Outcomes and genotype-phenotype correlations in 52 individuals with VLCAD deficiency diagnosed by NBS and enrolled in the IBEM-IS database

Diagnostic challenges and outcome of fatty acid oxidation defects in a tertiary care center in Lebanon

BACKGROUND

Fatty acid oxidation defects are rare autosomal recessive disorders with variable clinical manifestations and outcome. Early detection by systematic neonatal screening may improve their prognosis. Long-term outcome studies of these disorders in the Middle East and North Africa region are limited. The purpose of this study is to report the diagnostic challenges and outcome of fatty acid oxidation defects in a major tertiary care center in Lebanon, a resource-constrained country in the Middle East.

METHODS

A retrospective review of charts of all fatty acid oxidation defects sequential patients diagnosed and followed at our center was conducted. Collected data included: parental consanguinity, age at diagnosis, clinical presentation, biochemical profile, confirmatory diagnosis, treatment and outcome. A genotype-phenotype correlation was also performed, when available.

RESULTS

Seven types of fatty acid oxidation defects were identified in a total of 34 patients from 21 families. Most families (79%) were consanguineous (first-degree cousins). The majority were diagnosed when clinically symptomatic (78%), at various ages between 10 days and 19 years (average: 2 years). Follow-up duration spanned between 2 months and 15 years (average: 5 years). The remainder of the patients were detected while still asymptomatic by systematic neonatal screening (9%) or due to positive family history (9%). The most common defect was carnitine transporter deficiency (50%) with an exclusive cardiac presentation related to a founder variant c.981C > T, (p.Arg254*) in the SLC22A5 gene. Medium chain acyl-CoA dehydrogenase deficiency was found in 13% only, which could be explained by the absence of systematic neonatal screening. Rare gene variants were detected in very long chain and multiple acyl-CoA dehydrogenase deficiency. The worse prognosis was observed in very long chain acyl-CoA dehydrogenase deficiency. The overall survival at last follow-up reached 75% with a complete reversal of symptoms with treatment in most patients (63%), despite their late diagnosis.

CONCLUSIONS

Our experience highlights the diagnostic challenges and outcome of fatty acid oxidation defects in a resource-constrained country with high consanguinity rates. Physicians' awareness and systematic neonatal screening are key for diagnosis. Larger genotype-phenotype studies are still needed to understand the natural history of these rare diseases and possibly improve their outcome.

Four novel variants identified in the ACADVL gene causing very-long-chain acyl-coenzyme A dehydrogenase deficiency in four unrelated Chinese families

Background: The biochemical and genetic characteristics of four very-long-chain acyl-coenzyme A dehydrogenase deficiency (VLCADD) patients, clarifying their pathogenic genetic factors and evaluating the application value of genetic diagnosis in the early diagnosis of VLCADD, are reported and discussed in this article. Methods: Patients underwent blood tandem mass spectrometry (MS/MS), urine gas chromatography (GC/MS), and high-throughput sequencing technology. New variants were analyzed for pathogenicity using bioinformatics software. Swiss-PdbViewer software was used to predict the effect of variants on the structure of the very-long-chain acyl-CoA dehydrogenase (VLCAD) protein. Result: A total of four VLCADD patients were diagnosed. They revealed elevated levels of C14, C14:1, C14:2, C14:1/C2, C14:1/C10, and C14:1/C12:1. Two patients were early-onset neonatal cases and died during infancy and the neonatal period, respectively. Seven kinds of variants were detected, including four novel variants. Bioinformatics software revealed that the variants were harmful, and the Swiss-PdbViewer results suggest that variation affects protein conformation. Conclusion: This study identified four novel ACADVL gene variants. These findings contribute to the understanding of the genetic basis and pathogenesis of VLCADD. Meanwhile, the study enriches the genetic mutation spectrum and the correlation between genotypes and phenotypes of VLCADD, indicating that genetic diagnosis plays an essential role in the early diagnosis and treatment of VLCADD.

206,977 newborn screening results reveal the ethnic differences in the spectrum of inborn errors of metabolism in Huaihua, China

Background

Inborn errors of metabolism (IEMs) are rare diseases caused by inherited defects in various biochemical pathways that strongly correlate with early neonatal mortality and stunting. Currently, no studies have reported on the incidence of IEMs of multi-ethnic groups in Huaihua, China.

Methods

A total of 206,977 neonates with self-reported ethnicity who underwent IEM screening at Huaihua from 2015 to 2021 were selected for observation. Among them, 69 suspected IEM-positive neonates were referred for urine gas chromatography-mass spectrometry analysis, biochemical detection, next-generation sequencing, and Sanger sequencing.

Results

Sixty-nine newborns were diagnosed with IEMs, with an overall incidence of 1:3,000. The two most common disorders were 2-methylbutyryl glycinuria (1:7,137) and phenylalanine hydroxylase deficiency (1:22,997). Moreover, the incidence of IEMs in the minority ethnic group (Miao, Dong, Tujia and Yao) (1:1,852) was markedly higher than in the Han ethnic group (1:4,741). Some ethnic features variants were identified; NM_001609.4:c.1165A>G in the ACADSB gene for Miao and Dong ethnic groups, NM_014251.2:c.852_855del in the SLC25A13 gene for Miao ethnic groups.

Conclusion

This study revealed the IEM incidence within the minority ethnic groups is markedly higher than among the Han nationality and the gene variant spectrum is dramatically different in Huaihua, China. Hence, It serves as a theoretical reference for the screening and diagnosing of neonatal IEMs of multi-ethnic groups in the Huaihua area, and across China.

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.

[Disease spectrum and pathogenic genes of inherited metabolic disorder in Gansu Province of China]

OBJECTIVES

To investigate the disease spectrum and pathogenic genes of inherited metabolic disorder (IMD) among neonates in Gansu Province of China.

METHODS

A retrospective analysis was conducted on the tandem mass spectrometry data of 286 682 neonates who received IMD screening in Gansu Provincial Maternal and Child Health Hospital from January 2018 to December 2021. A genetic analysis was conducted on the neonates with positive results in tandem mass spectrometry during primary screening and reexamination.

