Effects of triheptanoin (UX007) in patients with long-chain fatty acid oxidation disorders: Results from an open-label, long-term extension study

Triheptanoin in patients with long-chain fatty acid oxidation disorders: clinical experience in Italy

BACKGROUND

Long-chain fatty acid oxidation disorders (LC-FAOD) are rare and potentially life-threatening diseases that cause deficient energy production and accumulation of toxic metabolites. Despite dietary management, adherence to maximum fasting guidelines, restricted long-chain triglyceride intake and supplementation with medium-chain triglyceride (MCT) oil (current standard of care), most patients experience recurrent decompensation episodes that can require hospitalisation. Herein, we analysed the effectiveness and safety of triheptanoin (a highly purified, synthetic medium odd-chain triglyceride) treatment in a cohort of Italian patients with LC-FAOD.

METHODS

This retrospective, nationwide study included nine patients with LC-FAOD who switched from standard therapy with MCT oil to triheptanoin oral liquid. Data were collected between 2018 and 2022. Clinical outcome measures were the number and duration of intercurrent catabolic episodes and number and duration of metabolic decompensation episodes requiring hospitalisation. Creatine kinase (CK) levels and treatment-related adverse effects were also reported.

RESULTS

Patients were provided a mean ± standard deviation (SD) triheptanoin dose of 1.5 ± 0.9 g/kg/day in four divided administrations, which accounted for 23.9 ± 8.9% of patients' total daily caloric intake. Triheptanoin treatment was started between 2.7 and 16 years of age and was continued for 2.2 ± 0.9 years. The number of intercurrent catabolic episodes during triheptanoin treatment was significantly lower than during MCT therapy (4.3 ± 5.3 vs 22.0 ± 22.2; p = 0.034), as were the number of metabolic decompensations requiring hospitalisation (mean ± SD: 2.0 ± 2.5 vs 18.3 ± 17.7; p = 0.014), and annualised hospitalisation rates and duration. Mean CK levels (outside metabolic decompensation episodes) were lower with triheptanoin treatment versus MCT oil for seven patients. No intensive care unit admissions were required during triheptanoin treatment. Epigastric pain and diarrhoea were recorded as adverse effects during both MCT and triheptanoin treatment.

CONCLUSIONS

The significant improvement in clinical outcome measures after the administration of triheptanoin highlights that this treatment approach can be more effective than MCT supplementation in patients with LC-FAOD. Triheptanoin was well tolerated and decreased the number of intercurrent catabolic episodes, metabolic decompensation episodes requiring hospitalisation, and the annualised rate and duration of hospitalisations.

Triheptanoin Did Not Show Benefit versus Placebo for the Treatment of Paroxysmal Movement Disorders in Glut1 Deficiency Syndrome: Results of a Randomized Phase 3 Study

BACKGROUND

Paroxysmal movement disorders are common in Glut1 deficiency syndrome (Glut1DS). Not all patients respond to or tolerate ketogenic diets.

OBJECTIVES

The objective was to evaluate the effectiveness and safety of triheptanoin in reducing the frequency of disabling movement disorders in patients with Glut1DS not receiving a ketogenic diet.

METHODS

UX007G-CL301 was a randomized, double-blind, placebo-controlled, phase 3 crossover study. After a 6-week run-in, eligible patients were randomized 1:1 to the first sequence (triheptanoin/placebo or placebo/triheptanoin) titration plus maintenance, followed by washout and the opposite sequence titration plus maintenance. The placebo (safflower oil) matched the appearance, taste, and smell of triheptanoin. Open-label triheptanoin was administered in the extension. The frequency of disabling paroxysmal movement disorder events per 4 weeks (recorded by diary during maintenance; primary endpoint) was assessed by Wilcoxon rank-sum test.

RESULTS

Forty-three patients (children, n = 16; adults, n = 27) were randomized and treated. There was no difference between triheptanoin and placebo in the mean (interquartile range) number of disabling paroxysmal movement disorder events (14.3 [4.7-38.3] vs. 11.8; [3.2-28.7]; Hodges-Lehmann estimated median difference: 1.46; 95% confidence interval, -1.12 to 4.36; P = 0.2684). Treatment-emergent adverse events were mild/moderate in severity and included diarrhea, vomiting, upper abdominal pain, headache, and nausea. Two patients discontinued the study because of non-serious adverse events that were predominantly gastrointestinal. The study was closed early during the open-label extension because of lack of effectiveness. Seven patients continued to receive triheptanoin compassionately.

CONCLUSION

There were no significant differences between the triheptanoin and placebo groups in the frequency of disabling movement disorder events during the double-blind maintenance period. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Major clinical events and healthcare resource use among patients with long-chain fatty acid oxidation disorders in the United States: Results from LC-FAOD Odyssey program

Major clinical events (MCEs) related to long-chain fatty acid oxidation disorders (LC-FAOD) in triheptanoin clinical trials include inpatient or emergency room (ER) visits for three major clinical manifestations: rhabdomyolysis, hypoglycemia, and cardiomyopathy. However, outcomes data outside of LC-FAOD clinical trials are limited. The non-interventional cohort LC-FAOD Odyssey study examines data derived from US medical records and patient reported outcomes to quantify LC-FAOD burden according to management strategy including MCE frequency and healthcare resource utilization (HRU). Thirty-four patients were analyzed of which 21 and 29 patients had received triheptanoin and/or medium chain triglycerides (MCT), respectively. 36% experienced MCEs while receiving triheptanoin versus 54% on MCT. Total mean annualized MCE rates on triheptanoin and MCT were 0.1 and 0.7, respectively. Annualized disease-related inpatient and ER events were lower on triheptanoin (0.2, 0.3, respectively) than MCT (1.2, 1.0, respectively). Patients were managed more in an outpatient setting on triheptanoin (8.9 annualized outpatient visits) vs MCT (7.9). Overall, this shows that those with LC-FAOD in the Odyssey program experienced fewer MCEs and less HRU in inpatient and ER settings during triheptanoin-treated periods compared with the MCT-treated periods. The MCE rate was lower after initiation of triheptanoin, consistent with clinical trials.

