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).

Leigh syndrome associated with the T9176C mutation in the ATPase 6 gene of mitochondrial DNA

A child with clinical and neuroradiologic evidence of Leigh syndrome (LS) had the T-to-C transition at nt 9176 in the ATPase 6 gene of mtDNA. The mutation was homoplasmic in muscle and maternally inherited. The proband's mother had ataxia and harbored 93% of mutant genomes in blood, whereas three clinically unaffected maternal relatives had varying degrees of heteroplasmy in blood. These data confirm the association of the T9176C mutation with LS and extend the clinical heterogeneity of mutations in the ATPase 6 gene.

Gene dosage effect in one family with myoclonic epilepsy and ragged-red fibers (MERRF)

OBJECTIVES

We analyzed the percentage of mitochondrial DNA (mtDNA) heteroplasmy in blood samples of 13 individuals belonging to a three family generation of myoclonic epilepsy with ragged-red fibers (MERRF) and compared the 5 affected patients and the 8 unaffected relatives.

MATERIAL AND METHODS

DNA was extracted from blood and muscle of the proband and from blood of 12 maternal relatives. A PCR restriction analysis method was used to detect the mutation.

RESULTS

The proband had the complete MERRF phenotype. The phenotype in three other individuals in the maternal lineage was consistent with the MERRF syndrome. The remaining were asymptomatic. The np 8344 mutation was observed in muscle and blood of the proband, and in blood from every one of 12 maternal relatives, ranging from 44% to 83% of mutated genomes. Symptomatic individuals had higher levels (P < 0.001) of mutated mtDNA than asymptomatic maternal relatives. However, high proportions of mutant genomes (up to 63%) were found in asymptomatic relatives.

CONCLUSIONS

Although there seems to be a gene dosage effect in MERRF, we found no absolute relationship between the relative proportion of mutant genomes in blood and clinical severity. Factors other than gene dosage in blood may account for the differences in clinical phenotype.

Evidence for two distinct members of the amylase gene family in the yellow fever mosquito, Aedes aegypti

Genomic DNA fragments encoding a salivary gland-specific alpha-amylase gene, Amylase I (Amy I), and an additional amylase, Amylase II (AmyII) of the yellow fever mosquito, Aedes aegypti, were isolated and characterized. Two independently isolated DNA fragments, G34-F and G34-14A, encode polymorphic alleles of Amy I. A 3.2 kilobase (kb) EcoR I fragment of G34-F, F2, has been sequenced in its entirety and contains 832 base pairs (bp) of the 5'-end, non-coding and putative promoter regions that are adjacent to 2.4 kb of the Amy I coding region. One intron, 59 bp in length, is found towards the 3'-end of the clone. A third genomic clone, 3A, corresponding to Amy II, was sequenced and shown not to contain the primary DNA sequence that encodes the 260 amino acid region that uniquely characterizes the amino terminal end of the Amy I product. Amy I was assigned by restriction fragment length polymorphism (RFLP) mapping to chromosome 2 (23.0 cM) and Amy II to chromosome 1 (44.0 cM). Amy I and Amy II are highly polymorphic and there may be multiple linked copies at each locus. Comparisons between Amy I and Amy II are presented for the putative promoter and conceptual translation products. The identification of two distinct amylase genes and their separate linkage assignments provides evidence for a multigene family of alpha-amylases in Ae. aegypti.