RESULTS

A total of 23 types of IMD caused by 28 pathogenic genes were found in the 286 682 neonates, and the overall prevalence rate of IMD was 0.63 (1/1 593), among which phenylketonuria showed the highest prevalence rate of 0.32 (1/3 083), followed by methylmalonic acidemia (0.11, 1/8 959) and tetrahydrobiopterin deficiency (0.06, 1/15 927). In this study, 166 variants were identified in the 28 pathogenic genes, with 13 novel variants found in 9 genes. According to American College of Medical Genetics and Genomics guidelines, 5 novel variants were classified as pathogenic variants, 7 were classified as likely pathogenic variants, and 1 was classified as the variant of uncertain significance.

CONCLUSIONS

This study enriches the database of pathogenic gene variants for IMD and provides basic data for establishing an accurate screening and diagnosis system for IMD in this region.

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.

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.

Postmortem diagnosis of very long chain acyl-CoA dehydrogenase (VLCAD) deficiency in a neonate with sudden cardiac death

Very long chain acyl-CoA dehydrogenase (VLCAD) deficiency is an autosomal recessive long chain fatty acid β-oxidation disorder with a variable clinical spectrum, ranging from an acute neonatal presentation with cardiac and hepatic failure to childhood or adult onset of symptoms with hepatomegaly or rhabdomyolysis provoked by illness or exertion. Neonatal cardiac arrest or sudden unexpected death can be the presenting phenotype in some patients, emphasizing the importance of early clinical suspicion and intervention. We report a patient who had a cardiac arrest and died at one day of age. Following her death, the newborn screen reported biochemical evidence of VLCAD deficiency, which was confirmed with pathologic findings at autopsy and by molecular genetic testing.

A Distinctive Metabolomics Profile and Potential Biomarkers for Very Long Acylcarnitine Dehydrogenase Deficiency (VLCADD) Diagnosis in Newborns

Very long-chain acylcarnitine dehydrogenase deficiency (VLCADD) is a rare inherited metabolic disorder associated with fatty acid β-oxidation and characterized by genetic mutations in the ACADVL gene and accumulations of acylcarnitines. VLCADD, developed in neonates or later adults, can be diagnosed using newborn bloodspot screening (NBS) or genetic sequencing. These techniques have limitations, such as a high false discovery rate and variants of uncertain significance (VUS). As a result, an extra diagnostic tool is needed to deliver improved performance and health outcomes. As VLCADD is linked with metabolic disturbance, we postulated that newborn patients with VLCADD could display a distinct metabolomics pattern compared to healthy newborns and other disorders. Herein, we applied an untargeted metabolomics approach using liquid chromatography-high resolution mass spectrometry (LC-HRMS) to measure the global metabolites in dried blood spot (DBS) cards collected from VLCADD newborns (n = 15) and healthy controls (n = 15). Two hundred and six significantly dysregulated endogenous metabolites were identified in VLCADD, in contrast to healthy newborns. Fifty-eight and one hundred and eight up- and down-regulated endogenous metabolites were involved in several pathways such as tryptophan biosynthesis, aminoacyl-tRNA biosynthesis, amino sugar and nucleotide sugar metabolism, pyrimidine metabolism and pantothenate, and CoA biosynthesis. Furthermore, biomarker analyses identified 3,4-Dihydroxytetradecanoylcarnitine (AUC = 1), PIP (20:1)/PGF1alpha) (AUC = 0.982), and PIP2 (16:0/22:3) (AUC = 0.978) as potential metabolic biomarkers for VLCADD diagnosis. Our findings showed that compared to healthy newborns, VLCAADD newborns exhibit a distinctive metabolic profile, and identified potential biomarkers that can be used for early diagnosis, which improves the identification of the affected patients earlier. This allows for the timely administration of proper treatments, leading to improved health. However, further studies with large independent cohorts of VLCADD patients with different ages and phenotypes need to be studied to validate our potential diagnostic biomarkers and their specificity and accuracy during early life.

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.

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

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

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%.

Screening for newborn fatty acid oxidation disorders in Chongqing and the follow-up of confirmed children

OBJECTIVE

To investigate the incidence, clinical characteristics, gene mutations and prognosis of fatty acid oxidation disorders (FAOD) in newborns in Chongqing.

METHODS

Blood samples were collected from 35 374 newborns for screening of FAOD in the Neonatal Screening Center of Women and Children's Hospital of Chongqing Medical University from July 2020 to February 2022. The acylcarnitine spectrum was detected by tandem mass spectrometry, the positive children in primary screening were recalled within 2 weeks, and the diagnosis of FAOD was confirmed by urine organic acid measurement, blood biochemistry testing and genetic analysis. The confirmed children were given early intervention, treatment and followed-up.

RESULTS

Among 35 374 newborns, there were 267 positive children in primary screening, with a positive rate of 0.75%. Five children with FAOD were diagnosed by gene detection, with an incidence rate of 1/7075. Among them, there were 3 cases of primary carnitine deficiency (PCD, 1/11 791), 1 case of short-chain acyl-CoA dehydrogenase deficiency (SCADD, 1/35 374) and 1 case of very long-chain acyl-CoA dehydrogenase deficiency (VLCADD, 1/35 374). The c.1400C>G and c.338G>A were the common mutations of SLC22A5 gene in 3 children with PCD, while c.621G>T was a novel mutation. There were no clinical manifestations during the follow-up period in 2 children with supplementation of L-carnitine. Another child with PCD did not follow the doctor's advice of L-carnitine treatment, and had acute attack at the age of 6 months. The child recovered after treatment, and developed normally during the follow-up. The detected ACADS gene mutations were c.417G>C and c.1054G>A in child with SCADD, who showed normal intelligence and physical development without any clinical symptoms. The mutations of ACADVL gene were c.1349G>A and c.1843C>T in child with VLCADD, who showed acute attack in the neonatal period and recovered after treatment; the child was fed with milk powder rich in medium-chain fatty acids and had normal development during the follow-up.

CONCLUSIONS

The incidence of FAOD in Chongqing area is relatively high. PCD is the most common type, and the clinical phenotype of VLCADD is serious. After early diagnosis through neonatal screening, standardized treatment and management is followed, most of FAOD children can have good prognosis.

