Fatty acid oxidation disorders: outcome and long-term prognosis

Medium-chain acyl-CoA dehydrogenase deficiency in North Macedonia - ten years experience

OBJECTIVES

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is an autosomal recessive disorder of fatty acid oxidation, with potentialy fatal outcome. Early diagnosis of MCADD by acylcarnitine analysis on newborn screening using tandem mass spectrometry can potentially reduce morbidity and mortality. In this study, we evaluate the prevalence and genetic background of MCADD in North Macedonia.

METHODS

Medium chain length acylcarnitines, were measured on newborn screening blood spot cards by tandem mass spectrometry. The molecular diagnosis was performed by whole exome sequencing of the ACADM gene, and detected mutations were confirmed with Sanger sequencing in all neonates with positive MCAD screening markers, and their parents as well.

RESULTS

A total of 52,942 newborns were covered by metabolic screening during the period May 2014-May 2024. 11 unrelated Macedonian neonates were detected with positive MCADD screening markers, and prevalence of 1/4,813 live births was estimated. Molecular analysis of the ACADM gene showed that c.985A>G was the most prevalent mutation occurred on 77.27 % of the alleles, while 18.18 % alleles carried c.244dupT pathogenic variant. Seven patients were homozygous for c.985A>G (63.6 %) while one was homozygous for c.244dupT (9.1 %) variant. Two patients were compound heterozygotes with c.985A>G/c.244dupT genotype (18.2 %), and one patient had c.985A>G allele without detection of the second ACADM mutant allele.

CONCLUSIONS

The NBS estimated prevalence of MCADD in Macedonian population was more frequent than in the other European population and worldwide incidence in general. This is the first report of the genetic background of MCADD in North Macedonia.

ACADVL Deep Sequencing in a Case Study: Beyond the Common c.848T>C Pathogenic Variant

Background: Very-long-chain acyl-CoA dehydrogenase deficiency (VLCADD) is caused by biallelic pathogenic variants in ACADVL (acyl-CoA dehydrogenase very-long-chain), leading to impaired fatty acid oxidation and the accumulation of long-chain acylcarnitine. We report a single case of a two-year-old girl, whose neonatal metabolic screening revealed an acylcarnitine profile suggestive of VLCADD, with residual enzymatic activity of 19.8%. Methods: We performed ACADVL whole-gene sequencing. We then carried out an in silico analysis of the potential effects of the variants with dedicated tools, assessing splicing, RNA structure, RNA binding factors, and protein structure. We also conducted gene expression analysis. Results: Genetic testing identified her as compound heterozygous for the pathogenic ACADVL variant (NM_000018.3):c.848T>C, inherited from her mother, and for the two paternal variants, c.-64T>C in the basal promoter and c.957G>A, a synonymous substitution in exon 10. Gene expression analysis revealed reduced ACADVL mRNA levels in the proband's blood cells but without abnormal isoform production. A decreased expression of the paternal allele carrying the 957A was also observed. Despite this significant reduction in mRNA levels, the underlying mechanism remains unclear. Conclusions: Although currently healthy, due to the VLCAD residual activity within the range associated with the mild form of the disease, the child might be at potential risk for metabolic decompensation or late-onset VLCADD. Our results indicated an allelic imbalance in mRNA expression and c.957G>A is identified as a hypomorphic allele. This suggests that deep ACADVL sequencing is a valuable tool for correlating genetic variants with enzymatic activity levels.

An Explorative Qualitative Study of the Role of a Genetic Counsellor to Parents Receiving a Diagnosis After a Positive Newborn Bloodspot Screening

Newborn Bloodspot Screening (NBS) can detect severe treatable health conditions with onset during infancy. The parents of a newborn baby are vulnerable in the days after birth, and the optimal way to deliver the shocking and distressing news of a potential serious diagnosis is yet to be defined. More data are needed to determine whether access to a genetic counsellor (GC) improves families' experiences with genetic conditions identified by NBS. This study aimed to explore the similarities and differences for parents who received a positive NBS result for Spinal Muscular Atrophy (SMA) and received access to a GC (GC cohort), to a cohort of parents who received a diagnosis for inborn errors of metabolism (IEM) and did not have access to a GC (non-GC cohort). Semi-structured interviews explored the retrospective experiences of receiving the NBS result, including diagnosis implications and subsequent adaptation to respective genetic diagnoses. Inductive thematic analysis was used from group comparison. 7 SMA families and 5 IEM families were included in the study. Four themes were identified: 1. minimal pre-test counselling; 2. perceived lack of local healthcare team knowledge; 3. enabling factors for adaptation; 4. implications for both individuals and their families. Both the GC and non-GC cohorts reported insufficient counselling in the pre-test period and described feeling traumatised at the time of the diagnosis delivery. Families without subsequent GC input described limited understanding of the disease due to the use of medicalized terms, as well as a decreased understanding of reproductive options, familial communication and subsequent cascade screening. GCs can support information needs and adaptation following a NBS diagnosis.

Insights from the Newborn Screening Program for Very Long-Chain Acyl-CoA Dehydrogenase (VLCAD) Deficiency in Kuwait

Newborn screening for very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency in Kuwait was initiated in October 2014. Over a 7-year period (January 2015 to December 2021), 43 newborns were diagnosed with VLCAD deficiency out of 356,819 screened, corresponding to an incidence of 1:8290 and 1:5405 among only Kuwaiti newborns. This study represents the first comprehensive review of newborn screening for VLCAD deficiency in Kuwait. The screening process begins with the detection of elevated blood C14:1 levels in dried blood spots, followed by confirmatory testing using dried blood spots acylcarnitine profiling, with or without molecular testing. Furthermore, this study demonstrates that incorporating the C14:1/C2 ratio as a supplementary marker in first-tier testing alongside C14:1 improves the positive predictive value (PPV) of the current newborn screening for VLCAD deficiency. Adding molecular genetic testing for known VLCAD variants as a second-tier strategy to the national program is also recommended to further enhance specificity and improve PPV. Our findings provide evidence that the expanded newborn screening program in Kuwait has successfully facilitated the early detection of VLCAD deficiency, preventing death and disability in affected infants.

Prolonged Cholestatic Jaundice Associated with Carnitine Palmitoyltransferase IA Deficiency

Carnitine palmitoyltransferase 1A (CPT1A) deficiency is a type of fatty acid oxidation disorder in which long chain fatty acids cannot be transported into mitochondria for further processing and storage in our body. Typically, the patients present with lethargy, hypoglycemia, and raised serum transaminase levels before 2 years of age. Cholestatic jaundice as manifestation of this deficiency has been reported rarely; here, we report an adolescent male with CPT1A deficiency who developed prolonged cholestatic jaundice following a febrile illness.

Remodeling of lipid landscape in high fat fed very-long chain acyl-CoA dehydrogenase null mice favors pro-arrhythmic polyunsaturated fatty acids and their downstream metabolites

Very-long chain acyl-CoA dehydrogenase (VLCAD) catalyzes the initial step of mitochondrial long chain (LC) fatty acid β-oxidation (FAO). Inherited VLCAD deficiency (VLCADD) predisposes to neonatal arrhythmias whose pathophysiology is still not understood. We hypothesized that VLCADD results in global disruption of cardiac complex lipid homeostasis, which may set conditions predisposing to arrhythmia. To test this, we assessed the cardiac lipidome and related molecular markers in seven-month-old VLCAD-/- mice, which mimic to some extent the human cardiac phenotype. Mice were sacrificed in the fed or fasted state after receiving for two weeks a chow or a high-fat diet (HFD), the latter condition being known to worsen symptoms in human VLCADD. Compared to their littermate counterparts, HFD/fasted VLCAD-/- mouse hearts displayed the following lipid alterations: (1) Lower LC, but higher VLC-acylcarnitines accumulation, (2) higher levels of arachidonic acid (AA) and lower docosahexaenoic acid (DHA) contents in glycerophospholipids (GPLs), as well as (3) corresponding changes in pro-arrhythmogenic AA-derived isoprostanes and thromboxane B2 (higher), and anti-arrythmogenic DHA-derived neuroprostanes (lower). These changes were associated with remodeling in the expression of gene or protein markers of (1) GPLs remodeling: higher calcium-dependent phospholipase A2 and lysophosphatidylcholine-acyltransferase 2, (2) calcium handling perturbations, and (3) endoplasmic reticulum stress. Altogether, these results highlight global lipid dyshomeostasis beyond FAO in VLCAD-/- mouse hearts, which may set conditions predisposing the hearts to calcium mishandling and endoplasmic reticulum stress and thereby may contribute to the pathogenesis of arrhythmias in VLCADD in mice as well as in humans.

