Dilated cardiomyopathy due to type II X-linked 3-methylglutaconic aciduria: successful treatment with pantothenic acid

Impaired coenzyme A homeostasis in cardiac dysfunction and benefits of boosting coenzyme A production with vitamin B5 and its derivatives in the management of heart failure

Coenzyme A (CoA) is an essential cofactor required for over a hundred metabolic reactions in the human body. This cofactor is synthesized de novo in our cells from vitamin B5, also known as pantothenic acid, a water-soluble vitamin abundantly present in vegetables and animal-based foods. Neurodegenerative disorders, cancer, and infectious diseases have been linked to defects in de novo CoA biosynthesis or reduced levels of this coenzyme. There is now accumulating evidence that CoA limitation is a critical pathomechanism in cardiac dysfunction too. In the current review, we will summarize our current knowledge on CoA and heart failure, with emphasis on two primary cardiomyopathies, phosphopantothenoylcysteine synthetase and phosphopantothenoylcysteine decarboxylase deficiency disorders biochemically characterized by a decreased level of CoA in patients' samples. Hence, we will discuss the potential benefits of CoA restoration in these diseases and, more generally, in heart failure, by vitamin B5 and its derivatives pantethine and 4'-phosphopantetheine.

Role of Vitamins in Cardiovascular Health: Know Your Facts - Part 1

Cardiovascular (CV) disease (CVD) is a major cause of morbidity and mortality world-wide, thus it is important to adopt preventive interventions. Observational data demonstrating CV benefits of vitamin supplements, advanced by self-proclaimed experts have resulted in ~50% of Americans reporting the use of multivitamins for health promotion; this practice has led to a multi-billion-dollar business of the multivitamin-industry. However, the data on the extensive use of multivitamins show no consistent benefit for CVD prevention or all-cause mortality, while the use of certain vitamins might prove harmful. Thus, the focus of this two-part review is on the attributes or concerns about specific vitamins on CVD. In Part 1, the CV effects of specific vitamins are discussed, indicating the need for further supportive evidence of potential benefits. Vitamin A preserves CV homeostasis as it participates in many biologic functions, including atherosclerosis. However, supplementation could potentially be harmful. Betacarotene, a pro-vitamin A, conveys pro-oxidant actions that may mitigate any other benefits. Folic acid alone and certain B-vitamins (e.g., B1/B2/B6/B12) may reduce CVD, heart failure, and/or stroke, while niacin might increase mortality. Vitamin C has antioxidant and cardioprotective effects. Vitamin D may confer CV protection, but all the data are not in agreement. Combined vitamin E and C have antiatherogenic effects but clinical evidence is inconsistent. Vitamin K seems neutral. Thus, there are individual vitamin actions with favorable CV impact (certain B-vitamins and vitamins C and D), but other vitamins (β-carotene, niacin) may potentially have deleterious effects, which also holds true for high doses of fat-soluble vitamins (A/D/E/K).

Metabolic Therapy of Heart Failure: Is There a Future for B Vitamins?

Heart failure (HF) is a plague of the aging population in industrialized countries that continues to cause many deaths despite intensive research into more effective treatments. Although the therapeutic arsenal to face heart failure has been expanding, the relatively short life expectancy of HF patients is pushing towards novel therapeutic strategies. Heart failure is associated with drastic metabolic disorders, including severe myocardial mitochondrial dysfunction and systemic nutrient deprivation secondary to severe cardiac dysfunction. To date, no effective therapy has been developed to restore the cardiac energy metabolism of the failing myocardium, mainly due to the metabolic complexity and intertwining of the involved processes. Recent years have witnessed a growing scientific interest in natural molecules that play a pivotal role in energy metabolism with promising therapeutic effects against heart failure. Among these molecules, B vitamins are a class of water soluble vitamins that are directly involved in energy metabolism and are of particular interest since they are intimately linked to energy metabolism and HF patients are often B vitamin deficient. This review aims at assessing the value of B vitamin supplementation in the treatment of heart failure.

