Biochemical, molecular, and clinical characteristics of children with short chain acyl-CoA dehydrogenase deficiency detected by newborn screening in California

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.

Diagnostic and Prognostic Performance of Metabolic Signatures in Pancreatic Ductal Adenocarcinoma: The Clinical Application of Quantitative NextGen Mass Spectrometry

With 64,050 new diagnoses and 50,550 deaths in the US in 2023, pancreatic ductal adenocarcinoma (PDAC) is among the most lethal of all human malignancies. Early detection and improved prognostication remain critical unmet needs. We applied next-generation metabolomics, using quantitative tandem mass spectrometry on plasma, to develop biochemical signatures that identify PDAC. We first compared plasma from 10 PDAC patients to 169 samples from healthy controls. Using metabolomic algorithms and machine learning, we identified ratios that incorporate amino acids, biogenic amines, lysophosphatidylcholines, phosphatidylcholines and acylcarnitines that distinguished PDAC from normal controls. A confirmatory analysis then applied the algorithms to 30 PDACs compared with 60 age- and sex-matched controls. Metabolic signatures were then analyzed to compare survival, measured in months, from date of diagnosis to date of death that identified metabolite ratios that stratified PDACs into distinct survival groups. The results suggest that metabolic signatures could provide PDAC diagnoses earlier than tumor markers or radiographic measures and offer insights into disease severity that could allow more judicious use of therapy by stratifying patients into metabolic-risk subgroups.

Primary carnitine deficiency: Estimation of prevalence in Chinese population and insights into newborn screening

Primary carnitine deficiency (PCD) caused by pathogenic variants in the solute carrier family 22 member 5 (SLC22A5) gene is a rare autosomal recessive disease that results in defective fatty acid oxidation. PCD can be detected through tandem mass spectrometry (MS/MS), but transplacental transport of free carnitine from mothers may cause false negatives or positives during newborn screening (NBS). This study aimed to analyze the genetic characteristics of SLC22A5 and estimate the prevalence of PCD in the Chinese population, providing useful information for NBS and genetic counseling. We manually curated SLC22A5 pathogenic or likely pathogenic (P/LP) variants according to the American College of Medical Genetics and Genomics (ACMG) guidelines and identified 128 P/LP variants. Based on the China Neonatal Genomes Project (CNGP), the estimated PCD prevalence was 1:17,456, which was higher than that in other populations. The genotype-phenotype association analysis showed that patients carrying homozygous c.760C>T and c.844C>T were more likely to present cardiomyopathy, whereas those carrying homozygous c.1400C>G were more likely to be asymptomatic (all p-values < 0.05). We found that there was no significant difference in initial C0 concentrations between patients and carriers, but there was a significant difference in the second-tier screening of C0 concentration between them (p-value < 0.05). We established a cost-effective variant panel containing 10 high-frequency sites and developed a screening algorithm incorporating gene panels with MS/MS, which could rescue one more patient who was undetected from MS/MS. In conclusion, the prevalence of PCD in the Chinese population is relatively high. The combination of conventional NBS with genetic sequencing is suggested for early diagnosis of PCD.

The Physiological and Pathological Role of Acyl-CoA Oxidation

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

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

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

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.

Reproductive genetic carrier screening and inborn errors of metabolism: The voice of the inborn errors of metabolism community needs to be heard

Reproductive genetic carrier screening (RGCS) has a history spanning more than 50 years, but for most of that time has been limited to screening for one or a few conditions in targeted population groups. The advent of massively parallel sequencing has led to rapid growth in screening for panels of up to hundreds of genes. Such panels typically include numerous genes associated with inborn errors of metabolism (IEM). There are considerable potential benefits for families from screening, but there are also risks and potential pitfalls. The IEM community has a vital role to play in guiding gene selection and assisting with the complexities that arise from screening, including interpreting complex biochemical assays and counselling at-risk couples about phenotypes and treatments.

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

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

Accelerating the genetic diagnosis of neurological disorders presenting with episodic apnoea in infancy

Unexplained episodic apnoea in infants (aged ≤1 year), including recurrent brief (<1 min) resolved unexplained events (known as BRUE), can be a diagnostic challenge. Recurrent unexplained apnoea might suggest a persistent, debilitating, and potentially fatal disorder. Genetic diseases are prevalent among this group, particularly in those who present with paroxysmal or episodic neurological symptoms. These disorders are individually rare and challenging for a general paediatrician to recognise, and there is often a delayed or even posthumous diagnosis (sometimes only made in retrospect when a second sibling becomes unwell). The disorders can be debilitating if untreated but pharmacotherapies are available for the vast majority. That any child should suffer from unnecessary morbidity or die from one of these disorders without a diagnosis or treatment having been offered is a tragedy; therefore, there is an urgent need to simplify and expedite the diagnostic journey. We propose an apnoea gene panel for hospital specialists caring for any infant who has recurrent apnoea without an obvious cause. This approach could remove the need to identify individual rare conditions, speed up diagnosis, and improve access to therapy, with the ultimate aim of reducing morbidity and mortality.

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.

Clinical characteristics and related gene mutations of infants with short-chain acyl-CoA dehydrogenase deficiency by neonatal screening in Beijing

OBJECTIVE

To investigate the clinical characteristics of infants with short-chain acyl-CoA dehydrogenase deficiency (SCADD) and related gene mutations in Beijing.

METHODS

The acylcarnitine levels in the blood samples of 100 603 neonates in Beijing during August 2014 and March 2022 were measured by tandem mass spectrometry (MS/MS). The suspected SCADD neonates were rechecked by MS/MS, urine gas chromatography-mass spectrometry (GC/MS) and next-generation sequencing (NGS) for diagnosis. The clinical, biochemical and gene mutation characteristics of infants with SCADD were analyzed; the growth and intellectual development of these patients were observed regularly.

