Hypoglycemia, hepatic dysfunction, muscle weakness, cardiomyopathy, free carnitine deficiency and long-chain acylcarnitine excess responsive to medium chain triglyceride diet

Impact of Parenteral Lipid Emulsion Components on Cholestatic Liver Disease in Neonates

Total parenteral nutrition (TPN) is a life-saving intervention for infants that are unable to feed by mouth. Infants that remain on TPN for extended periods of time are at risk for the development of liver injury in the form of parenteral nutrition associated cholestasis (PNAC). Current research suggests the lipid component of TPN is a factor in the development of PNAC. Most notably, the fatty acid composition, vitamin E concentration, and presence of phytosterols are believed key mediators of lipid emulsion driven PNAC development. New emulsions comprised of fish oil and medium chain triglycerides show promise for reducing the incidence of PNAC in infants. In this review we will cover the current clinical studies on the benefit of fish oil and medium chain triglyceride containing lipid emulsions on the development of PNAC, the current constituents of lipid emulsions that may modulate the prevalence of PNAC, and potential new supplements to TPN to further reduce the incidence of PNAC.

Effect of lifelong carnitine supplementation on plasma and tissue carnitine status, hepatic lipid metabolism and stress signalling pathways and skeletal muscle transcriptome in mice at advanced age

While strong evidence from clinical studies suggests beneficial effects of carnitine supplementation on metabolic health, serious safety concerns associated with carnitine supplementation have been raised from studies in mice. Considering that the carnitine doses in these mice studies were up to 100 times higher than those used in clinical studies, the present study aimed to address possible safety concerns associated with long-term supplementation of a carnitine dose used in clinical trials. Two groups of NMRI mice were fed either a control or a carnitine-supplemented diet (1 g/kg diet) from weaning to 19 months of age, and parameters of hepatic lipid metabolism and stress signalling and skeletal muscle gene expression were analysed in the mice at 19 months of age. Concentrations of free carnitine and acetylcarnitine in plasma and tissues were higher in the carnitine than in the control group (P<0·05). Plasma concentrations of free carnitine and acetylcarnitine were higher in mice at adult age (10 and 15 months) than at advanced age (19 months) (P<0·05). Hepatic mRNA and protein levels of genes involved in lipid metabolism and stress signalling and hepatic and plasma lipid concentrations did not differ between the carnitine and the control group. Skeletal muscle transcriptome analysis in 19-month-old mice revealed only a moderate regulation between carnitine and control group. Lifelong carnitine supplementation prevents an age-dependent impairment of plasma carnitine status, but safety concerns associated with long-term supplementation of carnitine at doses used in clinical trials can be considered as unfounded.

Disorders of mitochondrial long-chain fatty acid oxidation and the carnitine shuttle

Mitochondrial fatty acid oxidation is an essential pathway for energy production, especially during prolonged fasting and sub-maximal exercise. Long-chain fatty acids are the most abundant fatty acids in the human diet and in body stores, and more than 15 enzymes are involved in long-chain fatty acid oxidation. Pathogenic mutations in genes encoding these enzymes result in a long-chain fatty acid oxidation disorder in which the energy homeostasis is compromised and long-chain acylcarnitines accumulate. Symptoms arise or exacerbate during catabolic situations, such as fasting, illness and (endurance) exercise. The clinical spectrum is very heterogeneous, ranging from hypoketotic hypoglycemia, liver dysfunction, rhabdomyolysis, cardiomyopathy and early demise. With the introduction of several of the long-chain fatty acid oxidation disorders (lcFAOD) in newborn screening panels, also asymptomatic individuals with a lcFAOD are identified. However, despite early diagnosis and dietary therapy, a significant number of patients still develop symptoms emphasizing the need for individualized treatment strategies. This review aims to function as a comprehensive reference for clinical and laboratory findings for clinicians who are confronted with pediatric and adult patients with a possible diagnosis of a lcFAOD.

Downregulation of carnitine acyl-carnitine translocase by miRNAs 132 and 212 amplifies glucose-stimulated insulin secretion

We previously demonstrated that micro-RNAs (miRNAs) 132 and 212 are differentially upregulated in response to obesity in two mouse strains that differ in their susceptibility to obesity-induced diabetes. Here we show the overexpression of miRNAs 132 and 212 enhances insulin secretion (IS) in response to glucose and other secretagogues including nonfuel stimuli. We determined that carnitine acyl-carnitine translocase (CACT; Slc25a20) is a direct target of these miRNAs. CACT is responsible for transporting long-chain acyl-carnitines into the mitochondria for β-oxidation. Small interfering RNA-mediated knockdown of CACT in β-cells led to the accumulation of fatty acyl-carnitines and enhanced IS. The addition of long-chain fatty acyl-carnitines promoted IS from rat insulinoma β-cells (INS-1) as well as primary mouse islets. The effect on INS-1 cells was augmented in response to suppression of CACT. A nonhydrolyzable ether analog of palmitoyl-carnitine stimulated IS, showing that β-oxidation of palmitoyl-carnitine is not required for its stimulation of IS. These studies establish a link between miRNA-dependent regulation of CACT and fatty acyl-carnitine-mediated regulation of IS.

Disorders of fatty acid oxidation

Recognition of fatty acid oxidation (FAO) disorders is important for the pediatric neurologist as they present with a spectrum of clinical disorders, including progressive lipid storage myopathy, recurrent myoglobinuria, neuropathy, progressive cardiomyopathy, recurrent hypoglycemic hypoketotic encephalopathy or Reye-like syndrome, seizures, and mental retardation. They constitute a critical group of diseases because they are potentially rapidly fatal and a source of major morbidity. There is frequently a family history of sudden infant death syndrome in siblings. Early recognition and prompt institution of therapy and appropriate preventive measures, and in certain cases specific therapy, may be life-saving and may significantly decrease long-term morbidity, particularly with respect to CNS sequelae. All currently known conditions are inherited as autosomal recessive traits. There are now at least 25 enzymes and specific transport proteins in the β-oxidation pathway and 18 have been associated with human disease. The most common defect is medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, which had an incidence of 1 in 8930 live births in one series. The identification of serum acylcarnitines by electrospray ionization-tandem mass spectrometry of dried blood spots on filter paper in newborn screening programs has significantly enhanced the early recognition of these disorders.

Role of carnitine in the regulation of glucose homeostasis and insulin sensitivity: evidence from in vivo and in vitro studies with carnitine supplementation and carnitine deficiency

BACKGROUND

Although carnitine is best known for its role in the import of long-chain fatty acids (acyl groups) into the mitochondrial matrix for subsequent β-oxidation, carnitine is also necessary for the efflux of acyl groups out of the mitochondria. Since intracellular accumulation of acyl-CoA derivatives has been implicated in the development of insulin resistance, carnitine supplementation has gained attention as a tool for the treatment of insulin resistance. More recent studies even point toward a causative role for carnitine insufficiency in developing insulin resistance during states of chronic metabolic stress, such as obesity, which can be reversed by carnitine supplementation.