Specifications of the ACMG/AMP guidelines for ACADVL variant interpretation

Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency (VLCADD) is a relatively common inborn error of metabolism, but due to difficulty in accurately predicting affected status through newborn screening, molecular confirmation of the causative variants by sequencing of the ACADVL gene is necessary. Although the ACMG/AMP guidelines have helped standardize variant classification, ACADVL variant classification remains disparate due to a phenotype that can be nonspecific, the possibility of variants that produce late-onset disease, and relatively high carrier frequency, amongst other challenges. Therefore, an ACADVL-specific variant curation expert panel (VCEP) was created to facilitate the specification of the ACMG/AMP guidelines for VLCADD. We expect these guidelines to help streamline, increase concordance, and expedite the classification of ACADVL variants.

A Review of Disparities and Unmet Newborn Screening Needs over 33 Years in a Cohort of Mexican Patients with Inborn Errors of Intermediary Metabolism

Advances in an early diagnosis by expanded newborn screening (NBS) have been achieved mainly in developed countries, while populations of middle- and low-income countries have poor access, leading to disparities. Expanded NBS in Mexico is not mandatory. Herein, we present an overview of the differences and unmet NBS needs of a group of Mexican patients with inborn errors of intermediary metabolism (IEiM), emphasizing the odyssey experienced to reach a diagnosis. We conducted a retrospective observational study of a historical cohort of patients with IEiM from a national reference center. A total of 924 patients with IEiM were included. Although 72.5% of the diseases identified are detectable by expanded NBS, only 35.4% of the patients were screened. The mortality in the unscreened group was almost two-fold higher than that in the screened group. Patients experienced a median diagnostic delay of 4 months, which is unacceptably long considering that to prevent disability and death, these disorders must be treated in the first days of life. Patients had to travel long distances to our reference center, contributing to their unacceptable diagnostic odyssey. This study highlights the urgent need to have an updated, expanded NBS program with adequate follow up in Mexico and promote the creation of regional medical care centers. We also provide compelling evidence that could prove valuable to decision makers overseeing public health initiatives for individuals impacted by IEiM from middle- and low-income countries.

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.

Recognizing and Managing a Metabolic Crisis

In some relatively common inborn errors of metabolism there can be the accumulation of toxic compounds including ammonia and organic acids such as lactate and ketoacids, as well as energy deficits at the cellular level. The clinical presentation is often referred to as a metabolic emergency or crisis. Fasting and illness can result in encephalopathy within hours, and without appropriate recognition and intervention, the outcome may be permanent disability or death. This review outlines easy and readily available means of recognizing and diagnosing a metabolic emergency as well as general guidelines for management. Disease-specific interventions focus on parenteral nutrition to reverse catabolism, toxin removal strategies, and vitamin/nutrition supplementation.

Functional and structural impact of 10 ACADM missense mutations on human medium chain acyl-Coa dehydrogenase

Medium chain acyl-CoA dehydrogenase (MCAD) deficiency (MCADD) is associated with ACADM gene mutations, leading to an impaired function and/or structure of MCAD. Importantly, after import into the mitochondria, MCAD must incorporate a molecule of flavin adenine dinucleotide (FAD) per subunit and assemble into tetramers. However, the effect of MCAD amino acid substitutions on FAD incorporation has not been investigated. Herein, the commonest MCAD variant (p.K304E) and 11 additional rare variants (p.Y48C, p.R55G, p.A88P, p.Y133C, p.A140T, p.D143V, p.G224R, p.L238F, p.V264I, p.Y372N, and p.G377V) were functionally and structurally characterized. Half of the studied variants presented a FAD content <65 % compared to the wild-type. Most of them were recovered as tetramers, except the p.Y372N (mainly as dimers). No correlation was found between the levels of tetramers and FAD content. However, a correlation between FAD content and the cofactor's affinity, proteolytic stability, thermostability, and thermal inactivation was established. We showed that the studied amino acid changes in MCAD may alter the substrate chain-length dependence and the interaction with electron-transferring-flavoprotein (ETF) necessary for a proper functioning electron transfer thus adding additional layers of complexity to the pathological effect of ACADM missense mutations. Although the majority of the variant MCADs presented an impaired capacity to retain FAD during their synthesis, some of them were structurally rescued by cofactor supplementation, suggesting that in the mitochondrial environment the levels and activity of those variants may be dependent of FAD's availability thus contributing for the heterogeneity of the MCADD phenotype found in patients presenting the same genotype.

Recent advances in neurometabolic diseases: The genetic role in the modern era

The global birth prevalence of all inborn errors of metabolism (IEMs) in children (49 studies, 1980-2017) is approximately 50.9/100,000 live births. Regional pooled birth prevalence showed higher rates in Eastern Mediterranean regions (75.7/100,000 live births) and highest in Saudi Arabia (169/100,000) with higher parental consanguinity rates of ∼60%. Case fatality rates globally are estimated to be 33% or higher. IEMs are a group of >600 heterogeneous disorders often presenting in newborns and infants with drug-resistant seizures and/or encephalopathy. Early diagnosis and treatments are key in the prevention of morbidity, early mortality, and high lifetime health care costs, such as the early recognition of the newborn with pyridoxine- or pyridoxal-L-phosphate-dependent seizures which do not respond to standard antiepileptic drugs. The earlier the recognition and intervention in the specific cofactor- or vitamin-responsive epilepsies, the better the outcome and prevention of intractable seizures and encephalopathy leading to irreversible neurologic injury. In recent years, the genetics of IEMs has been transformed by the emergence of new molecular genetic technologies. Depending upon the clinical phenotype, current genetic testing may include chromosomal microarray (deletion/duplication analysis), single target gene sequencing, gene panels (sequencing and deletion/duplication analysis), DNA methylation analysis, mitochondrial nuclear gene panel, and mtDNA sequencing and/or trio WES or WGS (which have reduced in costs). A meta-analysis, showed WES and epilepsy gene panels to be the most cost-effective genetic tests for unknown epilepsies versus chromosomal microarray. Most recently, rapid genomic sequencing (RGS) has been associated with a shorter time to diagnosis (3 days) and increased diagnostic yield when compared with standard-of-care testing, including gene panels and microarrays. A randomized controlled trial (RCT) of rapid(r) WGS or rWES in acutely ill infants with diseases of unknown etiology in pediatric ICUs in San Diego, California found RGS to be highly clinically useful for 77% of 201 infants. RGS changed clinical management in 28% of infants and outcomes in 15%. An Australian study of ultra-rapid (ur) exome sequencing (mean time to genomic test report of 3.3 days) in 108 critically ill infants and children with suspected monogenic conditions, had a molecular diagnostic yield of 51% with 20% requiring further genetic analysis. In 42/55 (76%), ur exome sequencing was felt to have influenced clinical management for targeted treatments, surveillance, or palliative care, however, the study was not designed or powered to measure differences in major clinical outcomes compared to standard care of critically ill patients. Further research is needed to understand this tool's clinical value and generalizability balanced against its high costs. A paradigm shift is evolving from pattern- and evidence-based medicine toward algorithm-based, precision medicine targeted to individual mutations. Meticulous clinical phenotyping and pedigree analysis, combined with advances in high-throughput metabolomics, proteomics, transcriptomics (RNAseq in clinically relevant tissues), and genomics, have expedited the identification of novel pathomechanisms and new therapeutic targets. Evaluation of these therapies in IEMs, many of which manifest with encephalopathy and epilepsy, will depend on international registries of well-characterized phenotypes in RCTs and measurement of clinically relevant endpoints. The earlier the recognition and diagnosis and intervention with targeted therapies, the better the overall outcome in terms of the impact on intellectual disability and the effective management of the associated epilepsy.