RESULTS

Among 100 603 live births, the elevated C4 concentration or elevated C4/C3 ratio were detected in the initial screening from 196 neonates, and 131 were recalled. Five cases of SCADD were diagnosed with an incidence rate of 4.97/100 000 (1/20 121). There was no significant abnormality in clinical manifestations, however, the blood butyrylcarnitine (C4) level and the ratio of C4 to propionylcarnitine (C3) were raised in all diagnosed cases. Urinary organic acids were analyzed in 4 cases, all of whom had increased ethyl malonate acid levels. Seven mutations were detected in the ACADS gene, all of which were known missense mutations. One patient had homozygous mutation, and the others showed compound heterozygous mutations. No clinical symptoms were observed, and the physical and intellectual development was normal in all patients at a median age of 33 (4-40) months during follow-up.

CONCLUSIONS

The incidence rate of SCADD was 1/20 121 in Beijing. Neonates with early diagnosis and without clinical symptoms usually have good prognosis.

Phenotype, genotype and long-term prognosis of 40 Chinese patients with isobutyryl-CoA dehydrogenase deficiency and a review of variant spectra in ACAD8

Background

Isobutyryl-CoA dehydrogenase deficiency (IBDD) is a rare autosomal recessive metabolic disorder resulting from variants in ACAD8, and is poorly understood, as only dozens of cases have been reported previously. Based on a newborn screening program, we evaluated the incidence, phenotype and genotype of IBDD as well as the prognosis. Moreover, we reviewed the variant spectrum in ACAD8 associated with IBDD.

Methods

Forty unrelated patients with IBDD were retrospectively screened for newborns between Jan 2012 and Dec 2020. Tandem mass spectrometry (MS/MS) was used to determine the concentrations of C4-acylcarnitine, C4/C2 (acetylcarnitine), and C4/C3 (propionylcarnitine). All suspected cases were genetically tested by metabolic genes panel.

Results

The incidence of IBDD here was 1: 62,599. All patients presented continuously elevated C4-acylcarnitine levels with higher ratios of C4/C2 and C4/C3. Isobutyrylglycine occurred in only 8 patients. During follow-up, four patients had a transient motor delay, and two patients had growth delay. Notably, one case harbored both ACAD8 compound heterozygous variants and a KMT2A de novo variant (c.2739del, p.E914Rfs*35), with IBDD and Wiedemann–Steiner syndrome together, had exact severe global developmental delay. All patients were regularly monitored once they were diagnosed, and each patient gradually had a normal diet after 6 months of age. After 3–108 months of follow-up, most individuals were healthy except the case harboring the KMT2A variant. A total of 16 novel variants in ACAD8, c.4_5delCT, c.109C > T, c.110–2A > T, c.236G > A, c.259G > A, c.381–14G > A, c.413delA, c.473A > G, c.500delG, c.758 T > G, c.842–1G > A, c.911A > T, c.989G > A, c.1150G > C, c.1157A > G and c.1165C > T, were identified. Along with a literature review on 51 ACAD8 variants in 81 IBDD patients, we found that the most common variant was c.286G > A (27.2%), which has been observed solely in the Chinese population to date, followed by c.1000C > T (8.6%), c.1176G > T (3.7%) and c.455 T > C (3.1%).

Conclusion

The concentration of C4-acylcarnitine in NBS plus subsequent genetic testing is necessary for IBDD diagnosis. Both the genotypes and ACAD8 variants in IBDD are highly heterogeneous, and no significant correlations between genotype and phenotype are present here in patients with IBDD. Our IBDD cohort with detaied clinical characteristics, genotypes and long-term prognosis will be helpful for the diagnosis and management of patients with IBDD in the future.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-02018-6.

Newborn Screening and Genetic Analysis Identify Six Novel Genetic Variants for Primary Carnitine Deficiency in Ningbo Area, China

Primary carnitine deficiency (PCD) is an autosomal recessive disorder that could result in sudden death. It is caused by a defect in the carnitine transporter encoded by SLC22A5 (Solute Carrier Family 22 Member 5, MIM:603377). Currently, a number of variants in SLC22A5 have been identified, however, the PCD prevalence and its variants in Ningbo area are unclear. In this study, we screened 265,524 newborns by using tandem mass spectrometry. Variants in SLC22A5 were further detected by next-generation sequencing in individuals with abnormal free carnitine levels (C0). We identified 53 newborns with abnormal C0 levels and 26 with variants in SLC22A5. Among them, 16 with compound heterozygous or homozygous variants in SLC22A5 were diagnosed with PCD, suggesting the PCD birth prevalence in Ningbo city was 1/16,595. Moreover, the C0 level was significantly (P = 0.013) higher in PCD patients than in those with one variant. Besides, the c.1400C > G (p. S467C) and c.51C > G (p. F17L) variants were the most frequent and six novel variants are all predicted to be damaging. This study reports the largest PCD patients in Ningbo area by newborn screening and expands the variant spectrum of SLC22A5. Our findings demonstrate the clinical value of combining NBS program results with DNA analysis for the diagnosis of PCD.

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.

The role of exome sequencing in newborn screening for inborn errors of metabolism

Public health newborn screening (NBS) programs provide population-scale ascertainment of rare, treatable conditions that require urgent intervention. Tandem mass spectrometry (MS/MS) is currently used to screen newborns for a panel of rare inborn errors of metabolism (IEMs)1-4. The NBSeq project evaluated whole-exome sequencing (WES) as an innovative methodology for NBS. We obtained archived residual dried blood spots and data for nearly all IEM cases from the 4.5 million infants born in California between mid-2005 and 2013 and from some infants who screened positive by MS/MS, but were unaffected upon follow-up testing. WES had an overall sensitivity of 88% and specificity of 98.4%, compared to 99.0% and 99.8%, respectively for MS/MS, although effectiveness varied among individual IEMs. Thus, WES alone was insufficiently sensitive or specific to be a primary screen for most NBS IEMs. However, as a secondary test for infants with abnormal MS/MS screens, WES could reduce false-positive results, facilitate timely case resolution and in some instances even suggest more appropriate or specific diagnosis than that initially obtained. This study represents the largest, to date, sequencing effort of an entire population of IEM-affected cases, allowing unbiased assessment of current capabilities of WES as a tool for population screening.

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.

