Screening of MCAD deficiency in Japan: 16years' experience of enzymatic and genetic evaluation

Structural insights into the pathogenicity of point mutations in human acyl-CoA dehydrogenase homotetramers

Acyl-CoA dehydrogenase deficiency (ACAD) is an inherited and potentially fatal disorder with variable clinical symptoms. The relationship between pathogenicity and deleterious point mutations is investigated here in ACAD structures of short (SCAD) and medium-chain (MCAD) types. Structures and dynamic features of native and mutant forms of enzymes models were compared. A total of 2.88 µs molecular dynamics simulations were performed at four different temperatures. Total energy, RMSD, protein ligand interactions and affinity, RMSF measures, secondary structure changes, and important interactions were studied. Mutations in the three main domains of ACADs are pathogenic, while those located at linker turns are not. Mutations affect mostly tetramer formations, secondary structures, and many contacts and interactions. In R206H (MCAD mutant) which is experimentally known to cause a huge turnover decrease, the lack of a single H-bond between substrate and FAD was observed. Secondary structures showed temperature-dependent changes, and SCAD activity was found to be highly correlated to the enzyme helix 3-10 content. Finally, RMSF patterns pointed to one important loop that maintains the substrate close to the active site and is a cause of substrate wobbling upon mutation. Despite similar structure, function, and cellular location, SCAD and MCAD may have different optimum temperatures that are related to the structure taken at that specific temperature. In conclusion, new insight has been provided on the effect of various SCAD and MCAD pathogenic mutations on the structure and dynamical features of the enzymes.

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.

Medium-chain Acyl-COA dehydrogenase deficiency: Pathogenesis, diagnosis, and treatment

INTRODUCTION

Medium-Chain Acyl-CoA Dehydrogenase Deficiency (MCADD) is the most common inherited metabolic disorder of β-oxidation. Patients with MCADD present with hypoketotic hypoglycemia, which may quickly progress to lethargy, coma, and death. Prognosis for MCADD patients is highly promising once a diagnosis has been established, though management strategies may vary depending on the severity of illness and the presence of comorbidities.

METHODS AND RESULTS

Given the rapid developments in the world of gene therapy and implementation of newborn screening for inherited metabolic disorders, the provision of concise and contemporary knowledge of MCADD is essential for clinicians to effectively manage patients. Thus, this review aims to consolidate current information for physicians on the pathogenesis, diagnostic tools, and treatment options for MCADD patients.

CONCLUSION

MCADD is a commonly inherited metabolic disease with serious implications for health outcomes, particularly in children, that may be successfully managed with proper intervention.

Newborn screening and genetic variation of medium chain acyl-CoA dehydrogenase deficiency in the Chinese population

OBJECTIVES

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is an autosomal recessive disorder of the fatty acid oxidative metabolism. This study aimed to investigate the epidemiological characteristics, the spectrum of variation, clinical phenotype, and prognosis of MCADD in Chinese newborns.

METHODS

We retrospectively analysed newborn screening (NBS) data in the Zibo area from January 2016 to March 2022 and summarized 42 cases recently reported in Chinese neonates. High-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) and next-generation sequencing (NGS) were used to detect the concentrations of carnitine in the blood spots and for diagnosis.

RESULTS

A total of 183,082 newborns were detected, and six patients were diagnosed with MCADD (1/3,0514). The primary octanoylcarnitine (C8) and the octanoylcarnitine/decanoylcarnitine ratio (C8/C10) were elevated in all patients. Gene analysis revealed four known and four novel variants of the ACADM gene. Five patients were asymptomatic and developed normally under dietary guidance. One child died of vaccination-induced MCADD, presenting with hypoglycemia and elevated acylcarnitines.

CONCLUSIONS

The incidence of MCADD in Chinese newborns varies geographically from 1/222,903 to 1/30,514, and the most common pathogenic variant is c.449_452 del CTGA (p. T150Rfs∗4) in ACADM gene with a frequency of 27.7%. HPLC-MS/MS and genetic analysis are beneficial for early prevention and good prognosis of MCADD.

Analysis of gene mutations of Medium-chain acyl-coenzyme A dehydrogenase deficiency (MCADD) by next-generation sequencing in Henan, China

BACKGROUND

Medium-chain acyl-coenzyme A dehydrogenase deficiency (MCADD) is a rare inherited metabolic disorder of fatty acid β-oxidation and one of the most common inborn errors of metabolism. The incidence of MCADD varies among regions and ethnic groups. To date, few cases of MCADD have been documented in China.