Barth syndrome: cardiolipin, cellular pathophysiology, management, and novel therapeutic targets

Barth syndrome is a rare X-linked genetic disease classically characterized by cardiomyopathy, skeletal myopathy, growth retardation, neutropenia, and 3-methylglutaconic aciduria. It is caused by mutations in the tafazzin gene localized to chromosome Xq28.12. Mutations in tafazzin may result in alterations in the level and molecular composition of the mitochondrial phospholipid cardiolipin and result in large elevations in the lysophospholipid monolysocardiolipin. The increased monolysocardiolipin:cardiolipin ratio in blood is diagnostic for the disease, and it leads to disruption in mitochondrial bioenergetics. In this review, we discuss cardiolipin structure, synthesis, and function and provide an overview of the clinical and cellular pathophysiology of Barth Syndrome. We highlight known pharmacological management for treatment of the major pathological features associated with the disease. In addition, we discuss non-pharmacological management. Finally, we highlight the most recent promising therapeutic options for this rare mitochondrial disease including lipid replacement therapy, peroxisome proliferator-activated receptor agonists, tafazzin gene replacement therapy, induced pluripotent stem cells, mitochondria-targeted antioxidants and peptides, and the polyphenolic compound resveratrol.

The Pathophysiological Role of CoA

The importance of coenzyme A (CoA) as a carrier of acyl residues in cell metabolism is well understood. Coenzyme A participates in more than 100 different catabolic and anabolic reactions, including those involved in the metabolism of lipids, carbohydrates, proteins, ethanol, bile acids, and xenobiotics. However, much less is known about the importance of the concentration of this cofactor in various cell compartments and the role of altered CoA concentration in various pathologies. Despite continuous research on these issues, the molecular mechanisms in the regulation of the intracellular level of CoA under pathological conditions are still not well understood. This review summarizes the current knowledge of (a) CoA subcellular concentrations; (b) the roles of CoA synthesis and degradation processes; and (c) protein modification by reversible CoA binding to proteins (CoAlation). Particular attention is paid to (a) the roles of changes in the level of CoA under pathological conditions, such as in neurodegenerative diseases, cancer, myopathies, and infectious diseases; and (b) the beneficial effect of CoA and pantethine (which like CoA is finally converted to Pan and cysteamine), used at pharmacological doses for the treatment of hyperlipidemia.

Tafazzin deficiency impairs CoA-dependent oxidative metabolism in cardiac mitochondria

Barth syndrome is a mitochondrial myopathy resulting from mutations in the tafazzin (TAZ) gene encoding a phospholipid transacylase required for cardiolipin remodeling. Cardiolipin is a phospholipid of the inner mitochondrial membrane essential for the function of numerous mitochondrial proteins and processes. However, it is unclear how tafazzin deficiency impacts cardiac mitochondrial metabolism. To address this question while avoiding confounding effects of cardiomyopathy on mitochondrial phenotype, we utilized Taz-shRNA knockdown (Taz^KD ) mice, which exhibit defective cardiolipin remodeling and respiratory supercomplex instability characteristic of human Barth syndrome but normal cardiac function into adulthood. Consistent with previous reports from other models, mitochondrial H₂O₂ emission and oxidative damage were greater in Taz^KD than in wild-type (WT) hearts, but there were no differences in oxidative phosphorylation coupling efficiency or membrane potential. Fatty acid and pyruvate oxidation capacities were 40-60% lower in Taz^KD mitochondria, but an up-regulation of glutamate oxidation supported respiration rates approximating those with pyruvate and palmitoylcarnitine in WT. Deficiencies in mitochondrial CoA and shifts in the cardiac acyl-CoA profile paralleled changes in fatty acid oxidation enzymes and acyl-CoA thioesterases, suggesting limitations of CoA availability or "trapping" in Taz^KD mitochondrial metabolism. Incubation of Taz^KD mitochondria with exogenous CoA partially rescued pyruvate and palmitoylcarnitine oxidation capacities, implicating dysregulation of CoA-dependent intermediary metabolism rather than respiratory chain defects in the bioenergetic impacts of tafazzin deficiency. These findings support links among cardiolipin abnormalities, respiratory supercomplex instability, and mitochondrial oxidant production and shed new light on the distinct metabolic consequences of tafazzin deficiency in the mammalian heart.