Neonatal Screening on Tandem Mass Spectrometry as a Powerful Tool for the Reassessment of the Prevalence of Underestimated Diseases in Newborns and Their Family Members: A Focus on Short Chain Acyl-CoA Dehydrogenase Deficiency

Early detection of disabling diseases, prior to clinical manifestations, is the primary goal of newborn screening (NS). Indeed, the required number of core and secondary conditions selected for screening panels is increasing in many countries. Furthermore, newborn screening can lead to diagnosis of maternal diseases such as vitamin B12 deficiency or 3-MethylcrotonylCoA-carboxylase deficiency (3MCC). NS became mandatory in Sicily in December 2017. Here we report NS data collected between December 2017 and April 2020. Our results show that tandem mass spectrometry is a powerful tool for discovery of underestimated disease in newborns and their family members. Our panel included short chain acyl-CoA dehydrogenase deficiency (SCADD). Here, we report that results of our investigation led to reassessment of SCADD prevalence in our population. The infant and adult patients diagnosed in our study had previously not shown overt symptoms.

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.

Genomic Analysis of Historical Cases with Positive Newborn Screens for Short-Chain Acyl-CoA Dehydrogenase Deficiency Shows That a Validated Second-Tier Biochemical Test Can Replace Future Sequencing

Short-chain acyl-CoA dehydrogenase deficiency (SCADD) is a rare autosomal recessive disorder of β-oxidation caused by pathogenic variants in the ACADS gene. Analyte testing for SCADD in blood and urine, including newborn screening (NBS) using tandem mass spectrometry (MS/MS) on dried blood spots (DBSs), is complicated by the presence of two relatively common ACADS variants (c.625G>A and c.511C>T). Individuals homozygous for these variants or compound heterozygous do not have clinical disease but do have reduced short-chain acyl-CoA dehydrogenase (SCAD) activity, resulting in elevated blood and urine metabolites. As part of a larger study of the potential role of exome sequencing in NBS in California, we reviewed ACADS sequence and MS/MS data from DBSs from a cohort of 74 patients identified to have SCADD. Of this cohort, approximately 60% had one or more of the common variants and did not have the two rare variants, and thus would need no further testing. Retrospective analysis of ethylmalonic acid, glutaric acid, 2-hydroxyglutaric acid, 3-hydroxyglutaric acid, and methylsuccinic acid demonstrated that second-tier testing applied before the release of the newborn screening result could reduce referrals by over 50% and improve the positive predictive value for SCADD to above 75%.

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.

Increased parental anxiety and a benign clinical course: Infants identified with short-chain acyl-CoA dehydrogenase deficiency and isobutyryl-CoA dehydrogenase deficiency through newborn screening in Georgia

The long-term consequences and need for therapy in children with short-chain acyl-CoA dehydrogenase deficiency (SCADD) or isobutyryl-CoA dehydrogenase deficiency (IBDD) identified via newborn screening (NBS) remains controversial. Initial clinical descriptions were severe; however, while most cases identified through NBS have remained asymptomatic, clinical concerns have been raised in these populations. It is not clear whether these children are asymptomatic because of the success of NBS, or because the normal clinical course of these disorders is relatively benign. To evaluate these possibilities in our program, we evaluated the clinical outcomes of children with SCADD or IBDD identified by the Georgia NBS compared to the health status of a healthy age-matched control group. We also assessed parental anxiety during a phone interview both subjectively and objectively using the Pediatric Inventory for Parents (PIP), a validated measure of illness-related parental stress. The general health of 52 SCADD and nine IBDD cases from 2007 to 2016 were compared to the general health of unaffected control children obtained through the Centers for Disease Control and Prevention (CDC) parent listserv. We also collected statements from parents who participated in a phone survey regarding events they experienced during and after their diagnostic process. Overall, the children with SCADD and IBDD had no major health problems. There was no significant difference in cognitive development (p = .207). We identified a slightly higher incidence of reported neonatal hypoglycemia in the SCADD group; two of these occurred in the context of maternal diabetes. All interviewed parents reported extreme anxiety during the diagnostic period and current feelings of uncertainty about their child's future. PIP scores for all six caregivers who responded to that portion of the survey were consistent with some degree of parental stress. The greatest reported stressor was the unknown long-term impact of the illness. All children with SCADD and IBDD had no significant long-term sequelae. The phone interviews revealed substantial parental anxiety about the identification and follow-up of SCADD and IBDD. Based on our findings, the anxiety parents experience may be unwarranted given that we see no disease-associated morbidity or mortality in these children. Consideration should be given to the removal of these conditions from NBS panels, or if that is not possible, clinicians could educate parents on the benign nature of these diagnoses and release them from follow-up without treatment.

Expanded Newborn Screening for Inborn Errors of Metabolism by Tandem Mass Spectrometry in Suzhou, China: Disease Spectrum, Prevalence, Genetic Characteristics in a Chinese Population