Using Long-Term Follow-Up Data to Classify Genetic Variants in Newborn Screened Conditions

With the rapid increase in publicly available sequencing data, healthcare professionals are tasked with understanding how genetic variation informs diagnosis and affects patient health outcomes. Understanding the impact of a genetic variant in disease could be used to predict susceptibility/protection and to help build a personalized medicine profile. In the United States, over 3.8 million newborns are screened for several rare genetic diseases each year, and the follow-up testing of screen-positive newborns often involves sequencing and the identification of variants. This presents the opportunity to use longitudinal health information from these newborns to inform the impact of variants identified in the course of diagnosis. To test this, we performed secondary analysis of a 10-year natural history study of individuals diagnosed with metabolic disorders included in newborn screening (NBS). We found 564 genetic variants with accompanying phenotypic data and identified that 161 of the 564 variants (29%) were not included in ClinVar. We were able to classify 139 of the 161 variants (86%) as pathogenic or likely pathogenic. This work demonstrates that secondary analysis of longitudinal data collected as part of NBS finds unreported genetic variants and the accompanying clinical information can inform the relationship between genotype and phenotype.

Defects in Very Long-Chain Fatty Acid Oxidation Presenting as Different Types of Cardiomyopathy

Cardiac involvement may accompany various inborn errors of metabolism (IEM) including fatty acid oxidation (FAO) disorders, presenting as rhythm disturbances, conduction abnormalities, cardiomyopathies, pericardial effusion, and sudden cardiac death. FAO disorders are rare mitochondrial diseases with variable organ involvements and clinical presentations. Very long-chain acyl-CoA dehydrogenase deficiency (VLCADD) is a FAO disorder with diverse clinical presentations. We report two VLCADD patients with cardiac involvement and diverse presentations. The first patient represents with cardiogenic shock and dilated cardiomyopathy (DCM) at childhood. The second patient represents with suspicious sepsis at early infancy and hypertrophic cardiomyopathy (HCM) at further evaluation. IEM should be thought of in every individual case with suspicious sepsis or cardiac failure regardless of age or previous history.

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

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

Expert consensus on diagnosis and treatment of very long-chain acyl-CoA dehydrogenase deficiency

Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is a metabolic disease of long chain fatty acid oxidation. The clinical manifestations are heterogeneous, mainly with heart, liver, skeletal muscle and brain damage, and the onset of which can be from newborn to adult. Cardiomyopathy type is more serious with high mortality. The liver failure type and myopathy type would be potentially lethal, but generally the prognosis is relatively good. Recurrent hypoglycemia, energy metabolism disorder, liver dysfunction, cardiomyopathy and serious arrhythmia are the main causes of death. Most patients can be identified through neonatal screening, and the prognosis is usually good in patients with early diagnosis and treatment. The purpose of this consensus is to standardize the diagnosis, treatment and management of VLCAD deficiency, so as to improve the prognosis of patients and reduce death and disability.

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.

Probability of high-risk genetic matching with oocyte and semen donors: complete gene analysis or genotyping test?

PURPOSE

To estimate the probability of high-risk genetic matching when assisted reproductive techniques (ART) are applied with double gamete donation, following an NGS carrier test based on a complete study of the genes concerned. We then determine the results that would have been obtained if the genotyping tests most widely used in Spanish gamete banks had been applied.

METHODS

In this descriptive observational study, 1818 gamete donors were characterised by NGS. The pathogenic variants detected were analysed to estimate the probability of high-risk genetic matching and to determine the results that would have been obtained if the three most commonly used genotyping tests in ART had been applied.

RESULTS

The probability of high-risk genetic matching with gamete donation, screened by NGS and complete gene analysis, was 5.5%, versus the 0.6-2.7% that would have been obtained with the genotyping test. A total of 1741 variants were detected, including 607 different variants, of which only 22.6% would have been detected by all three genotyping tests considered and 44.7% of which would not have been detected by any of these tests.

CONCLUSION

Our study highlights the considerable heterogeneity of the genotyping tests, which present significant differences in their ability to detect pathogenic variants. The complete study of the genes by NGS considerably reduces reproductive risks when genetic matching is performed with gamete donors. Accordingly, we recommend that carrier screening in gamete donors be carried out using NGS and a complete study with nontargeted analysis of the variants of the screened genes.

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.

Analysis of a family with mitochondrial trifunctional protein deficiency caused by HADHA gene mutations

Mitochondrial trifunctional protein (MTP) deficiency (MTPD; MIM 609015) is a metabolic disease of fatty acid oxidation. MTPD is an autosomal recessive disorder caused by mutations in the HADHA gene, encoding the α-subunit of a trifunctional protease, or in the HADHB gene, encoding the β-subunit of a trifunctional protease. To the best of our knowledge, only two cases of families with MTPD due to HADHB gene mutations have been reported in China, and the HADHA gene mutation has not been reported in a Chinese family with MTPD. The present study reported the clinical characteristics and compound heterozygous HADHA gene mutations of two patients with MTPD in the Chinese population. The medical history, routine examination data, blood acyl-carnitine analysis results, results of pathological examination after autopsy and family pedigree map were collected for patients with MTPD. The HADHA gene was analyzed by Sanger sequencing or high-throughput sequencing, the pathogenicity of the newly discovered variant was interpreted by bioinformatics analysis, and the function of the mutated protein was modeled and analyzed according to 3D structure. The two patients with MTPD experienced metabolic crises and died following an infectious disease. Lactate dehydrogenase, creatine kinase (CK), CK-MB and liver enzyme abnormalities were observed in routine examinations. Tandem mass spectrometry revealed that long-chain acyl-carnitine was markedly elevated in blood samples from the patients with MTPD. The autopsy results for one child revealed fat accumulation in the liver and heart. Next-generation sequencing detected compound heterozygous c.703C>T (p.R235W) and c.2107G>A (p.G703R) mutations in the HADHA gene. The mother did not have acute fatty liver during pregnancy with the two patients. Using amniotic fluid prenatal diagnostic testing, the unborn child was confirmed to carry only c.2107G>A (p.G703R). Molecular mechanistic analysis indicated that the two variants affected the conformation of the α-subunit of the MTP enzyme complex, and consequently affected the stability and function of the enzyme complex. The present study comprehensively analyzed the cases, including exome sequencing and protein structure analysis and, to the best of our knowledge, describes the first observation of compound heterozygous mutations in the HADHA gene underlying this disorder in China. The clinical phenotypes of the two heterozygous variants of the HADHA gene are non-lethal. The present study may improve understanding of the HADHA gene mutation spectrum and clinical phenotype in the Chinese population.

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.