OBJECTIVE

The present study aimed to find out the novel genetic pathogenic variants in the Chinese patients and evaluate the detection rate of the disease of high-frequency ACADM pathogenic variants in different regions of China.

METHODS

6 cases of MCADD were screened by tandem mass spectrometric (MS/MS) among 245 054 newborns. We performed next-generation sequencing on 6 families of infants with MCADD. We used the REVEL method to predict the protein function of the detected missense variants and used SPDBV 4.10 to predict the protein 3D structure model. We identified pathogenic variants of ACADM gene in 6 cases of MCADD, and then assessed these variants through Sanger sequencing and association analysis.

RESULTS

The incidence of neonatal MCADD was 1/40,842 in Henan province. Among the 6 patients, five cases were compound heterozygous variants, one case was homozygous variants. DNA sequencing revealed 4 known (c.449_452del, c.1085G>A, c.1229T>C, c.589A>G) and 3 novel mutations (c.849+5_849+8del, c.427A>G, c.1181C>T) in the ACADM gene. Mutation c.1085G>A (p.G362E) was most frequent among Henan people and shows obvious differences between North and South of China.

CONCLUSION

MCADD is relatively rare in China, and c.1085G>A (p.G362E) is a common mutation in Henan population. Our findings, especially novel variants, will help improve the understanding of the genetic background and have facilitated clinical diagnosis and genetic counseling for the affected families.

Lymphocyte Medium-Chain Acyl-CoA Dehydrogenase Activity and Its Potential as a Diagnostic Confirmation Tool in Newborn Screening Cases

The determination of acylcarnitines (AC) in dried blood spots (DBS) by tandem mass spectrometry in newborn screening (NBS) programs has enabled medium-chain acyl-coA dehydrogenase deficiency (MCADD) to be identified in presymptomatic newborns. Nevertheless, different confirmatory tests must be performed to confirm the diagnosis. In this work, we have collected and analyzed the NBS results and confirmatory test results (plasma AC, molecular findings, and lymphocyte MCAD activity) of forty individuals, correlating them with clinical outcomes and treatment, with the aim of obtaining useful diagnostic information that could be applied in the follow-up of the patients. Our results led us to classify patients into two groups. The first group (14 cases) had high increased octanoylcarnitine (C8) levels, biallelic pathogenic variants, and severe impaired enzyme activity (<10% of the intra-assay control (IAC)); all of these cases received nutritional therapy and required carnitine supplementation during follow-up, representing the most severe form of the disease. The second group (16 patients) was a heterogeneous group presenting moderate increases in C8, biallelic likely pathogenic/pathogenic variants, and intermediate activity (<41% IAC). All of them are currently asymptomatic and could be considered as having a milder form of the disease. Finally, eight cases presented a normal−mild increase in plasma C8, with only one pathogenic variant detected, and high−intermediate residual activity (15−100%). Based on our results, we confirm that combined evaluation of acylcarnitine profiles, genetic findings, and residual enzyme activities proves useful in predicting the risk of future metabolic decompensation, in making decisions regarding future treatment or follow-up, and also in confirming the clinical effects of unknown clinical variants.

MCAD deficiency caused by compound heterozygous pathogenic variants in ACADM

Medium-chain acyl-coenzyme A dehydrogenase (MCAD) deficiency is an autosomal recessive disease caused by biallelic pathogenic ACADM variants. We report a case of an asymptomatic Japanese girl with MCAD deficiency caused by compound heterozygous pathogenic variants (NM_000016.5:c.1040G > T (p.Gly347Val) and c.449_452delCTGA (p.Thr150ArgfsTer4)). Because the MCAD residual activity in lymphocytes of the patient was below the limit of quantification, both variants are likely to cause complete loss of MCAD enzymatic activity.

Clinical, Biochemical, and Molecular Analyses of Medium-Chain Acyl-CoA Dehydrogenase Deficiency in Chinese Patients

Objective

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is a rare inherited metabolic disorder of fatty acid β-oxidation. The present study aimed to evaluate clinical and biochemical manifestations, and the mutation spectrum of this disorder in a large cohort of Chinese patients.

Methods

A total of 24 patients were enrolled, and blood acylcarnitine and urinary organic acid levels were measured by tandem mass spectrometry and gas chromatography–mass spectrometry (GC–MS), respectively. Mutations in the ACADM gene were detected by Sanger or next-generation sequencing. Clinical progression, acylcarnitine spectra, and mutations were analyzed and described in detail.