Expanded newborn screening for inborn errors of metabolism (IEMs) by tandem mass spectrometry (MS/MS) could simultaneously analyze more than 40 metabolites and identify about 50 kinds of IEMs. Next generation sequencing (NGS) targeting hundreds of IMEs-associated genes as a follow-up test in expanded newborn screening has been used for genetic analysis of patients. The spectrum, prevalence, and genetic characteristic of IEMs vary dramatically in different populations. To determine the spectrum, prevalence, and gene mutations of IEMs in newborns in Suzhou, China, 401,660 newborns were screened by MS/MS and 138 patients were referred to genetic analysis by NGS. The spectrum of 22 IEMs were observed in Suzhou population of newborns, and the overall incidence (excluding short chain acyl-CoA dehydrogenase deficiency (SCADD) and 3-Methylcrotonyl-CoA carboxylase deficiency (3-MCCD)) was 1/3,163. The prevalence of each IEM ranged from 1/401,660 to 1/19,128, while phenylketonuria (PKU) (1/19,128) and Mild hyperphenylalaninemia (M-HPA) (1/19,128) were the most common IEMs, followed by primary carnitine uptake defect (PCUD) (1/26,777), SCADD (1/28,690), hypermethioninemia (H-MET) (1/30,893), 3-MCCD (1/33,412) and methylmalonic acidemia (MMA) (1/40,166). Moreover, 89 reported mutations and 51 novel mutations in 25 IMEs-associated genes were detected in 138 patients with one of 22 IEMs. Some hotspot mutations were observed for ten IEMs, including PAH gene c.728G > A, c.611A > G, and c.721C > T for Phenylketonuria, PAH gene c.158G > A, c.1238G > C, c.728G > A, and c.1315+6T > A for M-HPA, SLC22A5 gene c.1400C > G, c.51C > G, and c.760C > T for PCUD, ACADS gene c.1031A > G, c.164C > T, and c.1130C > T for SCAD deficiency, MAT1A gene c.791G > A for H-MET, MCCC1 gene c.639+2T > A and c.863A > G for 3-MCCD, MMUT gene c.1663G > A for MMA, SLC25A13 gene c.IVS16ins3Kb and c.852_855delTATG for cittrullinemia II, PTS gene c.259C > T and c.166G > A for Tetrahydrobiopterin deficiency, and ACAD8 gene c.1000C > T and c.286C > A for Isobutyryl coa dehydrogenase deficiency. All these hotspot mutations were reported to be pathogenic or likely pathogenic, except a novel mutation of ACAD8 gene c.286C > A. These mutational hotspots could be potential candidates for gene screening and these novel mutations expanded the mutational spectrum of IEMs. Therefore, our findings could be of value for genetic counseling and genetic diagnosis of IEMs.

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.

Fatty acid oxidation disorders

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

Clinical, biochemical and genetic analysis of Chinese patients with isobutyryl-CoA dehydrogenase deficiency

Isobutyryl-CoA dehydrogenase deficiency (IBDHD) is a rare autosomal recessive metabolic disorder related to valine catabolism and results from variants in ACAD8. Here, we present the clinical, biochemical, and genotypes of seven patients with IBDHD in China for the first time. Five patients remained asymptomatic during follow-up, whereas one juvenile had speech delay and one newborn exhibited clinical symptoms. All patients showed remarkably increased concentrations of C4-aclycarnitine with elevated C4/C2 and C4/C3 ratios. In urine organic acid tests, only one patient presented with an increased concentration of isobutyrylglycine excretion. Genetic testing was performed to detect the causative variants. Five previously unreported variants, c.235C > G, c.286G > A, c.444G > T c.1092 + 1G > A, and c.1176G > T, and one known variant, c.1000C > T, in ACAD8 were identified. These previously unreported variants in ACAD8 were predicted to be disease-causing and the c.1092 + 1G > A variant was confirmed to cause skipping of exon 9 by reverse transcription PCR. The most common variant was c.286G > A, which showed an allelic frequency of 50% (7/14), and thus may be a prevalent variant among Chinese patients. Our results broaden the mutational spectrum of ACAD8 and improve the understanding of the clinical phenotype of IBDHD.

Follow-up status during the first 5 years of life for metabolic disorders on the federal Recommended Uniform Screening Panel

PURPOSE

To investigate the 5-year follow-up status for newborns diagnosed with metabolic disorders designated as "primary disorders" on the federal Recommended Uniform Screening Panel (RUSP).

METHODS

Follow-up status and demographic characteristics are described for 426 newborns diagnosed with one of 20 primary metabolic disorders on the RUSP between 2005 and 2009. Newborn screening program data were linked to birth certificate data. Follow-up status is described for each year through age 5 and by disorder type. Maternal characteristics of those who stayed in active care were compared with those who did not.

RESULTS

Of 426 diagnosed newborns, by the end of 5 years of follow-up 55.2% stayed in active care, 20.4% became lost to follow-up, 8.7% moved out of state, 6.3% were determined to require no further follow-up, 4.7% refused follow-up, and 4.7% died. Among the initial group of disorders with more than 10 diagnosed cases, phenylketonuria (90%) had the highest percentage of patients still in active care after 5 years. Patients in active care had similar characteristics to patients not in active care when maternal age, race/ethnicity, completed education years, and expected source of payment for delivery were compared.

CONCLUSION

Staying in active care may associate with disorder type but not maternal characteristics.

Short-chain acyl-CoA dehydrogenase deficiency: from gene to cell pathology and possible disease mechanisms

Short-chain acyl-CoA dehydrogenase deficiency (SCADD) is an inherited disorder of mitochondrial fatty acid oxidation that is characterized by the presence of increased butyrylcarnitine and ethylmalonic acid (EMA) concentrations in plasma and urine. Individuals with symptomatic SCADD may show relatively severe phenotype, while the majority of those who are diagnosed through newborn screening by tandem mass spectrometry may remain asymptomatic. As such, the associated clinical symptoms are very diverse, ranging from severe metabolic or neuromuscular disabilities to asymptomatic. Molecular analysis of affected individuals has identified rare gene variants along with two common gene variants, c.511C > T and c.625G > A. In vitro studies have demonstrated that the common variants as well as the great majority of rare variants, which are missense variants, impair folding, that may lead to toxic accumulation of the encoded protein, and/or metabolites, and initiate excessive production of ROS and chronic oxidative stress. It has been suggested that this cell toxicity in combination with yet unknown factors can trigger disease development. This association and the full implications of SCADD are not commonly appreciated. Accordingly, there is a worldwide discussion of the relationship of clinical manifestation to SCADD, and whether SCAD gene variants are disease associated at all. Therefore, SCADD is not part of the newborn screening programs in most countries, and consequently many patients with SCAD gene variants do not get a diagnosis and the possibilities to be followed up during development.