Very long-chain acyl-CoA dehydrogenase deficiency and type I diabetes mellitus: Case report and management challenges

BACKGROUND

Very long-chain acyl-CoA dehydrogenase deficiency (VLCADD) is a rare autosomal recessive disorder of fatty acid metabolism. Its clinical presentation includes hypoketotic hypoglycemia and potentially life-threatening multiorgan dysfunction.Therefore, the cornerstone of management includes avoiding fasting, dietary modification, and monitoring for complications. The co-occurrence of type 1 diabetes mellitus (DM1) with VLCADD has not been described in the literature.

CASE REPORT

A 14-year-old male with a known diagnosis of VLCADD presented with vomiting, epigastric pain, hyperglycemia, and high anion gap metabolic acidosis. He was diagnosed with DM1 and managed with insulin therapy while maintaining his high complex carbohydrate, low long-chain fatty acids diet with medium-chain triglyceride supplementation. The primary diagnosis (VLCADD) makes the management of DM1 in this patient challenging as hyperglycemia related to the lack of insulin puts the patient at risk of intracellular glucose depletion and hence increases the risk for major metabolic decompensation.Conversely, adjustment of the dose of insulin requires more attention to avoid hypoglycemia. Both situations represent increased risks compared to managing DM1 alone and need a patient-centred approach, with close follow-up by a multidisciplinary team.

CONCLUSION

We present a novel case of DM1 in a patient with VLCADD. The case describes a general management approach and highlights the challenging aspects of managing a patient with two diseases with different potentially paradoxical life-threatening complications.

Epilepsy and inborn errors of metabolism in adults: The diagnostic odyssey of a young woman with medium-chain acyl-coenzyme A dehydrogenase deficiency

We describe a case of epileptic encephalopathy in a young woman with undiagnosed medium-chain acyl-coenzyme A dehydrogenase deficiency (MCADD), who presented with an early-onset focal motor status epilepticus (SE) then followed by permanent left hemiplegia and drug-resistant epilepsy with neurodevelopmental delay. Throughout her clinical history, recurrent episodes of lethargy, feeding difficulties, and clustering seizures occurred, progressing into a super refractory SE and death at the age of 25 years. Although epilepsy is not a distinctive feature of MCADD, we advise considering this metabolic disease as a possible etiology of epileptic encephalopathy and hemiconvulsion-hemiplegia-epilepsy syndrome of unknown origin, on the chance to provide a timely and targeted treatment preventing development delay and evolution to SE. Adult patients with epilepsy of unknown etiology not screened at birth for inborn errors of metabolism, such as MCADD, should be promptly investigated for these treatable conditions.

Acylcarnitines and Genetic Variation in Fat Oxidation Genes in HIV-infected, Antiretroviral-treated Children With and Without Myopathy

BACKGROUND

Mitochondrial toxicity resulting in myopathy and lactic acidosis has been described in antiretroviral (ARV)-exposed patients. We hypothesized that myopathy in HIV-infected, ARV-treated children would be associated with metabolic (acylcarnitines) and genetic (variants in metabolic genes) markers of dysfunctional fatty acid oxidation (FAO).

METHODS

Acylcarnitine profiles (ACP) were analyzed for 74 HIV-infected children on nucleoside reverse transcriptase inhibitor (NRTI)-containing ARV. Thirty-seven participants with ≥2 creatine kinase measurements >500 IU (n = 18) or evidence of echocardiographic cardiomyopathy (n = 19) were matched with 37 participants without myopathy. Single nucleotide polymorphisms (SNPs) in FAO genes were also evaluated.

RESULTS

Abnormal ACP was 73% (95% CI: 56%-86%) and 62% (95% CI: 45%-78%) in the myopathic and nonmyopathic groups, respectively. No significant association was found between myopathy and having an abnormal ACP (OR = 2.10, P = 0.22). In univariate analysis, a 1-year increase in NRTI use was associated with a 20% increase in odds of at least 1 ACP abnormality [OR (95% CI) = 1.20 (1.03-1.41); P = 0.02), and a 1-year increase in protease inhibitor use was associated with 28% increase in the odds of having at least 1 ACP abnormality [OR (95% CI) = 1.28 (1.07-1.52); P = 0.006). Three SNPs, all in the gene for the carnitine transporter ( SLC22A5 ), were associated with the cardiomyopathy phenotype.

CONCLUSION

FAO appears to be altered in HIV-infected children with and without myopathy, but abnormal FAO does not fully explain myopathy in ARV-exposed children. Further study of SLC22A5 variation in ARV-exposed people is warranted carnitine transporter dysfunction-related cardiomyopathy may be treatable.

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.

The frequencies of very long-chain acyl-CoA dehydrogenase deficiency genetic variants in Japan have changed since the implementation of expanded newborn screening

Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency has been a target of expanded newborn screening (ENBS) using tandem mass spectrometry in Japan. Since the implementation of ENBS, a number of novel ACADVL variants responsible for VLCAD deficiency have been identified. In this study, genotypic differences in Japanese patients with VLCAD deficiency were investigated before and after ENBS. The ACADVL variants in 61 subjects identified through ENBS (ENBS group) and in 40 patients who subsequently developed clinical symptoms without undergoing ENBS (pre-ENBS group) were compared. Subjects in the ENBS group underwent genetic testing and/or VLCAD enzyme activity measurements. Patients in the pre-ENBS group were stratified into three clinical phenotypes and underwent genetic testing. This study revealed that the variants p.K264E, p.K382Q and c.996dupT were found in both groups, but their frequencies were lower in the ENBS group (5.2%, 3.1% and 4.2%, respectively) than in the pre-ENBS group (16.5%, 12.7% and 10.1%, respectively). In addition, p.C607S, p.T409M, p.M478I, p.G289R, p.C237R, p.T260M, and p.R229* were exclusively identified in the ENBS group. Among these variants, p.C607S exhibited the highest frequency (18.8%). The patients who were heterozygous for p.C607S demonstrated 7-42% of control enzyme activity. p.C607S is suspected to be unique to Japanese individuals. According to a comparison of enzyme activity, patients with the p.C607S variant may exhibit higher enzyme activity than those with the p.A416T, p.A180T, p.R450H, and p.K264E variants, which are responsible for the myopathic form of the disease. The VLCAD deficiency genotypes have changed since the initiation of ENBS in Japan.

Characterization of exonic variants of uncertain significance in very long-chain acyl-CoA dehydrogenase identified through newborn screening

Very long-chain acyl-CoA dehydrogenase deficiency (VLCADD) is an autosomal recessive disease resulting from mutations in the ACADVL gene and is among the disorders tested for in newborn screening (NBS). Confirmatory sequencing following suspected VLCADD NBS results often identifies variants of uncertain significance (VUS) in the ACADVL gene, leading to uncertainty of diagnosis and providing effective treatment regimen. Currently, ACADVL has >300 VUSs in the ClinVar database that requiring characterization to determine potential pathogenicity. In this study, CRISPR/Cas9 genome editing was used to knock out ACADVL in HEK293T cells, and targeted deletion was confirmed by droplet digital polymerase chain reaction (PCR). No VLCAD protein was detected and an 84% decrease in enzyme activity using the electron transfer flavoprotein fluorescence reduction assay and C21-CoA as substrate was observed compared to control. Plasmids containing control or variant ACADVL coding sequence were transfected into the ACADVL null HEK293T. While transfection of control ACADVL restored VLCAD protein and enzyme activity, cells expressing the VLCAD Val283Ala mutant had 18% VLCAD enzyme activity and reduced protein compared to control. VLCAD Ile420Leu, Gly179Arg, and Gln406Pro produced protein comparable to control but 25%, 4%, and 5% VLCAD enzyme activity, respectively. Leu540Pro and Asp570_Ala572dup had reduced VLCAD protein and 10% and 3% VLCAD enzyme activity, respectively. VLCADD fibroblasts containing the same variations had decreased VLCAD protein and activity comparable to the transfection experiments. Generating ACADVL null HEK293T cell line allowed functional studies to determine pathogenicity of ACADVL exonic variants. This approach can be applied to multiple genes for other disorders identified through NBS.