Understanding patient, caregiver, and healthcare provider perspectives of the management of long-chain fatty acid oxidation disorders

Long-chain fatty acid oxidation disorders (LC-FAODs) are a group of rare, inherited, metabolic disorders that can lead to a wide range of symptoms that predominantly affect organ systems with high energy needs, such as the heart, liver, skeletal muscle, and nervous system. Clinical management primarily consists of close attention to and monitoring of diet and activity and avoidance of prolonged fasting. In addition, patients and caregivers must be alert for signs of life-threatening metabolic decompensation. As a result, LC-FAODs can have significant and wide-ranging impacts on the lives of patients and their caregivers. This article describes the effects of LC-FAODs at different life stages and in the context of the North American healthcare system from the perspective of a group of patients, caregivers, and healthcare providers (n = 6). We explain how challenges and needs change throughout life. Following an early diagnosis, an adjustment phase occurs during which caregivers may feel overwhelmed by their new roles and deeply concerned for their children's futures. As children grow, they become more aware of the differences between themselves and their peers, and with increasing independence comes more responsibility for managing their own condition. Major life events, such as new employment and moving house, pose challenges for people of all ages. In addition, it may be difficult to find and connect with qualified and experienced healthcare providers; navigate the health insurance system; and educate and align primary, specialist, and emergency care providers. We propose several strategies to improve the care of patients with LC-FAODs, such as educating local healthcare teams, improving trust between patients/caregivers and healthcare providers, and raising awareness of the challenges faced by patients and caregivers across the different life stages.

Heptanoate Improves Compensatory Mechanism of Glucose Homeostasis in Mitochondrial Long-Chain Fatty Acid Oxidation Defect

Defects in mitochondrial fatty acid β-oxidation (FAO) impair metabolic flexibility, which is an essential process for energy homeostasis. Very-long-chain acyl-CoA dehydrogenase (VLCADD; OMIM 609575) deficiency is the most common long-chain mitochondrial FAO disorder presenting with hypoglycemia as a common clinical manifestation. To prevent hypoglycemia, triheptanoin-a triglyceride composed of three heptanoates (C7) esterified with a glycerol backbone-can be used as a dietary treatment, since it is metabolized into precursors for gluconeogenesis. However, studies investigating the effect of triheptanoin on glucose homeostasis are limited. To understand the role of gluconeogenesis in the pathophysiology of long-chain mitochondrial FAO defects, we injected VLCAD-deficient (VLCAD-/-) mice with 13C3-glycerol in the presence and absence of heptanoate (C7). The incorporation of 13C3-glycerol into blood glucose was higher in VLCAD-/- mice than in WT mice, whereas the difference disappeared in the presence of C7. The result correlates with 13C enrichment of liver metabolites in VLCAD-/- mice. In contrast, the C7 bolus significantly decreased the 13C enrichment. These data suggest that the increased contribution of gluconeogenesis to the overall glucose production in VLCAD-/- mice increases the need for gluconeogenesis substrate, thereby avoiding hypoglycemia. Heptanoate is a suitable substrate to induce glucose production in mitochondrial FAO defect.

The Physiological and Pathological Role of Acyl-CoA Oxidation

Fatty acid metabolism, including β-oxidation (βOX), plays an important role in human physiology and pathology. βOX is an essential process in the energy metabolism of most human cells. Moreover, βOX is also the source of acetyl-CoA, the substrate for (a) ketone bodies synthesis, (b) cholesterol synthesis, (c) phase II detoxication, (d) protein acetylation, and (d) the synthesis of many other compounds, including N-acetylglutamate-an important regulator of urea synthesis. This review describes the current knowledge on the importance of the mitochondrial and peroxisomal βOX in various organs, including the liver, heart, kidney, lung, gastrointestinal tract, peripheral white blood cells, and other cells. In addition, the diseases associated with a disturbance of fatty acid oxidation (FAO) in the liver, heart, kidney, lung, alimentary tract, and other organs or cells are presented. Special attention was paid to abnormalities of FAO in cancer cells and the diseases caused by mutations in gene-encoding enzymes involved in FAO. Finally, issues related to α- and ω- fatty acid oxidation are discussed.

Diagnosis and management of metabolic myopathies

Metabolic myopathies are a set of rare inborn errors of metabolism leading to disruption in energy production. Relevant to skeletal muscle, glycogen storage disease and fatty acid oxidation defects can lead to exercise intolerance, rhabdomyolysis, and weakness in children and adults, distinct from the severe forms that involve multiple-organ systems. These nonspecific, dynamic symptoms along with conditions that mimic metabolic myopathies can make diagnosis challenging. Clinicians can shorten the time to diagnosis by recognizing the typical clinical phenotypes and performing next generation sequencing. With improved access and affordability of molecular testing, clinicians need to be well-versed in resolving variants of uncertain significance relevant to metabolic myopathies. Once identified, patients can improve quality of life, safely engage in exercise, and reduce episodes of rhabdomyolysis by modifying diet and lifestyle habits.

Fifty years of research on mitochondrial fatty acid oxidation disorders: The remaining challenges

Since the identification of the first disorder of mitochondrial fatty acid oxidation defects (FAOD) in 1973, more than 20 defects have been identified. Although there are some differences, most FAOD have similar clinical signs, which are mainly due to energy depletion and toxicity of accumulated metabolites. However, some of them have an unusual clinical phenotype or specific clinical signs. This manuscript focuses on what we have learnt so far on the pathophysiology of these disorders, which present with clinical signs that are not typical of categorical FAOD. It also highlights that some disorders have not yet been identified and tries to make assumptions to explain why. It also deals with new treatments under consideration in FAOD, including triheptanoin and similar anaplerotic substrates, ketone body treatments, RNA and gene therapy approaches. Finally, it suggests challenges for the diagnosis of FAOD in the coming years, both for symptomatic patients and for those diagnosed through newborn screening. The ultimate goal would be to identify all the patients born with FAOD and ensure for them the best possible quality of life.