METHODS

The present review provides an overview about data from both animal and human studies reporting effects of either carnitine supplementation or carnitine deficiency on parameters of glucose homeostasis and insulin sensitivity in order to establish the less well-recognized role of carnitine in regulating glucose homeostasis.

RESULTS

Carnitine supplementation studies in both humans and animals demonstrate an improvement of glucose tolerance, in particular during insulin-resistant states. In contrast, less consistent results are available from animal studies investigating the association between carnitine deficiency and glucose intolerance. The majority of studies dealing with this question could either find no association or even reported that carnitine deficiency lowers blood glucose and improves insulin sensitivity.

CONCLUSIONS

In view of the abovementioned beneficial effect of carnitine supplementation on glucose tolerance during insulin-resistant states, carnitine supplementation might be an effective tool for improvement of glucose utilization in obese type 2 diabetic patients. However, further studies are necessary to explain the conflicting observations from studies dealing with carnitine deficiency.

Glucose metabolism in children: influence of age, fasting, and infectious diseases

This review describes the occurrence of hypoglycemia in young children as a common and serious complication that needs to be avoided because of the high risk of brain damage and mortality. Young age, fasting, and severe infectious disease are considered important risk factors. The limited data on the effect of these risk factors on glucose metabolism in children are discussed and compared with data on glucose metabolism in adults. The observations discussed may have implications for further research on glucose kinetics in young children with infectious disease.

Acute dilated cardiomyopathy in a patient with deficiency of long-chain 3-hydroxyacyl-CoA dehydrogenase

Deficiency of long-chain 3-hydroxyacyl-coenzyme A (CoA) dehydrogenase (LCHADD) is a rare inborn error of metabolism. It is associated with hypertrophic cardiomyopathy and less frequently with dilated cardiomyopathy. The incidence and pathophysiology of cardiac involvement in LCHADD is poorly understood. This report describes the acute decompensation of a 3-year-old girl who had LCHADD with rapidly developing dilated cardiomyopathy. A review of the literature and possible causes of cardiomyopathy in LCHADD are explored.

Hyperammonemic encephalopathy caused by carnitine deficiency

Carnitine is an essential co-factor in fatty acid metabolism. Carnitine deficiency can impair fatty acid oxidation, rarely leading to hyperammonemia and encephalopathy. We present the case of a 35-year-old woman who developed acute mental status changes, asterixis, and diffuse muscle weakness. Her ammonia level was elevated at 276 microg/dL. Traditional ammonia-reducing therapies were initiated, but proved ineffective. Pharmacologic, microbial, and autoimmune causes for the hyperammonemia were excluded. The patient was severely malnourished and her carnitine level was found to be extremely low. After carnitine supplementation, ammonia levels normalized and the patient's mental status returned to baseline. In the setting of refractory hyperammonemia, this case illustrates how careful investigation may reveal a treatable condition.

Hypocarnitinaemia Induced by Sodium Pivalate in the Rat is Associated with Left Ventricular Dysfunction and Impaired Energy Metabolism

Carnitine is a naturally occurring compound that is essential in energy metabolism of the mammalian heart. In addition to its essential role in facilitating beta-oxidation, carnitine eliminates excess toxic acyl residues and regulates the mitochondrial acetyl coenzyme A (CoA)/CoA ratio. Thus, it is not surprising that patients with carnitine deficiency syndromes exhibit defects in energy metabolism and in some cases demonstrate left ventricular dysfunction. Pivalic acid is commonly used to create prodrugs, such as pivampicillin and pivmecillinam, to facilitate enteral absorption and increase oral bioavailability. Pivalic acid released from the drug following absorption readily forms an ester with carnitine, which is then excreted as pivaloylcarnitine. Sustained loss of carnitine in the form of this ester induces a state of carnitine deficiency, exemplified by low plasma and tissue carnitine content. This review examines the effects in the rat of short- and long-term sodium pivalate treatment on: (1) cardiac carnitine content; (2) in vitro mechanical function; (3) markers of glycolytic and fatty acid metabolism; and (4) energy substrate metabolism. Treatment with sodium pivalate induces a gradual loss of cardiac carnitine content for up to 12 weeks. Doubling the duration of treatment is not associated with any further decrease in cardiac carnitine content. While heart function following short-term treatment (2 weeks) is normal under aerobic conditions, impaired recovery of function following ischaemia is seen. In contrast, long-term treatment (11-28 weeks) is associated with impaired heart function, which is dependent on workload and substrate availability. Impaired heart function is also associated with reductions in activity of 3-hydroxyacyl CoA dehydrogenase and rates of fatty acid oxidation. However, to maintain adenosine triphosphate production, glucose metabolism, expressed as hexokinase activity and glucose oxidation, is increased in carnitine-deficient hearts. Hearts from sodium pivalate-treated animals demonstrate a cardiomyopathy that is dependent on duration of treatment, workload and substrate supply. This model of hypocarnitinaemia may thus be useful to study the metabolic and cardiac consequences of carnitine-deficiency syndromes.

Cataract in long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD)

Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) is a rare metabolic disorder that can lead to acute encephalopathy, liver disease, cardiomyopathy, rhabdomyolysis, and long-term complications involving the eye and peripheral nerves. LCHADD is a peroxisome biogenesis disorder (PBD). Except for the series presented by Tyni and colleagues (Ophthalmology 1998;105:810-824), which described visually insignificant lens opacities in association with LCHADD, previous ophthalmic papers have only reported retinal complications. We report on one case with progressive asymmetrical cataract. The more mildly affected eye had a similar morphology to that previously reported and the more severely affected eye had an unusual morphology we believe is unique to LCHADD. We discuss the range of ophthalmic presentations in our cases and in the literature. The variability of the severity of ocular complications, even between eyes in one individual, makes it difficult to test the effectiveness of therapeutic options upon the ophthalmic complications.

What is the role of medium-chain triglycerides in the management of long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency?

Cardiomyopathy is common in infants with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency. Resolution of the cardiomyopathy can often be achieved by avoidance of fasting and changing from a conventional infant formula to one in which most long-chain fat is replaced by medium-chain triglycerides (MCT). It is uncertain whether the clinical improvement is due to the restriction of long-chain fat or whether the MCT have specific beneficial effects. To clarify this, the metabolic effects of MCT were examined in 5 patients. When given at around the level found in MCT-based infant formula, MCT had no effect on blood concentrations of ketone bodies, specific fatty acids or acylcarnitines. The present study cannot, however, exclude the possibility that MCT per se may have beneficial effects.