Novel magnetic resonance imaging findings in a patient with short chain acyl CoA dehydrogenase deficiency

Reports on magnetic resonance imaging findings in patients with short chain acyl -Coenzyme A dehydrogenase (SCAD) deficiency, an autosomal recessive disorder caused by mutations in the acyl-Coenzyme A dehydrogenase (ACADS), are limited. Many asymptomatic carriers of ACAD variants have also been described necessitating careful evaluation of clinical and biochemical findings for an accurate diagnosis. Here we report a an infant with short chain acyl -Coenzyme A dehydrogenase (SCAD) deficiency diagnosed based on the characteristic biochemical findings and confirmed by genetic testing. He presented with refractory seizures and neuro regression at 4 months of age. His metabolic work up revealed elevated butyryl carnitine in plasma and ethyl malonic acid in urine. Magnetic resonance imaging of the brain showed cortical and basal ganglia signal changes with cortical swelling. Serial scans showed progression of the lesions resulting in cystic leukomalacia with brain atrophy. Exome sequencing revealed a novel homozygous nonsense variation, c.1146C > G (p.Y382Ter) in exon ten of ACADS which was further validated by Sanger sequencing. Both parents were heterozygous carriers. Follow up at 15 months showed gross psychomotor retardation and refractory seizures despite being on optimal doses of anti-epileptic medications, carnitine and multivitamin supplementation. This report expands the phenotypic and genotypic spectrum of SCAD deficiency.

Brain carnitine deficiency causes nonsyndromic autism with an extreme male bias: A hypothesis

Could 10-20% of autism be prevented? We hypothesize that nonsyndromic or "essential" autism involves extreme male bias in infants who are genetically normal, but they develop deficiency of carnitine and perhaps other nutrients in the brain causing autism that may be amenable to early reversal and prevention. That brain carnitine deficiency might cause autism is suggested by reports of severe carnitine deficiency in autism and by evidence that TMLHE deficiency - a defect in carnitine biosynthesis - is a risk factor for autism. A gene on the X chromosome (SLC6A14) likely escapes random X-inactivation (a mixed epigenetic and genetic regulation) and could limit carnitine transport across the blood-brain barrier in boys compared to girls. A mixed, common gene variant-environment hypothesis is proposed with diet, minor illnesses, microbiome, and drugs as possible risk modifiers. The hypothesis can be tested using animal models and by a trial of carnitine supplementation in siblings of probands. Perhaps the lack of any Recommended Dietary Allowance for carnitine in infants should be reviewed. Also see the video abstract here: https://youtu.be/BuRH_jSjX5Y.

Long-term outcome of expanded newborn screening at Boston children's hospital: benefits and challenges in defining true disease

INTRODUCTION

There is no universal consensus of the disorders included in newborn screening programs. Few studies so far, mostly short-term, have compared the outcome of disorders detected by expanded newborn screening (ENBS) to the outcome of the same disorders detected clinically.

METHODS

We compared the clinical and neurodevelopmental outcomes in patients with metabolic disorders detected by ENBS, including biotinidase testing, with those detected clinically and followed at the Metabolism Clinic at Boston Children's Hospital.

RESULTS

One hundred eighty-nine patients came to attention from ENBS and 142 were clinically diagnosed. 3-methylcrotonyl-CoA carboxylase, biotinidase, and carnitine deficiencies were exclusively identified by ENBS and medium chain acyl-CoA dehydrogenase (MCADD) and very long chain acyl-CoA dehydrogenase deficiencies (VLCADD) were predominantly identified by ENBS whereas the organic acid disorders more often came to attention clinically. Only 2% of the ENBS-detected cases had clinically severe outcomes compared to 42% of those clinically detected. The mean IQ score was 103 + 17 for the ENBS-detected cases and 77 + 24 for those clinically detected. Those newly included disorders that seem to derive the greatest benefit from ENBS include the fatty acid oxidation disorders, profound biotinidase deficiency, tyrosinemia type 1, and perhaps carnitine deficiency.

CONCLUSION

Although the NBS-identified and clinically-identified cohorts were not completely comparable, this long-term study shows likely substantial improvement overall in the outcome of these metabolic disorders in the NBS infants. Infants with mild disorders and benign variants may represent a significant number of infants identified by ENBS. The future challenge will be to unequivocally differentiate the disorders most benefitting from ENBS and adjust programs accordingly.

Acylcarnitine Profiles Reflect Metabolic Vulnerability for Necrotizing Enterocolitis in Newborns Born Premature

OBJECTIVE

To evaluate the association between newborn acylcarnitine profiles and the subsequent development of necrotizing enterocolitis (NEC) with the use of routinely collected newborn screening data in infants born preterm.

STUDY DESIGN

A retrospective cohort study was conducted with the use of discharge records for infants born preterm admitted to neonatal intensive care units in California from 2005 to 2009 who had linked state newborn screening results. A model-development cohort of 94 110 preterm births from 2005 to 2008 was used to develop a risk-stratification model that was then applied to a validation cohort of 22 992 births from 2009.

RESULTS

Fourteen acylcarnitine levels and acylcarnitine ratios were associated with increased risk of developing NEC. Each log unit increase in C5 and free carnitine /(C16 + 18:1) was associated with a 78% and a 76% increased risk for developing NEC, respectively (OR 1.78, 95% CI 1.53-2.02, and OR 1.76, 95% CI 1.51-2.06). Six acylcarnitine levels, along with birth weight and total parenteral nutrition, identified 89.8% of newborns with NEC in the model-development cohort (area under the curve 0.898, 95% CI 0.889-0.907) and 90.8% of the newborns with NEC in the validation cohort (area under the curve 0.908, 95% CI 0.901-0.930).

CONCLUSIONS

Abnormal fatty acid metabolism was associated with prematurity and the development of NEC. Metabolic profiling through newborn screening may serve as an objective biologic surrogate of risk for the development of disease and thus facilitate disease-prevention strategies.

Challenges for Worldwide Harmonization of Newborn Screening Programs

BACKGROUND

Inherited metabolic disorders (IMDs) are caused by a defect in a metabolic pathway, leading to malfunctioning metabolism and/or the accumulation of toxic intermediate metabolites. To date, hundreds of IMDs have been identified. Many of these diseases are potentially fatal conditions that are not apparent at birth. Newborn screening (NBS) programs involve the clinical and laboratory examination of neonates who exhibit no health problems, with the aim of discovering those infants who are, in fact, suffering from a treatable condition.

