Intrauterine cardiomyopathy and cardiac mitochondrial proliferation in mitochondrial trifunctional protein (TFP) deficiency

Neonatal Long-Chain 3-Ketoacyl-CoA Thiolase deficiency: Clinical-biochemical phenotype, sodium-D,L-3-hydroxybutyrate treatment experience and cardiac evaluation using speckle echocardiography

Isolated long-chain 3-keto-acyl CoA thiolase (LCKAT) deficiency is a rare long-chain fatty acid oxidation disorder caused by mutations in HADHB. LCKAT is part of a multi-enzyme complex called the mitochondrial trifunctional protein (MTP) which catalyzes the last three steps in the long-chain fatty acid oxidation. Until now, only three cases of isolated LCKAT deficiency have been described. All patients developed a severe cardiomyopathy and died before the age of 7 weeks. Here, we describe a newborn with isolated LCKAT deficiency, presenting with neonatal-onset cardiomyopathy, rhabdomyolysis, hypoglycemia and lactic acidosis. Bi-allelic 185G > A (p.Arg62His) and c1292T > C (p.Phe431Ser) mutations were found in HADHB. Enzymatic analysis in both lymphocytes and cultured fibroblasts revealed LCKAT deficiency with a normal long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD, also part of MTP) enzyme activity. Clinically, the patient showed recurrent cardiomyopathy, which was monitored by speckle tracking echocardiography. Subsequent treatment with special low-fat formula, low in long chain triglycerides (LCT) and supplemented with medium chain triglycerides (MCT) and ketone body therapy in (sodium-D,L-3-hydroxybutyrate) was well tolerated and resulted in improved carnitine profiles and cardiac function. Resveratrol, a natural polyphenol that has been shown to increase fatty acid oxidation, was also considered as a potential treatment option but showed no in vitro benefits in the patient's fibroblasts. Even though our patient deceased at the age of 13 months, early diagnosis and prompt initiation of dietary management with addition of sodium-D,L-3-hydroxybutyrate may have contributed to improved cardiac function and a much longer survival when compared to the previously reported cases of isolated LCKAT-deficiency.

Neonatal carnitine concentrations in relation to gestational age and weight

BACKGROUND

Free carnitine has been measured in the Dutch newborn screening (NBS) program since 2007 with a referral threshold of ≤5 μmol/L, regardless of gestational age or birthweight. However, several studies suggest that carnitine concentrations may depend on gestational age and birthweight. We evaluated differences in postnatal day-to-day carnitine concentrations in newborns based on gestational age (GA) and/or weight for GA (WfGA).

METHODS

A retrospective study was performed using data from the Dutch NBS. Dried blood spot (DBS) carnitine concentrations, collected between the 3rd and 10th day of life, of nearly 2 million newborns were included. Individuals were grouped based on GA and WfGA. Median carnitine concentrations were calculated for each group. Mann-Whitney U tests, and chi-square tests were applied to test for significant differences between groups.

RESULTS

Preterm, postterm, and small for GA (SGA) newborns have higher carnitine concentrations at the third day of life compared to term newborns. The median carnitine concentration of preterm newborns declines from day 3 onwards, and approximates that of term newborns at the sixth day of life, while median concentrations of postterm and SGA newborns remain elevated at least throughout the first 10 days of life. Carnitine concentrations ≤5 μmol/L were found less frequently in SGA newborns and newborns born between 32 and 37 weeks of gestation, compared to term newborns.

CONCLUSIONS

Median carnitine concentrations in NBS DBS vary with day of sampling, GA, and WfGA. It is important to take these variables into account when interpreting NBS results..

Clinical and biochemical outcome of patients with very long-chain acyl-CoA dehydrogenase deficiency

BACKGROUND

Very-Long-Chain Acyl-CoA Dehydrogenase (VLCAD) deficiency is a disorder of fatty acid oxidation included in the recommended uniform newborn screening (NBS) panel in the USA. It can have variable clinical severity and there is limited information on the natural history of this condition, clinical presentation according to genotype and effectiveness of newborn screening.