Management of fatty acid oxidation disorders: a survey of current treatment strategies

Standardization of the nutritional care for patients with fatty-acid oxidation disorders is lacking. A literature review and national survey of metabolic dietitians describes the range of therapeutic strategies currently employed in the U.S. to treat patients with fatty-acid oxidation disorders. Questionnaire responses provided by dietitians specializing in metabolic disorders evaluated practices used for treatment of fatty acid oxidation disorders, medium-chain acyl-CoA dehydrogenase deficiency (MCAD), very-long-chain acyl-CoA dehydrogenase deficiency (VLCAD), long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHAD), long-chain acyl-CoA dehydrogenase deficiency (LCAD), and Trifunctional Protein deficiency (TFP). This survey reveals a significant lack of evidence supporting the protocols in use. Recent advances in tandem mass spectrometry technology promises an increase in the number of identified patients with fatty-acid oxidation disorders, which reinforces the need for comprehensive, clinical research studies to determine optimal care for patients with these genetic disorders.

Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency: clinical presentation and follow-up of 50 patients

OBJECTIVES

To assess the mode of presentation, biochemical abnormalities, clinical course, and effects of therapy in patients of long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency.

BACKGROUND

LCHAD deficiency is a rare, autosomal recessive inborn error of fatty acid oxidation. Although case reports and small series of patients have been published, these may not give a true picture of the clinical and biochemical spectrum associated with this disorder. To improve the early recognition and management of this potentially lethal disorder, we have reviewed a large cohort of LCHAD-deficient patients.

METHODS

A questionnaire was sent to the referring physicians of 61 unselected patients with LCHAD deficiency diagnosed in our center. The standardized questionnaire requested information about the clinical signs and symptoms at presentation, the clinical history, family history, pregnancy, biochemical parameters at presentation, treatment, and clinical outcome.

RESULTS

Questionnaires on 50 patients (82%) were returned and included in this study. The mean age of clinical presentation was 5.8 months (range: 1 day-26 months). Seven (15%) of the patients presented in the neonatal period. Thirty-nine patients (78%) presented with hypoketotic hypoglycemia, the classical features of a fatty acid oxidation disorder. Eleven patients (22%) presented with chronic problems, consisting of failure to thrive, feeding difficulties, cholestatic liver disease, and/or hypotonia. In retrospect, most (82%) of the patients presenting with an acute metabolic derangement also suffered from a combination of chronic nonspecific symptoms before the metabolic crises. Mortality in this series was high (38%), all dying before or within 3 months after diagnosis. Morbidity in the surviving patients is also high, with recurrent metabolic crises and muscle problems despite therapy.

CONCLUSIONS

LCHAD deficiency often presents with a combination of chronic nonspecific symptoms. Early diagnosis is difficult in the absence of the classical metabolic derangement. Survival can be improved by prompt diagnosis, but morbidity remains alarmingly high despite current therapeutic regimes.

Hepatic carnitine palmitoyl transferase 1 (CPT1 A) deficiency in North American Hutterites (Canadian and American): evidence for a founder effect and results of a pilot study on a DNA-based newborn screening program

We describe six patients with hepatic carnitine palmitoyl transferase (CPT1 A) deficiency who are members of a large extended Hutterite kindred living in widely scattered communities in the United States and Canadian Prairies. Two patients have significant neurological impairment due to severe recurrent hypoglycemic crises. The remaining four patients with earlier detection and treatment have near normal outcomes. The Canadian and American Hutterite families share two common ancestors who married in 1812, about 60 years before the Hutterites arrived in North America and prior to their subdivision into the three groups (Schmiedeleut, Dariusleut, and the Lehrerleut). These patients share a common haplotype on chromosome 11q13 and are all homozygous for a common CPT1 A G710E mutation, suggesting a founder effect. The clustering of such a rare disorder of fatty acid oxidation prompted us to initiate a pilot DNA-based neonatal screening program to determine the carrier frequency of this mutation in Hutterite newborns with the participation and support of the community. To date our carrier frequency is 1/16, close to the predicted frequency based on diagnosed patients and number of births. We believe our newborn screening program for CPT1 A deficiency in the Hutterite community will serve as a prototype model for delivery of targeted genetic services to other similar unique genetic isolates.

Coronary artery blood flow visualization signifies hemodynamic deterioration in growth-restricted fetuses

OBJECTIVE

To determine the relationship between fetal coronary blood flow (CBF) visualization in intrauterine growth restriction (IUGR), longitudinal changes in arterial and venous flow velocity waveforms and perinatal outcome.

METHODS

A total of 48 IUGR fetuses (abdominal circumference below the 5th percentile for gestational age) with absent or reversed umbilical artery (UA) end-diastolic velocity (AREDV) were examined longitudinally by echocardiography attempting CBF visualization at each examination. Doppler evaluation of the middle cerebral artery, inferior vena cava (IVC), ductus venosus (DV) and umbilical vein (UV) was performed at each examination. Doppler measurements were correct for gestational age by conversion into Z-scores (delta-indices). Doppler results and outcome from fetuses in which CBF was visualized (group 1, n = 20) and those in which CBF was never visualized (group 2, n = 28) were compared. Outcome parameters analyzed included Apgar scores, cord arterial blood gases, perinatal mortality, respiratory distress, bronchopulmonary dysplasia, intraventricular hemorrhage, necrotizing enterocolitis and postpartum circulatory failure requiring pressor support.

RESULTS

There was no difference in Doppler indices between groups at study entry. CBF visualization coincides with a significant increase of UA-, IVC- and DV delta-indices. The greatest rate of change was observed for indices in the ductus venosus which occurred in the 24 h preceding CBF visualization. Group 1 fetuses required earlier delivery (median 27 + 4, vs. median 30 + 0), had lower birthweight (682 +/- 305 g vs. 936 +/- 416 g), lower cord pH (7.21 +/- 0.1 vs. 7.27 +/- 0.06) and cord pO2 (13 +/- 4.5 vs. 24.1 +/- 13.5 mmHg) compared to group 2 (all values P < 0.05). Mortality was similar (group 1 = 6/20, 30%; group 2 = 6/28, 21.4%).

CONCLUSIONS

In IUGR, fetuses with AREDV and centralization are at high risk for hypoxemia, acidemia and adverse outcome. CBF visualization coincides with deteriorating venous flows. Operator dependence of CBF visualization and the strong association with abnormal venous flow stresses the importance of venous Doppler surveillance in these fetuses.

Relationship between arterial and venous Doppler and perinatal outcome in fetal growth restriction

OBJECTIVE

The aim of this investigation was to assess the relationship between abnormal arterial and venous Doppler findings and perinatal outcome in fetuses with intrauterine growth restriction (IUGR).