Triheptanoin for the treatment of long-chain fatty acid oxidation disorders: Final results of an open-label, long-term extension study

Long-chain fatty acid oxidation disorders (LC-FAODs) result in life-threatening energy metabolism deficiencies/energy source depletion. Triheptanoin is an odd-carbon, medium chain triglyceride (that is an anaplerotic substrate of calories and fatty acids) for treating pediatric and adult patients with LC-FAODs. Study CL202 (NCT02214160), an open-label extension study of study CL201 (NCT01886378), evaluated the long-term safety/efficacy of triheptanoin in patients with LC-FAODs (N = 94), including cohorts who were triheptanoin naïve (n = 33) or had received triheptanoin in study CL201 (n = 24) or in investigator-sponsored trials/expanded access programs (IST/EAPs; n = 37). Primary endpoint was the annualized rate of LC-FAOD major clinical events (MCEs; rhabdomyolysis, hypoglycemia, cardiomyopathy). Mean ± standard deviation (SD) triheptanoin treatment durations were 27.4 ± 19.9, 46.9 ± 13.6, and 49.6 ± 21.4 months for the triheptanoin-naïve, CL201 rollover, and IST/EAP cohorts, respectively. In the triheptanoin-naïve cohort, median (interquartile range [IQR]) MCE rate significantly decreased from 2.00 (0.67-3.33) events/patient/year pre-triheptanoin to 0.28 (0.00-1.43) events/patient/year with triheptanoin (p = 0.0343), a reduction of 86%. In the CL201 rollover cohort, mean ± SD MCE rate significantly decreased from 1.76 ± 1.64 events/patient/year pre-triheptanoin to 1.00 ± 1.00 events/patient/year with triheptanoin (p = 0.0347), a reduction of 43%. In the IST/EAP cohort, mean ± SD MCE rate was 1.40 ± 2.37 (median [IQR] 0.57 [0.00-1.67]) events/patient/year with triheptanoin. Safety data were consistent with previous observations. Treatment-related treatment-emergent adverse events (TEAEs) occurred in 68.1% of patients and were mostly mild/moderate in severity. Five patients had seven serious treatment-related TEAEs; all resolved. Our results confirm the long-term efficacy of triheptanoin for patients with LC-FAOD.

Juvenile-Onset Recurrent Rhabdomyolysis Due to Compound Heterozygote Variants in the ACADVL Gene

Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is a rare autosomal recessive long-chain fatty acid oxidation disorder caused by mutations in the ACADVL gene. The myopathic form presents with exercise intolerance, exercise-related rhabdomyolysis, and muscle pain, usually starting during adolescence or adulthood. We report on a 17-year-old boy who has presented with exercise-induced muscle pain and fatigue since childhood. In recent clinical history, episodes of exercise-related severe hyperCKemia and myoglobinuria were reported. Electromyography was normal, and a muscle biopsy showed only "moth-eaten" fibers, and a mild increase in lipid storage in muscle fibers. NGS analysis displayed the already known heterozygote c.1769G>A variant and the unreported heterozygote c.523G>C change in ACADVL both having disease-causing predictions. Plasma acylcarnitine profiles revealed high long-chain acylcarnitine species levels, especially C14:1. Clinical, histopathological, biochemical, and genetic tests supported the diagnosis of VLCAD deficiency. Our report of a novel pathogenic missense variant in ACADVL expands the allelic heterogeneity of the disease. Since dietary treatment is the only therapy available for treating VLCAD deficiency and it is more useful the earlier it is started, prompt diagnosis is essential in order to minimize muscle damage and slow the disease progression.

Challenges and strategies for clinical trials in propionic and methylmalonic acidemias

Clinical trial development in rare diseases poses significant study design and methodology challenges, such as disease heterogeneity and appropriate patient selection, identification and selection of key endpoints, decisions on study duration, choice of control groups, selection of appropriate statistical analyses, and patient recruitment. Therapeutic development in organic acidemias (OAs) shares many challenges with other inborn errors of metabolism, such as incomplete understanding of natural history, heterogenous disease presentations, requirement for sensitive outcome measures and difficulties recruiting a small sample of participants. Here, we review strategies for the successful development of a clinical trial to evaluate treatment response in propionic and methylmalonic acidemias. Specifically, we discuss crucial decisions that may significantly impact success of the study, including patient selection, identification and selection of endpoints, determination of the study duration, consideration of control groups including natural history controls, and selection of appropriate statistical analyses. The significant challenges associated with designing a clinical trial in rare disease can sometimes be successfully met through strategic engagement with experts in the rare disease, seeking regulatory and biostatistical guidance, and early involvement of patients and families.

Effects of Triheptanoin on Mitochondrial Respiration and Glycolysis in Cultured Fibroblasts from Neutral Lipid Storage Disease Type M (NLSD-M) Patients

Neutral lipid storage disease type M (NLSD-M) is an ultra-rare, autosomal recessive disorder that causes severe skeletal and cardiac muscle damage and lipid accumulation in all body tissues. In this hereditary pathology, the defective action of the adipose triglyceride lipase (ATGL) enzyme induces the enlargement of cytoplasmic lipid droplets and reduction in the detachment of mono- (MG) and diglycerides (DG). Although the pathogenesis of muscle fiber necrosis is unknown, some studies have shown alterations in cellular energy production, probably because MG and DG, the substrates of Krebs cycle, are less available. No tests have been tried with medium-chain fatty acid molecules to evaluate the anaplerotic effect in NLSD cells. In this study, we evaluated the in vitro effect of triheptanoin (Dojolvi®), a highly purified chemical triglyceride with seven carbon atoms, in fibroblasts obtained from five NLSD-M patients. Glycolytic and mitochondrial functions were determined by Seahorse XF Agylent Technology, and cellular viability and triglyceride content were measured through colorimetric assays. After the addition of triheptanoin, we observed an increase in glycolysis and mitochondrial respiration in all patients compared with healthy controls. These preliminary results show that triheptanoin is able to induce an anaplerotic effect in NLSD-M fibroblasts, paving the way towards new therapeutic strategies.

Odd- and even-numbered medium-chained fatty acids protect against glutathione depletion in very long-chain acyl-CoA dehydrogenase deficiency

Recent trials have reported the ability of triheptanoin to improve clinical outcomes for the severe symptoms associated with long-chain fatty acid oxidation disorders, including very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency. However, the milder myopathic symptoms are still challenging to treat satisfactorily. Myopathic pathogenesis is multifactorial, but oxidative stress is an important component. We have previously shown that metabolic stress increases the oxidative burden in VLCAD-deficient cell lines and can deplete the antioxidant glutathione (GSH). We investigated whether medium-chain fatty acids provide protection against GSH depletion during metabolic stress in VLCAD-deficient fibroblasts. To investigate the effect of differences in anaplerotic capacity, we included both even-(octanoate) and odd-numbered (heptanoate) medium-chain fatty acids. Overall, we show that modulation of the concentration of medium-chain fatty acids in culture media affects levels of GSH retained during metabolic stress in VLCAD-deficient cell lines but not in controls. Lowered glutamine concentration in the culture media during metabolic stress led to GSH depletion and decreased viability in VLCAD deficient cells, which could be rescued by both heptanoate and octanoate in a dose-dependent manner. Unlike GSH levels, the levels of total thiols increased after metabolic stress exposure, the size of this increase was not affected by differences in cell culture medium concentrations of glutamine, heptanoate or octanoate. Addition of a PPAR agonist further exacerbated stress-related GSH-depletion and viability loss, requiring higher concentrations of fatty acids to restore GSH levels and cell viability. Both odd- and even-numbered medium-chain fatty acids efficiently protect VLCADdeficient cells against metabolic stress-induced antioxidant depletion.