Abnormal VLCADD newborn screening resembling MADD in four neonates with decreased riboflavin levels and VLCAD activity

Early detection of congenital disorders by newborn screening (NBS) programs is essential to prevent or limit disease manifestation in affected neonates. These programs balance between the detection of the highest number of true cases and the lowest number of false-positives. In this case report, we describe four unrelated cases with a false-positive NBS result for very-long-chain acyl-CoA dehydrogenase deficiency (VLCADD). Three neonates presented with decreased but not deficient VLCAD enzyme activity and two of them carried a single heterozygous ACADVL c.1844G>A mutation. Initial biochemical investigations after positive NBS referral in these infants revealed acylcarnitine and organic acid profiles resembling those seen in multiple acyl-CoA dehydrogenase deficiency (MADD). Genetic analysis did not reveal any pathogenic mutations in the genes encoding the electron transfer flavoprotein (ETF alpha and beta subunits) nor in ETF dehydrogenase. Subsequent further diagnostics revealed decreased levels of riboflavin in the newborns and oral riboflavin administration normalized the MADD-like biochemical profiles. During pregnancy, the mothers followed a vegan, vegetarian or lactose-free diet which probably caused alimentary riboflavin deficiency in the neonates. This report demonstrates that a secondary (alimentary) maternal riboflavin deficiency in combination with reduced VLCAD activity in the newborns can result in an abnormal VLCADD/MADD acylcarnitine profile and can cause false-positive NBS. We hypothesize that maternal riboflavin deficiency contributed to the false-positive VLCADD neonatal screening results.

Metabolic Outcomes of Anaplerotic Dodecanedioic Acid Supplementation in Very Long Chain Acyl-CoA Dehydrogenase (VLCAD) Deficient Fibroblasts

Very long-chain acyl-CoA dehydrogenase deficiency (VLCADD, OMIM 609575) is associated with energy deficiency and mitochondrial dysfunction and may lead to rhabdomyolysis and cardiomyopathy. Under physiological conditions, there is a fine balance between the utilization of different carbon nutrients to maintain the Krebs cycle. The maintenance of steady pools of Krebs cycle intermediates is critical formitochondrial energy homeostasis especially in high-energy demanding organs such as muscle and heart. Even-chain dicarboxylic acids are established as alternative energy carbon sources that replenish the Krebs cycle by bypassing a defective β-oxidation pathway. Despite this, even-chain dicarboxylic acids are eliminated in the urine of VLCAD-affected individuals. In this study, we explore dodecanedioic acid (C12; DODA) supplementation and investigate its metabolic effect on Krebs cycle intermediates, glucose uptake, and acylcarnitine profiles in VLCAD-deficient fibroblasts. Our findings indicate that DODA supplementation replenishes the Krebs cycle by increasing the succinate pool, attenuates glycolytic flux, and reduces levels of toxic very long-chain acylcarnitines.

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.

Very Long-Chain Acyl-CoA Dehydrogenase Deficiency: High Incidence of Detected Patients With Expanded Newborn Screening Program

Very long-chain acyl-CoA dehydrogenase deficiency (VLCADD) is a rare autosomal recessive disorder of fatty acid metabolism with a variable presentation. The aim of this study was to describe five patients with VLCADD diagnosed through the pilot study and expanded newborn screening (NBS) program that started in 2018 in Slovenia. Four patients were diagnosed through the expanded NBS program with tandem mass spectrometry; one patient was previously diagnosed in a pilot study preceding the NBS implementation. Confirmatory testing consisted of acylcarnitines analysis in dried blood spots, organic acids profiling in urine, genetic analysis of ACADVL gene, and enzyme activity determination in lymphocytes or fibroblasts. Four newborns with specific elevation of acylcarnitines diagnostic for VLCADD and disease-specific acylcarnitines ratios (C14:1, C14, C14:2, C14:1/C2, C14:1/C16) were confirmed with genetic testing: all were compound heterozygotes, two of them had one previously unreported ACDVL gene variant each (NM_000018.3) c.1538C > G; (NP_000009) p.(Ala513Gly) and c.661A > G; p.(Ser221Gly), respectively. In addition, one patient diagnosed in the pilot study also had a specific elevation of acylcarnitines. Subsequent ACDVL genetic analysis confirmed compound heterozygosity. In agreement with the diagnosis, enzyme activity was reduced in five patients tested. In seven other newborns with positive screening results, only single allele variants were found in the ACDVL gene, so the diagnosis was not confirmed. Among these, two variants were novel, c.416T > C and c.1046C > A, respectively (p.Leu139Pro and p.Ala349Glu). In the first 2 years of the expanded NBS program in Slovenia altogether 30,000 newborns were screened. We diagnosed four cases of VLCADD. The estimated VLCADD incidence was 1:7,500 which was much higher than that of the medium-chain acyl-CoA dehydrogenase deficiency (MCADD) cases in the same period. Our study also provided one of the first descriptions of ACADVL variants in Central-Southeastern Europe and reported on 4 novel variants.

Electrophysiological Abnormalities in VLCAD Deficient hiPSC-Cardiomyocytes Do not Improve with Carnitine Supplementation

Patients with a deficiency in very long-chain acyl-CoA dehydrogenase (VLCAD), an enzyme that is involved in the mitochondrial beta-oxidation of long-chain fatty acids, are at risk for developing cardiac arrhythmias. In human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs), VLCAD deficiency (VLCADD) results in a series of abnormalities, including: 1) accumulation of long-chain acylcarnitines, 2) action potential shortening, 3) higher systolic and diastolic intracellular Ca²⁺ concentrations, and 4) development of delayed afterdepolarizations. In the fatty acid oxidation process, carnitine is required for bidirectional transport of acyl groups across the mitochondrial membrane. Supplementation has been suggested as potential therapeutic approach in VLCADD, but its benefits are debated. Here, we studied the effects of carnitine supplementation on the long-chain acylcarnitine levels and performed electrophysiological analyses in VLCADD patient-derived hiPSC-CMs with a ACADVL gene mutation (p.Val283Ala/p.Glu381del). Under standard culture conditions, VLCADD hiPSC-CMs showed high concentrations of long-chain acylcarnitines, short action potentials, and high delayed afterdepolarizations occurrence. Incubation of the hiPSC-CMs with 400 µM L-carnitine for 48 h led to increased long-chain acylcarnitine levels both in medium and cells. In addition, carnitine supplementation neither restored abnormal action potential parameters nor the increased occurrence of delayed afterdepolarizations in VLCADD hiPSC-CMs. We conclude that long-chain acylcarnitine accumulation and electrophysiological abnormalities in VLCADD hiPSC-CMs are not normalized by carnitine supplementation, indicating that this treatment is unlikely to be beneficial against cardiac arrhythmias in VLCADD patients.