METHODS

Doppler velocimetry of the umbilical artery (UA), middle cerebral artery (MCA), inferior vena cava (IVC), ductus venosus (DV) and free umbilical vein was performed in 121 IUGR fetuses with a UA pulsatility index (PI) > 2 SD above the gestational age mean and subsequent birth weight < 10th centile for gestational age. Groups based on the last Doppler exam were: 1 = abnormal UA-PI only (n = 42, 34.7%), 2 = MCA-PI > 2 SD below the gestational age mean (= 'brain sparing') in addition to abnormal UA-PI (n = 29, 24.0%), 3 = DV or IVC peak velocity index (PVIV) > 2 SD above the gestational age mean and/or pulsatile UV flow (n = 50, 41.3%). Z-scores (delta indices) were calculated for Doppler indices. Perinatal mortality, respiratory distress (RDS), bronchopulmonary dysplasia (BPD), intraventricular hemorrhage (IVH), necrotizing enterocolitis (NEC), circulatory failure and umbilical artery blood gases were recorded.

RESULTS

Absence or reversal of umbilical artery end-diastolic flow was observed in 4 (9.5%) of fetuses in group 1, 10 (34.5%) fetuses in group 2 and 41 (82%) fetuses in group 3. A low middle cerebral artery pulsatility index was found in 39 (78%) fetuses in group 3. Multiple regression analysis with gestational age at delivery, delta indices and cord artery blood gas as independent parameters and individual perinatal outcomes as dependent variables was performed. In this analysis the association was strongest with gestational age for each complication. There were no significant differences in Apgar scores between groups. At delivery, 'brain sparing' was associated with hypoxemia and abnormal venous flows with acidemia. Perinatal mortality was highest in group 3 and stillbirth was only observed when venous flow was abnormal. All postpartum complications were more frequent in fetuses with abnormal venous flows. The only statistically significant relation between Doppler indices and outcome was the association between abnormal ductus venosus flow and fetal death (r2 = 0.24, P < 0.05).

CONCLUSION

Growth restricted fetuses with abnormal venous flow have worse perinatal outcome compared to those where flow abnormality is confined to the umbilical or middle cerebral artery. In fetuses with low middle cerebral artery pulsatility, venous Doppler allows detection of further deterioration. While abnormal venous flows can be significantly associated with fetal demise, gestational age at delivery significantly impacts on all short-term outcomes.

Hypoglycemia in association with various organic and amino acid disorders

A number of organic and amino acidemias, particularly those that involve the oxidation of fatty acids, cause hypoglycemia intermittently. This may be associated with distrubances of acid base equilibrium and accumulation of lactic acid and/or ketone bodies. When such diseases are not diagnosed rapidly, they might lead to neurological crippling and, at times, death. As a group, these disorders involve more than 1 organ and their phenotypic expression may include all or a single system. The symptoms may appear soon after birth or as late as 1 year of age. Their early recognition and rapid intervention provide rewarding clinical outcome. With the recent advances in diagnostic techniques, such as the introduction of tandem mass spectrometry (MS), screening for these diseases now can be performed because rapid identification on a large scale is possible. The phenotypes, mutations involved, pathognomonic laboratory findings, prognosis, and treatment procedures available have been reviewed for major diseases.

Disorders of mitochondrial fatty acyl-CoA beta-oxidation

In recent years tremendous progress has been made with respect to the enzymology of the mitochondrial fatty acid beta-oxidation machinery and defects therein. Firstly, a number of new mitochondrial beta-oxidation enzymes have been identified, including very-long-chain acyl-CoA dehydrogenase (VLCAD) and mitochondrial trifunctional protein (MTP). Secondly, the introduction of tandem MS for the analysis of plasma acylcarnitines has greatly facilitated the identification of patients with a defect in fatty acid oxidation (FAO). These two developments explain why the number of defined FAO disorders has increased dramatically, making FAO disorders the most rapidly growing group of inborn errors of metabolism. In this review we describe the current state of knowledge of the enzymes involved in the mitochondrial oxidation of straight-chain, branched-chain and (poly)unsaturated fatty acyl-CoAs as well as disorders of fatty acid oxidation. The laboratory diagnosis of these disorders is described, with particular emphasis on the methods used to identify the underlying enzyme defect and the molecular mutations. In addition, a simple flowchart is presented as a guide to the identification of mitochondrial FAO-disorders. Finally, treatment strategies are discussed briefly.

Neonatal metabolic myopathies

The primary presentations of neuromuscular disease in the newborn period are hypotonia and weakness. Although metabolic myopathies are inherited disorders that present from birth and may present with subtle to marked neonatal hypotonia, a number of these defects are diagnosed classically in childhood, adolescence, or adulthood. Disorders of glycogen, lipid, or mitochondrial metabolism may cause three main clinical syndromes in muscle, namely, (1) progressive weakness with hypotonia (e.g., acid maltase, debrancher enzyme, and brancher enzyme deficiencies among the glycogenoses; carnitine uptake and carnitine acylcarnitine translocase defects among the fatty acid oxidation (FAO) defects; and cytochrome oxidase deficiency among the mitochondrial disorders) or (2) acute, recurrent, reversible muscle dysfunction with exercise intolerance and acute muscle breakdown or myoglobinuria (with or without cramps), e.g., phosphorylase, phosphofructokinase, and phosphoglycerate kinase among the glycogenoses and carnitine palmitoyltransferase II deficiency among the disorders of FAO or (3) both (e.g., long-chain or very long-chain acyl coenzyme A (CoA) dehydrogenase, short-chain L-3-hydroxyacyl-CoA dehydrogenase, and trifunctional protein deficiencies among the FAO defects). Episodes of exercise-induced myoglobinuria tend to present in later childhood or adolescence; however, myoglobinuria in the first year of life may occur in FAO disorders during catabolic crises precipitated by fasting or infection. The following is a survey of genetic disorders of glycogen and lipid metabolism resulting in myopathy, focusing primarily on those defects, to date, that have presented in the neonatal or early infancy period. Disorders of mitochondrial metabolism are discussed in another chapter.

Systolic blood pressure in babies of less than 32 weeks gestation in the first year of life. Northern Neonatal Nursing Initiative

AIM

To define the normal range of systolic blood pressure in a non-selective population based sample of babies of low gestation throughout early infancy.

METHODS

Daily measurements of systolic blood pressure were made in all the babies of less than 32 weeks gestation born in the North of England in 1990 and 1991 during the first 10 days of life. Additional measurements were obtained from 135 of these babies throughout the first year of life. Systolic pressure was measured by sensing arterial flow with a Doppler ultrasound probe. It was assumed that blood pressure had never been pathologically abnormal in the neonatal period if the child was alive and free from severe disability two years later. Data of adequate quality were available from 398 such children. Additional data wer collected, for comparative purposes, from 123 babies of 32, 36, or 40 weeks of gestation.