Synthetic mRNA rescues very long-chain acyl-CoA dehydrogenase deficiency in patient fibroblasts and a murine model

Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is an inborn error of long chain fatty acid β-oxidation (FAO) with limited treatment options. Patients present with heterogeneous clinical phenotypes affecting predominantly heart, liver, and skeletal muscle. While VLCAD deficiency is a systemic disease, restoration of liver FAO has the potential to improve symptoms more broadly due to increased total body ATP production and reduced accumulation of potentially toxic metabolites. We explored the use of synthetic human VLCAD (hVLCAD) mRNA and lipid nanoparticle encapsulated hVLCAD mRNA (LNP-VLCAD) to generate functional VLCAD enzyme in patient fibroblasts derived from VLCAD deficient patients, mouse embryonic fibroblasts, hepatocytes isolated from VLCAD knockout (Acadvl-/-) mice, and Acadvl-/- mice to reverse the metabolic effects of the deficiency. Transfection of all cell types with hVLCAD mRNA resulted in high level expression of protein that localized to mitochondria with increased enzyme activity. Intravenous administration of LNP-VLCAD to Acadvl-/- mice produced a significant amount of VLCAD protein in liver, which declined over a week. Treated Acadvl-/- mice showed reduced hepatic steatosis, were more resistant to cold stress, and accumulated less toxic metabolites in blood than untreated animals. Results from this study support the potential for hVLCAD mRNA for treatment of VLCAD deficiency.

A case report of necrotizing enterocolitis in a moderately preterm neonate with LCHADD-A call to focus on the basics while utilizing advanced new therapies

Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) is an autosomal recessive condition of impaired beta-oxidation. Traditionally, treatment included restriction of dietary long-chain fatty acids via a low-fat diet and supplementation of medium chain triglycerides. In 2020, triheptanoin received FDA approval as an alternative source of medium chain fatty acids for individuals with long-chain fatty acid oxidation disorders (LC-FAOD). We present a case of a moderately preterm neonate born at 33 2/7 weeks gestational age with LCHADD who received triheptanoin and developed necrotizing enterocolitis (NEC). Prematurity is known as a major risk factor for NEC, with risk increasing with decreasing gestational age. To our knowledge, NEC has not previously been reported in patients with LCHADD or with triheptanoin use. While metabolic formula is part of the standard of care for LC-FAOD in early life, preterm neonates may benefit from more aggressive attempts to use skimmed human milk to minimize exposure to formula during the risk period for NEC during feed advancement. This risk period may be longer in neonates with LC-FAOD compared to otherwise healthy premature neonates.

Integrated multi-omics reveals anaplerotic rewiring in methylmalonyl-CoA mutase deficiency

Methylmalonic aciduria (MMA) is an inborn error of metabolism with multiple monogenic causes and a poorly understood pathogenesis, leading to the absence of effective causal treatments. Here we employ multi-layered omics profiling combined with biochemical and clinical features of individuals with MMA to reveal a molecular diagnosis for 177 out of 210 (84%) cases, the majority (148) of whom display pathogenic variants in methylmalonyl-CoA mutase (MMUT). Stratification of these data layers by disease severity shows dysregulation of the tricarboxylic acid cycle and its replenishment (anaplerosis) by glutamine. The relevance of these disturbances is evidenced by multi-organ metabolomics of a hemizygous Mmut mouse model as well as through identification of physical interactions between MMUT and glutamine anaplerotic enzymes. Using stable-isotope tracing, we find that treatment with dimethyl-oxoglutarate restores deficient tricarboxylic acid cycling. Our work highlights glutamine anaplerosis as a potential therapeutic intervention point in MMA.

Metabolic Myopathies

PURPOSE OF REVIEW

Metabolic myopathies are disorders that affect skeletal muscle substrate oxidation. Although some drugs and hormones can affect metabolism in skeletal muscle, this review will focus on the genetic metabolic myopathies.

RECENT FINDINGS

Impairments in glycogenolysis/glycolysis (glycogen storage disease), fatty acid transport/oxidation (fatty acid oxidation defects), and mitochondrial metabolism (mitochondrial myopathies) represent most metabolic myopathies; however, they often overlap clinically with structural genetic myopathies, referred to as pseudometabolic myopathies. Although metabolic myopathies can present in the neonatal period with hypotonia, hypoglycemia, and encephalopathy, most cases present clinically in children or young adults with exercise intolerance, rhabdomyolysis, and weakness. In general, the glycogen storage diseases manifest during brief bouts of high-intensity exercise; in contrast, fatty acid oxidation defects and mitochondrial myopathies usually manifest during longer-duration endurance-type activities, often with fasting or other metabolic stressors (eg, surgery, fever). The neurologic examination is often normal between events (except in the pseudometabolic myopathies) and evaluation requires one or more of the following tests: exercise stress testing, blood (eg, creatine kinase, acylcarnitine profile, lactate, amino acids), urine (eg, organic acids, myoglobin), muscle biopsy (eg, histology, ultrastructure, enzyme testing), and targeted (specific gene) or untargeted (myopathy panels) genetic tests.

SUMMARY

Definitive identification of a specific metabolic myopathy often leads to specific interventions, including lifestyle, exercise, and nutritional modifications; cofactor treatments; accurate genetic counseling; avoidance of specific triggers; and rapid treatment of rhabdomyolysis.

Population Pharmacokinetics of Heptanoate in Healthy Subjects and Patients With Long-Chain Fatty Acid Oxidation Disorders Treated With Triheptanoin

Triheptanoin is an odd-carbon, medium-chain triglyceride consisting of three fatty acids with seven carbons each on a glycerol backbone, indicated for the treatment of adult and pediatric patients with long-chain fatty acid oxidation disorders (LC-FAOD). A total of 562 plasma concentrations of heptanoate, the most abundant and pharmacologically active metabolite of triheptanoin, from 13 healthy adult subjects and 30 adult and pediatric subjects with LC-FAOD were included in the population pharmacokinetic (PK) analyses. Multiple peaks of heptanoate observed in several subjects were characterized by dual first-order absorption with a lag time in the second absorption compartment. The disposition of heptanoate in human plasma was adequately described by one-compartmental distribution with a linear elimination. The apparent clearance (CL/F) and apparent volume of distribution were allometrically scaled with body weight to describe PK data across a wide range of age groups in subjects with LC-FAOD. The typical CL/F in adult subjects with LC-FAOD was ≈19% lower than that in healthy subjects. Model-estimated elimination half-life for LC-FAOD patients was ∼1.7 hours, supporting a recommended dosing frequency of ≥4 times per day. Covariate analyses indicate that age, race, and sex did not lead to clinically meaningful changes in the exposure of heptanoate.