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.

Sudden neonatal death in individuals with medium-chain acyl-coenzyme A dehydrogenase deficiency: limit of newborn screening

Medium-chain acyl-coenzyme A dehydrogenase (MCAD) deficiency is the most common disorder of mitochondrial β-oxidation of fatty acids resulting in hypoketotic hypoglycemia, hepatopathy, and often fatal outcome in undiagnosed children. Introduction of tandem mass spectrometry-based newborn screening programs in the late 1990s has significantly reduced morbidity and mortality in MCAD deficiency; however, neonatal death in individuals with early disease manifestation and severe hypoglycemia may still occur. We describe the fatal disease course in eight newborns with MCAD deficiency, aiming to raise awareness for early clinical symptoms and the life-saving treatment, and promote systematic post-mortem protocols for biochemical and genetic testing, necessary for correct diagnosis and counselling of the family if unexpected death occurred in the neonatal period.Conclusion: Early newborn screening and awareness for clinical symptoms is lifesaving in MCAD deficiency, which may present with fatal neonatal crisis. Systematic post-mortem diagnostic protocols are needed for sudden neonatal deaths.

Cardiologic evaluation of Turkish mitochondrial fatty acid oxidation disorders

BACKGROUND

Mitochondrial fatty acid oxidation disorders (FAODs) cause impairment in energy metabolism and can lead to a spectrum of cardiac pathologies including cardiomyopathy and arrhythmias. The frequency of underlying cardiac pathologies and the response to recommended treatment in FAODs was investigated.

METHODS

Sixty-eight children (35 males, 33 females) with the diagnosis of a FAOD were included in the study. Cardiac function was evaluated with 12-lead standard electrocardiography, echocardiography, and 24 h Holter monitoring.

RESULTS

Forty-five patients (66%) were diagnosed after disease symptoms developed and 23 patients (34%) were diagnosed in the pre-symptomatic period. Among symptomatic patients (n: 45), cardiovascular findings were detected in 18 (40%) patients, including cardiomyopathy in 14 (31.1%) and conduction abnormalities in 4 (8.8%) patients. Cardiac symptoms were more frequently detected in primary systemic carnitine deficiency (57.1%). Patients with multiple acyl-CoA dehydrogenase, long-chain 3-hydroxyacyl-CoA dehydrogenase, and mitochondrial trifunctional protein deficiencies also had an increased frequency of cardiac symptoms. Patients with medium-chain acyl-CoA dehydrogenase, very long-chain acyl-CoA dehydrogenase, and carnitine palmitoyltransferase I deficiencies had a lower prevalence of cardiac symptoms both during admission and during clinical follow up. Cardiomyopathy resolved completely in 8/14 (57%) patients and partially in 2/14 (14.3%) patients with treatment. Two patients with cardiomyopathy died in the newborn period; cardiomyopathy persisted in 1 (7.1%) patient with very long-chain acyl-CoA dehydrogenase deficiency.

CONCLUSION

Early diagnosis, treatment and follow up made a significant contribution to the improvement of cardiac symptoms of patients with FAODs.

Novel mutations associated with carnitine-acylcarnitine translocase and carnitine palmitoyl transferase 2 deficiencies in Malaysia

OBJECTIVE

Carnitine-acylcarnitine Translocase (CACT) deficiency (OMIM 212138) and carnitine palmitoyl transferase 2 (CPT2) deficiency (OMIM 60065050) are rare inherited disorders of mitochondrial long chain fatty acid oxidation. The aim of our study is to review the clinical, biochemical and molecular characteristics in children diagnosed with CACT and CPT2 deficiencies in Malaysia.

DESIGN AND METHODS

This is a retrospective study. We reviewed medical records of six patients diagnosed with CACT and CPT2 deficiencies. They were identified from a selective high-risk screening of 50,579 patients from January 2010 until Jun 2020.

RESULTS

All six patients had either elevation of the long chain acylcarnitines and/or an elevated (C16 + C18:1)/C2 acylcarnitine ratio. SLC25A20 gene sequencing of patient 1 and 6 showed a homozygous splice site mutation at c.199-10 T > G in intron 2. Two novel mutations at c.109C > T p. (Arg37*) in exon 2 and at c.706C > T p. (Arg236*) in exon 7 of SLC25A20 gene were found in patient 2. Patient 3 and 4 (siblings) exhibited a compound heterozygous mutation at c.638A > G p. (Asp213Gly) and novel mutation c.1073 T > G p. (Leu358Arg) in exon 4 of CPT2 gene. A significant combined prevalence at 0.01% of CACT and CPT2 deficiencies was found in the symptomatic Malaysian patients.

CONCLUSIONS

The use of the (C16 + C18:1)/C2 acylcarnitine ratio in dried blood spot in our experience improves the diagnostic specificity for CACT/CPT2 deficiencies over long chain acylcarnitine (C16 and C18:1) alone. DNA sequencing for both genes aids in confirming the diagnosis.

Altered mitochondrial metabolism in peripheral blood cells from patients with inborn errors of β-oxidation

Inborn errors of mitochondrial fatty acid oxidation (FAO), such as medium-chain acyl-CoA dehydrogenase deficiency (MCAD) and very long-chain acyl-CoA dehydrogenase deficiency (VLCAD) affects cellular function and whole-body metabolism. Carnitine uptake deficiency (CUD) disturbs the transportation of fatty acids into the mitochondria, but when treated is a mild disease without significant effects on FAO. For improved clinical care of VLCAD in particular, estimation of FAO severity could be important. We have investigated whether the oxygen consumption rate (OCR) of peripheral blood mononuclear cells (PBMCs) obtained from patients with MCAD, VLCAD, and CUD can be used to study cellular metabolism in patients with FAO defects and to determine the severity of FAO impairment. PBMCs were isolated from patients with VLCAD (n = 9), MCAD (n = 5-7), and CUD (n = 5). OCR was measured within 6-hours of venous puncture using the Seahorse XFe96. The PBMCs were exposed to glucose alone or with caprylic acid (C8:0) or palmitic acid (C16:0). OCR was significantly lower in cells from patients with β-oxidation deficiencies (MCAD and VLCAD) compared to CUD at basal conditions. When exposed to C16:0, OCR in VLCAD cells was unchanged, whereas OCR in MCAD cells increased but not to the levels observed in CUD. However, C8:0 did not increase OCR, as would be expected, in VLCAD cells. There was no clear relationship between clinical severity level and OCR. In patients with β-oxidation deficiencies, changes of mitochondrial respiration in PBMCs are detectable, which indicate that PBMCs have translational potential for studies of β-oxidation defects. However, further studies are warranted.

