Four Years' Experience in the Diagnosis of Very Long-Chain Acyl-CoA Dehydrogenase Deficiency in Infants Detected in Three Spanish Newborn Screening Centers

Management and Outcomes of Very Long-Chain Acyl-CoA Dehydrogenase Deficiency (VLCAD Deficiency): A Retrospective Chart Review

Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is a rare genetic condition affecting the mitochondrial beta-oxidation of long-chain fatty acids. This study reports on the clinical outcomes of patients diagnosed by newborn screening with VLCAD deficiency comparing metabolic parameters, enzyme activities, molecular results, and clinical management. It is a single-center retrospective chart review of VLCAD deficiency patients who met the inclusion criteria between January 2002 and February 2020. The study included 12 patients, 7 of whom had an enzyme activity of more than 10%, and 5 patients had an enzyme activity of less than 10%. The Pearson correlation between enzyme activity and the C14:1 level at newborn screening showed a p-value of 0.0003, and the correlation between enzyme activity and the C14:1 level at diagnosis had a p-value of 0.0295. There was no clear correlation between the number of documented admissions and the enzyme activity level. Patients who had a high C14:1 value at diagnosis were started on a diet with a lower percentage of energy from long-chain triglycerides. The C14:1 result at diagnosis is the value that has been guiding our initial clinical management in asymptomatic diagnosed newborns. However, the newborn screening C14:1 value is the most sensitive predictor of low enzyme activity and may help guide dietary management.

Using the C14:1/Medium-Chain Acylcarnitine Ratio Instead of C14:1 to Reduce False-Positive Results for Very-Long-Chain Acyl-CoA Dehydrogenase Deficiency in Newborn Screening in Japan

Very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is a long-chain fatty acid oxidation disorder that manifests as either a severe phenotype associated with cardiomyopathy, a hypoglycemic phenotype, or a myopathic phenotype. As the hypoglycemic phenotype can cause sudden infant death, VLCAD deficiency is included in newborn screening (NBS) panels in many countries. The tetradecenoylcarnitine (C14:1) level in dried blood specimens is commonly used as a primary marker for VLCAD deficiency in NBS panels. Its ratio to acetylcarnitine (C2) and various other acylcarnitines is used as secondary markers. In Japan, tandem mass spectrometry-based NBS, initially launched as a pilot study in 1997, was introduced to the nationwide NBS program in 2013. In the present study, we evaluated levels of acylcarnitine with various chain lengths (C18 to C2), free carnitine, and their ratios in 175 infants who tested positive for VLCAD deficiency with C14:1 and C14:1/C2 ratios. Our analyses indicated that the ratios of C14:1 to medium-chain acylcarnitines (C10, C8, and C6) were the most effective markers in reducing false-positive rates. Their use with appropriate cutoffs is expected to improve NBS performance for VLCAD deficiency.

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.

Biochemical and molecular characteristics among infants with abnormal newborn screen for very-long-chain acyl-CoA dehydrogenase deficiency: A single center experience

Objective

To define the biochemical and molecular characteristics and diagnostic outcomes of a large US cohort of VLCAD deficiency positive cases as detected by newborn screening (NBS) with MS:MS. This relatively common disorder of fatty acid oxidation is screened for in every state in America and often results in extensive testing of multiple samples to arrive at a diagnostic conclusion.

Materials and methods

We compared NBS dried blood spot (DBS) acylcarnitine profile (ACP) C14, C14:1, C14:2, C14:1/C12:1 ratio and plasma C14, C14:1, C14:2, C14:1/C12:1, C14:1/C16 and C14:1/C2 ratios among true positive and false positive cases. Results of VLCAD enzyme analysis, molecular testing and fibroblast fatty acid oxidation probe assay were analyzed.

Results

The presence of compound heterozygous or homozygous pathogenic variants, along with elevations of C14, C14:1 and C14:1/C12:1 ratio, identified 19 VLCAD deficiency cases. All were asymptomatic at most recent follow-up visits. The C14:1/C12:1 ratio in NBS-DBS ACP and plasma acylcarnitine profiles at follow-up (follow-up plasma ACP), is the most useful marker to differentiate between true and false positive cases. Among all cases with molecular analysis data available, approximately 56.7% had a single pathogenic mutation. Lymphocyte enzyme analysis (n = 61) was uninformative in 23% of cases studied.