METHODS

Retrospective data (growth parameters, morbidity, biochemical and genetic testing results) were collected from patients with VLCAD deficiency, to evaluate biochemical and clinical outcomes. Descriptive statistics was used for qualitative variables, while linear regression analysis was used to correlate continuous variables.

RESULTS

VLCAD deficiency (screened by measuring elevated levels of C14:1-carnitine in blood spots) was more frequent in Utah than the national average (1:27,617 versus 1:63,481) in the first ten years of screening. Twenty-six patients had a confirmed diagnosis of VLCAD deficiency using DNA testing or functional studies. The c.848T>C (p.V283A) variant in the ACADVL gene was the most frequent in our population. Novel variants (c.623-21A>G (IVS7-21A>G); c.1052C>T (p.T351I); c.1183-7A>G (IVS11-7A>G); c.1281G>C (p.W427C); c.1923G>C (p.L641F); c.1924G>A (p.V642M)) were identified in this study, with their pathogenicity remaining unclear in most cases. C14:1-carnitine levels decreased with age and significantly correlated with CK levels as index of muscle involvement. There were no cases of HELLP syndrome nor liver disease during pregnancies in the mothers of VLCAD patients. None of our patients developed cardiac involvement after birth and all patients had normal growth parameters while on treatment. Clinical manifestations were related to concomitant infections and altered biochemical parameters.

DISCUSSION

VLCAD deficiency can be identified by neonatal screening. Most patients compliant with therapy normalized biochemical parameters and had no major clinical manifestations. Complications were completely prevented with a relatively low number of pre-emptive ER visits or hospital admissions. It remains unclear whether neonatal screening is now identifying less severely affected patient or if complications will arise as subjects become older. Observation beyond puberty is necessary to fully understand the impact of VLCAD deficiency on morbidity in patients with VLCAD deficiency.

Mitochondrial Trifunctional Protein Deficiency: Severe Cardiomyopathy and Cardiac Transplantation

We describe mitochondrial trifunctional protein deficiency (MTPD) in two male siblings who presented with severe cardiomyopathy in infancy. The first sibling presented in severe cardiac failure at 6 months of age and succumbed soon after. The second sibling came to attention after newborn screening identified a possible fatty acid oxidation defect. Dietary therapy and carnitine supplementation commenced in the neonatal period. Despite this the second child required cardiac transplantation at 3 years of age after a sudden and rapid decline in cardiac function. The outcome has been excellent, with no apparent extra-cardiac manifestations of a fatty acid oxidation disorder at the age of 7. Pathogenic HADHA mutations were subsequently identified via genome wide exome sequencing. This is the first reported case of MTPD to undergo cardiac transplantation. We suggest that cardiac transplantation could be considered in the treatment of cardiomyopathy in MTPD.

Disturbance of mitochondrial functions provoked by the major long-chain 3-hydroxylated fatty acids accumulating in MTP and LCHAD deficiencies in skeletal muscle

The pathogenesis of the muscular symptoms and recurrent rhabdomyolysis that are commonly manifested in patients with mitochondrial trifunctional protein (MTP) and long-chain 3-hydroxy-acyl-CoA dehydrogenase (LCHAD) deficiencies is still unknown. In this study we investigated the effects of the major long-chain monocarboxylic 3-hydroxylated fatty acids (LCHFA) accumulating in these disorders, namely 3-hydroxytetradecanoic (3HTA) and 3-hydroxypalmitic (3HPA) acids, on important mitochondrial functions in rat skeletal muscle mitochondria. 3HTA and 3HPA markedly increased resting (state 4) and decreased ADP-stimulated (state 3) and CCCP-stimulated (uncoupled) respiration. 3HPA provoked similar effects in permeabilized skeletal muscle fibers, validating the results obtained in purified mitochondria. Furthermore, 3HTA and 3HPA markedly diminished mitochondrial membrane potential, NAD(P)H content and Ca(2+) retention capacity in Ca(2+)-loaded mitochondria. Mitochondrial permeability transition (mPT) induction probably underlie these effects since they were totally prevented by cyclosporin A and ADP. In contrast, the dicarboxylic analogue of 3HTA did not alter the tested parameters. Our data strongly indicate that 3HTA and 3HPA behave as metabolic inhibitors, uncouplers of oxidative phosphorylation and mPT inducers in skeletal muscle. It is proposed that these pathomechanisms disrupting mitochondrial homeostasis may be involved in the muscle alterations characteristic of MTP and LCHAD deficiencies.