Clinical Characteristics and Outcomes of Cardiomyopathy in Barth Syndrome: The UK Experience

Barth syndrome (BTHS) is an X-linked disorder characterised by cardiomyopathy, neutropenia, skeletal myopathy and growth delay. This study describes the UK national clinical experience and outcome of cardiomyopathy in BTHS. The clinical course and echocardiographic changes of all patients with BTHS in the UK were reviewed from 2004 to 2014. In addition, strain analysis using 2D speckle tracking echocardiography was performed to further assess left ventricular function in the most recent follow-up. At last follow-up, 22 of 27 patients were alive with a median age of 12.6 (2.0-23.8) years; seven underwent cardiac transplantation at a median age of 2 (0.33-3.6) years, and five died (18.5%) at a median age of 1.8 (0.02-4.22) years. All deaths were related to cardiomyopathy or its management. Left ventricular diastolic dimension and systolic function measured by fractional shortening tended to normalise and stabilise after the first 3 years of life in the majority of patients. However, patients with BTHS (n = 16) had statistically significant reduction in global longitudinal and circumferential strain compared to controls (n = 18), (p < 0.001), despite apparent normal conventional measures of function. There was also reduced or reversed apical rotation and reduced left ventricular twist. Sustained ventricular arrhythmia was not seen at follow-up. Cardiac phenotype in BTHS is variable; however, longer-term outcome in our cohort suggests good prognosis after the first 5 years of life. Most patients appeared to have recovered near normal cardiac function by conventional echocardiographic measures, but strain analysis showed abnormal myocardial deformation and rotational mechanics.

Left ventricular noncompaction (LVNC) and low mitochondrial membrane potential are specific for Barth syndrome

Barth syndrome (BTHS) is an X-linked mitochondrial defect characterised by dilated cardiomyopathy, neutropaenia and 3-methylglutaconic aciduria (3-MGCA). We report on two affected brothers with c.646G > A (p.G216R) TAZ gene mutations. The pathogenicity of the mutation, as indicated by the structure-based functional analyses, was further confirmed by abnormal monolysocardiolipin/cardiolipin ratio in dry blood spots of the patients as well as the occurrence of this mutation in another reported BTHS proband. In both brothers, 2D-echocardiography revealed some features of left ventricular noncompaction (LVNC) despite marked differences in the course of the disease; the eldest child presented with isolated cardiomyopathy from late infancy, whereas the youngest showed severe lactic acidosis without 3-MGCA during the neonatal period. An examination of the patients' fibroblast cultures revealed that extremely low mitochondrial membrane potentials (mtΔΨ about 50 % of the control value) dominated other unspecific mitochondrial changes detected (respiratory chain dysfunction, abnormal ROS production and depressed antioxidant defense). 1) Our studies confirm generalised mitochondrial dysfunction in the skeletal muscle and the fibroblasts of BTHS patients, especially a severe impairment in the mtΔΨ and the inhibition of complex V activity. It can be hypothesised that impaired mtΔΨ and mitochondrial ATP synthase activity may contribute to episodes of cardiac arrhythmia that occurred unexpectedly in BTHS patients. 2) Severe lactic acidosis without 3-methylglutaconic aciduria in male neonates as well as an asymptomatic mild left ventricular noncompaction may characterise the ranges of natural history of Barth syndrome.