Conclusion

VLCAD deficiency NBS by MS:MS is highly effective at identifying asymptomatic affected infants. Our cohort showed that elevation of C14:1/C12:1, in both NBS DBS and plasma ACP, was informative in discriminating affected from unaffected individuals and contributes to improve the accuracy of confirmatory testing of infants with presumptive positive for VLCAD deficiency.

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.

Increased acylcarnitines in infant heart failure indicate fatty acid oxidation inhibition: towards therapeutic options?

AIMS

Heart failure in adults is characterized by reduction of long-chain fatty acid oxidation in favour of carbohydrate metabolism. This adaptive phenomenon becomes maladaptive because energy conversion decreases and lipid toxic derivatives known to impair cardiac function are accumulating. No data are available concerning metabolic modification in heart failure in children.

METHODS AND RESULTS

In order to evaluate the fatty acid oxidation in children suffering from heart failure, acylcarnitine profiles on dried blood spots were obtained from children under 16 years old with dilated cardiomyopathy and clinical heart failure (DCM-HF) and control children. Nine children were included in the DCM-HF group and eight in the control group. Acylcarnitine profiles revealed a significant 3.1-fold increase of total acylcarnitines (sum of C3 to C18 acylcarnitine species) in DCM-HF children compared with controls. This result persisted considering the sum of long-chain acylcarnitines (sum of C14 to C18 species), medium-chain acylcarnitines (sum of C8 to C12 species), and short-chain acylcarnitines (sum of C3 to C6 species), respectively, 2.0-, 2.6-, and 1.9-fold increase compared with the control group. A significant linear correlation was found between left ventricular dilatation or ejection fraction and acylcarnitines accumulation. Finally, acylcarnitine ratio C16OH/C16 and C18OH/C18 enhanced in the DCM-HF group, suggesting a diminution of the long-chain hydroxyl acyl-CoA dehydrogenase activity.

CONCLUSIONS

Our results suggest down-regulation of fatty acid oxidation in children with heart failure. Such lipidomic alteration could worsen heart function and may suggest considering a metabolic treatment of heart failure in children.

Severity estimation of very-long-chain acyl-CoA dehydrogenase deficiency via 13C-fatty acid loading test

BACKGROUND

The clinical severity of very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is difficult to predict using conventional diagnostic methods.

METHODS

Peripheral blood mononuclear cells obtained from 14 VLCAD deficiency patients and 23 healthy adults were loaded with carbon-13-universally labeled (U-¹³C-) fatty acids. Differences in acylcarnitine ratios between the patients and healthy groups and correlations between acylcarnitine ratios and a newly established clinical severity score (CSS) in the patient group were statistically examined.

RESULTS

There was a significant decrease in the ¹³C-C2/¹³C-C18 and ¹³C-C12/¹³C-C14 ratios in the U-¹³C-stearic acid loading test and in the ¹³C-C2/¹³C-C18:1 and ¹³C-C12:1/¹³C-C14:1 ratios in the U-¹³C-oleic acid loading test in the patient group. The values of each ratio were significantly correlated with the CSS, suggesting that they could predict disease severity. Additionally, patients with a higher ¹³C-C16/¹³C-C18 ratio than the ¹³C-C14/¹³C-C18 ratio in the U-¹³C-stearic acid loading test had a significantly higher CSS and were presumed to have more severe disease.

CONCLUSIONS

Our data indicated that this method could be used to predict the clinical severity of VLCAD deficiency, and identify patients at a risk of severe disease.

IMPACT

We established a novel method to predict the severity of VLCAD deficiency by performing a loading test with carbon-13-labeled fatty acids on peripheral blood mononuclear cells. The U-¹³C-oleic acid loading test was useful for comparing the patient group with the control group in terms of disease severity. The U-¹³C-stearic acid loading test was useful for identifying the more severely affected patients. These methods are relatively less invasive and enable rapid evaluation of the clinical severity.

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%.