Outcomes of mitochondrial long chain fatty acid oxidation and carnitine defects from a single center metabolic genetics clinic

Background

Mitochondrial long-chain fatty acid oxidation and carnitine metabolism defects are a group of inherited metabolic diseases. We performed a retrospective cohort study to report on the phenotypic and genotypic spectrum of mitochondrial long-chain fatty acid oxidation and carnitine metabolism defects as well as their treatment outcomes.

Methods

All patients with mitochondrial long-chain fatty acid oxidation and carnitine metabolism defects were included. We divided patients into two groups to compare outcomes of those treated symptomatically (SymX) and asymptomatically (AsymX). We reviewed patient charts for clinical features, biochemical investigations, molecular genetic investigations, cardiac assessments, neuroimaging, treatments, and outcomes.

Results

There were 38 patients including VLCAD (n = 5), LCHAD (n = 4), CACT (n = 3), MAD (n = 1), CPT-I (n = 13), CPT-II (n = 3) deficiencies and CTD (n = 9). Fourteen patients were diagnosed symptomatically (SymX), and 24 patients were diagnosed asymptomatically (AsymX). Twenty-eight variants in seven genes were identified in 36 patients (pathogenic/likely pathogenic n = 25; variant of unknown significance n = 3). Four of those variants were novel. All patients with LCHAD deficiency had the common variant (p.Glu474Gln) in HADHA and their phenotype was similar to the patients reported in the literature for this genotype. Only one patient with VLCAD deficiency had the common p.Val283Ala in ACADVL. The different genotypes in the SymX and AsymX groups for VLCAD deficiency presented with similar phenotypes. Eight patients were treated with carnitine supplementation [CTD (n = 6), CPT-II (n = 1), and MAD (n = 1) deficiencies]. Thirteen patients were treated with a long-chain fat restricted diet and MCT supplementation. A statistically significant association was found between rhabdomyolysis, and hypoglycemia in the SymX group compared to the AsymX group. A higher number of hospital admissions, longer duration of hospital admissions and higher CK levels were observed in the SymX group, even though the symptomatic group was only 37% of the study cohort.

Conclusion

Seven different mitochondrial long-chain fatty acid oxidation and carnitine metabolism defects were present in our study cohort. In our clinic, the prevalence of mitochondrial long-chain fatty acid oxidation and carnitine defects was 4.75%.

Treatment of VLCAD-Deficient Patient Fibroblasts with Peroxisome Proliferator-Activated Receptor δ Agonist Improves Cellular Bioenergetics

Background: Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is an autosomal recessive disease that prevents the body from utilizing long-chain fatty acids for energy, most needed during stress and fasting. Symptoms can appear from infancy through childhood and adolescence or early adulthood, and include hypoglycemia, recurrent rhabdomyolysis, myopathy, hepatopathy, and cardiomyopathy. REN001 is a peroxisome-proliferator-activated receptor delta (PPARδ) agonist that modulates the expression of the genes coding for fatty acid β-oxidation enzymes and proteins involved in oxidative phosphorylation. Here, we assessed the effect of REN001 on VLCAD-deficient patient fibroblasts. Methods: VLCAD-deficient patient and control fibroblasts were treated with REN001. Cells were harvested for gene expression analysis, protein content, VLCAD enzyme activity, cellular bioenergetics, and ATP production. Results: VLCAD-deficient cell lines responded differently to REN001 based on genotype. All cells had statistically significant increases in ACADVL gene expression. Small increases in VLCAD protein and enzyme activity were observed and were cell-line- and dose-dependent. Even with these small increases, cellular bioenergetics improved in all cell lines in the presence of REN001, as demonstrated by the oxygen consumption rate and ATP production. VLCAD-deficient cell lines containing missense mutations responded better to REN001 treatment than one containing a duplication mutation in ACADVL. Discussion: Treating VLCAD-deficient fibroblasts with the REN001 PPARδ agonist results in an increase in VLCAD protein and enzyme activity, and a decrease in cellular stress. These results establish REN001 as a potential therapy for VLCADD as enhanced expression may provide a therapeutic increase in total VLCAD activity, but suggest the need for mutation-specific treatment augmented by other treatment measures.

Acylcarnitines: Nomenclature, Biomarkers, Therapeutic Potential, Drug Targets, and Clinical Trials

Acylcarnitines are fatty acid metabolites that play important roles in many cellular energy metabolism pathways. They have historically been used as important diagnostic markers for inborn errors of fatty acid oxidation and are being intensively studied as markers of energy metabolism, deficits in mitochondrial and peroxisomal β -oxidation activity, insulin resistance, and physical activity. Acylcarnitines are increasingly being identified as important indicators in metabolic studies of many diseases, including metabolic disorders, cardiovascular diseases, diabetes, depression, neurologic disorders, and certain cancers. The US Food and Drug Administration-approved drug L-carnitine, along with short-chain acylcarnitines (acetylcarnitine and propionylcarnitine), is now widely used as a dietary supplement. In light of their growing importance, we have undertaken an extensive review of acylcarnitines and provided a detailed description of their identity, nomenclature, classification, biochemistry, pathophysiology, supplementary use, potential drug targets, and clinical trials. We also summarize these updates in the Human Metabolome Database, which now includes information on the structures, chemical formulae, chemical/spectral properties, descriptions, and pathways for 1240 acylcarnitines. This work lays a solid foundation for identifying, characterizing, and understanding acylcarnitines in human biosamples. We also discuss the emerging opportunities for using acylcarnitines as biomarkers and as dietary interventions or supplements for many wide-ranging indications. The opportunity to identify new drug targets involved in controlling acylcarnitine levels is also discussed. SIGNIFICANCE STATEMENT: This review provides a comprehensive overview of acylcarnitines, including their nomenclature, structure and biochemistry, and use as disease biomarkers and pharmaceutical agents. We present updated information contained in the Human Metabolome Database website as well as substantial mapping of the known biochemical pathways associated with acylcarnitines, thereby providing a strong foundation for further clarification of their physiological roles.