CONTENT

In recent years, the introduction of tandem mass spectrometry has allowed the expansion of screening programs. However, this expansion has brought a high degree of heterogeneity in the IMDs tested among different NBS programs. An attempt to harmonize the metabolic conditions recommended to be screened has been carried out. Two uniform screening panels have been proposed in the US and European Union, by knowledgeable organizations. Here, we review current evidence-based processes to assess and expand NBS programs. We also discuss the IMDs that have recently been introduced in some screening programs, such as severe combined immunodeficiencies, lysosomal storage disorders, and adrenoleukodystrophy.

SUMMARY

NBS programs have been an established public health function for more than 50 years to efficiently and cost-effectively identify neonates with severe conditions. However, NBS is not yet optimal. This review is intended to elucidate the current degree of harmonization of NBS programs worldwide as well as to describe the major controversial points and discuss the multiple challenges that must be confronted in expanded NBS strategies.

Clinical relevance of short-chain acyl-CoA dehydrogenase (SCAD) deficiency: Exploring the role of new variants including the first SCAD-disease-causing allele carrying a synonymous mutation

Short-chain acyl-coA dehydrogenase deficiency (SCADD) is an autosomal recessive inborn error of mitochondrial fatty acid oxidation caused by ACADS gene alterations. SCADD is a heterogeneous condition, sometimes considered to be solely a biochemical condition given that it has been associated with variable clinical phenotypes ranging from no symptoms or signs to metabolic decompensation occurring early in life.

A reason for this variability is due to SCAD alterations, such as the common p.Gly209Ser, that confer a disease susceptibility state but require a complex multifactorial/polygenic condition to manifest clinically.

Our study focuses on 12 SCADD patients carrying 11 new ACADS variants, with the purpose of defining genotype–phenotype correlations based on clinical data, metabolite evaluation, molecular analyses, and in silico functional analyses.

Interestingly, we identified a synonymous variant, c.765G > T (p.Gly255Gly) that influences ACADS mRNA splicing accuracy. mRNA characterisation demonstrated that this variant leads to an aberrant splicing product, harbouring a premature stop codon.

Molecular analysis and in silico tools are able to characterise ACADS variants, identifying the severe mutations and consequently indicating which patients could benefit from a long term follow- up. We also emphasise that synonymous mutations can be relevant features and potentially associated with SCADD.

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Molecular and functional analysis can identify severe genotypes

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Patients with severe genotype should receive a long term follow-up.

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We identified the first SCAD synonymous variant.

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The first SCAD silent variant was proven to achieve into a disease causing allele.

A Next Generation Multiscale View of Inborn Errors of Metabolism

Inborn errors of metabolism (IEM) are not unlike common diseases. They often present as a spectrum of disease phenotypes that correlates poorly with the severity of the disease-causing mutations. This greatly impacts patient care and reveals fundamental gaps in our knowledge of disease modifying biology. Systems biology approaches that integrate multi-omics data into molecular networks have significantly improved our understanding of complex diseases. Similar approaches to study IEM are rare despite their complex nature. We highlight that existing common disease-derived datasets and networks can be repurposed to generate novel mechanistic insight in IEM and potentially identify candidate modifiers. While understanding disease pathophysiology will advance the IEM field, the ultimate goal should be to understand per individual how their phenotype emerges given their primary mutation on the background of their whole genome, not unlike personalized medicine. We foresee that panomics and network strategies combined with recent experimental innovations will facilitate this.

A case report of short-chain acyl-CoA dehydrogenase deficiency (SCADD)

Background

Short-chain acyl-CoA dehydrogenase deficiency (SCADD) is a rare inherited mitochondrial fatty acid oxidation disorder associated with variations in the ACADS (Acyl-CoA dehydrogenase, C-2 to C-3 short chain) gene. SCADD has highly variable biochemical, genetic and clinical characteristics. Phenotypes vary from fatal metabolic decompensation to asymptomatic individuals.

Subject and methods

A Romani boy presented at 3 days after birth with hypoglycaemia, hypotonia and respiratory pauses with brief generalized seizures. Afterwards the failure to thrive and developmental delay were present. Organic acids analysis with gas chromatography-mass spectrometry (GS/MS) in urine and acylcarnitines analysis with liquid chromatography-tandem mass spectrometry (LC-MS/MS) in dried blood spot were measured. Deoxyribonucleic acid (DNA) was isolated from blood and polymerase chain reactions (PCRs) were performed for all exons. Sequence analysis of all exons and flanking intron sequences of ACADS gene was performed.

Results

Organic acids analysis revealed increased concentration of ethylmalonic acid. Acylcarnitines analysis showed increase of butyrylcarnitine, C4-carnitine. C4-carnitine was 3.5 times above the reference range (<0.68 µmol/L). Confirmation analysis for organic acids and acylcarnitine profile was performed on the second independent sample and showed the same pattern of increased metabolites. Sequence analysis revealed 3-bp deletion at position 310-312 in homozygous state (c.310_312delGAG). Mutation was previously described as pathogenic in heterozygous state, while it is in homozygous state in our patient.

Conclusions

In our case clinical features of a patient, biochemical parameters and genetic data were consistent and showed definitely SCAD deficiency.

Deficiency of ECHS1 causes mitochondrial encephalopathy with cardiac involvement

OBJECTIVE

Short-chain enoyl-CoA hydratase (ECHS1) is a multifunctional mitochondrial matrix enzyme that is involved in the oxidation of fatty acids and essential amino acids such as valine. Here, we describe the broad phenotypic spectrum and pathobiochemistry of individuals with autosomal-recessive ECHS1 deficiency.

METHODS

Using exome sequencing, we identified ten unrelated individuals carrying compound heterozygous or homozygous mutations in ECHS1. Functional investigations in patient-derived fibroblast cell lines included immunoblotting, enzyme activity measurement, and a palmitate loading assay.