Biochemical Markers for the Diagnosis of Mitochondrial Fatty Acid Oxidation Diseases

Mitochondrial fatty acid β-oxidation (FAO) contributes a large proportion to the body’s energy needs in fasting and in situations of metabolic stress. Most tissues use energy from fatty acids, particularly the heart, skeletal muscle and the liver. In the brain, ketone bodies formed from FAO in the liver are used as the main source of energy. The mitochondrial fatty acid oxidation disorders (FAODs), which include the carnitine system defects, constitute a group of diseases with several types and subtypes and with variable clinical spectrum and prognosis, from paucisymptomatic cases to more severe affectations, with a 5% rate of sudden death in childhood, and with fasting hypoketotic hypoglycemia frequently occurring. The implementation of newborn screening programs has resulted in new challenges in diagnosis, with the detection of new phenotypes as well as carriers and false positive cases. In this article, a review of the biochemical markers used for the diagnosis of FAODs is presented. The analysis of acylcarnitines by MS/MS contributes to improving the biochemical diagnosis, both in affected patients and in newborn screening, but acylglycines, organic acids, and other metabolites are also reported. Moreover, this review recommends caution, and outlines the differences in the interpretation of the biomarkers depending on age, clinical situation and types of samples or techniques.

A novel mutation in ACADVL causing very long-chain acyl-coenzyme-A dehydrogenase deficiency in a South Asian pediatric patient: a case report and review of the literature

BACKGROUND

Very long-chain acyl-coenzyme-A dehydrogenase deficiency is a rare, severe life-threatening metabolic disorder of mitochondrial fatty acid oxidation, caused by mutations in ACADVL gene. Here we present a genetically confirmed case of a South Asian baby girl with severe, early-onset form of very long-chain acyl-coenzyme-A dehydrogenase deficiency due to a novel mutation in ACADVL gene.

CASE PRESENTATION

Index case was the second baby girl of second-degree consanguineous South Asian parents. She had an uncomplicated antenatal period and was born by spontaneous vaginal delivery at term with a birth weight of 2910 g. She had been noted to have fair skin complexion, hypotonia, and 3 cm firm hepatomegaly. Since birth, the baby developed grunting, poor feeding, and recurrent episodes of symptomatic hypoglycemia and convulsions with multiple semiology. Her septic screening and urine ketone bodies were negative. The baby had high anion gap metabolic acidosis and elevated transaminases and serum creatine phosphokinase levels. Echocardiogram at 4 months revealed bilateral ventricular hypertrophy. Acylcarnitine profile revealed elevated concentrations of tetradecanoylcarnitine (C14), tetradecanoylcarnitine C14:1, and C14:1/C16. Unfortunately, the baby died due to intercurrent respiratory illness at 4 months of age. Sequence analysis of ACADVL gene in perimortem blood sample revealed homozygous frame shift novel variant NM_001270447.1, c.711_712del p.(Phe237Leufs*38), which confirmed the diagnosis of very long-chain acyl-coenzyme-A dehydrogenase deficiency.

CONCLUSIONS

This case demonstrates the importance of early diagnosis and management of very long-chain acyl-coenzyme-A dehydrogenase deficiency in improving the outcome of the patients. Implementation of newborn screening using tandem mass spectrometry in Sri Lanka will be beneficial to reduce the morbidity and mortality of treatable disorders of inborn errors.

Impact of newborn screening on the reported incidence and clinical outcomes associated with medium- and long-chain fatty acid oxidation disorders

Fatty acid oxidation disorders (FAODs) are potentially fatal inherited disorders for which management focuses on early disease detection and dietary intervention to reduce the impact of metabolic crises and associated spectrum of clinical symptoms. They can be divided functionally into long-chain (LC-FAODs) and medium-chain disorders (almost exclusively deficiency of medium-chain acyl-coenzyme A dehydrogenase). Newborn screening (NBS) allows prompt identification and management. FAOD detection rates have increased following the addition of FAODs to NBS programs in the United States and many developed countries. NBS-identified neonates with FAODs may remain asymptomatic with dietary management. Evidence from numerous studies suggests that NBS-identified patients have improved outcomes compared with clinically diagnosed patients, including reduced rates of symptomatic manifestations, neurodevelopmental impairment, and death. The limitations of NBS include the potential for false-negative and false-positive results, and the need for confirmatory testing. Although NBS alone does not predict the consequences of disease, outcomes, or management needs, subsequent genetic analyses may have predictive value. Genotyping can provide valuable information on the nature and frequency of pathogenic variants involved with FAODs and their association with specific phenotypes. Long-term follow-up to fully understand the clinical spectrum of NBS-identified patients and the effect of different management strategies is needed.

