Newborn screening for disorders of fatty-acid oxidation: experience and recommendations from an expert meeting

Prevalence and Mutation Analysis of Short-Chain acyl-CoA Dehydrogenase Deficiency Detected by Newborn Screening in Hefei, China

Short-chain acyl-CoA dehydrogenase deficiency (SCADD) is an autosomal recessive inborn error of mitochondrial fatty acid oxidation with highly variable biochemical and genetic characteristics. The present study aimed to estimate the prevalence and genetic characteristics of SCADD in newborns identified through screening. A total of 782,930 newborns were screened for SCADD in Hefei Neonatal Screening Center from January 2016 to December 2023. The blood samples from newborns were measured by tandem mass spectrometry (MS/MS). The suspected SCADD neonates were rechecked using next-generation gene sequencing for diagnosis. Sanger sequencing was used to verify the mutation site for patients with SCADD and their parents. A total of 21 SCADD cases were confirmed, with an incidence rate of 1/37,282. Genetic mutations were identified in all 21 cases, including 15 cases of compound heterozygous variation and 6 cases of homozygous variation. Twenty-one different mutation types and forty-two mutation sites were discovered, with the most frequent mutation being c.1031A>G, accounting for 21.43% (9/42), followed by c.1130C>T, accounting for 16.67% (7/42). Our findings expand the SCADD mutational spectra. c. 1031A>G and c.1130C>T are the common mutation sites for SCADD genes in newborns. SCADD diagnosed through NBS is primarily a benign condition, and early diagnosis is not necessarily essential.

Mitochondrial bioenergetics and cardiolipin remodeling abnormalities in mitochondrial trifunctional protein deficiency

Mitochondrial trifunctional protein (TFP) deficiency is an inherited metabolic disorder leading to a block in long-chain fatty acid β-oxidation. Mutations in HADHA and HADHB, which encode the TFP α and β subunits, respectively, usually result in combined TFP deficiency. A single common mutation, HADHA c.1528G>C (p.E510Q), leads to isolated 3-hydroxyacyl-CoA dehydrogenase deficiency. TFP also catalyzes a step in the remodeling of cardiolipin (CL), a phospholipid critical to mitochondrial membrane stability and function. We explored the effect of mutations in TFP subunits on CL and other phospholipid content and composition and the consequences of these changes on mitochondrial bioenergetics in patient-derived fibroblasts. Abnormalities in these parameters varied extensively among different fibroblasts, and some cells were able to maintain basal oxygen consumption rates similar to controls. Although CL reduction was universally identified, a simultaneous increase in monolysocardiolipins was discrepant among cells. A similar profile was seen in liver mitochondria isolates from a TFP-deficient mouse model. Response to new potential drugs targeting CL metabolism might be dependent on patient genotype.

Nutritional Management of Patients with Fatty Acid Oxidation Disorders

Treatment of fatty acid oxidation disorders is based on dietary, pharmacological and metabolic decompensation measures. It is essential to provide the patient with sufficient glucose to prevent lipolysis and to avoid the use of fatty acids as fuel as far as possible. Dietary management consists of preventing periods of fasting and restricting fat intake by increasing carbohydrate intake, while maintaining an adequate and uninterrupted caloric intake. In long-chain deficits, long-chain triglyceride restriction should be 10% of total energy, with linoleic acid and linolenic acid intake of 3-4% and 0.5-1% (5/1-10/1 ratio), with medium-chain triglyceride supplementation at 10-25% of total energy (total MCT+LCT ratio = 20-35%). Trihepatnoin is a new therapeutic option with a good safety and efficacy profile. Patients at risk of rhabdomyolysis should ingest MCT or carbohydrates or a combination of both 20 min before exercise. In medium- and short-chain deficits, dietary modifications are not advised (except during exacerbations), with MCT contraindicated and slow sugars recommended 20 min before any significant physical exertion. Parents should be alerted to the need to increase the amount and frequency of carbohydrate intake in stressful situations. The main measure in emergency hospital treatment is the administration of IV glucose. The use of carnitine remains controversial and new therapeutic options are under investigation.

Tracing the lipidome in inborn errors of metabolism

Inborn errors of metabolism (IEM) represent a heterogeneous group of more than 1800 rare disorders, many of which are causing significant childhood morbidity and mortality. More than 100 IEM are linked to dyslipidaemia, but yet our knowledge in connecting genetic information with lipidomic data is limited. Stable isotope tracing studies of the lipid metabolism (STL) provide insights on the dynamic of cellular lipid processes and could thereby facilitate the delineation of underlying metabolic (patho)mechanisms. This mini-review focuses on principles as well as technical limitations of STL and describes potential clinical applications by discussing recently published STL focusing on IEM.

Sudden death with cardiac involvement in a neonate with carnitine-acylcarnitine translocase deficiency

A female neonate born with normal Apgar scores at 38+2 weeks of gestational age unexpectedly passed away within less than 30 hours after birth. The situation mirrored her brother's earlier demise within 24 hours post-delivery, suggesting a possible genetic disorder. Gross examination revealed widespread cyanosis and distinct yellowish changes on the cardiac ventricles. Histopathological examination disclosed lipid accumulation in the liver, heart, and kidneys. Tandem mass spectrometry detected elevated levels of 10 amino acids and 14 carnitines in cardiac blood. Trio-whole genome sequencing (Trio-WGS) identified the SLC25A20 c.199-10T>G mutation associated with carnitine-acylcarnitine translocase disease (CACTD), a type of fatty acid oxidation disorders (FAODs) with a potential for sudden death. Further validation of gene expression confirmed the functional deficiency of SLC25A20, ultimately diagnosing CACTD as the underlying cause of the neonate's demise. This case highlights the importance of prenatal metabolic and genetic screening for prospective parents and emphasizes the need for forensic doctors to integrate metabolomic and genomic investigations into autopsies for suspected inherited metabolic diseases.

Prevalence of inherited metabolic disorders among newborns in Zhuzhou, a southern city in China

Background and aims: Defective enzymes, cofactors, or transporters of metabolic pathways cause inherited metabolic disorders (IMDs), a group of genetic disorders. Several IMDs have serious consequences for the affected neonates. Newborn screening for IMDs is conducted by measuring specific metabolites between 3 and 7 days of life. Herein, we analyzed the incidence, spectrum, and genetic characteristics of IMDs in newborns in the Zhuzhou area. Methods: Tandem mass spectrometry was conducted on 90,829 newborns who were admitted to the Women and Children Healthcare Hospital of Zhuzhou and requested for screening for IMDs. These newborns were subsequently subjected to next-generation sequencing and further validated using Sanger sequencing. Results: 30 IMDs cases were found in 90,829 cases of newborns screened for IMDs, and the overall incidence was 1/3,027. The incidence of amino acid, organic acid, fatty acid oxidation and urea cycle disorders were 1/8,257, 1/18,165, 1/7,569, and 1/45,414, respectively. Additionally, 9 cases of maternal IMDs were found in our study, and unreported gene mutations of 3 cases IMDs were identified. Conclusion: Our data indicated that IMDs are never uncommon in zhuzhou, meanwhile, we also found that primary carnitine deficiency was the only disorder of fatty acid oxidation in Zhuzhou, and the incidence (1/7,569) was higher than the national level, organic acid metabolic diseases are mostly inherited. Therefore, our study has clarified the disease spectrum and genetic backgrounds, contributing to the treatment and prenatal genetic counseling of these disorders in this region.