Novel ACADVL variants resulting in mitochondrial defects in long-chain acyl-CoA dehydrogenase deficiency

The pathogenesis of very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is highly heterogeneous and still unclear. Additional novel variants have been recently detected in the population. The molecular and cellular effects of these previously unreported variants are still poorly understood and require further characterization. To address this problem, we have evaluated the various functions and biochemical consequences of six novel missense variants that lead to mild VLCAD deficiency. Marked deficiencies in fatty acid oxidation (FAO) and other mitochondrial defects were observed in cells carrying one of these six variants (c.541C>T, c.863T>G, c.895A>G, c.1238T>C, c.1276G>A, and c.1505T>A), including reductions in mitochondrial respiratory-chain function and adenosine triphosphate (ATP) production, and increased levels of mitochondrial reactive oxygen species (ROS). Intriguingly, higher apoptosis levels were found in cells carrying the mutant VLCAD under glucose-limited stress. Moreover, the stability of the mutant homodimer was disturbed, and major conformational changes in each mutant VLCAD structure were predicted by molecular dynamics (MD) simulation. The data presented here may provide valuable information for improving management of diagnosis and treatment of VLCAD deficiency and for a better understanding of the general molecular bases of disease variability.

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

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

Evidence that Oxidative Disbalance and Mitochondrial Dysfunction are Involved in the Pathophysiology of Fatty Acid Oxidation Disorders

Mitochondrial fatty acid β-oxidation disorders (FAODs) are a group of about 20 diseases which are caused by specific mutations in genes that codify proteins or enzymes involved in the fatty acid transport and mitochondrial β-oxidation. As a consequence of these inherited metabolic defects, fatty acids can not be used as an appropriate energetic source during special conditions, such as prolonged fasting, exercise or other catabolic states. Therefore, patients usually present hepatopathy, cardiomyopathy, severe skeletal myopathy and neuropathy, besides biochemical features like hypoketotic hypoglycemia, metabolic acidosis, hypotony and hyperammonemia. This set of symptoms seems to be related not only with the energy deficiency, but also with toxic effects provoked by fatty acids and carnitine derivatives accumulated in the tissues of the patients. The understanding of the mechanisms by which these metabolites provoke tissue injury in FAODs is crucial for the developmental of novel therapeutic strategies that promote increased life expectancy, as well as improved life quality for patients. In this sense, the objective of this review is to present evidence from the scientific literature on the role of oxidative damage and mitochondrial dysfunction in the pathogenesis of the most prevalent FAODs: medium-chain acyl-CoA dehydrogenase (MCAD), long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) and very long-chain acyl-CoA dehydrogenase (VLCAD) deficiencies. It is expected that the findings presented in this review, obtained from both animal model and patients studies, may contribute to a better comprehension of the pathophysiology of these diseases.

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.

Nutrition management guideline for very-long chain acyl-CoA dehydrogenase deficiency (VLCAD): An evidence- and consensus-based approach

The nutrition management guideline for very-long chain acyl-CoA dehydrogenase deficiency (VLCAD) is the fourth in a series of web-based guidelines focusing on the diet treatment for inherited metabolic disorders and follows previous publication of guidelines for maple syrup urine disease (2014), phenylketonuria (2016) and propionic acidemia (2019). The purpose of this guideline is to establish harmonization in the treatment and monitoring of individuals with VLCAD of all ages in order to improve clinical outcomes. Six research questions were identified to support guideline development on: nutrition recommendations for the healthy individual, illness management, supplementation, monitoring, physical activity and management during pregnancy. This report describes the methodology used in its development including review, critical appraisal and abstraction of peer-reviewed studies and unpublished practice literature; expert input through two Delphi surveys and a nominal group process; and external review from metabolic physicians and dietitians. It includes the summary statements of the nutrition management recommendations for each research question, followed by a standardized rating based on the strength of the evidence. Online, open access of the full published guideline allows utilization by health care providers, researchers and collaborators who advise, advocate and care for individuals with VLCAD and their families and can be accessed from the Genetic Metabolic Dietitians International (https://GMDI.org) and Southeast Regional Genetics Network (https://southeastgenetics.org/ngp) websites.

Effects of fasting, feeding and exercise on plasma acylcarnitines among subjects with CPT2D, VLCADD and LCHADD/TFPD

BACKGROUND

The plasma acylcarnitine profile is frequently used as a biochemical assessment for follow-up in diagnosed patients with fatty acid oxidation disorders (FAODs). Disease specific acylcarnitine species are elevated during metabolic decompensation but there is clinical and biochemical heterogeneity among patients and limited data on the utility of an acylcarnitine profile for routine clinical monitoring.

METHODS

We evaluated plasma acylcarnitine profiles from 30 diagnosed patients with long-chain FAODs (carnitine palmitoyltransferase-2 (CPT2), very long-chain acyl-CoA dehydrogenase (VLCAD), and long-chain 3-hydroxy acyl-CoA dehydrogenase or mitochondrial trifunctional protein (LCHAD/TFP) deficiencies) collected after an overnight fast, after feeding a controlled low-fat diet, and before and after moderate exercise. Our purpose was to describe the variability in this biomarker and how various physiologic states effect the acylcarnitine concentrations in circulation.

RESULTS

Disease specific acylcarnitine species were higher after an overnight fast and decreased by approximately 60% two hours after a controlled breakfast meal. Moderate-intensity exercise increased the acylcarnitine species but it varied by diagnosis. When analyzed for a genotype/phenotype correlation, the presence of the common LCHADD mutation (c.1528G > C) was associated with higher levels of 3-hydroxyacylcarnitines than in patients with other mutations.

CONCLUSIONS

We found that feeding consistently suppressed and that moderate intensity exercise increased disease specific acylcarnitine species, but the response to exercise was highly variable across subjects and diagnoses. The clinical utility of routine plasma acylcarnitine analysis for outpatient treatment monitoring remains questionable; however, if acylcarnitine profiles are measured in the clinical setting, standardized procedures are required for sample collection to be of value.