Barth syndrome

First described in 1983, Barth syndrome (BTHS) is widely regarded as a rare X-linked genetic disease characterised by cardiomyopathy (CM), skeletal myopathy, growth delay, neutropenia and increased urinary excretion of 3-methylglutaconic acid (3-MGCA). Fewer than 200 living males are known worldwide, but evidence is accumulating that the disorder is substantially under-diagnosed. Clinical features include variable combinations of the following wide spectrum: dilated cardiomyopathy (DCM), hypertrophic cardiomyopathy (HCM), endocardial fibroelastosis (EFE), left ventricular non-compaction (LVNC), ventricular arrhythmia, sudden cardiac death, prolonged QTc interval, delayed motor milestones, proximal myopathy, lethargy and fatigue, neutropenia (absent to severe; persistent, intermittent or perfectly cyclical), compensatory monocytosis, recurrent bacterial infection, hypoglycaemia, lactic acidosis, growth and pubertal delay, feeding problems, failure to thrive, episodic diarrhoea, characteristic facies, and X-linked family history. Historically regarded as a cardiac disease, BTHS is now considered a multi-system disorder which may be first seen by many different specialists or generalists. Phenotypic breadth and variability present a major challenge to the diagnostician: some children with BTHS have never been neutropenic, whereas others lack increased 3-MGCA and a minority has occult or absent CM. Furthermore, BTHS was first described in 2010 as an unrecognised cause of fetal death. Disabling mutations or deletions of the tafazzin (TAZ) gene, located at Xq28, cause the disorder by reducing remodeling of cardiolipin, a principal phospholipid of the inner mitochondrial membrane. A definitive biochemical test, based on detecting abnormal ratios of different cardiolipin species, was first described in 2008. Key areas of differential diagnosis include metabolic and viral cardiomyopathies, mitochondrial diseases, and many causes of neutropenia and recurrent male miscarriage and stillbirth. Cardiolipin testing and TAZ sequencing now provide relatively rapid diagnostic testing, both prospectively and retrospectively, from a range of fresh or stored tissues, blood or neonatal bloodspots. TAZ sequencing also allows female carrier detection and antenatal screening. Management of BTHS includes medical therapy of CM, cardiac transplantation (in 14% of patients), antibiotic prophylaxis and granulocyte colony-stimulating factor (G-CSF) therapy. Multidisciplinary teams/clinics are essential for minimising hospital attendances and allowing many more individuals with BTHS to live into adulthood.

Barth syndrome: an X-linked cardiomyopathy with a novel mutation

The authors report a 6 yr old boy with Barth syndrome who presented with cardiomyopathy, neutropenia and hypotonia. Urine gas chromatography showed high level of 3-methylglutaconic acid. The DNA of both the patient and the mother showed a heterozygous 3 bp deletion in exon 8 of the tafazzin gene. This abnormality involves the deletion of the bases TGA starting at cDNA nucleotide 891 (c891_893delTGA), resulting in the absence of glutamic acid at codon 202 from a highly conserved area of the tafazzin protein, consistent with the diagnosis of Barth syndrome. This is the first case report of Barth syndrome in Arab population emphasizing the importance of detailed investigations in cases of hereditary cardiomyopathy.

Clinical approach to treatable inborn metabolic diseases: an introduction

In view of the major improvements in treatment, it has become increasingly important that in order for first-line physicians not to miss a treatable disorder they should be able initiate a simple method of clinical screening, particularly in the emergency room. We present a simplified classification of treatable inborn errors of metabolism in three groups. Group 1 includes inborn errors of intermediary metabolism that give rise to an acute or chronic intoxication. It encompasses aminoacidopathies, organic acidurias, urea cycle disorders, sugar intolerances, metal disorders and porphyrias. Clinical expression can be acute or systemic or can involve a specific organ, and can strike in the neonatal period or later and intermittently from infancy to late adulthood. Most of these disorders are treatable and require the emergency removal of the toxin by special diets, extracorporeal procedures, cleansing drugs or vitamins. Group 2 includes inborn errors of intermediary metabolism that affect the cytoplasmic and mitochondrial energetic processes. Cytoplasmic defects encompass those affecting glycolysis, glycogenosis, gluconeogenesis, hyperinsulinisms, and creatine and pentose phosphate pathways; the latter are untreatable. Mitochondrial defects include respiratory chain disorders, and Krebs cycle and pyruvate oxidation defects, mostly untreatable, and disorders of fatty acid oxidation and ketone bodies that are treatable. Group 3 involves cellular organelles and includes lysosomal, peroxisomal, glycosylation, and cholesterol synthesis defects. Among these, some lysosomal disorders can be efficiently treated by enzyme replacement or substrate reduction therapies. Physicians can be faced with the possibility of a treatable inborn error in an emergency, either in the neonatal period or late in infancy to adulthood, or as chronic and progressive symptoms--general (failure to thrive), neurological, or specific for various organs or systems. These symptoms are summarized in four tables. In addition, an extensive list of medications used in the treatment of inborn errors is presented.