A fetus with mitochondrial trifunctional protein deficiency: Elevation of 3-OH-acylcarnitines in amniotic fluid functionally assured the genetic diagnosis

Mitochondrial trifunctional protein (TFP) is a multienzyme complex that catalyzes the last three steps of the β-oxidation cycle of long-chain fatty acids. In the prenatal diagnosis of TFP deficiency, acylcarnitine (AC) analysis has been considered difficult because of limited excretion of long-chain ACs into the fetal urine and hence into the amniotic fluid. Here, we report our experience with prenatally diagnosing TFP deficiency using AC analysis of amniotic fluid. The index case was a boy born at 38 weeks gestation and weighing 2588 g. He suddenly became unconscious and hypoglycemic and died on day 6 of life. Postmortem blood AC analysis and gene sequencing revealed TFP deficiency. Therefore, the parents underwent prenatal diagnoses for their subsequent 2 pregnancies. Mutation analysis suggested that one (Case 1) was affected and the other (Case 2) was not. AC analysis also demonstrated identical results, with significantly elevated 3-hydroxy-AC levels in the amniotic fluid of the affected pregnancy compared with those of heterozygotes and normal controls (n = 2 for heterozygotes and n = 8 for normal controls). Our findings suggest that AC analysis can functionally confirm results even in families with unidentified mutations, without raising issues related to maternal cell contamination. During prenatal diagnosis, misdiagnosis has to be avoided, and combining AC analysis with gene sequencing may result in more accurate prenatal diagnosis of TFP deficiency.

Deregulation of mitochondrial functions provoked by long-chain fatty acid accumulating in long-chain 3-hydroxyacyl-CoA dehydrogenase and mitochondrial permeability transition deficiencies in rat heart--mitochondrial permeability transition pore opening as a potential contributing pathomechanism of cardiac alterations in these disorders

Mitochondrial trifunctional protein and long-chain 3-hydroxyacyl-CoA dehydrogenase deficiencies are fatty acid oxidation disorders biochemically characterized by tissue accumulation of long-chain fatty acids and derivatives, including the monocarboxylic long-chain 3-hydroxy fatty acids (LCHFAs) 3-hydroxytetradecanoic acid (3HTA) and 3-hydroxypalmitic acid (3HPA). Patients commonly present severe cardiomyopathy for which the pathogenesis is still poorly established. We investigated the effects of 3HTA and 3HPA, the major metabolites accumulating in these disorders, on important parameters of mitochondrial homeostasis in Ca(2+) -loaded heart mitochondria. 3HTA and 3HPA significantly decreased mitochondrial membrane potential, the matrix NAD(P)H pool and Ca(2+) retention capacity, and also induced mitochondrial swelling. These fatty acids also provoked a marked decrease of ATP production reflecting severe energy dysfunction. Furthermore, 3HTA-induced mitochondrial alterations were completely prevented by the classical mitochondrial permeability transition (mPT) inhibitors cyclosporin A and ADP, as well as by ruthenium red, a Ca(2+) uptake blocker, indicating that LCHFAs induced Ca(2+)-dependent mPT pore opening. Milder effects only achieved at higher doses of LCHFAs were observed in brain mitochondria, implying a higher vulnerability of heart to these fatty acids. By contrast, 3HTA and docosanoic acids did not change mitochondrial homeostasis, indicating selective effects for monocarboxylic LCHFAs. The present data indicate that the major LCHFAs accumulating in mitochondrial trifunctional protein and long-chain 3-hydroxyacyl-CoA dehydrogenase deficiencies induce mPT pore opening, compromising Ca(2+) homeostasis and oxidative phosphorylation more intensely in the heart. It is proposed that these pathomechanisms may contribute at least in part to the severe cardiac alterations characteristic of patients affected by these diseases.