Ethnic variability in newborn metabolic screening markers associated with false-positive outcomes

Newborn screening (NBS) programmes utilise information on a variety of clinical variables such as gestational age, sex, and birth weight to reduce false-positive screens for inborn metabolic disorders. Here we study the influence of ethnicity on metabolic marker levels in a diverse newborn population. NBS data from screen-negative singleton babies (n = 100 000) were analysed, which included blood metabolic markers measured by tandem mass spectrometry and ethnicity status reported by the parents. Metabolic marker levels were compared between major ethnic groups (Asian, Black, Hispanic, White) using effect size analysis, which controlled for group size differences and influence from clinical variables. Marker level differences found between ethnic groups were correlated to NBS data from 2532 false-positive cases for four metabolic diseases: glutaric acidemia type 1 (GA-1), methylmalonic acidemia (MMA), ornithine transcarbamylase deficiency (OTCD), and very long-chain acyl-CoA dehydrogenase deficiency (VLCADD). In the result, 79% of the metabolic markers (34 of 43) had ethnicity-related differences. Compared to the other groups, Black infants had elevated GA-1 markers (C5DC, Cohen's d = .37, P < .001), Hispanics had elevated MMA markers (C3, Cohen's d = .13, P < .001, and C3/C2, Cohen's d = .27, P < .001); and Whites had elevated VLCADD markers (C14, Cohen's d = .28, P < .001, and C14:1, Cohen's d = .22, P < .001) and decreased OTCD markers (citrulline, Cohen's d = -.26, P < .001). These findings correlated with the higher false-positive rates in Black infants for GA-1, in Hispanics for MMA, and in Whites for OTCD and for VLCADD. Web-based tools are available to analyse ethnicity-related changes in newborn metabolism and to support developing methods to identify false-positives in metabolic screening.

Newborn screening and genetic characteristics of patients with short- and very long-chain acyl-CoA dehydrogenase deficiencies

BACKGROUND AND AIMS

Acyl-CoA dehydrogenase deficiencies are a group of mitochondrial fatty-acid oxidation disorders rarely reported in mainland China. We assessed the biochemical and genetic characteristics of patients with short- and very-long-chain-acyl-CoA dehydrogenase deficiencies (SCADD/VLCADD) discovered through newborn screening.

MATERIALS AND METHODS

We investigated the effects of genetic variations on protein function using in silico prediction and structural modelling.

RESULTS

Of 364,545 screened newborns, four were diagnosed with SCADD and four with VLCADD. SCADD and VLCADD incidences in our population were 1:91,136. All patients exhibited elevated C4 or C14:1 levels. Three SCADD patients had increased urinary ethylmalonic acid concentrations. Six ACADS and eight ACADVL variants were identified, with no hotspot variants, and five were unreported, including four missense variants and one splice site variant. ACADVL c.1434 + 2 T > C is a splice site variant that could affect splicing, leading to exon 14 skipping. In silico tools predicted the missense variants as pathogenic. Structural modelling confirmed that the missense variants may affect quaternary structures, causing protein instability.

CONCLUSIONS

Our findings expanded the ACADS and ACADVL mutational spectra. The combination of in silico prediction and structural modelling can improve our understanding of the pathogenicity of unreported genetic variants, providing an explanation for variant assessment.

Nutritional ketosis improves exercise metabolism in patients with very long-chain acyl-CoA dehydrogenase deficiency

A maladaptive shift from fat to carbohydrate (CHO) oxidation during exercise is thought to underlie myopathy and exercise-induced rhabdomyolysis in patients with fatty acid oxidation (FAO) disorders. We hypothesised that ingestion of a ketone ester (KE) drink prior to exercise could serve as an alternative oxidative substrate supply to boost muscular ATP homeostasis. To establish a rational basis for therapeutic use of KE supplementation in FAO, we tested this hypothesis in patients deficient in Very Long-Chain acyl-CoA Dehydrogenase (VLCAD). Five patients (range 17-45 y; 4 M/1F) patients were included in an investigator-initiated, randomised, blinded, placebo-controlled, 2-way cross-over study. Patients drank either a KE + CHO mix or an isocaloric CHO equivalent and performed 35 minutes upright cycling followed by 10 minutes supine cycling inside a Magnetic Resonance scanner at individual maximal FAO work rate (fatmax; approximately 40% VO₂ max). The protocol was repeated after a 1-week interval with the alternate drink. Primary outcome measures were quadriceps phosphocreatine (PCr), Pi and pH dynamics during exercise and recovery assayed by in vivo ³¹ P-MR spectroscopy. Secondary outcomes included plasma and muscle metabolites and respiratory gas exchange recordings. Ingestion of KE rapidly induced mild ketosis and increased muscle BHB content. During exercise at FATMAX, VLCADD-specific plasma acylcarnitine levels, quadriceps glycolytic intermediate levels and in vivo Pi/PCr ratio were all lower in KE + CHO than CHO. These results provide a rational basis for future clinical trials of synthetic ketone ester supplementation therapy in patients with FAO disorders. Trial registration: ClinicalTrials.gov. Protocol ID: NCT03531554; METC2014.492; ABR51222.042.14.

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.

Electrophysiological Abnormalities in VLCAD Deficient hiPSC-Cardiomyocytes Can Be Improved by Lowering Accumulation of Fatty Acid Oxidation Intermediates

Patients with very long-chain acyl-CoA dehydrogenase deficiency (VLCADD) can present with life-threatening cardiac arrhythmias. The pathophysiological mechanism is unknown. We reprogrammed fibroblasts from one mildly and one severely affected VLCADD patient, into human induced pluripotent stem cells (hiPSCs) and differentiated these into cardiomyocytes (VLCADD-CMs). VLCADD-CMs displayed shorter action potentials (APs), more delayed afterdepolarizations (DADs) and higher systolic and diastolic intracellular Ca²⁺ concentration ([Ca²⁺]_i) than control CMs. The mitochondrial booster resveratrol mitigated the biochemical, electrophysiological and [Ca²⁺]_i changes in the mild but not in the severe VLCADD-CMs. Accumulation of potentially toxic intermediates of fatty acid oxidation was blocked by substrate reduction with etomoxir. Incubation with etomoxir led to marked prolongation of AP duration and reduced DADs and [Ca²⁺]_i in both VLCADD-CMs. These results provide compelling evidence that reduced accumulation of fatty acid oxidation intermediates, either by enhanced fatty acid oxidation flux through increased mitochondria biogenesis (resveratrol) or by inhibition of fatty acid transport into the mitochondria (etomoxir), rescues pro-arrhythmia defects in VLCADD-CMs and open doors for new treatments.