Cardiolipin metabolism and Barth Syndrome

Many advances have occurred in the field of Barth Syndrome biology in the 26 years since it was first described as an X-linked cardiomyopathy. Barth Syndrome is the first human disease recognized in which the primary causative factor is an alteration in cardiolipin remodeling. Cardiolipin is required for the optimal function of many proteins within the mitochondria, particularly in the respiratory chain and is involved in the mitochondrial-mediated apoptotic process. The appropriate content of cardiolipin appears to be critical for these functions. Cardiolipin is synthesized de novo in mitochondria and is rapidly remodeled to produce CL enriched in linoleic acid. The Barth Syndrome gene TAZ has been identified and expression of the gene yields proteins known as tafazzins. Mutations in TAZ result in a decrease in tetra-linoleoyl species of cardiolipin and an accumulation of monolysocardiolipin within cells from Barth Syndrome patients. Although the protein product of the TAZ gene shows sequence homology to the glycerolipid acyltransferase family of enzymes, its precise biochemical function remains to be elucidated. In this review we highlight some of the recent literature on cardiolipin metabolism and Barth Syndrome.

Clinicopathologic conference: Barth Syndrome

A case of Barth Syndrome is presented and discussed by both clinician and pathologist, in this traditional clinico-pathologic conference. The current understanding of etiology is included, including elevation of 3-methylglutaconic acid (3MGC).

X-linked cardioskeletal myopathy and neutropenia (Barth syndrome): an update

X-linked cardioskeletal myopathy and neutropenia (Barth syndrome, MIM302060, BTHS) is a disorder with mitochondrial functional impairments and 3-methylglutaconic aciduria that maps to Xq28. The associated G4.5 or TAZ gene has been identified but the encoded proteins have not yet been characterized. Following the prediction that the gene encodes one or more acyltransferases, lipid studies have shown a deficiency of cardiolipin, especially its tetralinoleoyl form (L(4)-CL). Deficiency of L(4)-CL was subsequently demonstrated in a variety of tissues, and determination in thrombocytes or cultured skin fibroblasts is now the most specific biochemical test available. BTHS is the first identified inborn error of metabolism that directly affects cardiolipin, a component of the inner mitochondrial membrane, necessary for proper functioning of the electron transport chain. We report here the finding of deficient docosahexaenoic acid and arachidonic acid in a proportion of patients with BTHS. The initial impression of a uniformly lethal infantile disease has to be modified. Age distribution in 54 living patients ranges between 0 and 49 years and peaks around puberty. Mortality is the highest in the first 4 years. The apex of the survival curve around puberty and the emergence of adults may reflect a dynamic shift towards increased survival. This trend is exemplified in a large pedigree previously published.

Long-term treatment of Barth syndrome with pantothenic acid: a retrospective study

We report on three patients (two are brothers) with confirmed Barth syndrome treated with pantothenic acid. This treatment is still controversial and only one study has reported positive results to date. In our patients, long-term treatment has failed to reduce the number of infectious episodes and prevent dilated cardiomyopathy. Our cases show that this treatment is not as effective in Barth syndrome as was previously claimed.

High-dose vitamin therapy stimulates variant enzymes with decreased coenzyme binding affinity (increased K(m)): relevance to genetic disease and polymorphisms

As many as one-third of mutations in a gene result in the corresponding enzyme having an increased Michaelis constant, or K(m), (decreased binding affinity) for a coenzyme, resulting in a lower rate of reaction. About 50 human genetic dis-eases due to defective enzymes can be remedied or ameliorated by the administration of high doses of the vitamin component of the corresponding coenzyme, which at least partially restores enzymatic activity. Several single-nucleotide polymorphisms, in which the variant amino acid reduces coenzyme binding and thus enzymatic activity, are likely to be remediable by raising cellular concentrations of the cofactor through high-dose vitamin therapy. Some examples include the alanine-to-valine substitution at codon 222 (Ala222-->Val) [DNA: C-to-T substitution at nucleo-tide 677 (677C-->T)] in methylenetetrahydrofolate reductase (NADPH) and the cofactor FAD (in relation to cardiovascular disease, migraines, and rages), the Pro187-->Ser (DNA: 609C-->T) mutation in NAD(P):quinone oxidoreductase 1 [NAD(P)H dehy-drogenase (quinone)] and FAD (in relation to cancer), the Ala44-->Gly (DNA: 131C-->G) mutation in glucose-6-phosphate 1-dehydrogenase and NADP (in relation to favism and hemolytic anemia), and the Glu487-->Lys mutation (present in one-half of Asians) in aldehyde dehydrogenase (NAD + ) and NAD (in relation to alcohol intolerance, Alzheimer disease, and cancer).