Results

Among the 24 patients, six cases were diagnosed because of disease onset with symptoms such as vomiting, diarrhea, convulsion, and hypoglycemia; 18 patients without symptoms were diagnosed by newborn screening (NBS). All patients who accepted treatment after diagnosis developed normal intelligence and physique. The concentrations of octanoylcarnitine, the octanoylcarnitine/decanoylcarnitine ratio, and the octanoylcarnitine/acetylcarnitine ratio in the blood and urinary dicarboxylic acid concentrations were consistently elevated. Blood biomarkers failed to decrease after treatment. DNA sequencing revealed seven known and 17 novel mutations in the ACADM gene of patients. Mutation p.T150Rfs^∗4 was most frequent, followed by p.R31C, p.F103Y, p.I223T, p.G362E, and c.387+1delG.

Conclusion

Despite biochemical abnormalities, medium-chain acyl-CoA dehydrogenase deficiency showed relatively mild clinical phenotypes with low mortality and optimistic prognoses in China. NBS is crucial for early diagnosis, treatment, and prognosis.

Spectrum analysis of inborn errors of metabolism for expanded newborn screening in a northwestern Chinese population

Expanded newborn screening facilitates early identification and intervention of patients with inborn errors of metabolism (IEMs), There is a lack of disease spectrum data for many areas in China. To determine the disease spectrum and genetic characteristics of IEMs in Xi'an city of Shaanxi province in northwest China, 146152 newborns were screening by MSMS from January 2014 to December 2019 and 61 patients were referred to genetic analysis by next generation sequencing (NGS) and validated by Sanger sequencing. Seventy-five newborns and two mothers were diagnosed with IEMs, with an overall incidence of 1:1898 (1:1949 without mothers). There were 35 newborns with amino acidemias (45.45%, 1:4176), 28 newborns with organic acidurias (36.36%, 1:5220), and 12 newborns and two mothers with FAO disorders (18.18%; 1:10439 or 1:12179 without mothers). Phenylketonuria and methylmalonic acidemia were the two most common disorders, accounting for 65.33% (49/75) of all confirmed newborn. Some hotspot mutations were observed for several IEMs, including PAH gene c.728G>A for phenylketonuria; MMACHC gene c.609G>A and c.567dupT, MMUT gene c.323G>A for methylmalonic acidemia and SLC25A13 gene c.852_855del for citrin deficiency. Our study provides effective clinical guidance for the popularization and application of expanded newborn screening, genetic screening, and genetic counseling of IEMs in this region.

Essential oils can cause false-positive results of medium-chain acyl-CoA dehydrogenase deficiency

Newborn screening is a public health care program worldwide to prevent patients from critical illness or conditions. Tandem mass spectrometry allows multiplex, inexpensive, and rapid newborn screening. However, mass spectrometry used for newborn screening to date is not able to separate peaks of compounds with similar m/z, which could lead to false-positive results without additional second-tier tests, such as fragmentation. We experienced three neonatal cases with high levels of markers, octanoylcarnitine and octanoylcarnitine/decanoylcarnitine ratio used to pick up possible cases of medium-chain acyl-CoA dehydrogenase (MCAD) deficiency. The babies were born consecutively in a maternity hospital. Their second acylcarnitine profiles were normal, and the genetic tests for ACADM were negative. Analysis of samples extracted from their first Guthrie cards where blood was not stained also showed peaks equivalent to octanoylcarnitine and decanoylcarnitine, indicating contamination. Environmental surveillance in the maternity ward suggested that essential oils used there might contain the contaminated compound. LC-HRMS/MS and in silico analysis revealed that false-positive results might be due to contamination with the essential oils in Guthrie cards, and causal agents were sphinganine (d17:0) and 2-[2-hydroxyethyl(pentadecyl)amino]ethanol. Thus, health care providers should be cautioned about use of essential oils when collecting blood samples on Guthrie cards. False-positive results can waste costly social resources and cause a physical and psychological burden for children and parents.

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.

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.

Medium-chain acyl-coenzyme A dehydrogenase deficiency: Six cases in the Chinese population

BACKGROUND

Medium-chain acyl-coenzyme A dehydrogenase deficiency (MCADD) is a rare autosomal recessive disorder that affects the degradation of medium-chain fatty acids. Few cases of MCADD have been documented to date in mainland China.