Performance of Expanded Newborn Screening in Norway Supported by Post-Analytical Bioinformatics Tools and Rapid Second-Tier DNA Analyses

In 2012, the Norwegian newborn screening program (NBS) was expanded (eNBS) from screening for two diseases to that for 23 diseases (20 inborn errors of metabolism, IEMs) and again in 2018, to include a total of 25 conditions (21 IEMs). Between 1 March 2012 and 29 February 2020, 461,369 newborns were screened for 20 IEMs in addition to phenylketonuria (PKU). Excluding PKU, there were 75 true-positive (TP) (1:6151) and 107 (1:4311) false-positive IEM cases. Twenty-one percent of the TP cases were symptomatic at the time of the NBS results, but in two-thirds, the screening result directed the exact diagnosis. Eighty-two percent of the TP cases had good health outcomes, evaluated in 2020. The yearly positive predictive value was increased from 26% to 54% by the use of the Region 4 Stork post-analytical interpretive tool (R4S)/Collaborative Laboratory Integrated Reports 2.0 (CLIR), second-tier biochemical testing and genetic confirmation using DNA extracted from the original dried blood spots. The incidence of IEMs increased by 46% after eNBS was introduced, predominantly due to the finding of attenuated phenotypes. The next step is defining which newborns would truly benefit from screening at the milder end of the disease spectrum. This will require coordinated international collaboration, including proper case definitions and outcome studies.

Harmonizing Newborn Screening Laboratory Proficiency Test Results Using the CDC NSQAP Reference Materials

Newborn screening (NBS) laboratories cannot accurately compare mass spectrometry-derived results and cutoff values due to differences in testing methodologies. The objective of this study was to assess harmonization of laboratory proficiency test (PT) results using quality control (QC) data. Newborn Screening Quality Assurance Program (NSQAP) QC and PT data reported from 302 laboratories in 2019 were used to compare results among laboratories. QC materials were provided as dried blood spot cards which included a base pool and the base pool enriched with specific concentrations of metabolites in a linear range. QC data reported by laboratories were regressed on QC data reported by the Centers for Disease Control and Prevention (CDC), and laboratory's regression parameters were used to harmonize their PT result. In general, harmonization tended to reduce overall variation in PT data across laboratories. The metabolites glutarylcarnitine (C5DC), tyrosine, and phenylalanine were displayed to highlight inter- and intra-method variability in NBS results. Several limitations were identified using retrospective data for harmonization, and future studies will address these limitations to further assess feasibility of using NSQAP QC data to harmonize PT data. Harmonizing NBS data using common QC materials appears promising to aid result comparison between laboratories.

False positive cases of elevated tetradecenoyl carnitine in newborn mass screening showed significant loss of body weight

Very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiency, a condition in which the body is unable to break down long-chain fatty acids properly, is the most common fatty acid oxidation disorder in Japan. Tandem mass spectrometry has been used in newborn screening (NBS), allowing the detection of patients with VLCAD deficiency even before symptoms manifest. However, tandem mass spectrometry has a high false positive rate. We investigated the clinical characteristics of patients with false positive results for tetradecenoyl acylcarnitine (C14:1). This case-control study used data collected between the 1st of January 2014 and the 31st of March 2019. The case group was defined as patients having levels of both C14:1 and C14:1/C2 ratio higher than cut-off levels in the first newborn mass screening, who were eventually diagnosed as false positives by attending doctors at Kobe University Hospital, Palmore Hospital, or Kakogawa Central City Hospital in Japan. The control group comprised 100 patients randomly selected from the three facilities. The false positive group included 17 cases, and the control group contained 300 patients. The demographics of each group did not show any significant differences in sex, body weight at birth, Cesarean section rate, complete breastfeeding rate, or the number of feedings per day. However, the change in body weight at the sampling day of NBS in the false positive and control groups was -10.2%, and - 4.6%, respectively, showing a statistically significant difference (p < 0.01). In addition, body weight gain at the one-month medical checkup was 38.9 g/day in the false positive group and 44.1 g/day in the control group (p < 0.05). An elevation of C14:1 carnitine has been reported in situations involving the catalysis of fatty acid. Therefore, patients with severe body weight loss might be associated with poor sucking or poor milk supply, which might cause a false positive elevation of C14:1 and C14:1/C2. In suspected VLCAD deficiency, attending doctors should pay attention to body weight changes recorded during newborn mass screening.