RESULTS

Patients showed a heterogeneous phenotype with disease onset in the first year of life and course ranging from neonatal death to survival into adulthood. The most prominent clinical features were encephalopathy (10/10), deafness (9/9), epilepsy (6/9), optic atrophy (6/10), and cardiomyopathy (4/10). Serum lactate was elevated and brain magnetic resonance imaging showed white matter changes or a Leigh-like pattern resembling disorders of mitochondrial energy metabolism. Analysis of patients' fibroblast cell lines (6/10) provided further evidence for the pathogenicity of the respective mutations by showing reduced ECHS1 protein levels and reduced 2-enoyl-CoA hydratase activity. While serum acylcarnitine profiles were largely normal, in vitro palmitate loading of patient fibroblasts revealed increased butyrylcarnitine, unmasking the functional defect in mitochondrial β-oxidation of short-chain fatty acids. Urinary excretion of 2-methyl-2,3-dihydroxybutyrate - a potential derivative of acryloyl-CoA in the valine catabolic pathway - was significantly increased, indicating impaired valine oxidation.

INTERPRETATION

In conclusion, we define the phenotypic spectrum of a new syndrome caused by ECHS1 deficiency. We speculate that both the β-oxidation defect and the block in l-valine metabolism, with accumulation of toxic methacrylyl-CoA and acryloyl-CoA, contribute to the disorder that may be amenable to metabolic treatment approaches.

Disturbance of energy and redox homeostasis and reduction of Na+,K+-ATPase activity provoked by in vivo intracerebral administration of ethylmalonic acid to young rats

Ethylmalonic acid (EMA) accumulation occurs in various metabolic diseases with neurological manifestation, including short acyl-CoA dehydrogenase deficiency (SCADD) and ethylmalonic encephalopathy (EE). Since pathophysiological mechanisms responsible for brain damage in these disorders are still poorly understood, we investigated the ex vivo effects of acute intrastriatal administration of EMA on important parameters of energy and redox homeostasis in striatum from young rats. We evaluated CO(2) production from glucose, glucose utilization and lactate production, as well as the activities of the citric acid cycle (CAC) enzymes, the electron transfer chain (ETC) complexes II-IV (oxidative phosphorylation, OXPHOS) and synaptic Na(+),K(+)-ATPase. We also tested the effect of EMA on malondialdehyde (MDA) levels (marker of lipid oxidation) and reduced glutathione (GSH) levels. EMA significantly reduced CO(2) production, increased glucose utilization and lactate production, and reduced the activities of citrate synthase and of complexes II and II-III of the ETC, suggesting an impairment of CAC and OXPHOS. EMA injection also reduced Na(+),K(+)-ATPase activity and GSH concentrations, whereas MDA levels were increased. Furthermore, EMA-induced diminution of Na(+),K(+)-ATPase activity and reduction of GSH levels were prevented, respectively, by the antioxidants melatonin and N-acetylcysteine, indicating that reactive species were involved in these effects. Considering the importance of CAC and ETC for energy production and Na(+),K(+)-ATPase for the maintenance of the cell membrane potential, the present data indicate that EMA compromises mitochondrial homeostasis and neurotransmission in striatum. We presume that these pathomechanisms may be involved to a certain extent in the neurological damage found in patients affected by SCADD and EE.

Birth Prevalence of Fatty Acid β-Oxidation Disorders in Iberia

Mitochondrial fatty acid β-oxidation disorders (FAOD) are main targets for newborn screening (NBS) programs, which are excellent data sources for accurate estimations of disease birth prevalence. Epidemiological data is of key importance for the understanding of the natural history of the disorders as well as to define more effective public health strategies. In order to estimate FAOD birth prevalence in Iberia, the authors collected data from six NBS programs from Portugal and Spain, encompassing the screening of more than 1.6 million newborns by tandem mass spectrometry (MS/MS), and compared it with available data from other populations. The participating NBS programs are responsible for the screening of about 46% of all Iberian newborns. Data reveals that Iberia has one of the highest FAOD prevalence in Europe (1:7,914) and that Portugal has the highest birth prevalence of FAOD reported so far (1:6,351), strongly influenced by the high prevalence of medium-chain acyl-CoA dehydrogenase deficiency (MCADD; 1:8,380), one of the highest ever reported. This is justified by the fact that more than 90% of Portuguese MCADD patients are of Gypsy origin, a community characterized by a high degree of consanguinity. From the comparative analysis of various populations with comparable data other differences emerge, which points to the existence of significant variations in FAOD prevalences among different populations, but without any clear European variation pattern. Considering that FAOD are one of the justifications for MS/MS NBS, the now estimated birth prevalences stress the need to screen all Iberian newborns for this group of inherited metabolic disorders.

Complex changes in the liver mitochondrial proteome of short chain acyl-CoA dehydrogenase deficient mice

Short-chain acyl-CoA dehydrogenase (SCAD) deficiency is an autosomal recessive inborn error of metabolism that leads to the impaired mitochondrial fatty acid β-oxidation of short chain fatty acids. It is heterogeneous in clinical presentation including asymptomatic in most patients identified by newborn screening. Multiple mutations have been identified in patients; however, neither clear genotype-phenotype relationships nor a good correlation between genotype and current biochemical markers for diagnosis has been identified. The definition and pathophysiology of this deficiency remain unclear. To better understand this disorder at a global level, quantitative alterations in the mitochondrial proteome in SCAD deficient mice were examined using a combined proteomics approach: two-dimensional gel difference electrophoresis (2DIGE) followed by protein identification with MALDI-TOF/TOF and iTRAQ labeling followed by nano-LC/MALDI-TOF/TOF. We found broad mitochondrial dysfunction in SCAD deficiency. Changes in the levels of multiple energy metabolism related proteins were identified indicating that a more complex mechanism for development of symptoms may exist. Affected pathways converge on disorders with neurologic symptoms, suggesting that even asymptomatic individuals with SCAD deficiency may be at risk to develop more severe disease. Our results also identified a pattern associated with hepatotoxicity implicated in mitochondrial dysfunction, fatty acid metabolism, decrease of depolarization of mitochondria and mitochondrial membranes, and swelling of mitochondria, demonstrating that SCAD deficiency relates more directly to mitochondrial dysfunction and alteration of fatty acid metabolism. We propose several candidate molecules that may serve as markers for recognition of clinical risk associated with this disorder.