Experience with carnitine palmitoyltransferase II deficiency: diagnostic challenges in the myopathic form

OBJECTIVES

Carnitine palmitoyltransferase II (CPT II) deficiency is an autosomal recessive disorder of long-chain fatty acid oxidation. Three clinical phenotypes, lethal neonatal form, severe infantile hepatocardiomuscular form, and myopathic form, have been described in CPT II deficiency. The myopathic form is usually mild and can manifest from infancy to adulthood, characterised by recurrent rhabdomyolysis episodes. The study aimed to investigate the clinical features, biochemical, histopathological, and genetic findings of 13 patients diagnosed with the myopathic form of CPT II deficiency at Ege University Hospital.

METHODS

A retrospective study was conducted with 13 patients with the myopathic form of CPT II deficiency. Our study considered demographic data, triggers of recurrent rhabdomyolysis attacks, biochemical metabolic screening, and molecular analysis.

RESULTS

Ten patients were examined for rhabdomyolysis of unknown causes. Two patients were diagnosed during family screening, and one was diagnosed during investigations due to increased liver function tests. Acylcarnitine profiles were normal in five patients during rhabdomyolysis. Genetic studies have identified a c.338C>T (p.Ser113Leu) variant homozygous in 10 patients. One patient showed a novel frameshift variant compound heterozygous with c.338C>T (p.Ser113Leu).

CONCLUSIONS

Plasma acylcarnitine analysis should be preferred as it is superior to DBS acylcarnitine analysis in diagnosing CPT II deficiency. Even if plasma acylcarnitine analysis is impossible, CPT2 gene analysis should be performed. Our study emphasizes that CPT II deficiency should be considered in the differential diagnosis of recurrent rhabdomyolysis, even if typical acylcarnitine elevation does not accompany it.

Long-term monitoring of fatty acid oxidation defects: results from a MetabERN survey

BACKGROUND

Implementation of long-chain fatty acid oxidation defects (LCFAOD) in newborn screening (NBS) programs allows for pre-symptomatic diagnosis and treatment. The long-term natural history of NBS LCFAOD patients is largely unknown and may differ from clinically diagnosed pre-NBS patients. This complicates long-term monitoring of LCFAOD and may cause high monitoring variability. To gain insight in current clinical practice, we performed a web-based questionnaire among all metabolic members of the European Reference Network for Hereditary Metabolic Disorders (MetabERN).

RESULTS

Thirty-seven colleagues representing at least 35 European metabolic centres shared their experience and results were discussed at the European Metabolic Group (EMG) meeting 2022. The centres concurred in many aspects of long-term monitoring of LCFAOD including the frequency of clinical visits, determination of laboratory parameters, cardiac monitoring and retinopathy screening. Main discrepancies comprised hepatic imaging, glucose monitoring and electrophysiological investigations.

CONCLUSIONS

Discrepancies may reflect differences in local availability of monitoring tools, the inclusion of LCFAOD in NBS programs as well as differences in local genotypes and phenotypes. Because monitoring strategies are largely based on the natural disease course of clinically identified patients, there might be over-monitoring of some NBS patients. Nevertheless, we advocate long-term monitoring because resulting information is essential to further characterize the natural disease course, develop evidence-based guidelines and provide a basis for evaluation of future therapies.

Newborn screening for fatty acid oxidation disorders in a southern Chinese population

Background and aims

Fatty acid oxidation disorders (FAODs) are a group of autosomal recessive metabolic diseases included in many newborn screening (NBS) programs, but the incidence and disease spectrum vary widely between ethnic groups. We aimed to elucidate the incidence, disease spectrum, and genetic features of FAODs in a southern Chinese population.

Materials and methods

The FAODs screening results of 643,606 newborns from 2014 to 2022 were analyzed.

Results

Ninety-two patients were eventually diagnosed with FAODs, of which 61 were PCD, 20 were MADD, 5 were SCADD, 4 were VLCADD, and 2 were CPT-IAD. The overall incidence of FAODs was 1:6996 (95 % CI: 1:5814-1:8772) newborns. All PCD patients had low C0 levels during NBS, while nine patients (14.8 %) had normal C0 levels during the recall review. All but one MADD patients had elevated C8, C10, and C12 levels during NBS, while eight patients (40 %) had normal acylcarnitine levels during the recall review. The most frequent SLC22A5 variant was c.760C > T (p.R254*) with an allele frequency of 29.51 %, followed by c.51C > G (p.F17L) (17.21 %) and c.1400C > G (p.S467C) (16.39 %). The most frequent ETFDH variant was c.250G > A (p.A84T) with an allelic frequency of 47.5 %, followed by c.524G > A (R175H) (12.5 %), c.998A > G (p.Y333C) (12.5 %), and c.1657T > C (p.Y553H) (7.5 %).

Conclusion

The prevalence, disease spectrum, and genetic characteristics of FAODs in a southern Chinese population were clarified. PCD was the most common FAOD, followed by MADD. Hotspot variants were found in SLC22A5 and ETFDH genes, while the remaining FAODs showed great molecular heterogeneity. Incorporating second-tier genetic screening is critical for FAODs.

Newborn Screening with (C16 + C18:1)/C2 and C14/C3 for Carnitine Palmitoyltransferase II Deficiency throughout Japan Has Revealed C12/C0 as an Index of Higher Sensitivity and Specificity

Carnitine palmitoyltransferase (CPT) II deficiency is a long-chain fatty acid oxidation disorder. It manifests as (1) a lethal neonatal form, (2) a hypoglycemic form, or (3) a myopathic form. The second form can cause sudden infant death and is more common among Japanese people than in other ethnic groups. Our study group had earlier used (C16 + C18:1)/C2 to conduct a pilot newborn screening (NBS) study, and found that the use of C14/C3 for screening yielded lower rates of false positivity; in 2018, as a result, nationwide NBS for CPT II deficiency started. In this study, we evaluated the utility of these ratios in 71 NBS-positive infants and found that the levels of both C14/C3 and (C16 + C18:1)/C2 in patients overlapped greatly with those of infants without the disease. Among the levels of acylcarnitines with various chain lengths (C18 to C2) and levels of free carnitine (C0) as well as their ratios of various patterns, C12/C0 appeared to be a promising index that could reduce false-positive results without missing true-positive cases detected by current indices. Although some cases of the myopathic form may go undetected even with C12/C0, its use will help prevent life-threatening onset of the hypoglycemic form of CPT II deficiency.