Exploring the contribution of mitochondrial dynamics to multiple acyl-CoA dehydrogenase deficiency-related phenotype

Mitochondrial fatty acid β-oxidation disorders (FAOD) are among the diseases detected by newborn screening in most developed countries. Alterations of mitochondrial functionality are characteristic of these metabolic disorders. However, many questions remain to be clarified, namely how the interplay between the signaling pathways harbored in mitochondria contributes to the disease-related phenotype. Herein, we overview the role of mitochondria on the regulation of cell homeostasis through the production of ROS, mitophagy, apoptosis, and mitochondrial biogenesis. Emphasis is given to the signaling pathways involving MnSOD, sirtuins and PGC-1α, which seem to contribute to FAOD phenotype, namely to multiple acyl-CoA dehydrogenase deficiency (MADD). The association between phenotype and genotype is not straightforward, suggesting that specific molecular mechanisms may contribute to MADD pathogenesis, making MADD an interesting model to better understand this interplay. However, more work needs to be done envisioning the development of novel therapeutic strategies.

Bezafibrate activation of PPAR drives disturbances in mitochondrial redox bioenergetics and decreases the viability of cells from patients with VLCAD deficiency

Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is the most common inborn long-chain fatty acid oxidation (FAO) disorder. VLCAD deficiency is characterized by distinct phenotypes. The severe phenotypes are potentially life-threatening and affect the heart or liver, with a comparatively milder phenotype characterized by myopathic symptoms. There is an unmet clinical need for effective treatment options for the myopathic phenotype. The molecular mechanisms driving the gradual decrease in mitochondrial function and associated alterations of muscle fibers are unclear. The peroxisome proliferator-activated receptor (PPAR) pan-agonist bezafibrate is a potent modulator of FAO and multiple other mitochondrial functions and has been proposed as a potential medication for myopathic cases of long-chain FAO disorders. In vitro experiments have demonstrated the ability of bezafibrate to increase VLCAD expression and activity. However, the outcome of small-scale clinical trials has been controversial. We found VLCAD deficient patient fibroblasts to have an increased oxidative stress burden and deranged mitochondrial bioenergetic capacity, compared to controls. Applying heat stress under fasting conditions to bezafibrate pretreated patient cells, caused a marked further increase of mitochondrial superoxide levels. Patient cells failed to maintain levels of the essential thiol peptide antioxidant glutathione and experienced a decrease in cellular viability. Our findings indicate that chronic PPAR activation is a plausible initiator of long-term pathogenesis in VLCAD deficiency. Our findings further implicate disruption of redox homeostasis as a key pathogenic mechanism in VLCAD deficiency and support the notion that a deranged thiol metabolism might be an important pathogenic factor in VLCAD deficiency.

Efficacy of bezafibrate for preventing myopathic attacks in patients with very long-chain acyl-CoA dehydrogenase deficiency

BACKGROUND

Very long-chain acyl-CoA dehydrogenase deficiency (VLCADD) is a mitochondrial fatty acid oxidation disorder that causes episodic attacks, such as general fatigue, hypotonia, myalgia, and rhabdomyolysis accompanied by lack of energy. As yet, there are no preventative drugs for these VLCADD-associated metabolic attacks.

PATIENTS AND METHODS

We conducted an open-label, non-randomized, multi-center study into the effects of bezafibrate on five patients with VLCADD. Bezafibrate was administered for 4 years, and we analyzed the number of myopathic attacks requiring hospitalization and treatment infusions.

RESULTS

The number of myopathic attacks requiring infusions of 24 h or longer significantly decreased during the study period. The patients' ability to conduct everyday activities was also improved by the treatment.

CONCLUSION

Our findings show the potential long-term efficacy of bezafibrate in preventing myopathic attacks for patients with VLCADD.

Enteral tube feeding in patients receiving dietary treatment for metabolic diseases: A retrospective analysis in a large French cohort

Context

A strictly controlled diet (often involving enteral tube feeding (ETF)) is part of the treatment of many inherited metabolic diseases (IMDs).

Objective

To describe the use of ETF in a large cohort of patients with IMDs.

Design

A retrospective analysis of ETF in patients with urea cycle disorders (UCDs), organic aciduria (OA), maple syrup disease (MSUD), glycogen storage diseases (GSDs) or fatty acid oxidation disorders (FAODs) diagnosed before the age of 12 months.

Setting

The reference center for IMDs at Necker Hospital (Paris, France).

Results

190 patients born between January 1991 and August 2017 were being treated for OA (n = 60), UCDs (n = 55), MSUD (n = 32), GSDs (n = 26) or FAODs (n = 17). Ninety-eight of these patients (52%) received ETF (OA subgroup: n = 40 (67%); UCDs: n = 12 (22%); MSUD: n = 9 (28%); GSDs: n = 23 (88%); FAODs: n = 14 (82%)). Indications for ETF were feeding difficulties in 64 (65%) patients, cessation of fasting in 39 (40%), and recurrent metabolic decompensation in 14 (14%). Complications of ETF were recorded in 48% of cases, more frequently with nasogastric tube (NGT) than with gastrostomy. Among patients in whom ETF was withdrawn, the mean duration of ETF was 5.9 (SD: 4.8) years (range: 0.6–19.8 years). The duration of ETF was found to vary from one disease subgroup to another (p = 0.051). While the longest median duration was found in the GSD subgroup (6.8 years), the shortest one was found in the UCD subgroup (0.9 years).

Conclusion

ETF is an integral part of the dietary management of IMDs. The long duration of ETF and the specific risks of NGT highlights the potential value of gastrostomy.

In this study at a French tertiary hospital, we documented the indications, modalities, duration and complications of enteral tube feeding in a cohort of patients with inherited metabolic diseases.

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.

Molecular and clinical characteristics of very-long-chain acyl-CoA dehydrogenase deficiency: A single-center experience in Saudi Arabia

Objectives:

To describe the clinical and molecular characteristics of patients with very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency.

Methods:

A retrospective observational cross-sectional analysis was conducted on all patients with VLCAD deficiency at (Genetic/Metabolic Section), Prince Sultan Military Medical City (PSMMC), Riyadh, Saudi Arabia from 2000 to 2019. Demographic, clinical, and laboratory data were abstracted from the electronic hospital records using a case report form.

Results:

A total of 14 children were analyzed. Six presented with hypoglycemia, 4 with cardiomyopathy, and 10 had rhabdomyolysis. Five patients had early onset severe phenotype, while 9 had mild form. The molecular study revealed homozygous mutations in ACADVL in all 14 patients. Three variants were not reported before. All patients were treated with medium-chain triglyceride and carnitine. Ten patients are alive and have normal development, while 4 died.

Conclusion:

Most of the patients in this cohort presented in the neonatal period either by newborn screening or clinically with hypoglycemia, cardiomyopathy, and rhabdomyolysis. The new molecular variants detected in this study broaden the genetic spectrum of VLCAD deficiency in Saudi Arabia.

Mitochondrial energetics is impaired in very long-chain acyl-CoA dehydrogenase deficiency and can be rescued by treatment with mitochondria-targeted electron scavengers

Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is the most common defect of mitochondrial long-chain fatty acid β-oxidation. Patients present with heterogeneous clinical phenotypes affecting heart, liver and skeletal muscle predominantly. The full pathophysiology of the disease is unclear and patient response to current therapeutic regimens is incomplete. To identify additional cellular alterations and explore more effective therapies, mitochondrial bioenergetics and redox homeostasis were assessed in VLCAD-deficient fibroblasts, and several protective compounds were evaluated. The results revealed cellular and tissue changes, including decreased respiratory chain (RC) function, increased reactive oxygen species (ROS) production and altered mitochondrial function and signaling pathways in a variety of VLCAD-deficient fibroblasts. The mitochondrially enriched electron and free radical scavengers JP4-039 and XJB-5-131 improved RC function and decreased ROS production significantly, suggesting that they are viable candidate compounds to further develop to treat VLCAD-deficient patients.