A Family With a Complex Phenotype Caused by Two Different Rare Metabolic Disorders: GLUT1 and Very-Long-Chain Fatty Acid Dehydrogenase (VLCAD) Deficiencies

GLUT1 Deficiency Syndrome (GLUT1-DS) is a rare and potentially treatable neurometabolic condition, caused by a reduced glucose transport into the brain and clinically characterized by an epileptic encephalopathy with movement disorders. A wide inter-intrafamilial phenotypic variability has been reported. Very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is an inherited metabolic disorder of mitochondrial long-chain fatty acid oxidation (FAO) with also a variable age of onset and clinical presentation including cardiomyopathy, hypoketotic hypoglycemia, and liver disease. Sometimes, VLCAD manifests later with a prevalent muscle involvement characterized by exercise intolerance and recurrent rhabdomyolysis. We report a 40-year-old man with mild mental retardation and sporadic choreo-athetoid movements, who complained of recurrent episodes of rhabdomyolysis triggered by exercise or fasting since his twenties. His 15-year-old son had a psychomotor developmental delay with episodes of drowsiness mainly at fasting and exercise-induced choreo-athetoid movements but no history of pigmenturia. Clinical and laboratory findings in the son suggested a diagnosis of GLUT1-DS confirmed by SCL2A1 genetic analysis that revealed a heterozygous mutation c.997C>T (p.R333W) that was also found in the proband. However, the presence in the latter of recurrent exercise-induced rhabdomyolysis, never reported in GLUT1-DS, implied a second metabolic disorder. Increased plasma C14:1-carnitine levels and the identification of two known heterozygous mutations c. 553G>A (p.G185S) and c.1153C>T (p.R385W) in ACADVL confirmed the additional diagnosis of VLCAD deficiency in the proband. Nowadays, there is an increasing evidence of "double trouble" cases of genetic origin. Consequently, when atypical features accompany a known phenotype, associated comorbidities should be considered.

High resolution mass spectrometry newborn screening applications for quantitative analysis of amino acids and acylcarnitines from dried blood spots

Amino acid and acylcarnitine first-tier newborn screening typically employs derivatized or non-derivatized sample preparation methods followed by FIA coupled to triple quadrupole (TQ) MS/MS. The low resolving power of TQ instruments results in difficulties distinguishing nominal isobaric metabolites, especially those with identical quantifying product ions such as malonylcarnitine (C3DC) and 4-hydroxybutylcarnitine (C4OH). Twenty-eight amino acids and acylcarnitines extracted from dried blood spots (DBS) were analyzed by direct injection (DI)-HRMS on a Q-Exactive Plus across available mass resolving powers in SIM, in PRM at 17,000 full width at half maximum (FWHM), and a developed SIM/PRM hybrid MS method. Most notably, quantitation of C3DC and C4OH was successful by HRMS in non-derivatized samples, thus, potentially eliminating sample derivatization requirements. Quantitation differed between SIM and PRM acquired data for several metabolites, and it was determined these quantitative differences were due to collision energy differences or kinetic isotope effects between the unlabeled metabolites and the corresponding labeled isotopologue internal standards. Overall quantitative data acquired by HRMS were similar to data acquired on TQ MS/MS platform. A proof-of-concept hybrid DI-HRMS and SIM/PRM/FullScan method was developed demonstrating the ability to hybridize targeted newborn screening with metabolomic screening.

Serum C14:1/C12:1 ratio is a useful marker for differentiating affected patients with very long-chain acyl-CoA dehydrogenase deficiency from heterozygous carriers

Introduction

Various markers, such as C14:1 and the C14:1/C2 ratio, are used as diagnostic markers of very long-chain acyl-CoA dehydrogenase deficiency (VLCADD). However, the levels of these markers in patients with VLCADD overlap with those in heterozygous carriers and even healthy subjects.

Materials and methods

In twenty-three affected patients and 15 heterozygous carriers with VLCADD, the accuracies of C14:1, C14:1/C12:1, C14:1/C2, and C14:1/C16 in dried blood spots (DBS) and serum were statistically estimated.