New Acylcarnitine Ratio as a Reliable Indicator of Long-Chain 3-Hydroxyacyl-CoA Dehydrogenase Deficiency

Long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) and mitochondrial trifunctional protein (MTP) deficiencies are rare fatal disorders of fatty acid β-oxidation with no apparent genotype-phenotype correlation. The measurement of acylcarnitines by MS/MS is a current diagnostic workup in these disorders. Nevertheless, false-positive and false-negative results have been reported, highlighting a necessity for more sensitive and specific biomarkers. This study included 54 patients with LCHAD/MTP deficiency that has been confirmed by biochemical and molecular methods. The analysis of acylcarnitines in dried blood spots was performed using ESI-MS/MS. The established "HADHA ratio" = (C16OH + C18OH + C18:1OH)/C0 was significantly elevated in all 54 affected individuals in comparison to the control group. Apart from 54 LCHAD deficiency patients, the "HADHA ratio" was calculated in 19 patients with very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiency. As VLCAD-deficient patients did not show increased "HADHA ratio", the results emphasized the high specificity of this new ratio. Therefore, the "HADHA ratio" was shown to be instrumental in improving the overall performance of MS/MS-based analysis of acylcarnitine levels in the diagnostics of LCHAD/MTP deficiencies. The ratio was demonstrated to increase the sensitivity and specificity of this method and reduce the chances of false-negative results.

Late-onset multiple acyl-CoA dehydrogenase deficiency: an insidious presentation

Multiple acyl-CoA dehydrogenase deficiency (MADD) is a rare inborn error of metabolism that results in impairment of mitochondrial β-oxidation of fatty acids. It is inherited in an autosomal recessive manner and impairs electron transfer in the electron transport chain. The clinical manifestations of MADD are highly variable and include exercise intolerance, myopathy, cardiomyopathy, encephalopathy, coma and death. Early-onset MADD is often associated with a high mortality with significant number of patients presenting with severe metabolic acidosis, non-ketotic hypoglycaemia and/or hyperammonaemic presentations. While late-onset MADD is suggested to have a lower mortality, the severe encephalopathic presentations may well be under-reported as a diagnosis of MADD may not be considered.MADD is treatable with riboflavin and appropriate nutrition with a focus on prevention and early management of metabolic decompensation. The neonatal phenotype differs significantly from late-onset MADD, where diagnosis may be delayed due to heterogeneity in clinical features, atypical presentation and confounding comorbidities, together with lower awareness among physicians.This report describes a woman in her 30s who presented with acute-onset ataxia, confusion and hyperammonaemic encephalopathy requiring intubation. Subsequent biochemical investigation revealed a diagnosis of MADD. At present, there are no national guidelines in Australia for the management of MADD. This case highlights the investigation and treatment of late-onset MADD.

Carnitine-acylcarnitine Translocase Deficiency with c.199-10T>G Mutation in Two Filipino Neonates Detected through Parental Carrier Testing

Carnitine-acylcarnitine translocase deficiency (CACTD), a fatty acid oxidation defect (FAOD), can present in the neonatal period with non-specific findings and hypoglycemia. A high index of suspicion is needed to recognize the disorder. The case is of a 24-year-old G2P2(2000) mother who sought consultation for recurrent neonatal deaths. The neonates, born two years apart, were apparently well at birth but had a fair cry and no spontaneous eye opening within the first 24 h of life and died before the 72nd hour of life. Newborn screening of both babies revealed elevated long chain acylcarnitines and hypocarnitinemia suggestive of a FAOD. However, due to their early demise, no confirmatory tests were done. Parental carrier testing was performed, revealing both parents to be heterozygous carriers of a pathogenic variant, c.199 10T>G (intronic), in the SLC25A20 gene associated with autosomal recessive CACTD. This is the first reported case of CACTD in the Filipino population.

Diverse and unselected adults with clinically relevant ACADS variants lack evidence of metabolic disease

INTRODUCTION

The clinical significance of Short-chain acyl CoA dehydrogenase deficiency (SCADD), caused by biallelic variation in the ACADS gene, is contested. Clinically ascertained individuals have a range of reported metabolic and physical symptoms. Conversely, individuals identified through newborn screening remain overwhelmingly asymptomatic. Two common ACADS variants, c.511C > T (p.Arg171Trp) and c.625G > A (p.Gly209Ser) are known to reduce enzymatic activity with undetermined clinical correlate. We applied a genome-first approach to evaluate the prevalence and clinical consequences of ACADS variants in an ancestrally diverse and unselected patient population.

MATERIAL AND METHODS

We used exome sequence data linked to electronic health records (EHRs) to identify clinically relevant ACADS variants, and estimate their prevalence and clinical implications in 27,447 ancestrally diverse and unrelated adults from the BioMe Biobank in New York, NY. We extracted International Classification of Diseases, ninth (ICD-9) and tenth (ICD-10) revision codes corresponding to eight SCADD-associated phenotypes relevant to adults from participants' EHRs. Phenotypes included intellectual disability, behavioral disorders with onset in childhood, epilepsy or seizure disorders, hypoglycemia, muscle weakness, metabolic acidosis, fatty liver, and a diagnosis of SCADD or disorder of fatty acid oxidation. We performed manual chart reviews for individuals homozygous for rare pathogenic variants. Multivariate logistic regression was used to determine the association between clinically relevant ACADS variants and phenotypes of interest.

RESULTS

1 in 10,000 BioMe participants were homozygous for rare pathogenic variants (PVs) in ACADS, 1 in 20 were homozygous or presumed compound heterozygous for common variants (CVs), and 1 in 300 harbored both a PV and a CV. Of the 2035 variant positive individuals, none had a documented diagnosis of SCADD. We identified five PV/PV positive individuals, none of whom had evidence of symptomatic SCADD on manual chart review. CV/CV positive and CV/PV positive individuals did not have increased odds of any of the eight ACADS phenotypes evaluated compared to variant negative individuals (OR for CV/CV 0.99, 95% CI 0.86-1.1, p = .88; OR for CV/PV OR 1.49, 95% CI 0.87-2.6, p = .15).

CONCLUSIONS

The prevalence of clinically relevant ACADS variants in an unselected population was higher than previously reported SCADD prevalence of 1 in 35,000 in the United States. Clinically relevant variants in ACADS were not associated with evidence of metabolic disease in a large and ancestrally diverse adult population. These findings support the assertion that SCADD is more likely a biochemical entity without clinical correlate, in particular when caused by one or more common variants.

Mitochondrial Fatty Acid β-Oxidation Disorders: From Disease to Lipidomic Studies-A Critical Review

Fatty acid oxidation disorders (FAODs) are inborn errors of metabolism (IEMs) caused by defects in the fatty acid (FA) mitochondrial β-oxidation. The most common FAODs are characterized by the accumulation of medium-chain FAs and long-chain (3-hydroxy) FAs (and their carnitine derivatives), respectively. These deregulations are associated with lipotoxicity which affects several organs and potentially leads to life-threatening complications and comorbidities. Changes in the lipidome have been associated with several diseases, including some IEMs. In FAODs, the alteration of acylcarnitines (CARs) and FA profiles have been reported in patients and animal models, but changes in polar and neutral lipid profile are still scarcely studied. In this review, we present the main findings on FA and CAR profile changes associated with FAOD pathogenesis, their correlation with oxidative damage, and the consequent disturbance of mitochondrial homeostasis. Moreover, alterations in polar and neutral lipid classes and lipid species identified so far and their possible role in FAODs are discussed. We highlight the need of mass-spectrometry-based lipidomic studies to understand (epi)lipidome remodelling in FAODs, thus allowing to elucidate the pathophysiology and the identification of possible biomarkers for disease prognosis and an evaluation of therapeutic efficacy.