Proteomic and Molecular Assessment of the Common Saudi Variant in ACADVL Gene Through Mesenchymal Stem Cells

Very-long-chain acyl-coenzyme A dehydrogenase (VLCAD) is a coenzyme encoded by ACADVL that converts very-long-chain fatty acids into energy. This process is disrupted by c.65C > A; p.Ser22^∗ mutation. To clarify mechanisms by which this mutation leads to VLCAD deficiency, we evaluated differences in molecular and cellular functions between mesenchymal stem cells with normal and mutant VLCAD. Saudi Arabia have a high incidence of this form of mutation. Stem cells with mutant VLCAD were isolated from skin of two patients. Metabolic activity and proliferation were evaluated. The Same evaluation was repeated on normal stem cells introduced with same mutation by CRISPR. Mitochondrial depiction was done by electron microscope and proteomic analysis was done on patients' cells. Metabolic activity and proliferation were significantly lower in patients' cells. Introducing the same mutation into normal stem cells resulted in the same defects. We detected mitochondrial abnormalities by electron microscopy in addition to poor wound healing and migration processes in mutant cells. Furthermore, in a proteomic analysis, we identified several upregulated or downregulated proteins related to hypoglycemia, liver disorder, and cardiac and muscle involvement. We concluded experimental assays of mutant ACADVL (c.65C > A; p.Ser22^∗) contribute to severe neonatal disorders with hypoglycemia, liver disorder, and cardiac and muscle involvement.

The Current State of Newborn Screening in the United States

Newborn screening has evolved since its introduction in 1963. The disorders that are being screened for continue to evolve as new treatments and new technologies advance. In this review, the authors discuss the current state of newborn screening in the United States, including the disorders currently being screened for and how newborn screening is performed. They also discuss the special considerations and limitations of newborn screening in sick and premature infants and as well as some ethical issues related to newborn screening. Finally, new disorders being considered for testing and new technologies that may be used in the future of newborn screening are discussed.

Health services use among children diagnosed with medium-chain acyl-CoA dehydrogenase deficiency through newborn screening: a cohort study in Ontario, Canada

BACKGROUND

We describe early health services utilization for children diagnosed with medium-chain acyl-CoA dehydrogenase (MCAD) deficiency through newborn screening in Ontario, Canada, relative to a screen negative comparison cohort.

METHODS

Eligible children were identified via newborn screening between April 1, 2006 and March 31, 2010. Age-stratified rates of physician encounters, emergency department (ED) visits and inpatient hospitalizations to March 31, 2012 were compared using incidence rate ratios (IRR) and incidence rate differences (IRD). We used negative binomial regression to adjust IRRs for sex, gestational age, birth weight, socioeconomic status and rural/urban residence.

RESULTS

Throughout the first few years of life, children with MCAD deficiency (n = 40) experienced statistically significantly higher rates of physician encounters, ED visits, and hospital stays compared with the screen negative cohort. The highest rates of ED visits and hospitalizations in the MCAD deficiency cohort occurred from 6 months to 2 years of age (ED use: 2.1-2.5 visits per child per year; hospitalization: 0.5-0.6 visits per child per year), after which rates gradually declined.

CONCLUSIONS

This study confirms that young children with MCAD deficiency use health services more frequently than the general population throughout the first few years of life. Rates of service use in this population gradually diminish after 24 months of age.

Follow-up of fatty acid β-oxidation disorders in expanded newborn screening era

Fatty acid β-oxidation (FAO) disorders have a wide variety of symptoms, not usually evident between episodes of acute decompensations. Cardiac involvement is frequent, and severe ventricular arrhythmias are suspected of causing sudden death. Expanded newborn screening (ENS) for these disorders, hopefully, contribute to prevent potentially acute life-threatening events. In order to characterize acute decompensations observed in FAO-deficient cases identified by ENS, a retrospective analysis was performed, covering a period of 9 years. Demographic data, number/type of acute decompensations, treatment, and follow-up were considered. Eighty-three clinical charts, including 66 medium-chain acyl-CoA dehydrogenase deficiency (MCADD), 5 carnitine-uptake deficiency (CUD), 3 carnitine palmitoyltransferase I and II (CPT I/II) deficiency, 5 very long-chain acyl-CoA dehydrogenase deficiency (VLCADD), and 4 multiple acyl-CoA dehydrogenase deficiency (MADD) cases were reviewed. Nineteen patients had acute decompensations (1 CPT I, 1 CPT II, 3 MADD, 14 MCADD). Six patients developed symptoms previously to ENS diagnosis. Severe clinical manifestations included multiple organ failure, liver failure, heart failure, and sudden death. Long-chain FAO disorders had the highest number of decompensations per patient.Conclusion: Despite earlier diagnosis by ENS, sudden deaths were not avoided and acute decompensations with severe clinical manifestations still occur as well. What is Known: • Severe ventricular arrhythmias are suspected to cause unexpected death in FAO disorders. • Neonatal screening intends to reduce the incidence of severe metabolic crisis and death. What is New: • Acute severe decompensations occurred in FAO disorders diagnosed through neonatal screening. • Sudden deaths were not avoided by starting treatment precociously.

Fatty acid oxidation disorders

Fatty acid oxidation disorders (FAODs) are inborn errors of metabolism due to disruption of either mitochondrial β-oxidation or the fatty acid transport using the carnitine transport pathway. The presentation of a FAOD will depend upon the specific disorder, but common elements may be seen, and ultimately require a similar treatment. Initial presentations of the FAODs in the neonatal period with severe symptoms include cardiomyopathy, while during infancy and childhood liver dysfunction and hypoketotic hypoglycemia are common. Episodic rhabdomyolysis is frequently the initial presentation during or after adolescence; although, these symptoms may develop at any age for most of the FAODs The treatment of all FAOD's include avoidance of fasting, aggressive treatment during illness, and supplementation of carnitine, if necessary. The long-chain FAODs differ by requiring a fat-restricted diet and supplementation of medium chain triglyceride oil and often docosahexaenoic acid (DHA)-an essential fatty acid, crucial for brain, visual, and immune functions and prevention of fat soluble vitamin deficiencies. The FAOD are a group of autosomal recessive disorders associated with significant morbidity and mortality, but early diagnosis on newborn screening (NBS) and early initiation of treatment are improving outcomes. There is a need for clinical studies including randomized, controlled, therapeutic trials to continue to evaluate current understanding and to implement future therapies.

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.

Open-label clinical trial of bezafibrate treatment in patients with fatty acid oxidation disorders in Japan

Introduction

Fatty acid oxidation disorders (FAODs) are rare diseases caused by defects in mitochondrial fatty acid oxidation (FAO) enzymes. While the efficacy of bezafibrate, a peroxisome proliferator-activated receptor agonist, on the in vitro FAO capacity has been reported, the in vivo efficacy remains controversial. Therefore, we conducted a clinical trial of bezafibrate in Japanese patients with FAODs.

Materials and methods

This trial was an open-label, non-randomized, and multicenter study of bezafibrate treatment in 6 patients with very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency and 2 patients with carnitine palmitoyltransferase-II (CPT-2) deficiency (median age, 8.2 years; ranging from 5.8 to 26.4 years). Bezafibrate was administered for 6 months following a 6-month observation period. The primary endpoint was the frequency of myopathic attacks, and the secondary endpoints were serum acylcarnitines (ACs, C14:1 or C16 + C18:1), creatine kinase (CK) levels, degree of muscle pain (VAS; visual analog scale) during myopathic attacks, and quality of life (QOL; evaluated using validated questionnaires).

Results

The frequency of myopathic attacks after bezafibrate administration decreased in 3 patients, increased in 3, and did not change in 2. The CK, AC, and VAS values during attacks could be estimated in only three or four patients, but a half of the patients did not experience attacks before or after treatment. Changes in CK, AC, and VAS values varied across individuals. In contrast, three components of QOL, namely, physical functioning, role limitation due to physical problems (role physical), and social functioning, were significantly elevated. No adverse drug reactions were observed.

Conclusion

In this study, the frequency of myopathic attacks and CK, AC, and VAS values during the attacks could not be evaluated due to several limitations, such as a small trial population. Our findings indicate that bezafibrate improves the QOL of patients with FAODs, but its efficacy must be examined in future investigations.