METHODS

Medium-chain acyl-coenzyme A dehydrogenase deficiency was diagnosed in six patients (three girls and three boys) from six unrelated Chinese families at ages ranging from 10 days to 3 years old. The diagnosis was confirmed by the identification of a primary biomarker of serum octanoyl-carnitine (C8) and genetic pathogenic mutations.

RESULTS

Only two patients were admitted because of vomiting, diarrhea, myasthenia, and coma; the other four patients were diagnosed via the newborn screening process. Six mutations were found in acyl-CoA dehydrogenase medium chain (ACADM). One mutation (c.727C>T) was novel and the others (c.158G>A, c.387+1delG, c.449_452del, c.1045C>T, and c.1085G>A) have been previously reported.

CONCLUSIONS

Six Chinese cases of MCADD were identified. One novel mutation was found. c.449_452del and c.1085G>A were common mutations in this study.

Lipid Myopathies

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

Diversity in the incidence and spectrum of organic acidemias, fatty acid oxidation disorders, and amino acid disorders in Asian countries: Selective screening vs. expanded newborn screening

Background

Expanded newborn screening (ENBS) utilizing tandem mass spectrometry (MS/MS) for inborn metabolic diseases (IMDs), such as organic acidemias (OAs), fatty acid oxidation disorders, (FAODs), and amino acid disorders (AAs), is increasingly popular but has not yet been introduced in many Asian countries. This study aimed to determine the incidence rates of OAs, FAODs, and AAs in Asian countries and Germany using selective screening and ENBS records.

Materials and methods

Selective screening for IMDs using gas chromatography–mass spectrometry and MS/MS was performed among patients suspected to be afflicted in Asian countries (including Japan, Vietnam, China, and India) between 2000 and 2015, and the results from different countries were compared. Similarly, ENBS results from Japan, South Korea, Taiwan, and Germany were compared. Additionally, the results of selective screening and ENBS in Japan were compared.

Results

Among 39,270 patients who underwent selective screening, IMDs were detected in 1170. Methylmalonic acidemia was frequently identified in several countries, including Japan (81/377 diagnosed IMDs), China (94/216 IMDs), and India (72/293 IMDs). In Vietnam, however, β-ketothiolase deficiency was particularly frequent (33/250 IMDs). ENBS yielded differences in overall IMD rates by country: 1:8557 in Japan, 1:7030 in Taiwan, 1:13,205 in South Korea, and 1:2200 in Germany. Frequently discovered diseases included propionic acidemia (PPA) and phenylketonuria (PKU) in Japan, 3-methylcrotonyl-CoA carboxylase deficiency (MCCD) and PKU in Taiwan, MCCD and citrullinemia type I in South Korea, and PKU and medium-chain acyl-CoA dehydrogenase deficiency in Germany. Furthermore, in Japan, selective screening and ENBS yielded respective PPA frequencies of 14.7% and 49.4% among all organic acidemias.

Conclusion

The incidence rates of IMDs vary by country. Moreover, the disease spectra of IMDs detected via selective screening differ from those detected via ENBS.

Diagnostic potential of stored dried blood spots for inborn errors of metabolism: a metabolic autopsy of medium-chain acyl-CoA dehydrogenase deficiency

AIM

It is estimated that 1-5% of sudden infant death syndrome (SIDS) cases might be caused by undiagnosed inborn errors of metabolism (IEMs); however, the postmortem identification of IEMs remains difficult. This study aimed to evaluate the usefulness of dried blood spots (DBSs) stored after newborn screening tests as a metabolic autopsy to determine the causes of death in infants and children who died suddenly and unexpectedly.

METHODS

Infants or toddlers who had suddenly died without a definite diagnosis between July 2008 and December 2012 at Kyushu University Hospital in Japan were enrolled in this study. Their Guthrie cards, which had been stored for several years at 4-8°C, were used for an acylcarnitine analysis by tandem mass spectrometry to identify inborn errors of metabolism.

RESULTS

Fifteen infants and children who died at less than 2 years of age and for whom the cause of death was unknown were enrolled for the study. After correcting the C0 and C8 values assuming the hydrolysation of acylcarnitine in the stored DBSs, the corrected C8 value of one case just exceeded the cut-off level for medium-chain acyl-CoA dehydrogenase (MCAD) deficiency screening. Genetic and biochemical analyses confirmed this patient to have MCAD deficiency.

CONCLUSION

DBSs stored after newborn screening tests are a promising tool for metabolic autopsy. The appropriate compensation of acylcarnitine data and subsequent genetic and biochemical analyses are essential for the postmortem diagnosis of inborn errors of metabolism.