Rare case of primary carnitine deficiency presenting as acute liver failure

Systemic primary carnitine deficiency (PCD) is an autosomal recessive disorder caused by mutations in the SLC22A5 gene that encodes carnitine transporter, OCTN2. Transporter deficiency leads to defective fatty acid oxidation. Signs and symptoms ranging from liver injury in children to cardiomyopathy and skeletal myopathy in adults, manifest during periods of stress and fasting. Though acute liver failure is infrequently described, young children presenting as acute liver failure should be screened for fatty acid oxidation defects including PCD by testing plasma for amino acids and further confirmed by genetic sequencing. Early identification and treatment using L-carnitine is lifesaving. Our patient presented as acute liver failure and diagnosis of PCD was confirmed by metabolic screening and genetic sequencing. He responded to the treatment.

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.

Estimating the Prevalence of Rare Diseases: Long-Chain Fatty Acid Oxidation Disorders as an Illustrative Example

Introduction

Determining the epidemiology of disease is critical for multiple reasons, including to perform risk assessment, compare disease rates in varying populations, support diagnostic decisions, evaluate health care needs and disease burden, and determine the economic benefit of treatment. However, establishing epidemiological measures for rare diseases can be difficult owing to small patient populations, variable diagnostic techniques, and potential disease and diagnostic heterogeneity. To determine the epidemiology of rare diseases, investigators often develop estimation models to account for missing or unobtainable data, and to ensure that their findings are representative of their desired patient population.

Methods

A modeling methodology to estimate the prevalence of rare diseases in one such population—patients with long-chain fatty acid oxidation disorders (LC-FAOD)—as an illustrative example of its applicability.

Results

The proposed model begins with reliable source data from newborn screening reports and applies to them key modifiers. These modifiers include changes in population growth over time and variable standardization rates of LC-FAOD screening that lead to (1) a confirmed diagnosis and (2) improvements in standards of care and survival estimates relative to the general population. The model also makes necessary assumptions to allow the broad applicability of the estimation of LC-FAOD prevalence, including rates of diagnosed versus undiagnosed patients in the USA over time.

Conclusions

Although each rare disease is unique, the approach described here and demonstrated in the estimation of LC-FAOD prevalence provides the necessary tools to calculate key epidemiological estimates useful in performing risk assessment analyses; comparing disease rates between different subgroups of people; supporting diagnostic decisions; planning health care needs; comparing disease burden, including cost; and determining the economic benefit of treatment.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12325-022-02186-2.

Newborn Screening for Mitochondrial Carnitine-Acylcarnitine Cycle Disorders in Zhejiang Province, China

Background: Disorders of mitochondrial carnitine–acylcarnitine cycle is a heterogeneous group of hereditary diseases of mitochondrial β-oxidation of fatty acids tested in NBS program in Zhejiang province, China. Large-scale studies reporting disorders of mitochondrial carnitine–acylcarnitine cycle among Chinese population in NBS are limited. The aim of this study was to explain the incidence and biochemical, clinical, and genetic characteristics of disorders of mitochondrial carnitine–acylcarnitine cycle in NBS.

Methods: From January 2009 to June 2021, 4,070,375 newborns were screened by tandem mass spectrometry. Newborns with elevated C0 levels and/or C0/(C16 + C18) ratios were identified as having CPT1D, whereas those with decreased C0 levels and/or C0/(C16 + C18) ratios and/or elevated C12-C18:1 level were identified as having CPT2D or CACTD. Suspected positive patients were further subjected to genetic analysis. All confirmed patients received biochemical and nutritional treatment, as well as follow-up sessions.

Results: Overall, 20 patients (12 with CPT1D, 4 with CPT2D, and 4 with CACTD) with disorders of mitochondrial carnitine–acylcarnitine cycle were diagnosed by NBS. The overall incidence of these disorders was one in 203,518 newborns. In toal, 11 patients with CPT1D exhibited increased C0 levels and C0/(C16 + C18) ratios. In all patients of CPT2D, all long chain acyl-carnitines levels were elevated except for case 14 having normal C12 levels. In all patients with CACTD, all long chain acyl-carnitines levels were elevated except for case 17 having normal C12, C18, and C18:1 levels. Most patients with CPT1D were asymptomatic. Overall, two of 4 patients with CPT2D did not present any clinical symptom, but other two patients died. In 4 cases with CACTD, the disease was onset after birth, and 75% patients died. In total, 14 distinct mutations were identified in CPT1A gene, of which 11 were novel and c.1910C > A (p.S637T), c.740C > T (p.P247L), and c.1328T > C (p.L443P) were the most common mutations. Overall, 3 novel mutations were identified in CPT2 gene, and the most frequent mutation was c.1711C > A (p.P571T). The most common variant in SLC25A20 gene was c.199-10T > G.

Conclusion: Disorders of mitochondrial carnitine–acylcarnitine cycle can be detected by NBS, and the combined incidence of these disorders in newborns was rare in Zhejiang province, China. Most patients presented typical acylcarnitine profiles. Most patients with CPT1D presented normal growth and development, whereas those with CPT2D/CACTD exhibited a high mortality rate. Several novel CPT1A and CPT2 variants were identified, which expanded the variant spectrum.

Whole exome sequencing analysis in a couple with three children who died prematurely due to carnitine-acylcarnitine translocase deficiency

OBJECTIVE

We investigated a strategy of exome sequencing DNA from the unaffected parents and applied a set of filtering criteria to identify genes where both partners are heterozygous for a potentially pathogenic variant.

CASE REPORT

We report a non-consanguineous couple who had three daughters, all spontaneous preterm birth at 36 weeks gestation and died in the first period after birth, suspected inborn errors of metabolism. Two days after birth, the first daughter presented with difficulty breathing, cyanosis and died; the second died at 33 days old; the third daughter was isolated under special care and was taken to the mother's room, developed the same symptoms and died after 5 days. Dried blood spot testing screen of 55 congenital metabolic disorders was negative.

CONCLUSION

Heterogenous variant in SLC25A20 gene was found in both parents, contributing to the delineations of the neonatal phenotypes related to SLC25A20 mutation in CACTD.