RESULTS

Systolic pressure correlated with weight and gestation at birth, and rose progressively during the first 10 days of life. The coefficient of variation did not vary with gestational or postnatal age (mean value 17%), the relation with gestation being closer than with birthweight. Systolic pressure rose 20% during the first 10 days from an initial mean of 42 mm Hg in babies of 24 weeks gestation, and by 42% from an initial mean of 48 mm Hg in babies of 31 weeks gestation. These findings were not altered by the exclusion of data from 14 babies who had inotropic support during this time. Simultaneous measurements in three centres using an oscillometric technique revealed that this technique tended to overestimate systolic pressure when this was below average. Systolic pressure finally stabilised at a mean of 92 (95% CI 72-112) mm Hg at a postconceptional age of 44-48 weeks irrespective of gestation at birth.

CONCLUSION

Systolic blood pressure 4-24 hours after birth was less than gestational age (in weeks) in only 3% of non-disabled long term survivors. Systolic pressure rose with increasing gestation and increasing postnatal age, but stabilised some six weeks after term, regardless of gestation at birth.

Characterisation of carnitine palmitoyltransferases in patients with a carnitine palmitoyltransferase deficiency: implications for diagnosis and therapy

OBJECTIVES

Carnitine palmitoyltransferase (CPT) deficiency is one of the most common defects of mitochondrial fatty acid oxidation. Two different enzymes (CPT-I and CPT-II) are involved. Due to problems in measuring enzyme activity, relatively little is known about the substrate specificity of each of the human enzymes. This is of considerable importance in the treatment of patients. The objectives were to establish a reliable method for the measurement of CPT activity in whole cells, to use this to characterise the substrate specificity of each enzyme, and finally, to determine if medium chain triglycerides would be of benefit in the treatment of deficient patients.

METHODS

A simple permeabilisation technique was used which allows the measurement of CPT activity in a small amount of cultured skin fibroblasts or peripheral blood cells. Using this technique three patients were identified with CPT deficiency. In two of these patients, one with CPT-I deficiency and one with CPT-II deficiency, a complete substrate specificity profile of the mitochondrial carnitine acyltransferases was established for all saturated even chain acyl-CoA esters.

RESULTS

For both enzymes the highest CPT activity was with C12-CoA. About 70% of total cellular carnitine octanoyltransferase activity was due to mitochondrial CPT. As CPT is involved in the transport of medium chain fatty acids the metabolic response of a patient with CPT-II deficiency to dietary medium chain triglycerides was assessed. Despite the normal production of ketone bodies there was a significant medium chain dicarboxylic aciduria in the patient, indicating a limited capacity of the CPT independent mitochondrial uptake of medium chain fatty acids.

CONCLUSIONS

CPT deficiency can easily be diagnosed in permeabilised cultured skin fibroblasts. Both CPT-I and CPT-II are more active with medium chain length substrates than previously assumed. Care should therefore be taken in the treatment of these patients with medium chain triglycerides.

Metabolic myopathies

Disorders of glycogen, lipid or mitochondrial metabolism may cause two main clinical syndromes, namely (1) progressive weakness (eg, acid maltase, debrancher enzyme, and brancher enzyme deficiencies among the glycogenoses; long- and very-long-chain acyl-CoA dehydrogenase (LCAD, VLCAD), and trifunctional enzyme deficiencies among the fatty acid oxidation (FAO) defects; and mitochondrial enzyme deficiencies) or (2) acute, recurrent, reversible muscle dysfunction with exercise intolerance and acute muscle breakdown or myoglobinuria (with or without cramps) (eg, phosphorylase (PPL), phosphorylase b kinase (PBK), phosphofructokinase (PFK), phosphoglycerate kinase (PGK), phosphoglycerate mutase (PGAM), and lactate dehydrogenase (LDH) among the glycogenoses and carnitine palmitoyltransferase II (CPT II) deficiency among the disorders of FAO or (3) both (eg, PPL, PBK, PFK among the glycogenoses; LCAD, VLCAD, short-chain L-3-hydroxyacyl-CoA dehydrogenase (SCHAD), and trifunctional enzyme deficiencies among the FAO defects; and multiple mitochondrial DNA (mtDNA) deletions). Myoadenylate deaminase deficiency, a purine nucleotide cycle defect, is somewhat controversial and is characterized by exercise-related cramps leading rarely to myoglobinuria.

The clinical spectrum of long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency

Four patients with long-chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency are presented. Clinical onset in the form of acute encephalopathy occurred between the ages of 9 months and 3 years. The clinical course included recurrent metabolic crises in 4 patients, cardiac involvement and retinopathy in 3, and myopathy in 2. None had signs of peripheral neuropathy. Three patients died and one is currently well. Hypoketotic hypoglycemia with C6-C14 3-hydroxy-dicarboxylic aciduria during metabolic crises associated with decreased plasma carnitine levels was the main biochemical finding. Enzymologic studies disclosed long-chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency in all patients. Homozygosity for a G to C mutation at position 1528 in the encoding region of the enzyme was found in 2 patients. Histologic and electron microscopic studies of liver biopsy specimens revealed steatosis in 3 patients and mitochondrial abnormalities in 2. Skeletal muscle biopsies disclosed nonspecific degenerative changes in 2 patients and were normal in the remaining 2. Ultrastructural abnormalities in mitochondria were found in 3 patients. A review of the literature combined with the data from our series (total 22 patients) disclosed acute clinical onset in 77% of cases and subacute in 23%. In the combined series, the average age at onset was 11 months, family history was positive in 32% of patients and overall mortality was 50%. We describe the clinical spectrum of this disease and emphasize that, among patients with suspected beta-oxidation defects the finding of pigmentary retinopathy should lead to the suspicion of long-chain 3-hydroxyacyl-coenzyme A-dehydrogenase deficiency.

Use of enalapril in neonatal hypertension

Treatment of hypertension with enalapril in a preterm infant is described. Enalapril is a new converting enzyme blocker with a longer plasma half-life and less side effects than captopril. Oral administration of enalapril 0.1 mg/kg caused severe hypotension and renal failure in a preterm infant. We recommend an oral starting dose of 0.01 mg/kg in preterm infants and extremely close monitoring of infants receiving the first dose of enalapril.