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.

Utilization of archived neonatal dried blood spots for genome-wide genotyping

Introduction

Heel pricks are performed on newborns for diagnostic screenings of various pre-symptomatic metabolic and genetic diseases. Excess blood is spotted on Guthrie cards and archived by many states in biobanks for follow-up diagnoses and public health research. However, storage environment may vary across biobanks and across time within biobanks. With increased applications of DNA extracted from spots for genetic studies, identifying factors associated with genotyping success is critical to maximize DNA quality for future studies.

Method

We evaluated 399 blood spots, which were part of a genome-wide association study of childhood leukemia risk in children with Down syndrome, archived at the Michigan Neonatal Biobank between 1992 and 2008. High quality DNA was defined as having post-quality control call rate ≥ 99.0% based on the Illumina GenomeStudio 2.0 GenCall algorithm after processing the samples on the Illumina Infinium Global Screening Array. Bivariate analyses and multivariable logistic regression models were applied to evaluate effects of storage environment and storage duration on DNA genotyping quality.

Results

Both storage environment and duration were associated with sample genotyping call rates (p-values < 0.001). Sample call rates were associated with storage duration independent of storage environment (p-trend = 0.006 for DBS archived in an uncontrolled environment and p-trend = 0.002 in a controlled environment). However, 95% of the total sample had high genotyping quality with a call rate ≥ 95.0%, a standard threshold for acceptable sample quality in many genetic studies.

Conclusion

Blood spot DNA quality was lower in samples archived in uncontrolled storage environments and for samples archived for longer durations. Still, regardless of storage environment or duration, neonatal biobanks including the Michigan Neonatal Biobanks can provide access to large collections of spots with DNA quality acceptable for most genotyping studies.

Prediction of VLCAD deficiency phenotype by a metabolic fingerprint in newborn screening bloodspots

PURPOSE

Newborns who test positive for very long-chain acyl-CoA dehydrogenase deficiency (VLCADD) in newborn screening may have a severe phenotype with early onset of life-threatening symptoms but may also have an attenuated phenotype and never become symptomatic. The objective of this study is to investigate whether metabolomic profiles in dried bloodspots (DBS) of newborns allow early phenotypic prediction, permitting tailored treatment and follow-up.

METHODS

A metabolic fingerprint was generated by direct infusion high resolution mass spectrometry in DBS of VLCADD patients (n = 15) and matched controls. Multivariate analysis of the metabolomic profiles was applied to differentiate subgroups.

RESULTS

Concentration of six acylcarnitine species differed significantly between patients and controls. The concentration of C18:2- and C20:0-carnitine, 13,14-dihydroretinol and deoxycytidine monophosphate allowed separation between mild and severe patients. Two patients who could not be prognosticated on early clinical symptoms, were correctly fitted for severity in the score plot based on the untargeted metabolomics.

CONCLUSION

Distinctive metabolomic profiles in DBS of newborns with VLCADD may allow phenotypic prognostication. The full potential of this approach as well as the underlying biochemical mechanisms need further investigation.

Disturbance of mitochondrial functions associated with permeability transition pore opening induced by cis-5-tetradecenoic and myristic acids in liver of adolescent rats

Patients affected by very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency commonly present liver dysfunction whose pathogenesis is poorly known. We demonstrate here that major metabolites accumulating in this disorder, namely cis-5-tetradecenoic acid (Cis-5) and myristic acid (Myr), markedly impair mitochondrial respiration, decreasing ATP production in liver mitochondrial preparations from adolescent rats. Other parameters of mitochondrial homeostasis such as membrane potential (ΔΨm) and Ca²⁺retention capacity were strongly compromised by these fatty acids, involving induction of mitochondrial permeability transition. The present data indicate that disruption of mitochondrial bioenergetics and Ca²⁺homeostasis may contribute to the liver dysfunction of VLCAD deficient patients.

New Ratios for Performance Improvement for Identifying Acyl-CoA Dehydrogenase Deficiencies in Expanded Newborn Screening: A Retrospective Study

Some success in identifying acyl-CoA dehydrogenase (ACAD) deficiencies before they are symptomatic has been achieved through tandem mass spectrometry. However, there has been several challenges that need to be confronted, including excess false positives, the occasional false negatives and indicators selection. To select ideal indicators and evaluate their performance for identifying ACAD deficiencies, data from 352,119 newborn babies, containing 20 cases, were used in this retrospective study. A total of three new ratios, C4/C5DC+C6-OH, C8/C14:1, and C14:1/C16-OH, were selected from 43 metabolites. Around 903 ratios derived from pairwise combinations of all metabolites via multivariate logistic regression analysis were used. In the current study, the regression analysis was performed to identify short chain acyl-CoA dehydrogenase (SCAD) deficiency, medium chain acyl-CoA dehydrogenase (MCAD) deficiency, and very long chain acyl-CoA dehydrogenase (VLCAD) deficiency. In both model-building and testing data, the C4/C5DC+C6-OH, C8/C14:1 and C14:1/C16-OH were found to be better indicators for SCAD, MCAD and VLCAD deficiencies, respectively, compared to [C4, (C4, C4/C2)], [C8, (C6, C8, C8/C2, C4DC+C5-OH/C8:1)], and [C14:1, (C14:1, C14:1/C16, C14:1/C2)], respectively. In addition, 22 mutations, including 5 novel mutations and 17 reported mutations, in ACADS, ACADM, and ACADL genes were detected in 20 infants with ACAD deficiency by using high-thorough sequencing based on target capture. The pathogenic mutations of c.1031A > G in ACADS, c.449_452delCTGA in ACADM and c.1349G > A in ACADL were found to be hot spots in Suzhou patients with SCAD, MCAD, and VLCAD, respectively. In conclusion, we had identified three new ratios that could improve the performance for ACAD deficiencies compared to the used indicators. We considered to utilize C4/C5DC+C6-OH, C8/C14:1, and C14:1/C16-OH as primary indicators for SCAD, MCAD, and VLCAD deficiency, respectively, in further expanded newborn screening practice. In addition, the spectrum of mutations in Suzhou population enriches genetic data of Chinese patients with one of ACAD deficiencies.