Results

Among the serum markers, the sensitivity, specificity, positive predictive value, negative predictive value, false-positive rate, false-negative rate, and validity of C14:1/C12:1 were superior to those of C14:1, C14:1/C2, and C14:1/C16, but C14:1/C2 demonstrated a statistical advantage compared with only C14:1 and C14:1/C16. Elevation in serum C14:1/C12:1 was observed in only one heterozygous carrier, whereas almost half of the carriers displayed false positive results for the other markers. Among the DBS markers, although the accuracy of C14:1/C2 was ostensibly the best, no statistical significance was observed.

Discussion

Serum C14:1/C12:1 might be useful for differentiating patients with VLCADD from heterozygous carriers. Although serum C14:1/C2 was significantly useful for the detection of VLCADD, this marker could not distinguish the affected patients from carriers. C14:1/C12:1 might be optimal compared with the other markers.

Combined HIIT and Resistance Training in Very Long-Chain Acyl-CoA Dehydrogenase Deficiency: A Case Report

Very long-chain acyl-CoA dehydrogenase deficiency (VLCADD) is a rare disorder of mitochondrial fatty acid β-oxidation characterized by a spectrum of clinical manifestations. Patients with the adult-onset form can present with muscle pain, rhabdomyolysis and myoglobinuria after physiological stress, such as fasting and exercise. We report on a 23-year-old female patient with a history of recurrent rhabdomyolysis. The patient completed a 6-month supervised combined (high-intensity interval training [HIIT] + resistance training) program, with the addition of a medium chain triglyceride + carbohydrate supplement provided 60 min before each session. The HIIT consisted of 6 sets of 70–80 s performed at maximum intensity with a minimum cadence of 100 rpm. Resistance training consisted of a circuit of basic exercises with dumbbells and elastic bands, with sets of 4–7 repetitions. The patient was evaluated at months 0, 3 and 6 using an incremental discontinuous step protocol, with steps of 1 min of exercise/1 min of passive recovery, at a high pedal cadence. The test started at 10 W, with a load increase of 10 W/step. Blood creatine kinase (CK) concentration was measured before each evaluation. There was a training-induced increment of 90.2% in peak oxygen uptake (VO_2peak), 71.4% in peak power output and 24.7% in peak heart rate. The patient reported no muscle pain, contractures, rhabdomyolysis (basal CK concentration was always <200 U/L) or hospital admissions during the training period. After completion of 6-month program, the patient remained active, doing similar but non-supervised training for 1.5 years (to date). During this period, the patient has not reported myalgias, contractures, rhabdomyolysis or hospital admissions. Our preliminary data suggest that it is possible to carry out a combined (HIIT + strength) training program in patients with VLCADD, safely (without muscle contractures or rhabdomyolysis) and obtaining high values of VO_2peak and cycling power output.

Value of genetic analysis for confirming inborn errors of metabolism detected through the Spanish neonatal screening program

The present work describes the value of genetic analysis as a confirmatory measure following the detection of suspected inborn errors of metabolism in the Spanish newborn mass spectrometry screening program. One hundred and forty-one consecutive DNA samples were analyzed by next-generation sequencing using a customized exome sequencing panel. When required, the Illumina extended clinical exome panel was used, as was Sanger sequencing or transcriptional profiling. Biochemical tests were used to confirm the results of the genetic analysis. Using the customized panel, the metabolic disease suspected in 83 newborns (59%) was confirmed. In three further cases, two monoallelic variants were detected for two genes involved in the same biochemical pathway. In the remainder, either a single variant or no variant was identified. Given the persistent absence of biochemical alterations, carrier status was assigned in 39 cases. False positives were recorded for 11. In five cases in which the biochemical pattern was persistently altered, further genetic analysis allowed the detection of two variants affecting the function of BCAT2, ACSF3, and DNAJC12, as well as a second, deep intronic variant in ETFDH or PTS. The present results suggest that genetic analysis using extended next-generation sequencing panels can be used as a confirmatory test for suspected inborn errors of metabolism detected in newborn screening programs. Biochemical tests can be very helpful when a diagnosis is unclear. In summary, simultaneous genomic and metabolomic analyses can increase the number of inborn errors of metabolism that can be confirmed following suggestive newborn screening results.