Fatty acid oxidation and cardiac function in the sodium pivalate model of secondary carnitine deficiency

Carnitine-deficiency syndromes are often associated with alterations in lipid metabolism and cardiac function. The present study was designed to determine whether this is also seen in an experimental model of carnitine deficiency. Carnitine deficiency was induced in male Sprague-Dawley rats supplemented with sodium pivalate for 26 to 28 weeks. This treatment resulted in nearly a 60% depletion of myocardial total carnitine content as compared with control hearts. When isolated working hearts from these animals were perfused with 5.5 mmol/L glucose and 1.2 mmol/L palmitate and subjected to incremental increases in left-atrial filling pressures, cardiac function remained dramatically depressed. The effects of carnitine deficiency on glucose and palmitate utilization were also assessed in hearts perfused at increased workload conditions. At this workload, function was depressed in carnitine-deficient hearts, as were rates of 1.2-mmol/L [U-14C]-palmitate oxidation, when compared with control hearts (544 +/- 37 vs 882 +/- 87 nmol/g dry weight.min, P < .05). However, glucose oxidation rates from 5.5 mmol/L [U-14C]-glucose were slightly increased in carnitine-deficient hearts. To determine whether the depressed fatty acid oxidation rates were a result of reduced mechanical function in carnitine-deficient hearts, the workload of hearts was reduced. Under these conditions, mechanical function was similar among control and carnitine-deficient hearts. Palmitate oxidation rates were also similar in these hearts (526 +/- 69 v 404 +/- 47 nmol/g dry weight.min for control and carnitine-deficient hearts, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical and neurophysiologic response of myopathy and neuropathy in long-chain L-3-hydroxyacyl-CoA dehydrogenase deficiency to oral prednisone

The purpose of this study was to evaluate the clinical and neurophysiologic responses to oral prednisone therapy in a boy with enzymatically confirmed long-chain L-3-hydroxyacyl-CoA dehydrogenase deficiency in biopsied muscle and cultured skin fibroblasts. This boy presented with progressive limb girdle myopathy, recurrent myoglobinuria, peripheral sensorimotor axonopathy, and intraventricular conduction delays. Prior to prednisone therapy, at age 8 years, he exhibited marked distal weakness greater than proximal weakness with a waddling and high-steppage gait, Gowers' maneuver (10 s to rise from the floor), fatigue after 3-20 yards of walking and the ability to climb only 2 stairs. Serum levels of creatine kinase rose from 34 to 4,124 U/L following mild exertion. Nerve conduction studies revealed progressive axonopathy with secondary demyelination. Four weeks after initiation of oral prednisone (0.75 mg/kg/day) therapy, there was approximately a 100% increase in power and endurance. He was able to walk at least 100 yards before tiring, could rise from sitting on the floor in 3-4 s, and was able to climb 20 steps in 30 s. There was concurrent improvement in nerve conduction studies. Prednisone was gradually withdrawn over the next 4 months to 0.19 mg/kg/day; lower doses of 0.08 mg/kg/day resulted in a marked deterioration in power to the prior state. Although 0.19 mg/kg/day did not maintain the peak power achieved at 0.75 mg/kg/day, it provided adequate baseline power and endurance. It is concluded that there was a significant clinical and neurophysiologic response to prednisone at a dosage > or = 0.16 mg/kg/day. Prednisone may stabilize muscle and neuronal plasma membranes, as well as the fatty acid oxidation enzyme complex in the mitochondrial membrane.

Organic acidurias and related abnormalities

Organic acid analysis is a powerful technique in the diagnosis of inborn errors of metabolism. Since the development of the technique over twenty-five years ago, it has evolved into a sophisticated and powerful method and is an essential tool in the diagnosis of the organic acidurias. The chemistry and biochemistry of organic acids, as well as sample preparation, instrumentation, and many aspects of the more commonly used methods for the analysis of these compounds, are reviewed. The biochemical and clinical characteristics of each of the primary organic acidurias are described. In addition, the various noninherited causes of secondary organic acidurias that lead to the excretion of abnormal organic acids are also described, and ways of differentiating primary from secondary causes are discussed.

Hereditary dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is a common and important cause of morbidity and mortality. Many factors can contribute to the development of this disorder, although most commonly the etiology is unexplained. However, recent studies in individuals with idiopathic DCM now reveal a heritable cause in 20-30% of individuals. Diverse modes of inheritance have been demonstrated, encompassing an autosomal dominant type (by far the most common), together with recessive and X-linked forms, and maternal inheritance through mitochondrial DNA. The hereditary forms of DCM (HDCM) predominantly affect the left ventricle, although inherited abnormalities affecting primarily the right ventricle also are described. HDCM may occur as a primary cardiomyopathy, or secondary to inherited systemic metabolic or neuromuscular disorders. The causative genes for primary HDCM of the autosomal dominant and recessive types have not yet been discovered, but the combination of family pedigree analysis and phenotyping by echocardiography, together with new genetic techniques, should now allow their identification. Knowledge of the gene or genes responsible for HDCM would improve diagnostic accuracy, facilitate genetic counseling, advance understanding of pathogenesis, and provide the starting point for new methods of treatment. Because of the frequently heritable nature of DCM, it is of great importance that a diligent search for all potentially affected family members be undertaken.

Acute fatty liver of pregnancy and long-chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency

The pathogenesis of acute fatty liver of pregnancy is unknown, but similarities in the clinical presentation and the histological appearance of the liver with those found in children with metabolic defects in the intramitochondrial beta-oxidation pathway of the liver suggest that a disturbance in hepatic fatty acid oxidation may play a role. We report a woman with acute fatty liver of pregnancy who gave birth to a seemingly normal full-term infant who was seen at 4 mo of age with hypoglycemia, coma and profound hepatic steatosis. The infant had a defect in fatty acid oxidation, long-chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency, and the mother proved to be heterozygous for this metabolic condition. We hypothesize that the interaction of an affected fetus with a female heterozygous for this defect in fatty acid oxidation in the late third trimester accounts for some cases of acute fatty liver of pregnancy.

Topical medications and breastfeeding

Little data are available regarding the topical application of drugs to breast, nipple, or areolar tissue. Absorption of therapeutic agents applied to the breast may be of concern in the breastfed infant. Absorption may occur by direct contact with the drug while nursing, or by milk levels of the drug attained from systemic absorption. The safety of each individual agent should be assessed prior to application to the breast while nursing.

Long-chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency--diagnosis, plasma carnitine fractions and management in a further patient

Long-chain 3-hydroxyacyl-coenzyme A dehydrogenase (LCHAD), the third enzyme of the mitochondrial beta-oxidation pathway, carries out the dehydrogenation of 3-hydroxyacyl-CoA compounds of 12-18 carbon length. To date only nine cases of LCHAD deficiency have been documented. We report a further patient who as a neonate developed non-specific gastrointestinal symptoms and at 5 months of age cardiomyopathy, recurrent hypoketotic hypoglycaemia and gross alterations of plasma carnitine fractions. Dietary management with medium chain triglycerides led rapidly to clinical improvement. There was a close correlation between the clinical condition, plasma carnitine fractions and cardiac function. At 2 years of age she is developing normally.

