to mitochondrial primary disorders. We have found that although the mitochondrial DNA copy number and the concentration of COI and ND4 transcripts remain fairly constant, there is an important increase (up to 6-fold) in respiratory enzyme activities affecting to several oxidative phosphorylation complexes. Idiopathic dilated cardiomyopathy shows the greatest increase, followed by ischemic heart and ventricular hypertrophy due to aortic stenosis. The results suggest an energetic compensatory mechanism in the heart muscle, in the absence of mitochondrial proliferation or activation of mitochondrial gene expression.

Leishmania sp.: growth and survival are impaired by ion channel blockers

In the present work we examined the effect of ion transport blockers on the growth and viability of Leishmania sp. and on the infection of macrophages by the parasite. 4-aminopyridine and glibenclamide block voltage-dependent and K+ ATP channels, respectively; amiloride is used to detect Na+ channels and Na+/H+ antiporters; and anthracene-9-carboxylic acid affects chloride channels. The EC50 for promastigote cultures of three strains of the Leishmania subgenus, namely, Leishmania (Leishmania) NR, Leishmania (Leishmania) amazonensis LTB0016, and Leishmania (Leishmania) major, at their stationary phase of growth, were, respectively, 39, 46, and 464 microM for 4-aminopyridine; 7, 0.8, and 10 microM for glibenclamide and 66, 170, and 10 microM for anthracene-9-carboxylic acid. The amiloride EC50 for NR was 264 microM and 10 microM for L. (L.) major, but was never reached for LTB0016. Higher concentrations of the drugs impaired the exponential growth of Leishmania promastigotes. These results suggest the susceptibility of Leishmania sp. to blockers associated with K+ and Cl- and to Na+ or Na+/H+ transport systems. Blockade of such systems might have impaired the survival of the parasites as promastigotes. In addition, it affected the persistence of parasites in host cells. Although the infection of the macrophage cell line J774 and peritoneal-exudate macrophages was not significantly decreased by concentrations of the drugs around the promastigotes' EC50, the survival of intracellular parasites decreased significantly in the presence of these drugs without affecting the viability of the macrophages. Some blockers consistently gave small EC50 and significantly decreased the infection process as well as the survival of intracellular parasites. Thus, elucidation of their mechanism of action in Leishmania is relevant, since they could represent a potential subject for the development of leishmanicidal drugs.

Bilateral striatal necrosis and MELAS associated with a new T3308C mutation in the mitochondrial ND1 gene

We found a novel maternally inherited T3308C mutation in the mtDNA ND1 gene in a patient with bilateral striatal necrosis and stroke-like episodes. Muscle biopsy from the proband showed mitochondrial proliferation in blood vessels and normal respiratory chain activities. The mutation, which was not present in 100 normal controls or in 30 patients with mitochondrial disease, was heteroplasmic in both muscle and blood of the proband and in blood from her asymptomatic mother. This mutation results in a Met --> Thr change at the highly conserved amino acid position 1. The T3308C mutation may alter the hydrophobicity and antigenicity of the N-terminal peptide of ND1.

Syndrome of encephalopathy, petechiae, and ethylmalonic aciduria

We report a boy 20 months of age with encephalopathy, petechiae, and ethylmalonic aciduria (EPEMA). Other clinical features were severe hypotonia, orthostatic acrocyanosis, and chronic diarrhea. Magnetic resonance imaging (MRI) of the brain demonstrated bilateral lesions in the lenticular and caudate nuclei, periaqueductal region, subcortical areas, white matter, and brainstem. Short and medium chain Acyl-CoA dehydrogenase and cytochrome c oxidase (COX) activities in fibroblasts were normal. Muscle histochemistry disclosed diffuse COX deficiency, and respiratory chain activities in muscle disclosed severe COX deficiency. Twelve other patients with similar clinical features have been reported. Muscle COX activity, studied only in four, demonstrated a clear-cut defect.

Association of genetically proven deficiencies of myophosphorylase and AMP deaminase: a second case of 'double trouble'

We studied a 25-year-old man with paresis of the limbs and neck, scapular atrophy, facial weakness, exercise intolerance and frequent episodes of myoglobinuria. Muscle histochemistry and biochemistry revealed a combined defect of myophosphorylase and AMP deaminase. Molecular genetic analysis showed that the patient was homozygous for the two most common mutations associated with myophosphorylase and AMP deaminase deficiencies. This is the second documented case of genetic 'double trouble', which should be looked for in patients with unusual severe phenotypes.

Sensitivity of Leishmania spp. to glibenclamide and 4-aminopyridine: a tool for the study of drug resistance development

We have demonstrated that Leishmania spp. grown as promastigotes, are sensitive to the K+ channel inhibitors 4-aminopyridine and glibenclamide. Their host cells, the macrophages, are not affected by similar concentrations of the drugs. We have also initiated the molecular characterization of the mechanisms involved in the development of drug resistance to glibenclamide by the parasite. Therefore, we have selected experimentally and begun to characterize the Venezuelan Leishmania (Leishmania) strain, NR resistant to glibenclamide [NR(Gr)]. The analysis of genomic DNA evidenced the existence of a fragment which apparently is amplified in NR(Gr). The fragment recognized by the pgpA probe, related to the Leishmania P-glycoprotein family and which was originally isolated from L. tarentolae, showed a size polymorfism between the sensitive and the resistant strain. These results suggest that the development of resistance to glibenclamide in the strain NR(Gr) might be associated with the amplification of the ltpgpA or related gene(s).