Acute fatty liver of pregnancy associated with fetal mitochondrial trifunctional protein deficiency

Acute fatty liver of pregnancy (AFLP) is a devastating disorder of the maternal liver in the third trimester. Recent studies have demonstrated an association between AFLP and fetal fatty acid oxidation disorders. Here, we report a case of AFLP caused by fetal mitochondrial trifunctional protein (TFP) deficiency. A 21-year-old parous woman presented with nausea, genital bleeding and abdominal pain at 33 weeks of gestation. Laboratory data revealed hepatic failure and disseminated intravascular coagulopathy. The patient underwent emergency cesarean section and was diagnosed with AFLP from the clinical characteristics. She was successfully treated with frequent plasma exchange. The newborn presented severe heart failure and died on the 39th day after birth. Tandem mass spectrometry indicated long-chain fatty acid oxidation disorder. Gene analysis demonstrated homozygous mutation in exon 13 of HADHB, the gene responsible for mitochondrial TFP deficiency. The parents carried a heterozygous mutation at the same location in HADHB.

Long-chain 3-hydroxy fatty acids accumulating in long-chain 3-hydroxyacyl-CoA dehydrogenase and mitochondrial trifunctional protein deficiencies uncouple oxidative phosphorylation in heart mitochondria

Cardiomyopathy is a common clinical feature of some inherited disorders of mitochondrial fatty acid β-oxidation including mitochondrial trifunctional protein (MTP) and isolated long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiencies. Since individuals affected by these disorders present tissue accumulation of various fatty acids, including long-chain 3-hydroxy fatty acids, in the present study we investigated the effect of 3-hydroxydecanoic (3 HDCA), 3-hydroxydodecanoic (3 HDDA), 3-hydroxytetradecanoic (3 HTA) and 3-hydroxypalmitic (3 HPA) acids on mitochondrial oxidative metabolism, estimated by oximetry, NAD(P)H content, hydrogen peroxide production, membrane potential (ΔΨ) and swelling in rat heart mitochondrial preparations. We observed that 3 HTA and 3 HPA increased resting respiration and diminished the respiratory control and ADP/O ratios using glutamate/malate or succinate as substrates. Furthermore, 3 HDDA, 3 HTA and 3 HPA decreased ΔΨ, the matrix NAD(P)H pool and hydrogen peroxide production. These data indicate that these fatty acids behave as uncouplers of oxidative phosphorylation. We also verified that 3 HTA-induced uncoupling-effect was not mediated by the adenine nucleotide translocator and that this fatty acid induced the mitochondrial permeability transition pore opening in calcium-loaded organelles since cyclosporin A prevented the reduction of mitochondrial ΔΨ and swelling provoked by 3 HTA. The present data indicate that major 3-hydroxylated fatty acids accumulating in MTP and LCHAD deficiencies behave as strong uncouplers of oxidative phosphorylation potentially impairing heart energy homeostasis.

Mitochondrial fatty acid oxidation disorders: pathophysiological studies in mouse models