Spectrum Analysis of Inherited Metabolic Disorders for Expanded Newborn Screening in a Central Chinese Population

Neonatal inherited metabolic disorders (IMDs) are closely associated with early neonatal death and abnormal growth and development. Increasing attention has been paid to IMDs because of their high incidence and diversity. However, there are no reports about the incidence of IMDs in Changsha, China. Therefore, we retrospectively analyzed the screening results of neonates to evaluate the characteristics of IMDs in the area. From January 2016 to December 2020, 300,849 neonates were enrolled for expanded newborn screening by tandem mass spectrometry in the Neonatal Disease Screening Center of the Changsha Hospital for Maternal & Child Health Care. Newborns with mild initial results were recalled for repeated tests; if the second test was still positive, the patient was referred for confirmatory tests. A total of 71 confirmed cases were identified in our study, with an incidence rate of 1:4,237. There were 28 cases of amino acid metabolic disorders, representing 39.44% of the IMDs diagnosed, with an incidence rate of 1:10,745. Twelve newborns were diagnosed with organic acid metabolic disorders, accounting for 16.66% of IMDs, with an incidence rate of 1:25,071. There were 31 cases of fatty acid oxidation disorders, representing 43.05% of IMDs, with an incidence rate of 1:9,705. Overall, 14 types of IMDs were found in Changsha. The most common disorders in the region were primary carnitine deficiency, hyperphenylalaninemia and short-chain acyl-CoA dehydrogenase deficiency. Their incidence rate is respectively 1:13,675, 1:16,714 and 1:42,978. The mutations in PAH, SLC22A5, and ACADS are the leading causes of IMDs in this area. This study demonstrates the importance of utilizing MS/MS in IMD screening for early diagnosis and treatment. This strategy may be used for prenatal genetic counseling to avoid irreversible growth and intellectual development disorders in children.

Qualitative evaluation of the symptoms and quality of life impacts of long-chain fatty acid oxidation disorders

BACKGROUND

Long-chain fatty acid oxidation disorders (LC-FAOD) are a group of rare autosomal-recessive genetic disorders characterized by metabolic deficiencies in which the body is unable to convert long-chain fatty acids into energy. To date, however, there is limited understanding of the patient experience of LC-FAOD.

METHODS

The symptoms, observable signs, and quality of life (QoL) impacts associated with LC-FAOD were explored via a focus group (n = 8) and semi-structured interviews (n = 6) with patients and caregivers of patients with LC-FAOD, and interviews (n = 4) with expert clinicians. Data were analyzed via thematic analysis and summarized in a conceptual model.

RESULTS

Participants reported a wide range of signs and symptoms associated with LC-FAOD, broadly categorized as musculoskeletal, endocrine/nutritional/metabolic, neurological, gastrointestinal/digestive, sensory, cardiovascular, respiratory, urological, and constitutional. LC-FAOD were reported to have a significant impact on various aspects of patients' lives including physical functioning, participation in daily activities, emotional/psychological wellbeing, and social functioning. Lifestyle modifications (such as diet and exercise restrictions) were necessary because of the condition. Symptoms were typically episodic in presentation often arising or exacerbated during catabolic conditions such as prolonged exercise, fasting, physiological stress, and illness/infection. Symptoms were also commonly reported to lead to emergency room visits, hospitalization, and clinical complications.

CONCLUSION

LC-FAOD have a considerable impact on patients' lives. There is a high degree of concordance in the signs, symptoms, and impacts of LC-FAOD reported by patients, caregivers, and clinicians; however, there were many symptoms and impacts that were only reported by patients and caregivers, thus demonstrating that insights from patient/caregiver experience data are integral for informing medical product development and facilitating patient-centered care.

Neonatal sudden death caused by a novel heterozygous mutation in SLC25A20 gene: A case report and brief literature review

Carnitine-acylcarnitine translocase deficiency (CACTD) is a rare and life-threatening autosomal recessive disorder of fatty acid β-oxidation (FAO). Most patients with CACTD develop severe metabolic decompensation which deteriorates progressively and rapidly, causing death in infancy or childhood. As CACTD in some patients is asymptomatic or only with some nonspecific symptoms, the diagnosis is easy to be ignored, resulting in sudden death, which often triggers medical disputes. Herein, we report a case of neonatal sudden death with CACTD. The neonate showed a series of severe metabolic crisis, deteriorated rapidly and eventually died 3 days after delivery. Tandem mass spectrometry (MS-MS) screening of dry blood spots before death showed that the level of long-chain acylcarnitines, especially C12-C18 acylcarnitine, was increased significantly, and therefore a diagnosis of inherited metabolic disease (IMD) was suspected. Autopsy and histopathological results demonstrated that there were diffuse vacuoles in the heart and liver of the deceased. Mutation analysis revealed that the patient was a compound heterozygote with c.199-10 T > G and a novel c.1A > T mutation in the SLC25A20 gene. Pathological changes such as heart failure, arrhythmia and cardiac arrest related to mitochondrial FAO disorders are the direct cause of death, while gene mutation is the underlying cause of death.

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.

Hybrid Poly(AMPS-CS)-Au Microneedle Arrays to Enrich Metabolites from Skin for Early Disease Diagnosis

Recently, some metabolites in skin interstitial fluid (SIF) have become emerging re×sources for early disease diagnosis. However, their low level in SIF and difficulty to sampling are the biggest obstacle to further potential application. Here, a swellable microneedle array patch (MNAP) with high mechanical strength is presented, and the rapid enrichment of positively charged metabolites is achieved. The MNAP is fabricated by poly (chondroitin sulfate-acrylamido-2-methylpropane sulfonic acid)-gold nanoparticles (GNPs) composites via a micro-molding. The negatively charged copolymer hydrogel not only enrich positively charged metabolites, but also provide swellable capacity. The in situ synthesis of GNPs in the process of copolymerization make the GNPs cross-link to the hydrogel, which further enhance the MNAP mechanical strength and enrichment efficiency for positively charged metabolites. By using the MNAP, around 5 mg SIF in 10 min from the high fat/cholecalciferol/methimazole-induced atherogenesis rat is extracted and 23 metabolites including 13 quaternary ammonium cationic compounds can be detected and quantified by using a LC-QTOF-MS. Dysregulated L-carnitine and choline metabolism are discovered a week earlier in the SIF than in the serum, achieving early diagnosis of the metabolism syndrome disease. This MNAP also helps users complete home sampling for early disease diagnosis and monitoring.

Multiple Acyl-CoA Dehydrogenase Deficiency with Variable Presentation Due to a Homozygous Mutation in a Bedouin Tribe

Multiple acyl-CoA dehydrogenase deficiency (MADD) is a fatty acid and amino acid oxidation defect caused by a deficiency of the electron-transfer flavoprotein (ETF) or the electron-transfer flavoprotein dehydrogenase (ETFDH). There are three phenotypes of the disease, two neonatal forms and one late-onset. Previous studies have suggested that there is a phenotype-genotype correlation. We report on six patients from a single Bedouin tribe, five of whom were sequenced and found to be homozygous to the same variant in the ETFDH gene, with variable severity and age of presentation. The variant, NM_004453.3 (ETFDH): c.524G>A, p.(R175H), was previously recognized as pathogenic, although it has not been reported in the literature in a homozygous state before. R175H is located near the FAD binding site, likely affecting the affinity of FAD for EFT:QO. The single homozygous ETFDH pathogenic variant was found to be causing MADD in this cohort with an unexpectedly variable severity of presentation. The difference in severity could partly be explained by early diagnosis via newborn screening and early treatment with the FAD precursor riboflavin, highlighting the importance of early detection by newborn screening.