Lipid Myopathies

Disorders of lipid metabolism affect several tissues, including skeletal and cardiac muscle tissues. Lipid myopathies (LM) are rare multi-systemic diseases, which most often are due to genetic defects. Clinically, LM can have acute or chronic clinical presentation. Disease onset can occur in all ages, from early stages of life to late-adult onset, showing with a wide spectrum of clinical symptoms. Muscular involvement can be fluctuant or stable and can manifest as fatigue, exercise intolerance and muscular weakness. Muscular atrophy is rarely present. Acute muscular exacerbations, resulting in rhabdomyolysis crisis are triggered by several factors. Several classifications of lipid myopathies have been proposed, based on clinical involvement, biochemical defect or histopathological findings. Herein, we propose a full revision of all the main clinical entities of lipid metabolism disorders with a muscle involvement, also including some those disorders of fatty acid oxidation (FAO) with muscular symptoms not included among previous lipid myopathies classifications.

Management and diagnosis of mitochondrial fatty acid oxidation disorders: focus on very-long-chain acyl-CoA dehydrogenase deficiency

Mitochondrial fatty acid oxidation disorders (FAODs) are caused by defects in β-oxidation enzymes, including very long-chain acyl-CoA dehydrogenase (VLCAD), trifunctional protein (TFP), carnitine palmitoyltransferase-2 (CPT2), carnitine-acylcarnitine translocase (CACT) and others. During prolonged fasting, infection, or exercise, patients with FAODs present with hypoglycemia, rhabdomyolysis, cardiomyopathy, liver dysfunction, and occasionally sudden death. This article describes the diagnosis, newborn screening, and treatment of long-chain FAODs with a focus on VLCAD deficiency. VLCAD deficiency is generally classified into three phenotypes based on onset time, but the classification should be comprehensively determined based on genotype, residual enzyme activity, and clinical course, due to a lack of apparent genotype-phenotype correlation. With the expansion of newborn screening for FAODs, several issues have arisen, such as missed detection, overdiagnosis (including detection of benign/asymptomatic type), and poor prognosis of the neonatal-onset form. Meanwhile, dietary management and restriction of exercise have been unnecessary for patients with the benign/asymptomatic type of VLCAD deficiency with a high fatty acid oxidation flux score. Although L-carnitine therapy for VLCAD/TFP deficiency has been controversial, supplementation with L-carnitine may be accepted for CPT2/CACT and multiple acyl-CoA dehydrogenase deficiencies. Recently, a double-blind, randomized controlled trial of triheptanoin (seven-carbon fatty acid triglyceride) versus trioctanoin (regular medium-chain triglyceride) was conducted and demonstrated improvement of cardiac functions on triheptanoin. Additionally, although the clinical efficacy of bezafibrate remains controversial, a recent open-label clinical trial showed efficacy of this drug in improving quality of life. These drugs may be promising for the treatment of FAODs, though further studies are required.

The diagnostic challenge in very-long chain acyl-CoA dehydrogenase deficiency (VLCADD)

Very long-chain acyl-CoA dehydrogenase deficiency (VLCADD) is the most common defect of mitochondrial β-oxidation of long-chain fatty acids. However, the unambiguous diagnosis of true VLCADD patients may be challenging, and a high rate of false positive individuals identified by newborn screening undergo confirmation diagnostics. In this study, we show the outcome of enzyme testing in lymphocytes as a confirmatory tool in newborns identified by screening, and the correlation with molecular sequencing of the ACADVL gene. From April 2013 to March 2017, in 403 individuals with characteristic acylcarnitine profiles indicative of VLCADD, palmitoyl-CoA oxidation was measured followed by molecular genetic analysis in most of the patients with residual activity (RA) <50%. In almost 50% of the samples (209/403) the RA was >50%, one-third of the individuals (125/403) displayed a RA of 30-50% and 69/403 individuals showed a residual activity of 0-30%. Sequencing of the ACADVL gene revealed that all individuals with activities below 24% were true VLCADD patients, individuals with residual activities between 24 and 27% carried either one or two mutations. Twenty new mutations could be identified and functionally classified based on their effect on enzyme function. Finally, we observed an up-regulation of MCAD-activity in many patients. However, this did not correlate with the degree of VLCAD RA. Although the likely clinical phenotype cannot be fully foreseen by genetic and functional tests as it depends on many factors, our data demonstrate the strength of this functional enzyme test in lymphocytes as a quick and reliable method for confirmation diagnostics of VLCADD.