Genetic, biochemical, and clinical spectrum of patients with mitochondrial trifunctional protein deficiency identified after the introduction of newborn screening in the Netherlands

Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) is included in many newborn screening (NBS) programs. Acylcarnitine-based NBS for LCHADD not only identifies LCHADD, but also the other deficiencies of the mitochondrial trifunctional protein (MTP), a multi-enzyme complex involved in long-chain fatty acid β-oxidation. Besides LCHAD, MTP harbors two additional enzyme activities: long-chain enoyl-CoA hydratase (LCEH) and long-chain ketoacyl-CoA thiolase (LCKAT). Deficiency of one or more MTP activities causes generalized MTP deficiency (MTPD), LCHADD, LCEH deficiency (not yet reported), or LCKAT deficiency (LCKATD). To gain insight in the outcomes of MTP-deficient patients diagnosed after the introduction of NBS for LCHADD in the Netherlands, a retrospective evaluation of genetic, biochemical, and clinical characteristics of MTP-deficient patients, identified since 2007, was carried out. Thirteen patients were identified: seven with LCHADD, five with MTPD, and one with LCKATD. All LCHADD patients (one missed by NBS, clinical diagnosis) and one MTPD patient (clinical diagnosis) were alive. Four MTPD patients and one LCKATD patient developed cardiomyopathy and died within 1 month and 13 months of life, respectively. Surviving patients did not develop symptomatic hypoglycemia, but experienced reversible cardiomyopathy and rhabdomyolysis. Five LCHADD patients developed subclinical neuropathy and/or retinopathy. In conclusion, patient outcomes were highly variable, stressing the need for accurate classification of and discrimination between the MTP deficiencies to improve insight in the yield of NBS for LCHADD. NBS allowed the prevention of symptomatic hypoglycemia, but current treatment options failed to treat cardiomyopathy and prevent long-term complications. Moreover, milder patients, who might benefit from NBS, were missed due to normal acylcarnitine profiles.

Twenty years of the Fabry Outcome Survey (FOS): insights, achievements, and lessons learned from a global patient registry

Background

Patient registries provide long-term, real-world evidence that aids the understanding of the natural history and progression of disease, and the effects of treatment on large patient populations with rare diseases. The year 2021 marks the 20th anniversary of the Fabry Outcome Survey (FOS), an international, multicenter, observational registry (NCT03289065). The primary aims of FOS are to broaden the understanding of Fabry disease (FD), an X-linked lysosomal storage disorder, and to improve the clinical management of affected patients. Here, we review the history of FOS and the analyses and publications disseminated from the registry, and we discuss the contributions FOS studies have made in understanding FD.

Results

FOS was initiated in April 2001 and, as of January 2021, 4484 patients with a confirmed diagnosis and patient informed consent have been enrolled from 144 centers across 26 countries. Data from FOS have been published in nearly 60 manuscripts on a wide variety of topics relevant to FD. Analyses of FOS data have investigated the long-term effectiveness and safety of enzyme replacement therapy (ERT) with agalsidase alfa and its effects on morbidity and mortality, as well as the benefits of prompt and early treatment with agalsidase alfa on the progression of cardiomyopathy and the decline in renal function associated with FD. Based on analyses of FOS data, ERT with agalsidase alfa has also been shown to improve additional signs and symptoms of FD experienced by patients. FOS data analyses have provided a better understanding of the natural history of FD and the specific populations of women, children, and the elderly, and have provided practical tools for the study of FD. FOS has also provided methodology and criteria for assessing disease severity which contributed to the continuous development of medical practice in FD and has largely improved our understanding of the challenges and needs of long-term data collection in rare diseases, aiding in future rare disease real-world evidence studies.

Conclusion

FOS over the last 20 years has substantially increased the scientific knowledge around improved patient management of FD and continues to expand our understanding of this rare disease.

Response to triheptanoin therapy in critically ill patients with LC-FAOD: Report of patients treated through an expanded access program

Long-chain fatty acid oxidation disorders (LC-FAOD) are a group of inborn errors of metabolism wherein patients are unable to process long-chain fatty acids into useable energy in the mitochondria. LC-FAOD commonly affects organ systems with high energy demand, manifesting as hypoketotic hypoglycemia, liver dysfunction, cardiomyopathy, rhabdomyolysis, and skeletal myopathy, as well as peripheral neuropathy and retinopathy in some subtypes. Collectively, LC-FAOD have a high mortality rate, especially in cases of early onset disease, and in the presence of cardiomyopathy. Triheptanoin is a synthetic medium-odd chain triglyceride, produced using a GMP-compliant process, which was designed to replenish mitochondrial metabolic deficits and restore energy homeostasis. Prior to its approval, triheptanoin was only available through clinical trials or to seriously ill patients as part of an expanded access program (EAP) following physician request. This retrospective study examined the impact of triheptanoin on cardiovascular parameters, in critically ill patients who participated in the EAP from February 2013 to January 2018. These patients persisted in critical condition despite receiving standard treatment in highly qualified centers by expert metabolic physicians and dietitians. Physician-completed questionnaires and narrative summaries were used to evaluate the disease presentation and management prior to the trigger event leading to triheptanoin request and use, and the response to triheptanoin treatment. Following triheptanoin initiation, most patients survived the initial trigger event (e.g., severe urinary tract infection, pneumonia) and demonstrated improvements in both short-term and long-term LC-FAOD manifestations. In patients with cardiomyopathy, stabilization or improvement from pretreatment levels was reported in left ventricular ejection fraction and left ventricular mass, in particular, all infants with cardiomyopathy showed improvement in cardiac function during triheptanoin therapy. Triheptanoin therapy was generally well tolerated. The study results are consistent with the existing positive benefit/risk profile of triheptanoin and reflect the effect of triheptanoin improving cardiac function in patients experiencing severe episodes of metabolic decompensation despite standard therapy.

A randomized, double-blind trial of triheptanoin for drug-resistant epilepsy in glucose transporter I deficiency syndrome (Glut1DS)

OBJECTIVE

Evaluate efficacy and long-term safety of triheptanoin in patients >1 year old, not on a ketogenic diet, with drug-resistant seizures associated with Glucose Transporter Type 1 Deficiency Syndrome (Glut1DS).

METHODS

UX007G-CL201 was a randomized, double-blind, placebo-controlled trial. Following a 6-week baseline period, eligible patients were randomized 3:1 to triheptanoin or placebo. Dosing was titrated to 35% total daily calories over 2 weeks. After an 8-week placebo-controlled period, all patients received open-label triheptanoin through Week 52.