Triheptanoin versus trioctanoin for long-chain fatty acid oxidation disorders: a double blinded, randomized controlled trial

BACKGROUND

Observational reports suggest that supplementation that increases citric acid cycle intermediates via anaplerosis may have therapeutic advantages over traditional medium-chain triglyceride (MCT) treatment of long-chain fatty acid oxidation disorders (LC-FAODs) but controlled trials have not been reported. The goal of our study was to compare the effects of triheptanoin (C7), an anaplerotic seven-carbon fatty acid triglyceride, to trioctanoin (C8), an eight-carbon fatty acid triglyceride, in patients with LC-FAODs.

METHODS

A double blinded, randomized controlled trial of 32 subjects with LC-FAODs (carnitine palmitoyltransferase-2, very long-chain acylCoA dehydrogenase, trifunctional protein or long-chain 3-hydroxy acylCoA dehydrogenase deficiencies) who were randomly assigned a diet containing 20% of their total daily energy from either C7 or C8 for 4 months was conducted. Primary outcomes included changes in total energy expenditure (TEE), cardiac function by echocardiogram, exercise tolerance, and phosphocreatine recovery following acute exercise. Secondary outcomes included body composition, blood biomarkers, and adverse events, including incidence of rhabdomyolysis.

RESULTS

Patients in the C7 group increased left ventricular (LV) ejection fraction by 7.4% (p = 0.046) while experiencing a 20% (p = 0.041) decrease in LV wall mass on their resting echocardiogram. They also required a lower heart rate for the same amount of work during a moderate-intensity exercise stress test when compared to patients taking C8. There was no difference in TEE, phosphocreatine recovery, body composition, incidence of rhabdomyolysis, or any secondary outcome measures between the groups.

CONCLUSIONS

C7 improved LV ejection fraction and reduced LV mass at rest, as well as lowering heart rate during exercise among patients with LC-FAODs.

CLINICAL TRIAL REGISTRATION

Clinicaltrials.gov NCT01379625.

Infant with hepatomegaly and hypoglycemia: A setting for fatty acid oxidation defects

Fatty acid oxidation defects (FAOD) are one of the commonest metabolic liver diseases (MLDs) that can have varied presentations in different age groups. An infant presented with short history of jaundice and irritability, examination showed soft hepatomegaly. Investigations revealed non-ketotic hypoglycemia suggesting FAOD which was later confirmed as carnitine uptake defect with gas chromatography and mass spectrometry and mutation analysis. Patient improved with acute management of metabolic crisis, carnitine supplementation and corn starch therapy with reversal of encephalopathy, reduction in hepatomegaly, maintenance of euglycemia and improvement in liver function tests and creatine phosphokinase on follow up. Non-ketotic hypoglycemia is a characteristic finding in FAODs. Early diagnosis and appropriate management can result in excellent outcomes in patients with FAODs.

Pharmacological inhibition of carnitine palmitoyltransferase 1 restores mitochondrial oxidative phosphorylation in human trifunctional protein deficient fibroblasts

BACKGROUND

Mitochondrial Trifunctional Protein deficiency (TFPD) is a severe genetic disease characterized by altered energy metabolism and accumulation of long-chain (LC) acylcarnitines in blood and tissues. This accumulation could impair the mitochondrial oxidative phosphorylation (OxPhos), contributing to the non-optimal outcome despite conventional diet therapy with medium-chain triglycerides (MCT).

METHOD

Acylcarnitine and OxPhos parameters were measured in TFPD-fibroblasts obtained from 8 children and cultured in medium mimicking fasting (LCFA) or conventional treatment (MCT), with or without Etomoxir (ETX) an inhibitor of carnitine palmitoyltransferase 1 (CPT1) activity, and were compared to results obtained with fibroblasts from 5 healthy-control children. The effects of various acylcarnitines were also tested on control fibroblasts.

RESULTS

In the LCFA-condition, TFPD-fibroblasts demonstrated a large accumulation of LC-acylcarnitines associated with decreased O₂-consumption (63±3% of control, P<0.001) and ATP production (67±5%, P<0.001) without modification of coupling efficiency. A dose-dependent decrease in O₂-consumption was reproduced in control fibroblasts by addition of increasing dose of LC-acylcarnitines, while it was almost preserved with MC-acylcarnitines. The MCT-condition reduced LC-acylcarnitine accumulation and partially improved O₂-consumption (80±3%, P<0.01) in TFPD-fibroblasts. The addition of ETX in both LCFA- and MCT-conditions normalized acylcarnitine profiles and restored O₂-consumption and ATP production at the same levels than control.

CONCLUSION

Accumulation of LC-acylcarnitines plays a major role in the pathophysiology of TFPD, reducing OxPhos capacities. These deleterious effects could be partially prevented by MCT-therapy and totally corrected by ETX. Inhibition of CPT1 may be view as a new therapeutic target for patients with a severe form of TFPD.

Neonatal Screening for Inherited Metabolic Diseases in 2016

The scope of newborn screening (NBS) programs is continuously expanding. NBS programs are secondary prevention interventions widely recognized internationally in the "field of Public Health." These interventions are aimed at early detection of asymptomatic children affected by certain diseases, with the objective to establish a definitive diagnosis and apply the proper treatment to prevent further complications and sequelae and ensure a better quality of life. The most significant event in the history of neonatal screening was the discovery of phenylketonuria in 1934. This disease has been the paradigm of inherited metabolic diseases. The next paradigm was the introduction of tandem mass spectrometry in the NBS programs that make possible the simultaneous measurement of several metabolites and consequently, the detection of several diseases in one blood spot and in an unique analysis. We aim to review the current situation of neonatal screening in 2016 worldwide and show scientific evidence of the benefits for some diseases. We will also discuss future challenges. It should be taken into account that any consideration to expand an NBS panel should involve a rigorous process of decision-making that balances benefits against the risks of harm.

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.

Significance of ACADM mutations identified through newborn screening of MCAD deficiency in Japan

BACKGROUND

Since the first case was detected in 2000, there has been a remarkable increase in Japanese patients diagnosed with medium-chain acyl-CoA dehydrogenase (MCAD) deficiency. Genetic analysis has revealed a spectrum of mutations that is quite different from those observed in Caucasian populations. In 2014, Japan initiated nationwide newborn screening (NBS) for MCAD using tandem mass spectrometry (MS/MS). It is an urgent issue to assess the risk of acute metabolic decompensation from the respective novel mutations found thus far.

METHODS

To evaluate the pathogenic effect of each mutation, we established a eukaryotic cell expression system and prepared 11 mutant proteins identified in five symptomatic patients and eight MS/MS-NBS-positive newborns, as well as two common Caucasian mutations, p.K329E (c.985G>A) and p.Y67H (c.157C>T) for comparison.

RESULTS

The expression of four mutant proteins (p.Q45R, p.P92L, p.P128X and p.Y397N) were severely impaired, whereas the others expressed normally, as did p.K329E and p.Y67H. Based on their dehydrogenase activities toward n-octanoyl-CoA, we determined three mutations (p.R53C, p.R281S and p.G362E) to be disease-causing, two mutations having (p.R17H and p.M274V) to be of marginal risk, and two mutations (p.K271E and p.I416T) as benign. Their allele-specific activities were as a whole in accordance with those estimated from the results of measurement in peripheral blood mononuclear cells.

CONCLUSION

As most of the mutations detected in the Japanese population are unique, prudent genetic and enzymatic analysis is essential to precisely evaluate the latent risk of clinical onset for screening-positive newborns.