Retinopathy of prematurity--current diagnosis and management

Despite advances in ophthalmological care of premature infants, retinopathy of prematurity (ROP) remains a still unsolved problem for paediatricians as well as ophthalmologists. A survey of the current literature concerning drug therapy and surgical management as related to the different stages of ROP is given. The classification system for ROP according to the International Committee is presented as well as our screening policy in relation to the literature. The effectiveness in preventing severe cases of ROP and the toxicity of vitamin E supplementation in high-risk premature infants is still disputed and no recommendations can be given. Cryotherapy is recommended in symmetric cases of stage 3 + ROP. Nevertheless, quite a number of eyes still progress to more severe stages of ROP. Scleral buckling procedures and vitrectomy may lead to anatomical success in a few cases of retinal detachment, however, the visual outcome of such an operation is usually very poor despite reattachment of the central retina.

Combined enzyme defect of mitochondrial fatty acid oxidation

A young girl presented with recurrent episodes of muscle weakness culminating in a severe attack of generalized muscle weakness. In the muscle mitochondria from the patient there was an abnormal pattern of intermediates of beta-oxidation with an accumulation of 3-hydroxyacyl- and 2-enoyl-CoA and carnitine esters, and 3-oxoacylcarnitines. There was low activity of long-chain 3-hydroxyacyl-CoA dehydrogenase in mitochondria from all tissues. The activity of long-chain 2-enoyl-CoA hydratase was low in muscle mitochondria and 3-oxoacyl-CoA thiolase activity measured with 3-oxohexadecanoyl-CoA as substrate was low in fibroblast, muscle, and cardiac mitochondria but only partial deficiency was present when the activity was measured with 3-oxooctanoyl-CoA. The activity of the long-chain 3-hydroxyacyl-CoA dehydrogenase and long-chain 3-oxoacyl-CoA thiolase in fibroblasts from the patient's parents was intermediate between those of controls and the patient. The patient has a combined defect of the long-chain 3-hydroxyacyl-CoA dehydrogenase, long-chain 3-oxoacyl-CoA thiolase, and long-chain 2-enoyl-CoA hydratase which appears to be inherited in an autosomal recessive manner. This suggests there is a multifunctional enzyme catalyzing these activities in human mitochondria and that this enzyme is deficient in our patient.

Clinical and biochemical aspects of carnitine deficiency and insufficiency: transport defects and inborn errors of beta-oxidation

Carnitine is required for entry of long chain fatty acids into mitochondria where beta-oxidation occurs. Primary carnitine deficiency, due to a generic defect in cellular carnitine transport, exists in myopathic and systemic forms. Secondary carnitine deficiency may be due to multiplicity of inherited abnormalities, including deficiencies in carnitine palmitoyl-transferase acyl-CoA dehydrogenases, electron transfer flavoprotein, and 3-ketoacyl-CoA-thiolase. The clinical features, diagnosis, and treatment of these conditions are described.

Inborn errors of fatty acid oxidation in man

Inborn errors of fatty acid oxidation have only been recently identified. The clinical and biochemical presentations of these disorders are presented, as are analytic, biochemical and enzymatic approaches to their diagnosis. Recent clinical, biochemical and molecular information is summarized in detail. The identification and characterization of riboflavin-responsive beta-oxidation disorders is discussed. Approaches for clinical and biochemical screening are also described for these disorders.

Organic acidurias: a review. Part 1

Organic acidemias are disorders of intermediary metabolism that lead to accumulation of organic acids in biologic fluids, disturb acid-base balance, and derange intracellular biochemical pathways. Their clinical presentation reflects the resultant systemic disease and progressive encephalopathy. While in some organic acidemias, disturbed acid-base metabolism is the predominant presenting feature, in others it is less prominent or even absent. The etiologies of the more than 50 different phenotypes include impaired metabolism of branched-chain amino acids, vitamins, glucose, lipids, glutathione, and gamma-aminobutyric acid and defects of oxidative phosphorylation. Most organic acidemias present with neurologic manifestations, which include acutely or subacutely progressive encephalopathy that involves different parts of the nervous system. The age of presentation and the associated systemic, hematologic, and immune findings provide additional guidelines for differential diagnosis. We summarize major organic acidemias, while emphasizing their usual and unusual neurologic presentations.

3-Hydroxydicarboxylic aciduria due to long-chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency associated with sudden neonatal death: protective effect of medium-chain triglyceride treatment

Two siblings were found to be affected by long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency, one of which died suddenly and unexpectedly on the 3rd day of life suffering from extreme hypoketotic hypoglycaemia. The younger sibling started to have feeding problems, lowered consciousness, and liver dysfunction at the age of 5 months. Her urine contained large amounts of C6-C14 3-hydroxydicarboxylic acids and conjugated 3-hydroxyoctanoic acid, as verified by gas chromatography/mass spectrometry. Plasma long-chain acylcarnitine was increased. A clue to the diagnosis was given by the results of a phenylpropionic acid loading test. This revealed small, but significant amounts of conjugated 3-hydroxyphenylpropionic acid (phenylhydracrylic acid) in the patient's urine. Subsequently, the activity of long-chain 3-hydroxyacyl-CoA dehydrogenase was found to be deficient in cultured skin fibroblasts. Based on the findings obtained by a medium-chain triglyceride load, a diet enriched in this type of fat was prescribed. On this regimen the patient started to thrive, signs of cardiomyopathy disappeared, and her liver function normalized.

Hypoglycemia: a pathophysiologic approach

An exploration of the factors that sustain glucose levels in the normal fasting subject reveals that the single major component is conservation of glucose rather than gluconeogenesis. Conservation is achieved by recycling of glucose carbon as lactate, pyruvate and alanine, and a profound decrease in the oxidation of glucose by the brain brought about by the provision and use of ketones. What glucose continues to be oxidized is for the most part formed from glycerol. Gluconeogenesis from protein plays little part in the process. Fasting hypoglycemia results from disorders affecting either one of the two critical sustaining factors--the recycling process or the availability and use of ketones. Individual hypoglycemic entities are examined against this background.

Inborn errors of amino acid and fatty acid metabolism with hypoglycemia as a major clinical manifestation

During the last decade it has become increasingly clear that severe hypoglycemia may be caused by specific enzymatic defects of amino acid and fatty acid metabolism. Several reports have presented hypoglycemic syndromes with reduced fatty acid transport or oxidation, decreased ketogenesis, or abnormalities of the Krebs cycle and electron transport chain. It is of particular interest that several enzymatic defects here discussed may present as Reye's syndrome. An intriguing fact is a highly variable clinical presentation, even in the presence of well-defined enzyme deficiencies. Some patients are desperately ill in the newborn period, whereas in other cases there are symptoms only during catabolic phases later in childhood. The presence of hypoglycemia may be related to low levels of acetyl CoA, with consequently reduced gluconeogenesis; alternatively the glucose-sparing effect of ketones is lost in states of reduced ketone body production. Treatment with pharmacological doses of vitamins may be attempted, depending upon the established or suspected diagnoses. With manifest hypoglycemia i.v. glucose infusion is the treatment of choice. By such means convulsions, and brain damage may be prevented.