RESULTS

The study included 36 patients (15 children; 13 adolescents; 8 adults). A median 12.6% reduction in overall seizure frequency was observed in the triheptanoin arm relative to baseline and a 13.5% difference was observed relative to placebo (p = .58). In patients with absence seizures only (n = 9), a median 62.2% reduction in seizure frequency was observed in the triheptanoin arm relative to baseline. Only one patient with absence seizures only was present in the control group, preventing comparison. No statistically significant differences in seizure frequency were observed. Common treatment-emergent adverse events (TEAEs) included diarrhea, vomiting, abdominal pain, and nausea, most mild or moderate in severity. No serious AEs were considered treatment related. One patient discontinued due to status epilepticus.

SIGNIFICANCE

Triheptanoin did not significantly reduce seizure frequency in patients with Glut1DS not on the ketogenic diet. Treatment was associated with mild to moderate GI treatment-related events; most resolved following dose reduction or interruption and/or medication for treatment. Triheptanoin was not associated with any long-term safety concerns when administered at dose levels up to 35% total daily caloric intake for up to one year.

Very long-chain acyl-CoA dehydrogenase deficiency in a Swedish cohort: Clinical symptoms, newborn screening, enzyme activity, and genetics

Very long-chain acyl-CoA dehydrogenase deficiency (VLCADD) is a recessive disorder of fatty acid beta-oxidation with variable phenotype. Patients may present during the neonatal period with lethal multi-organ failure or during adulthood with a myopathic phenotype. VLCADD is included in the Swedish newborn screening (NBS) program since 2010. The study describes the phenotype and biochemical findings in relation to the genotype, enzyme activity, and screening data in a Swedish cohort of pediatric patients with VLCADD. A total of 22 patients (20 diagnosed via NBS between 2010 and 2019, two diagnosed pre NBS) were included. Parameters analyzed were enzyme activity (palmitoyl CoA oxidation rate); ACADVL genotype; NBS results including Collaborative Laboratory Integrated Reports (CLIR) score; biochemical findings; treatment; clinical outcome. A clinical severity score (CSS) was compiled using treatment interventions and clinical symptoms. A possible correlation between CSS and VLCAD residual enzyme activity and NBS CLIR score was analyzed. The most common ACADVL variant (c.848T>C) was identified in 24/44 alleles. Five novel variants were detected. Clinical manifestations varied from asymptomatic to severe. There was a correlation between CSS, residual enzyme activity, and CLIR scores. Most patients diagnosed via NBS had less severe disease compared to those clinically diagnosed. In conclusion, the identified correlation between the NBS CLIR score, residual enzyme activity, and clinical outcome suggests that information available neonatally may aid in treatment decisions.

Diagnosis and Clinical Management of Long-chain Fatty-acid Oxidation Disorders: A Review

Long-chain fatty-acid oxidation disorders (LC-FAODs) are autosomal recessive inherited metabolic conditions that occur due to a disruption in the body's ability to perform mitochondrial beta oxidation. Expanded newborn screening is widening phenotypic understanding of these disorders, as well improving our knowledge of disease incidence. Management of these disorders is focused on avoidance of fasting, dietary changes and supplementation with energy sources that bypass the metabolic block. Recent US Food and Drug Administration approval of triheptanoin has improved the outcome for affected individuals. New research into dietary modifications and novel pharmacologic therapies continues for these disorders. In this article, we review the major LC-FAODs and their clinical presentation.

Recent developments in the management of Huntington's disease

Huntington's disease (HD) is a rare, incurable, inheritedneurodegenerative disorder manifested by chorea, hyperkinetic, and hypokinetic movements. The FDA has approved only two drugs, viz. tetrabenazine, and deutetrabenazine, to manage the chorea associated with HD. However, several other drugs are used as an off-label to manage chorea and other symptoms such as depression, anxiety, muscle tremors, and cognitive dysfunction associated with HD. So far, there is no disease-modifying treatment available. Drug repurposing has been a primary drive to search for new anti-HD drugs. Numerous molecular targets along with a wide range of small molecules and gene therapies are currently under clinical investigation. More than 200 clinical studies are underway for HD, 75% are interventional, and 25% are observational studies. The present review discusses the small molecule clinical pipeline and molecular targets for HD. Furthermore, the biomarkers, diagnostic tests, gene therapies, behavioral and observational studies for HD were also deliberated.

The Pharmacokinetics of Triheptanoin and Its Metabolites in Healthy Subjects and Patients With Long-Chain Fatty Acid Oxidation Disorders

Long-chain fatty acid oxidation disorders (LC-FAODs) are a group of life-threatening autosomal recessive disorders caused by defects in nuclear genes encoding mitochondrial enzymes involved in the conversion of dietary long-chain fatty acids into energy. Triheptanoin is an odd-carbon, medium-chain triglyceride consisting of 3 fatty acids with 7 carbons each on a glycerol backbone developed to treat adult and pediatric patients with LC-FAODs. The pharmacokinetics of triheptanoin and circulating metabolites were explored in healthy subjects and patients with LC-FAODs using noncompartmental analyses. Systemic exposure to triheptanoin following an oral administration was negligible, as triheptanoin is extensively hydrolyzed to glycerol and heptanoate in the gastrointestinal tract. Multiple peaks for triheptanoin metabolites were observed in the plasma following oral administration of triheptanoin, generally coinciding with the time that meals were served. Heptanoate, the pharmacologically active metabolite of triheptanoin supplementing energy sources in patients with LC-FAODs, showed the greatest exposure among the metabolites of triheptanoin in human plasma following oral administration of triheptanoin. The exposure of heptanoate was approximately 10-fold greater than that of beta-hydroxypentoate, a downstream metabolite of heptanoate. Exposure to triheptanoin metabolites appeared to increase following multiple doses as compared with the single dose, and with the increase in triheptanoin dose levels.

Lipidomic and Proteomic Alterations Induced by Even and Odd Medium-Chain Fatty Acids on Fibroblasts of Long-Chain Fatty Acid Oxidation Disorders

Medium-chain fatty acids (mc-FAs) are currently applied in the treatment of long-chain fatty acid oxidation disorders (lc-FAOD) characterized by impaired β-oxidation. Here, we performed lipidomic and proteomic analysis in fibroblasts from patients with very long-chain acyl-CoA dehydrogenase (VLCADD) and long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHADD) deficiencies after incubation with heptanoate (C7) and octanoate (C8). Defects of β-oxidation induced striking proteomic alterations, whereas the effect of treatment with mc-FAs was minor. However, mc-FAs induced a remodeling of complex lipids. Especially C7 appeared to act protectively by restoring sphingolipid biosynthesis flux and improving the observed dysregulation of protein homeostasis in LCHADD under control conditions.