Novel mutation in carnitine palmitoyltransferase 1A detected through newborn screening for a presymptomatic case in China: a case report

Background

Carnitine palmitoyltransferase 1A (CPT1A) deficiency is a rare mitochondrial fatty acid oxidation (FAO) disorder that results in hypoketotic hypoglycemia and hepatic encephalopathy. It is caused by mutation in CPT1A. To date, only two symptomatic cases of CPT1A deficiency have been reported in China.

Case presentation

A newborn male, without any disease-related clinical manifestations, was diagnosed with CPT1A deficiency through newborn screening. Increased free carnitine levels and a significantly increased C0/(C16 + C18) ratio were detected by tandem mass spectrometry, and subsequently, mutations in CPT1A were found by gene sequence analysis. The patient was advised a low-fat, high-protein diet and followed up regularly. During three-years of follow-up since, the patient showed normal growth velocity and developmental milestones. Whole-exome sequence identified two mutations, c.2201 T > C (p.F734S) and c.1318G > A (p.A440T), in the patient. The c.2201 T > C mutation, which has been reported previously, was inherited from his father, while the c.1318G > A, a novel mutation, was inherited from his mother. The amino acid residues encoded by original sequences are highly conserved across different species. These mutations slightly altered the three-dimensional structure of the protein, as analyzed by molecular modeling, suggesting that they may be pathogenic.

Conclusion

This is the first case of CPT1A deficiency detected through newborn screening based on diagnostic levels of free carnitine, in China. Three years follow-up suggested that early diagnosis and diet management may improve the prognosis in CPT1A patient. In addition, we identified a novel mutation c.1318G > A in CPT1A,and a possible unique to Chinese lineage mutation c.2201 T > C. Our findings have expanded the gene spectrum of this rare condition and provided a basis for family genetic counseling and prenatal diagnosis.

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

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

Different Lipid Signature in Fibroblasts of Long-Chain Fatty Acid Oxidation Disorders

Long-chain fatty acid oxidation disorders (lc-FAOD) are a group of diseases affecting the degradation of long-chain fatty acids. In order to investigate the disease specific alterations of the cellular lipidome, we performed undirected lipidomics in fibroblasts from patients with carnitine palmitoyltransferase II, very long-chain acyl-CoA dehydrogenase, and long-chain 3-hydroxyacyl-CoA dehydrogenase. We demonstrate a deep remodeling of mitochondrial cardiolipins. The aberrant phosphatidylcholine/phosphatidylethanolamine ratio and the increased content of plasmalogens and of lysophospholipids support the theory of an inflammatory phenotype in lc-FAOD. Moreover, we describe increased ratios of sphingomyelin/ceramide and sphingomyelin/hexosylceramide in LCHAD deficiency which may contribute to the neuropathic phenotype of LCHADD/mitochondrial trifunctional protein deficiency.

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.

Inborn Errors of Mitochondrial Fatty Acid Oxidation: Overview from a Clinical Perspective

Mitochondrial fatty acid β-oxidation (mFAO), which is the major pathway for the degradation of fatty acids and is critical for maintaining energy homeostasis in the human body, consists of carnitine transport, the carnitine shuttle, and fatty acid β-oxidation. Inherited metabolic defects of mFAO result in more than 15 distinct mFAO disorders (mFAODs) with varying clinical manifestations. The common elements of the clinical presentation of mFAODs are hypoketotic hypoglycemia, (cardio)myopathy, arrhythmia, and rhabdomyolysis, indicating the importance of FAO during fasting or stressful situations. The management of all mFAODs includes avoidance of fasting, aggressive treatment during illness, and supplementation of carnitine or appropriate nutritional support, if necessary. Through the introduction of newborn screening using tandem mass spectrometry, early identification of mFAODs became feasible, leading to an early initiation of treatment with improved outcomes. However, many unmet needs remain with regard to the long-term management of patients with mFAODs.

Physiological Perspectives on the Use of Triheptanoin as Anaplerotic Therapy for Long Chain Fatty Acid Oxidation Disorders

Inborn errors of mitochondrial fatty acid oxidation (FAO) comprise the most common group of disorders identified through expanded newborn screening mandated in all 50 states in the United States, affecting 1:10,000 newborns. While some of the morbidity in FAO disorders (FAODs) can be reduced if identified through screening, a significant gap remains between the ability to diagnose these disorders and the ability to treat them. At least 25 enzymes and specific transport proteins are responsible for carrying out the steps of mitochondrial fatty acid metabolism, with at least 22 associated genetic disorders. Common symptoms in long chain FAODs (LC-FAODs) in the first week of life include cardiac arrhythmias, hypoglycemia, and sudden death. Symptoms later in infancy and early childhood may relate to the liver or cardiac or skeletal muscle dysfunction, and include fasting or stress-related hypoketotic hypoglycemia or Reye-like syndrome, conduction abnormalities, arrhythmias, dilated or hypertrophic cardiomyopathy, and muscle weakness or fasting- and exercise-induced rhabdomyolysis. In adolescent or adult-onset disease, muscular symptoms, including rhabdomyolysis, and cardiomyopathy predominate. Unfortunately, progress in developing better therapeutic strategies has been slow and incremental. Supplementation with medium chain triglyceride (MCT; most often a mixture of C8–12 fatty acids containing triglycerides) oil provides a fat source that can be utilized by patients with long chain defects, but does not eliminate symptoms. Three mitochondrial metabolic pathways are required for efficient energy production in eukaryotic cells: oxidative phosphorylation (OXPHOS), FAO, and the tricarboxylic (TCA) cycle, also called the Krebs cycle. Cell and mouse studies have identified a deficiency in TCA cycle intermediates in LC-FAODs, thought to be due to a depletion of odd chain carbon compounds in patients treated with a predominantly MCT fat source. Triheptanoin (triheptanoyl glycerol; UX007, Ultragenyx Pharmaceuticals) is chemically composed of three heptanoate (seven carbon fatty acid) molecules linked to glycerol through ester bonds that has the potential to replete TCA cycle intermediates through production of both acetyl-CoA and propionyl-CoA through medium chain FAO. Compassionate use, retrospective, and recently completed prospective studies demonstrate significant reduction of hypoglycemic events and improved cardiac function in LC-FAOD patients, but a less dramatic effect on muscle symptoms.

Management Principles for Acute Illness in Patients With Medium-Chain Acyl-Coenzyme A Dehydrogenase Deficiency

Medium-chain acyl-coenzyme A dehydrogenase deficiency (MCADD) is a fatty acid oxidation disorder in which the patient is unable to break down fats to produce energy. This disorder places children at risk for metabolic decompensation during periods of stress, such as routine childhood illnesses. The intent of this clinical report is to provide pediatricians with additional information regarding the acute clinical care of patients with MCADD. Although each patient with MCADD will still be expected to have a primary metabolic physician, the involvement of the primary care provider is crucial as well. Appropriate treatment of children with MCADD can lead to avoidance of morbidity and mortality.