Dilated cardiomyopathy and myocarditis: natural history, etiology, clinical manifestations, and management

This monograph begins and ends with a statement of uncertainty regarding many aspects of dilated cardiomyopathy. Natural history studies identify patients with widely differing outcomes. A host of prognostic factors have emerged, yet it would appear that the major determinants of survival are as yet unrecognized. The diagnosis remains primarily one of exclusion, and management is largely nonspecific and supportive. The frequency of sudden cardiac death is well documented, but the ability to accurately identify patients at risk and the efficacy of antiarrhythmic therapy is unestablished. The emerging success of cardiac transplantation is a source of encouragement. The causes of dilated cardiomyopathy remain a source of intense investigation. Accumulating evidence (much of it circumstantial) does, however, implicate a viral etiology and perhaps altered function of the immunoregulatory system. However, the disparity between the severity of functional disturbance with the relative lack of histologic markers of cellular necrosis implies a disturbance at a cellular level. The etiology or etiologies remain elusive. Future investigation directed at fundamental aspects of cardiac cellular biology may provide the answers.

Myocardial failure in cats associated with low plasma taurine: a reversible cardiomyopathy

Thousands of pet cats die each year with dilated cardiomyopathy, the cause of which is unknown. Although taurine is present in millimolar concentrations in the myocardium of all mammals, taurine depletion has not previously been associated with a decrease in myocardial function in any species. In this study, low plasma taurine concentrations associated with echocardiographic evidence of myocardial failure were observed in 21 cats fed commercial cat foods and in 2 of 11 cats fed a purified diet containing marginally low concentrations of taurine for 4 years. Oral supplementation of taurine resulted in increased plasma taurine concentrations and was associated with normalization of left ventricular function in both groups of cats. Since myocardial concentrations of taurine are directly related to plasma concentrations and low plasma concentrations were found to be associated with myocardial failure in cats, a direct link between decreased taurine concentration in the myocardium and decreased myocardial mechanical function is proposed.

The role of the carnitine system in myocardial fatty acid oxidation: carnitine deficiency, failing mitochondria and cardiomyopathy

The carnitine system functions in the transport of activated acyl groups over the mitochondrial inner membrane, and is needed for oxidation of long-chain fatty acids by all mitochondria. The rate of cardiac fatty acid oxidation is determined by availability of fatty acids, oxygen and the activity of carnitine palmitoyltransferase I, which is regulated by a variety of factors. It is inhibited by malonyl-CoA, which in rat heart was found to be synthesized by acetyl-CoA carboxylase. It is also inhibited by long-chain acylcarnitine. Linoleoylcarnitine was found to be a better inhibitor than palmitoylcarnitine. The concentration of carnitine in human heart, muscle and other tissues is much higher than is needed for the optimal beta-oxidation rate. In contrast to controls, we found in several myopathic patients that extra carnitine (from 1/2 to 5 mM) caused a considerable increase in beta-oxidation rate of isolated muscle mitochondria. In some of these patients we detected medium-chain acyl-CoA dehydrogenase deficiency. Patients with primary carnitine deficiency caused by a renal carnitine leak often show cardiomyopathy, which completely disappears under carnitine therapy. Cardiomyopathy may also be the cause of secondary carnitine deficiency resulting from a mitochondrial defect in acyl-CoA metabolism, or by the mitochondrial defect itself, which may be induced by drugs or viral attack, or be the result of a genetic error. In cardiomyopathic patients with a (subclinical) myopathy, study of isolated mitochondria and homogenate from skeletal muscle may reveal a mitochondrial dysfunction, which, in some patients, is treatable by dietary measures and supplementation with vitamins, CoQ and/or carnitine. When the cause of cardiomyopathy is not known, determination of plasma carnitine and carnitine supplementation of hypocarnitinemic patients is of great therapeutic value.

Evolution of a hereditary cardiac conduction and muscle disorder: a study involving a family with six generations affected

This study describes six generations of a family with autosomal dominant cardiac conduction system and myocardial disease with recognizable clinical stages. A 20 year follow-up of nine family members, a medical questionnaire of 196, electrocardiographic screening of 91, noninvasive testing of 20, and catheterization with endomyocardial biopsy of six are the basis of this report. The clinical stages are as follows: Stage I occurs in the second and third decades of life and is characterized by an absence of symptoms, normal heart size, sinus bradycardia, and premature atrial contractions. Stage II is marked by first-degree atrioventricular block in the third and fourth decades. Stage III occurs in the fourth and fifth decades and is accompanied by chest pain, fatigue, lightheadedness, and advanced atrioventricular block followed by the development of atrial fibrillation or flutter. Stage IV, in the fifth and sixth decades of life, is characterized by congestive heart failure and recurrent ventricular arrhythmias. Light microscopy of right ventricular endomyocardial biopsy specimens from patients in stage II revealed very mild fibrosis; electron microscopy of the specimens demonstrated mild dilatation of tubules, mitochondrial swelling, and minimal myofibrillar loss. Biopsy specimens from patients with stage III disease were similar to those from patients with stage II disease except for an increase of myofibrillar loss. The stage IV specimens had diffuse fibrosis and more severe tubular dilatation, mitochondrial cristolysis, and myofibrillar loss. At autopsy in the proband, the atrial changes were more severe than the ventricular and were especially marked in the sinoatrial and atrial myocardium. Early recognition of the disease and use of pacemakers and antiarrhythmic agents have proved beneficial for affected family members. Thorough family studies of patients with conduction system disease and/or dilated cardiomyopathy are necessary to better understand the hereditary basis and natural course of this category of disease.

A carnitine/acylcarnitine translocase assay applicable to biopsied muscle specimens without requiring mitochondrial isolation

A simple method for assaying the mitochondrial carnitine/acylcarnitine translocase of muscles that needs only few milligrams of fresh tissue is described. The procedure involves monitoring of the sulphobetaine (an inhibitor of the translocase)-sensitive acetylation of sub-saturating concentrations of carnitine in the medium, linked to the oxidation of [2-14C]pyruvate in the presence of malonate. Conditions affecting the reliability of the outlined procedure and the ancillary information to be collected, namely the activities of pyruvate oxidase system and carnitine acetyltransferase, for detecting possible deficiency of the translocase are described, together with data on the translocase activity in human skeletal muscle, in rat red and white skeletal muscles and in rat heart. The concepts outlined should allow development of assays of other mitochondrial transporters that also would require neither isolation of mitochondria nor availability of a large quantity of tissue, both of which are otherwise needed at present.