Neuropsychological outcomes in fatty acid oxidation disorders: 85 cases detected by newborn screening

Mitochondrial fatty acid oxidation disorders include conditions in which the transport of activated acyl-Coenzyme A (CoA) into the mitochondria or utilization of these substrates is disrupted or blocked. This results in a deficit in the conversion of fat into energy. Most patients with fatty acid oxidation defects are now identified through newborn screening by tandem mass spectrometry. With earlier identification and preventative treatments, mortality and morbidity rates have improved. However, in the absence of severe health and neurological effects from these disorders, subtle developmental delays or neuropsychological deficits have been noted. Medical records were reviewed to identify outcomes in 85 children with FAOD's diagnosed through newborn screening and followed at one metabolic center. Overall, 54% of these children identified through newborn screening experienced developmental challenges. Speech delay or relative weakness in language was noted in 26 children (31%) and motor delays were noted in 24 children (29%). The majority of the 46 children receiving psychological evaluations performed well within the average range, with only 11% scoring <85 on developmental or intelligence tests. These results highlight the importance of screening children with fatty acid oxidation disorders to identify those with language, motor, or cognitive delay. Although expanded newborn screening dramatically changes the health and developmental outcomes in many children with fatty acid oxidation disorders, it also complicates the interpretation of biochemical and molecular findings and raises questions about the effectiveness or necessity of treatment in a large number of cases. Only by systematically evaluating developmental and neuropsychological outcomes using standardized methods will the true implications of newborn screening, laboratory results, and treatments for neurocognitive outcome in these disorders become clear.

Proteomic investigation of cultivated fibroblasts from patients with mitochondrial short-chain acyl-CoA dehydrogenase deficiency

Short-chain acyl-CoA dehydrogenase (SCAD) deficiency is a rare inherited autosomal recessive disorder with not yet well established mechanisms of disease. In the present study, the mitochondrial proteome of five symptomatic patients homozygous for missense variations in the SCAD gene ACADS was investigated in an extensive large-scale proteomic study to map protein perturbations linked to the disease. Fibroblast cultures of patient cells homozygous for either c.319C>T/p.Arg107Cys (n=2) or c.1138C>T/p.Arg380Trp (n=3) in ACADS, and healthy controls (normal human dermal fibroblasts), were studied. The mitochondrial proteome derived from these cultures was analyzed by label free proteomics using high mass accuracy nanoliquid chromatography tandem mass spectrometry (nanoLC-MS/MS). More than 300 mitochondrial proteins were identified and quantified. Thirteen proteins had significant alteration in protein levels in patients carrying variation c.319C>T in ACADS compared to controls and they belonged to various pathways, such as the antioxidant system and amino acid metabolism. Twenty-two proteins were found significantly altered in patients carrying variation c.1138C>T which included proteins associated with fatty acid β-oxidation, amino acid metabolism and protein quality control system. Three proteins were found significantly regulated in both patient groups: adenylate kinase 4 (AK4), nucleoside diphosphate kinase A (NME1) and aldehyde dehydrogenase family 4 member A1 (ALDH4A1). Proteins AK4 and NME1 deserve further investigation because of their involvement in energy reprogramming, cell survival and proliferation with relevance for SCAD deficiency and related metabolic disorders.

Fatty Acid oxidation disorders in a chinese population in taiwan

BACKGROUND

Fatty acid oxidation (FAO) disorders are a heterogeneous group of inborn errors in the transportation and oxidation of fatty acids. FAO disorders were thought to be very rare in the Chinese population. Newborn screening for FAO disorders beginning in 2002 in Taiwan may have increased the diagnosis of this group of diseases.

MATERIALS AND METHODS

Till 2012, the National Taiwan University Hospital Newborn Screening Center screened more than 800,000 newborns for FAO disorders. Both patients diagnosed through screening and patients detected after clinical manifestations were included in this study.

RESULTS

A total of 48 patients with FAO disorders were identified during the study period. The disorders included carnitine palmitoyltransferase I deficiency, carnitine acylcarnitine translocase deficiency, carnitine palmitoyltransferase II deficiency, very long-chain acyl-CoA dehydrogenase deficiency, medium-chain acyl-CoA dehydrogenase deficiency, multiple acyl-CoA dehydrogenase deficiency, short-chain defects, and carnitine uptake defect. Thirty-nine patients were diagnosed through newborn screening. Five false-negative newborn screening cases were noted during this period, and four patients who were not screened were diagnosed based on clinical manifestations. The ages of all patients ranged from 6 months to 22.9 years (mean age 6.6 years). Except for one case of postmortem diagnosis, there were no other mortalities.

CONCLUSIONS

The combined incidence of FAO disorders estimated by newborn screening in the Chinese population in Taiwan is 1 in 20,271 live births. Newborn screening also increases the awareness of FAO disorders and triggers clinical diagnoses of these diseases.

Expanded newborn screening and confirmatory follow-up testing for inborn errors of metabolism detected by tandem mass spectrometry

Newborn screening (NBS) of inborn errors of metabolism (IEM) is a coordinated comprehensive system consisting of education, screening, follow-up of abnormal test results, confirmatory testing, diagnosis, treatment, and evaluation of periodic outcome and efficiency. The ultimate goal of NBS and follow-up programs is to reduce morbidity and mortality from the disorders. Over the past decade, tandem mass spectrometry (MS/MS) has become a key technology in the field of NBS. It has replaced classic screening techniques of one-analysis, one-metabolite, one-disease with one analysis, many-metabolites, and many-diseases. The development of electrospray ionization (ESI), automation of sample handling and data manipulation have allowed the introduction of expanded NBS for the identification of numerous conditions on a single sample and new conditions to be added to the list of disorders being screened for using MS/MS. In the case of a screened positive result, a follow-up analytical test should be performed for confirmation of the primary result. The most common confirmatory follow-up tests are amino acids and acylcarnitine analysis in plasma and organic acid analysis in urine. NBS should be integrated with follow-up and clinical management. Recent improvements in therapy have caused some disorders to be considered as potential candidates for NBS. This review covers some of the basic theory of expanded MS/MS and follow-up confirmatory tests applied for NBS of IEM.