Three Novel and One Potential Hotspot CPT1A Variants in Chinese Patients With Carnitine Palmitoyltransferase 1A Deficiency

Carnitine palmitoyltransferase 1A (CPT1A) deficiency is an inherited disorder of mitochondrial fatty acid β-oxidation that impairs fasting ketogenesis and gluconeogenesis in the liver. Few studies implementing newborn screening (NBS) for CPT1A deficiency in the Chinese population have been reported. This study aimed to determine the biochemical, clinical, and genetic characteristics of patients with CPT1A deficiency in China. A total of 204,777 newborns were screened using tandem mass spectrometry at Quanzhou Maternity and Children's Hospital between January 2017 and December 2018. Newborns with elevated C0 levels were recruited, and suspected patients were subjected to further genetic analysis. Additionally, all Chinese patients genetically diagnosed with CPT1A deficiency were reviewed and included in the study. Among the 204,777 screened newborns, two patients were diagnosed with CPT1A deficiency; thus, the estimated incidence in the selected population was 1:102,388. In addition to the two patients newly diagnosed with CPT1A deficiency, we included in our cohort 10 Chinese patients who were previously diagnosed. Five of these 12 patients were diagnosed via NBS. All patients exhibited elevated C0 and/or C0/(C16+C18) ratios. No clinical symptoms were observed in the five patients diagnosed via NBS, while all seven patients presented with clinical symptoms, including fever, cough, vomiting, diarrhea, and seizures. Eighteen distinct CPT1A variants were identified, 15 of which have been previously reported. The three novel variants were c.272T>C (p.L91P), c.734G>A (p.R245Q), and c.1336G>A (p.G446S). in silico analysis suggested that all three novel variants were potentially pathogenic. The most common variant was c.2201T>C (p.F734S), with an allelic frequency of 16.67% (4/24). Our findings demonstrated that NBS for CPT1A deficiency is beneficial. The three novel variants expand the mutational spectrum of CPT1A in the Chinese population, and c.2201T>C (p.F734S) may be a potential hotspot CPT1A mutation.

Clinical manifestations and management of fatty acid oxidation disorders

Fatty acid oxidation disorders (FAOD) are a group of rare, autosomal recessive, metabolic disorders caused by variants of the genes for the enzymes and proteins involved in the transport and metabolism of fatty acids in the mitochondria. Those affected by FAOD are unable to convert fatty acids into tricarboxylic acid cycle intermediates such as acetyl-coenzyme A, resulting in decreased adenosine triphosphate and glucose for use as energy in a variety of high-energy-requiring organ systems. Signs and symptoms may manifest in infants but often also appear in adolescents or adults during times of increased metabolic demand, such as fasting, physiologic stress, and prolonged exercise. Patients with FAOD present with a highly heterogeneous clinical spectrum. The most common clinical presentations include hypoketotic hypoglycemia, liver dysfunction, cardiomyopathy, rhabdomyolysis, and skeletal myopathy, as well as peripheral neuropathy and retinopathy in some subtypes. Despite efforts to detect FAOD through newborn screening and manage patients early, symptom onset can be sudden and serious, even resulting in death. Therefore, it is critical to identify quickly and accurately the key signs and symptoms of patients with FAOD to manage metabolic decompensations and prevent serious comorbidities.

Anesthesia management in a patient with very long-chain acyl-Coenzyme A dehydrogenase deficiency

Background

In a patient with very long-chain acyl-Coenzyme A dehydrogenase (VLCAD) deficiency, metabolism of fatty acids is impaired and a supply of alternative energy is limited when glucose level is insufficient on starvation.

Case presentation

A 37-year-old woman with VLCAD deficiency was diagnosed with an ovarian cyst and was scheduled for laparoscopic ovarian cystectomy. Glucose was administered intravenously with the start of fasting. Anesthesia was induced with remifentanil, midazolam, and thiamylal, maintained with desflurane and remifentanil. Body temperature was maintained at 36.2–36.7 °C. During anesthesia, hypoglycemia did not occur, creatine kinase levels were in the normal range, and myoglobinuria was not detected. No shivering was observed after extubation.

Conclusions

Glucose was administered to avoid perioperative hypoglycemia. Body temperature was controlled to avoid shivering, which would otherwise increase skeletal muscle energy needs. Blood creatine kinase did not increase, and myoglobinuria was not detected; thus, rhabdomyolysis was unlikely to develop.

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.

Diagnosis, genetic characterization and clinical follow up of mitochondrial fatty acid oxidation disorders in the new era of expanded newborn screening: A single centre experience

Introduction

Mitochondrial fatty acid oxidation disorders (FAODs) are a heterogeneous group of hereditary autosomal recessive diseases included in newborn screening (NBS) program in Italy. The aim of this study was to analyse FAODs cases, identified either clinically or by NBS,for clinical and genetic characterization and to evaluate a five years' experience of NBS, in the attempt to figure out the complexity of genotype-phenotype correlation and to confirm the clinical impact of NBS in our centre experience.

Materials and methods

We analysed FAODs patients diagnosed either by NBS or clinically, followed since February 2014 to April 2019 at the Regional Screening Centre and Inherited Metabolic Diseases Unit of Verona. Diagnosis was confirmed by plasma acylcarnitines, urinary organic acids, enzymatic and genetic testing. For not clear genotypes due to the presence of variants of uncertain significance, in silico predictive tools have been used as well as enzymatic activity assays. Patients underwent clinical, nutritional and biochemical follow up.

Results

We diagnosed 30 patients with FAODs. 20 by NBS: 3 CUD, 6 SCADD, 5 MCADD, 4 VLCADD, 2 MADD. Overall incidence of FAODs diagnosed by NBS was 1:4316 newborns. No one reported complications during the follow up period. 10 patients were diagnosed clinically: 2 CUD, 2 CPT2D, 1 VLCADD, 5 MADD. Mean age at diagnosis was 29.3 years. Within this group, complications or symptoms were reported at diagnosis, but not during follow-up. 12 mutations not previously reported in literature were found, all predicted as pathogenic or likely pathogenic.

Discussion and conclusions

Our study highlighted the great phenotypic variability and molecular heterogeneity of FAODs and confirmed the importance of a tailored follow up and treatment. Despite the short duration of follow up, early identification by NBS prevented diseases related complications and resulted in normal growth and psycho-motor development as well.

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Early identification by newborn screening prevents disease related complications.

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Newborn screening is changing prevalence clinical and molecular heterogeneity of FAODs.

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Genotype-phenotype correlation helps to achieve personalized follow-up and treatment.

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Enzymatic assay may be pivotal in predicting phenotype and symptoms severity.

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Diagnosis on clinical grounds is anyway important to change disease course.

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.

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.