Infantile dilated X-linked cardiomyopathy, G4.5 mutations, altered lipids, and ultrastructural malformations of mitochondria in heart, liver, and skeletal muscle

Mutations in the Xq28 gene G4.5 lead to dilated cardiomyopathy (DCM). Differential splicing of G4.5 results in a family of proteins called "tafazzins" with homology to acyltransferases. These enzymes assemble fatty acids into membrane lipids. We sequenced G4.5 in two kindreds with X-linked DCM and in two unrelated men, one with idiopathic DCM and the other with DCM of arrhythmogenic right ventricular dysplasia. We examined the ultrastructure of heart, liver, and muscle biopsy specimens in these three DCM types; we used gas chromatography to compare fatty acid composition in heart, liver, and muscle autopsy specimens of two patients of kindred 1 with that of controls. In X-linked DCM, G4.5 had a stop codon (E188X), a nonsense mutation, in kindred 1 and an amino acid substitution (G240R), a missense mutation, in kindred 2. In the two men with isolated DCM, G4.5 was not mutated. Ultrastructural mitochondrial malformations were present in the biopsy tissues of the patients with DCM. Cardiac biopsy specimens of both kindreds with X-linked DCM exhibited greatly enlarged mitochondria with large bundles of stacked, compacted, disarrayed cristae that differed from those of the two types of isolated DCM. Autopsy tissue of patients with X-linked DCM had decreased unsaturated and increased saturated fatty acid concentrations. Seven of 13 published G4.5 missense mutations, including the one presented here, occur in acyltransferase motifs. Impaired acyltransferase function could result in increased fatty acid saturation that would decrease membrane fluidity. Mitochondrial membrane proliferation may be an attempt to compensate for impaired function of acyltransferase. Cardiac ultrastructure separates X-linked DCM with G4.5 mutations from the two types of isolated DCM without G4.5 mutations. Electron microscopy of promptly fixed myocardial biopsy specimens has a role in defining the differential diagnosis of DCM. Mutational analysis of the G4.5 gene also serves this purpose.

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.

Mutation characterization and genotype-phenotype correlation in Barth syndrome

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

Clinical approach to genetic cardiomyopathy in children

BACKGROUND

Cardiomyopathy (CM) remains one of the leading cardiac causes of death in children, although in the majority of cases, the cause is unknown. To have an impact on morbidity and mortality, attention must shift to etiology-specific treatments. The diagnostic evaluation of children with CM of genetic origin is complicated by the large number of rare genetic causes, the broad range of clinical presentations, and the array of specialized diagnostic tests and biochemical assays.

METHODS AND RESULTS

We present a multidisciplinary diagnostic approach to pediatric CM of genetic etiology. We specify criteria for abnormal left ventricular systolic performance and structure that suggest CM based on established normal echocardiographic measurements and list other indications to consider an evaluation for CM. We provide a differential diagnosis of genetic conditions associated with CM, classified as inborn errors of metabolism, malformation syndromes, neuromuscular diseases, and familial isolated CM disorders. A diagnostic strategy is offered that is based on the clinical presentation: biochemical abnormalities, encephalopathy, dysmorphic features or multiple malformations, neuromuscular disease, apparently isolated CM, and pathological specimen findings. Adjunctive treatment measures are recommended for severely ill patients in whom a metabolic cause of CM is suspected. A protocol is provided for the evaluation of moribund patients.

CONCLUSIONS

In summary, we hope to assist pediatric cardiologists and other subspecialists in the evaluation of children with CM for a possible genetic cause using a presentation-based approach. This should increase the percentage of children with CM for whom a diagnosis can be established, with important implications for treatment, prognosis, and genetic counseling.

The treatment of congenital lactic acidoses

Congenital lactic acidoses form a heterogeneous group of disorders: this paper considers primarily defects of the pyruvate dehydrogenase complex and the respiratory chain. Attempts to treat these disorders are hampered by uncertainty concerning the pathophysiology and by the central role of the enzymes in cellular metabolism. Few strategies are of proven efficacy, though many have been tried, including dietary manipulation, enhancement of residual enzyme activity, artificial electron acceptors and free-radical scavengers. Evaluation of treatment is complicated by the rarity, heterogeneity and unpredictable course of the diseases. Double-blind placebo-controlled trials are needed.