Cardiac Phenotypes in Hereditary Muscle Disorders: JACC State-of-the-Art Review

Hereditary muscular diseases commonly involve the heart. Cardiac manifestations encompass a spectrum of phenotypes, including both cardiomyopathies and rhythm disorders. Common biomarkers suggesting cardiomuscular diseases include increased circulating creatine kinase and/or lactic acid levels or disease-specific metabolic indicators. Cardiac and extra-cardiac traits, imaging tests, family studies, and genetic testing provide precise diagnoses. Cardiac phenotypes are mainly dilated and hypokinetic in dystrophinopathies, Emery-Dreifuss muscular dystrophies, and limb girdle muscular dystrophies; hypertrophic in Friedreich ataxia, mitochondrial diseases, glycogen storage diseases, and fatty acid oxidation disorders; and restrictive in myofibrillar myopathies. Left ventricular noncompaction is variably associated with the different myopathies. Conduction defects and arrhythmias constitute a major phenotype in myotonic dystrophies and skeletal muscle channelopathies. Although the actual cardiac management is rarely based on the cause, the cardiac phenotypes need precise characterization because they are often the only or the predominant manifestations and the prognostic determinants of many hereditary muscle disorders.

Impact of newborn screening for very-long-chain acyl-CoA dehydrogenase deficiency on genetic, enzymatic, and clinical outcomes

Most infants with very-long-chain acyl-CoA dehydrogenase deficiency (VLCADD) identified by newborn screening (NBS) are asymptomatic at the time of diagnosis and remain asymptomatic. If this outcome is due to prompt diagnosis and initiation of therapy, or because of identification of individuals with biochemical abnormalities who will never develop symptoms, is unclear. Therefore, a 10-year longitudinal national cohort study of genetically confirmed VLCADD patients born before and after introduction of NBS was conducted. Main outcome measures were clinical outcome parameters, acyl-CoA dehydrogenase very long chain gene analysis, VLCAD activity, and overall capacity of long-chain fatty acid oxidation (LC-FAO flux) in lymphocytes and cultured skin fibroblasts. Median VLCAD activity in lymphocytes of 54 patients, 21 diagnosed pre-NBS and 33 by NBS was, respectively, 5.4% (95% confidence interval [CI]: 4.0-8.3) and 12.6% (95% CI: 10.7-17.7; P < 0.001) of the reference mean. The median LC-FAO flux was 33.2% (95% CI: 22.8-48.3) and 41% (95% CI: 40.8-68; P < 0.05) of the control mean, respectively. Clinical characteristics in 23 pre-NBS and 37 NBS patients revealed hypoglycemic events in 12 vs 2 patients, cardiomyopathy in 5 vs 4 patients and myopathy in 14 vs 3 patients. All patients with LC-FAO flux <10% developed symptoms. Of the patients with LC-FAO flux >10% 7 out of 12 diagnosed pre-NBS vs none by NBS experienced hypoglycemic events. NBS has a clear beneficial effect on the prevention of hypoglycemic events in patients with some residual enzyme activity, but does not prevent hypoglycemia nor cardiac complications in patients with very low residual enzyme activity. The effect of NBS on prevalence and prevention of myopathy-related complications remains unclear.

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

BACKGROUND

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

METHODS

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

RESULTS

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

DISCUSSION

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

Mitochondrial Genetic Disorders: Cell Signaling and Pharmacological Therapies

Mitochondrial fatty acid oxidation (FAO) and respiratory chain (RC) defects form a large group of inherited monogenic disorders sharing many common clinical and pathophysiological features, including disruption of mitochondrial bioenergetics, but also, for example, oxidative stress and accumulation of noxious metabolites. Interestingly, several transcription factors or co-activators exert transcriptional control on both FAO and RC genes, and can be activated by small molecules, opening to possibly common therapeutic approaches for FAO and RC deficiencies. Here, we review recent data on the potential of various drugs or small molecules targeting pivotal metabolic regulators: peroxisome proliferator activated receptors (PPARs), sirtuin 1 (SIRT1), AMP-activated protein kinase (AMPK), and protein kinase A (PKA)) or interacting with reactive oxygen species (ROS) signaling, to alleviate or to correct inborn FAO or RC deficiencies in cellular or animal models. The possible molecular mechanisms involved, in particular the contribution of mitochondrial biogenesis, are discussed. Applications of these pharmacological approaches as a function of genotype/phenotype are also addressed, which clearly orient toward personalized therapy. Finally, we propose that beyond the identification of individual candidate drugs/molecules, future pharmacological approaches should consider their combination, which could produce additive or synergistic effects that may further enhance their therapeutic potential.

Proposal for an individualized dietary strategy in patients with very long-chain acyl-CoA dehydrogenase deficiency

BACKGROUND

Patients with very long chain acyl-CoA dehydrogenase deficiency (VLCADD), a long chain fatty acid oxidation disorder, are traditionally treated with a long chain triglyceride (LCT) restricted and medium chain triglyceride (MCT) supplemented diet. Introduction of VLCADD in newborn screening (NBS) programs has led to the identification of asymptomatic newborns with VLCADD, who may have a more attenuated phenotype and may not need dietary adjustments.

OBJECTIVE

To define dietary strategies for individuals with VLCADD based on the predicted phenotype.

METHOD

We evaluated long-term dietary histories of a cohort of individuals diagnosed with VLCADD identified before the introduction of VLCADD in NBS and their beta-oxidation (LC-FAO) flux score (rate of oleate oxidation) in cultured skin fibroblasts in relation to the clinical outcome. Based on these results a dietary strategy is proposed.

RESULTS

Sixteen individuals with VLCADD were included. One had an LC-FAO flux score >90%, was not on a restricted diet and is asymptomatic to date. Four patients had an LC-FAO flux score <10%, and significant VLCADD related symptoms despite the use of strict diets including LCT restriction, MCT supplementation and nocturnal gastric drip feeding. Patients with an LC-FAO flux score between 10 and 90% (n = 11) showed a more heterogeneous phenotype.

CONCLUSIONS

This study shows that a strict diet cannot prevent poor clinical outcome in severely affected patients and that the LC-FAO flux is a good predictor of clinical outcome in individuals with VLCADD identified before its introduction in NBS. Hereby, we propose an individualized dietary strategy based on the LC-FAO flux score.