Mouse models have been designed for a number of fatty acid oxidation defects. Studies in these mouse models have demonstrated that different pathogenetic mechanisms play a role in the pathophysiology of defects of fatty acid oxidation. Supplementation with L-carnitine does not prevent low tissue carnitine levels and induces acylcarnitine production having potentially toxic effects, as presented in very-long-chain acyl-CoA dehydrogenase (VLCAD)-deficient mice. Energy deficiency appears to be an important mechanism in the development of cardiomyopathy and skeletal myopathy in fatty acid oxidation defects and is also the underlying mechanism of cold intolerance. Hypoglycemia as one major clinical sign in all fatty acid oxidation defects occurs due to a reduced hepatic glucose output and an enhanced peripheral glucose uptake rather than to transcriptional changes that are also observed simultaneously, as presented in medium-chain acyl-CoA dehydrogenase (MCAD)-deficient mice. There are reports that an impaired fatty acid oxidation also plays a role in intrauterine life. The embryonic loss demonstrated for some enzyme defects in the mouse supports this hypothesis. However, the exact mechanisms are unknown. This observation correlates to maternal hemolysis, elevated liver enzymes, low platelets (HELLP) syndrome, as observed in pregnancies carrying a long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD)-deficient fetus. Synergistic heterozygosity has been shown in isolated patients and in mouse models to be associated with clinical phenotypes common to fatty acid oxidation disorders. Synergistic mutations may also modulate severity of the clinical phenotype and explain in part clinical heterogeneity of fatty acid oxidation defects. In summary, knowledge about the different pathogenetic mechanisms and the resulting pathophysiology allows the development of specific new therapies.

Mitochondrial fatty acid oxidation disorders: clinical presentation of long-chain fatty acid oxidation defects before and after newborn screening

The different long-chain fatty acid oxidation defects present with similar heterogeneous clinical phenotypes of different severity. Organs mainly affected comprise the heart, liver, and skeletal muscles. All symptoms are reversible with sufficient energy supply. In some long-chain fatty acid oxidation defects, disease-specific symptoms occur. Only in disorders of the mitochondrial trifunctional protein (TFP) complex, including long-chain 3-hydroxyacyl-coenzyme A (CoA) dehydrogenase (LCHAD) deficiency, neuropathy and retinopathy develop that are progressive and irreversible despite current treatment measures. In most long-chain fatty acid oxidation defects, no clear genotype-phenotype correlation exists due to molecular heterogeneity. However, some isolated mutations have been identified to be associated with only mild phenotypes, e.g., the V243A mutation in very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiency. LCHAD deficiency is due to the prevalent homozygous 1528G>C mutation and presents with heterogeneous clinical phenotypes, suggesting the importance of other environmental and genetic factors. For some disorders, it was shown that residual enzyme activity measured in fibroblasts or lymphocytes correlated with severity of clinical phenotype. Implementation of newborn screening has significantly reduced morbidity and mortality of long-chain fatty acid oxidation defects. However, the severest forms of TFP deficiency are still highly associated with neonatal death. Newborn screening also identifies a great number of mildly affected patients who may never develop clinical symptoms throughout life. However, later-onset exercise-induced myopathic symptoms remain characteristic clinical features of long-chain fatty acid oxidation defects. Disease prevalence has increased with newborn screening.

Current issues regarding treatment of mitochondrial fatty acid oxidation disorders

Treatment recommendations in mitochondrial fatty acid oxidation (FAO) defects are diverse. With implementation of newborn screening and identification of asymptomatic patients, it is necessary to define whom to treat and how strictly. We here discuss critical questions that are currently under debate. For some asymptomatic long-chain defects, long-chain fat restriction plays a minor role, and a normal diet may be introduced. For patients presenting only with myopathic symptoms, e.g., during exercise, treatment may be adapted to energy demand. As a consequence, patients with exercise-induced myopathy may be able to return to normal activity when provided with medium-chain triglycerides (MCT) prior to exercise. There is no need to limit participation in sports. Progression of retinopathy in disorders of the mitochondrial trifunctional protein complex is closely associated with hydroxyacylcarnitine accumulation. A strict low-fat diet with MCT supplementation is recommended to slow or prevent progression of chorioretinopathy. Additional docosahexanoic acid does not prevent the decline in retinal function but does promote nonspecific improvement in visual acuity and is recommended. There is no evidence that L-carnitine supplementation is beneficial. Thus, supplementation with L-carnitine in a newborn identified by screening with either a medium-chain or long-chain defect is not supported. With respect to the use of the odd-chain medium-chain triglyceride triheptanoin in myopathic phenotypes, randomized trials are needed to establish whether triheptanoin is more effective than even-chain MCT. With increasing pathophysiological knowledge, new treatment options have been identified and are being clinically evaluated. These include the use of bezafibrates in myopathic long-chain defects.