Genetic characteristics and follow-up of patients with fatty acid β-oxidation disorders through expanded newborn screening in a Northern Chinese population

Background Fatty acid β-oxidation disorders (FAODs) include more than 15 distinct disorders and have a wide variety of symptoms, usually not evident between episodes of acute decompensation. After the introduction of newborn screening (NBS) using tandem mass spectrometry (MS/MS), early identification of FAODs has become feasible. We analyzed the MS/MS results in Tianjin, China during a six-year period to evaluate the incidence, disease spectrum, and genetic characteristics of FAODs. Methods We analyzed the MS/MS results for screening FAODs from May 2013 to December 2018 in Tianjin, China. Infants with positive screening results were confirmed through next-generation sequencing and validated by Sanger sequencing. Results A total of 220,443 infants were screened and 25 FAODs patients were identified (1:8,817). Primary carnitine deficiency (PCD) with an incidence rate up to 1:20,040 was the most common disorder among all FAODs. Recurrent mutations of relatively common diseases, like PCD and short-chain acyl-CoA dehydrogenase deficiency (SCADD), were identified. During the follow-up, two patients suffered from sudden death due to carnitine palmitoyl transferase-Ⅱ deficiency (CPT Ⅱ) and very-long-chain acyl-CoA dehydrogenase deficiency (VLCAD). Conclusion Our data indicated that FAODs are relatively common in Tianjin and may even cause infant death in certain cases. The elucidated disease spectrum and genetic backgrounds elucidated in this study may contribute to the treatment and prenatal genetic counseling of FAODs.

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.

Sex-specific perturbation of complex lipids in response to medium-chain fatty acids in very long-chain acyl-CoA dehydrogenase deficiency

Very-long-chain acyl-CoA dehydrogenase deficiency (VLCAD) is the most common defect of long-chain fatty acid β-oxidation. The recommended treatment includes the application of medium-chain triacylglycerols (MCTs). However, long-term treatment of VLCAD^-/- mice resulted in the development of a sex-specific metabolic syndrome due to the selective activation of the ERK/mTORc1 signalling in females and ERK/peroxisome proliferator-activated receptor gamma pathway in males. In order to investigate a subsequent sex-specific effect of MCT on the lipid composition of the cellular membranes, we performed lipidomic analysis, SILAC-based quantitative proteomics and gene expression in fibroblasts from WT and VLCAD^-/- mice of both sexes. Treatment with octanoate (C8) affected the composition of complex lipids resulting in a sex-specific signature of the molecular profile. The content of ceramides and sphingomyelins in particular differed significantly under control conditions and increased markedly in cells from mutant female mice but remained unchanged in cells from mutant males. Moreover, we observed a specific upregulation of biosynthesis of plasmalogens only in male mice, whereas in females C8 led to the accumulation of higher concentration of phosphatidylcholines and lysophosphatidylcholines. Our data on membrane lipids in VLCAD after supplementation with C8 provide evidence of a sex-specific lipid perturbation. We hypothesize a likely C8-induced pro-inflammatory response contributing to the development of a severe metabolic syndrome in female VLCAD^-/- mice on long-term MCT supplementation.

Understanding the role of OXPHOS dysfunction in the pathogenesis of ECHS1 deficiency

Mitochondria provide the main source of energy for eukaryotic cells, oxidizing fatty acids and sugars to generate ATP. Mitochondrial fatty acid β-oxidation (FAO) and oxidative phosphorylation (OXPHOS) are two key pathways involved in this process. Disruption of FAO can cause human disease, with patients commonly presenting with liver failure, hypoketotic glycaemia and rhabdomyolysis. However, patients with deficiencies in the FAO enzyme short-chain enoyl-CoA hydratase 1 (ECHS1) are typically diagnosed with Leigh syndrome, a lethal form of subacute necrotizing encephalomyelopathy that is normally associated with OXPHOS dysfunction. Furthermore, some ECHS1-deficient patients also exhibit secondary OXPHOS defects. This sequela of FAO disorders has long been thought to be caused by the accumulation of inhibitory fatty acid intermediates. However, new evidence suggests that the mechanisms involved are more complex, and that disruption of OXPHOS protein complex biogenesis and/or stability is also involved. In this review, we examine the clinical, biochemical and genetic features of all ECHS1-deficient patients described to date. In particular, we consider the secondary OXPHOS defects associated with ECHS1 deficiency and discuss their possible contribution to disease pathogenesis.

Mass Spectrometric Analysis of L-carnitine and its Esters: Potential Biomarkers of Disturbances in Carnitine Homeostasis

PURPOSE

After a golden age of classic carnitine research three decades ago, the spread of mass spectrometry opened new perspectives and a much better understanding of the carnitine system is available nowadays. In the classic period, several human and animal studies were focused on various distinct physiological functions of this molecule and these revealed different aspects of carnitine homeostasis in normal and pathological conditions. Initially, the laboratory analyses were based on the classic or radioenzymatic assays, enabling only the determination of free and total carnitine levels and calculation of total carnitine esters' amount without any information on the composition of the acyl groups. The introduction of mass spectrometry allowed the measurement of free carnitine along with the specific and sensitive determination of different carnitine esters. Beyond basic research, mass spectrometry study of carnitine esters was introduced into the newborn screening program because of being capable to detect more than 30 metabolic disorders simultaneously. Furthermore, mass spectrometry measurements were performed to investigate different disease states affecting carnitine homeostasis, such as diabetes, chronic renal failure, celiac disease, cardiovascular diseases, autism spectrum disorder or inflammatory bowel diseases.

RESULTS

This article will review the recent advances in the field of carnitine research with respect to mass spectrometric analyses of acyl-carnitines in normal and various pathological states.

CONCLUSION

The growing number of publications using mass spectrometry as a tool to investigate normal physiological conditions or reveal potential biomarkers of primary and secondary carnitine deficiencies shows that this tool brought a new perspective to carnitine research.

Oxidative damage in mitochondrial fatty acids oxidation disorders patients and the in vitro effect of l-carnitine on DNA damage induced by the accumulated metabolites

BACKGROUND

The mitochondrial fatty acids oxidation disorders (FAOD) are inherited metabolic disorders (IMD) characterized by the accumulation of fatty acids of different sizes of chain according to the affected enzyme.

METHODS

This study evaluated the lipid peroxidation by the measurement of 8-isoprostanes, nitrosative stress parameters by the measurement of nitrite and nitrate content and DNA and RNA oxidative damage by the measurement of oxidized guanine species in urine samples from long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD), medium-chain acyl-CoA dehydrogenase deficiency (MCADD) and multiple acyl-CoA dehydrogenase deficiency (MADD) patients. Also, we analyzed the in vitro DNA damage by comet assay induced by adipic acid, suberic acid, hexanoylglycine and suberylglycine, separated and in combination, as well as the effect of l-carnitine in human leukocytes.

RESULTS

An increase on 8-isoprostanes levels in all groups of patients was observed. The nitrite and nitrate levels were increased in LCHADD patients. DNA and RNA damage evaluation revealed increase on oxidized guanine species levels in LCHADD and MADD patients. The in vitro evaluation revealed an increase on the DNA damage induced by all metabolites, besides a potencialyzed effect. l-carnitine decreased the DNA damage induced by the metabolites.

CONCLUSION

These results demonstrate that toxic metabolites accumulated could be related to the increased oxidative and nitrosative stress of FAOD patients and that the metabolites, separated and in combination, cause DNA damage, which was reduced by l-carnitine, demonstrating antioxidant protection.

GENERAL SIGNIFICANCE

This work demonstrated oxidative stress in FAOD patients and the genotoxic potential of MCADD metabolites and the protective effect of l-carnitine.