Acylcarnitine Profiles in HIV-Exposed, Uninfected Neonates in the United States

We sought to determine the prevalence of abnormal acylcarnitine profiles (ACP) in HIV-exposed uninfected (HEU) newborns and to explore the association of abnormal ACP with clinical laboratory outcomes and antiretroviral drug exposures. Clinically, ACP are used to assess for fatty acid oxidation (FAO) dysfunction and normal FAO is necessary for optimal fetal/neonatal growth and development. We analyzed serum ACP in 522 HEU neonates enrolled in the Surveillance Monitoring for ART Toxicities (SMARTT) study of the Pediatric HIV/AIDS Cohort Study (PHACS) and evaluated the associations of abnormal ACP with in utero exposure to combination antiretroviral therapy (cART) in logistic regression models, adjusting for maternal demographic, disease, and behavioral characteristics. We evaluated the associations of abnormal ACP with laboratory parameters and measures of neurodevelopment and growth. Of 522 neonates, 89 (17%) had abnormal ACP. In adjusted analyses, in utero exposure to a protease inhibitor (PI) was associated with higher odds of having an abnormal ACP [adjusted odds ratio (aOR) = 2.35, 95% CI: 0.96, 5.76, p = 0.06] with marginal significance while exposure to a nonnucleoside reverse transcriptase inhibitor (NNRTI) was associated with lower odds (aOR = 0.23, 95% CI: 0.07, 0.80, p = 0.02). Mean ALT levels were slightly higher in those with abnormal ACP, but no differences in lactate, glucose, or CPK were observed. ACP status was not associated with neurodevelopment at 1 year or growth at 2 and 3 years of age. Abnormal ACP in HEU neonates are associated with exposure to PI-containing as opposed to NNRTI-containing antiretroviral (ARV) regimens but are not associated with serious postnatal clinical problems. Further studies are needed to determine the long-term health implications of abnormal acylcarnitine metabolism at birth in HEU children.

Recurrent ACADVL molecular findings in individuals with a positive newborn screen for very long chain acyl-coA dehydrogenase (VLCAD) deficiency in the United States

Very long chain acyl-coA dehydrogenase deficiency (VLCADD) is an autosomal recessive inborn error of fatty acid oxidation detected by newborn screening (NBS). Follow-up molecular analyses are often required to clarify VLCADD-suggestive NBS results, but to date the outcome of these studies are not well described for the general screen-positive population. In the following study, we report the molecular findings for 693 unrelated patients that sequentially received Sanger sequence analysis of ACADVL as a result of a positive NBS for VLCADD. Highlighting the variable molecular underpinnings of this disorder, we identified 94 different pathogenic ACADVL variants (40 novel), as well as 134 variants of unknown clinical significance (VUSs). Evidence for the pathogenicity of a subset of recurrent VUSs was provided using multiple in silico analyses. Surprisingly, the most frequent finding in our cohort was carrier status, 57% all individuals had a single pathogenic variant or VUS. This result was further supported by follow-up array and/or acylcarnitine analysis that failed to provide evidence of a second pathogenic allele. Notably, exon-targeted array analysis of 131 individuals screen positive for VLCADD failed to identify copy number changes in ACADVL thus suggesting this test has a low yield in the setting of NBS follow-up. While no genotype was common, the c.848T>C (p.V283A) pathogenic variant was clearly the most frequent; at least one copy was found in ~10% of all individuals with a positive NBS. Clinical and biochemical data for seven unrelated patients homozygous for the p.V283A allele suggests that it results in a mild phenotype that responds well to standard treatment, but hypoglycemia can occur. Collectively, our data illustrate the molecular heterogeneity of VLCADD and provide novel insight into the outcomes of NBS for this disorder.

The Newborn Screening Paradox: Sensitivity vs. Overdiagnosis in VLCAD Deficiency

OBJECTIVE

To improve the efficacy of newborn screening (NBS) for very long chain acyl-CoA dehydrogenase deficiency (VLCADD).

PATIENTS AND METHODS

Data on all dried blood spots collected by the Dutch NBS from October 2007 to 2010 (742.728) were included. Based solely on the C14:1 levels (cutoff ≥0.8 μmol/L), six newborns with VLCADD had been identified through NBS during this period. The ratio of C14:1 over C2 was calculated. DNA of all blood spots with a C14:1/C2 ratio of ≥0.020 was isolated and sequenced. Children homozygous or compound heterozygous for mutations in the ACADVL gene were traced back and invited for detailed clinical, biochemical, and genetic evaluation.

RESULTS

Retrospective analysis based on the C14:1/C2 ratio with a cutoff of ≥0.020 identified an additional five children with known ACADVL mutations and low enzymatic activity. All were still asymptomatic at the time of diagnosis (age 2-5 years). Increasing the cutoff to ≥0.023 resulted in a sensitivity of 93% and a positive predictive value of 37%. The sensitivity of the previously used screening approach (C14:1 ≥0.8) was 50%.

CONCLUSION

This study shows that the ratio C14:1/C2 is a more sensitive marker than C14:1 for identifying VLCADD patients in NBS. However, as these patients were all asymptomatic at the time of diagnosis, this suggests that a more sensitive screening approach may also identify individuals who may never develop clinical disease. Long-term follow-up studies are needed to establish the risk of these VLCADD-deficient individuals for developing clinical signs and symptoms.

The Frequencies of Different Inborn Errors of Metabolism in Adult Metabolic Centres: Report from the SSIEM Adult Metabolic Physicians Group

BACKGROUND

There are few centres which specialise in the care of adults with inborn errors of metabolism (IEM). To anticipate facilities and staffing needed at these centres, it is of interest to know the distribution of the different disorders.

METHODS

A survey was distributed through the list-serve of the SSIEM Adult Metabolic Physicians group asking clinicians for number of patients with confirmed diagnoses, types of diagnoses and age at diagnosis.

RESULTS

Twenty-four adult centres responded to our survey with information on 6,692 patients. Of those 6,692 patients, 510 were excluded for diagnoses not within the IEM spectrum (e.g. bone dysplasias, hemochromatosis) or for age less than 16 years, leaving 6,182 patients for final analysis. The most common diseases followed by the adult centres were phenylketonuria (20.6%), mitochondrial disorders (14%) and lysosomal storage disorders (Fabry disease (8.8%), Gaucher disease (4.2%)). Amongst the disorders that can present with acute metabolic decompensation, the urea cycle disorders, specifically ornithine transcarbamylase deficiency, were most common (2.2%), followed by glycogen storage disease type I (1.5%) and maple syrup urine disease (1.1%). Patients were frequently diagnosed as adults, particularly those with mitochondrial disease and lysosomal storage disorders.

CONCLUSIONS

A wide spectrum of IEM are followed at adult centres. Specific knowledge of these disorders is needed to provide optimal care including up-to-date knowledge of treatments and ability to manage acute decompensation.

Recurrent Ventricular Tachycardia in Medium-Chain Acyl-Coenzyme A Dehydrogenase Deficiency

We report a baby with medium-chain acyl-coenzyme A dehydrogenase (MCAD) deficiency who presented on day 2 with poor feeding and lethargy. She was floppy with hypoglycaemia (1.8 mmol/l) and hyperammonaemia (182 μmol/l). Despite correction of these and a continuous intravenous infusion of glucose at 4.5-6.2 mg/kg/min, she developed generalised tonic clonic seizures on day 3. She also suffered two episodes of pulseless ventricular tachycardia, from which she was resuscitated successfully. Unfortunately, she died on day 5, following a third episode of pulseless ventricular tachycardia. Arrhythmias are generally thought to be rarer in MCAD deficiency than in disorders of long-chain fatty acid oxidation. This is, however, the sixth report of ventricular tachyarrhythmias in MCAD deficiency. Five of these involved neonates and it may be that patients with MCAD deficiency are particularly prone to ventricular arrhythmias in the newborn period. Three of the patients (including ours) had normal blood glucose concentrations at the time of the arrhythmias and had been receiving intravenous glucose for many hours. These cases suggest that arrhythmias can be induced by medium-chain acylcarnitines or other metabolites accumulating in MCAD deficiency. Ventricular tachyarrhythmias can occur in MCAD deficiency, especially in neonates.