Altered Metabolic Flexibility in Inherited Metabolic Diseases of Mitochondrial Fatty Acid Metabolism

In general, metabolic flexibility refers to an organism's capacity to adapt to metabolic changes due to differing energy demands. The aim of this work is to summarize and discuss recent findings regarding variables that modulate energy regulation in two different pathways of mitochondrial fatty metabolism: β-oxidation and fatty acid biosynthesis. We focus specifically on two diseases: very long-chain acyl-CoA dehydrogenase deficiency (VLCADD) and malonyl-CoA synthetase deficiency (acyl-CoA synthetase family member 3 (ACSF3)) deficiency, which are both characterized by alterations in metabolic flexibility. On the one hand, in a mouse model of VLCAD-deficient (VLCAD^-/-) mice, the white skeletal muscle undergoes metabolic and morphologic transdifferentiation towards glycolytic muscle fiber types via the up-regulation of mitochondrial fatty acid biosynthesis (mtFAS). On the other hand, in ACSF3-deficient patients, fibroblasts show impaired mitochondrial respiration, reduced lipoylation, and reduced glycolytic flux, which are compensated for by an increased β-oxidation rate and the use of anaplerotic amino acids to address the energy needs. Here, we discuss a possible co-regulation by mtFAS and β-oxidation in the maintenance of energy homeostasis.

Clinical outcomes in a series of 18 patients with long chain fatty acids oxidation disorders treated with triheptanoin for a median duration of 22 months

INTRODUCTION

Triheptanoin provides long-chain fatty acid oxidation disorder (LC-FAOD) patients with an alternative to medium-even-chain triglycerides therapy.

MATERIAL-METHODS

Retrospective analysis of 18 French LC-FAOD patients benefiting from early access to triheptanoin treatment.

RESULTS

Eight female and 10 male patients with LC-FAOD (VLCAD, LCHAD, CACT, CPTII and MTP) were treated with triheptanoin for a median duration of 22 months (range: 9-228 months). At last consultation, triheptanoin accounted for 15-35% of their daily caloric intake. In the year following the introduction of triheptanoin, patients reported a reduction of intermittent snacking and nocturnal meals. Three patients, including 1 adult, became free of severe hypoglycaemic events. Ten of 12 paediatric patients and 4 of 6 adult patients reported reduced fatigue with reductions in the number and severity of episodes of myalgia. Of 6 patients, including 1 adult, that had required the use of a wheelchair in the year prior to triheptanoin, all but one no longer required its use. The number of emergency hospitalizations decreased, and none were recorded for paediatric patients during these 12 months. Cumulative annual days of emergency care in the home were reduced from 286 to 51 days in the year before and after initiation, respectively, and 13 patients required no such interventions. Adverse events were limited to digestive issues that dissipated over time.

CONCLUSIONS

Our case-series suggests that long-term treatment of LC-FAOD paediatric and adult patients with triheptanoin is safe and leads to marked improvement of symptoms and an improved quality of life.

Effects of triheptanoin (UX007) in patients with long-chain fatty acid oxidation disorders: Results from an open-label, long-term extension study

Long-chain fatty acid oxidation disorders (LC-FAOD) are autosomal recessive conditions that impair conversion of long-chain fatty acids into energy, leading to significant clinical symptoms. Triheptanoin is a highly purified, 7-carbon chain triglyceride approved in the United States as a source of calories and fatty acids for treatment of pediatric and adult patients with molecularly confirmed LC-FAOD. CL202 is an open-label, long-term extension study evaluating triheptanoin (Dojolvi) safety and efficacy in patients with LC-FAOD. Patients rolled over from the CL201 triheptanoin clinical trial (rollover); were triheptanoin-naïve (naïve); or had participated in investigator-sponsored trials/expanded access programs (IST/other). Results focus on rollover and naïve groups, as pretreatment data allow comparison. Primary outcomes were annual rate and duration of major clinical events (MCEs; rhabdomyolysis, hypoglycemia, and cardiomyopathy events). Seventy-five patients were enrolled (24 rollover, 20 naïve, 31 IST/other). Mean study duration was 23.0 months for rollover, 15.7 months for naïve, and 34.7 months for IST/other. In the rollover group, mean annualized MCE rate decreased from 1.76 events/year pre-triheptanoin to 0.96 events/year with triheptanoin (P = .0319). Median MCE duration was reduced by 66%. In the naïve group, median annualized MCE rate decreased from 2.33 events/year pre-triheptanoin to 0.71 events/year with triheptanoin (P = .1072). Median MCE duration was reduced by 80%. The most common related adverse events (AEs) were diarrhea, abdominal pain/discomfort, and vomiting, most mild to moderate. Three patients had serious AEs (diverticulitis, ileus, rhabdomyolysis) possibly related to drug; all resolved. Two patients had AEs leading to death; neither drug related. Triheptanoin reduced rate and duration of MCEs. Safety was consistent with previous observations.

Mitochondrial Fatty Acid Oxidation Disorders: Laboratory Diagnosis, Pathogenesis, and the Complicated Route to Treatment

Mitochondrial fatty acid (FA) oxidation deficiencies represent a genetically heterogeneous group of diseases in humans caused by defects in mitochondrial FA beta-oxidation (mFAO). A general characteristic of all mFAO disorders is hypoketotic hypoglycemia resulting from the enhanced reliance on glucose oxidation and the inability to synthesize ketone bodies from FAs. Patients with a defect in the oxidation of long-chain FAs are at risk to develop cardiac and skeletal muscle abnormalities including cardiomyopathy and arrhythmias, which may progress into early death, as well as rhabdomyolysis and exercise intolerance. The diagnosis of mFAO-deficient patients has greatly been helped by revolutionary developments in the field of tandem mass spectrometry (MS) for the analysis of acylcarnitines in blood and/or urine of candidate patients. Indeed, acylcarnitines have turned out to be excellent biomarkers; not only do they provide information whether a certain patient is affected by a mFAO deficiency, but the acylcarnitine profile itself usually immediately points to which enzyme is likely deficient. Another important aspect of acylcarnitine analysis by tandem MS is that this technique allows high-throughput analysis, which explains why screening for mFAO deficiencies has now been introduced in many newborn screening programs worldwide. In this review, we will describe the current state of knowledge about mFAO deficiencies, with particular emphasis on recent developments in the area of pathophysiology and treatment.