Selective screening for inborn errors of metabolism on clinical patients using tandem mass spectrometry in China: a four-year report

Determination of amino acid metabolic diseases from dried blood spots with a rapid extraction method coupled with nanoelectrospray ionization mass spectrometry

In this work, a rapid extraction method of methanol/water (95:5 v/v) with 0.1% formic acid was developed for extraction of amino acids from dried blood spots (DBS) for inherited metabolic diseases (IMDs). The combination of this extraction procedure with nanoelectrospray ionization mass spectrometry (nESI-MS) was used for the rapid analysis of amino acids. This approach with eliminating the chromatographic separation required only 2 min for the extraction of amino acids from DBS, which simplified the configuration and improved the timeliness. Dependence of the sensitivity on the operating parameters was systematically investigated. The LOD of 91.2-262.5 nmol/L and LOQ of 304-875 nmol/L which were lower than the cut-off values were obtained for amino acids within DBS. The accuracy was determined to be 93.82%-103.07% and the precision was determined to be less than 8.30%. The effectiveness of this method was also compared with the gold standard method (e.g., LC-MS/MS). The desalination mechanism was explored with interference mainly originated from the blood. These findings indicated that the rapid extraction procedure coupled with nESI-MS is capable of screening indicators for IMDs in complex biological samples.

Mass Spectrometry Analysis for Clinical Applications: A Review

Mass spectrometry (MS) has become an attractive analytical method in clinical analysis due to its comprehensive advantages of high sensitivity, high specificity and high throughput. Separation techniques coupled MS detection (e.g., LC-MS/MS) have shown unique advantages over immunoassay and have developed as golden criterion for many clinical applications. This review summarizes the characteristics and applications of MS, and emphasizes the high efficiency of MS in clinical research. In addition, this review also put forward further prospects for the future of mass spectrometry technology, including the introduction of miniature MS instruments, point-of-care detection and high-throughput analysis, to achieve better development of MS technology in various fields of clinical application. Moreover, as ambient ionization mass spectrometry (AIMS) requires little or no sample pretreatment and improves the flux of MS, this review also summarizes its potential applications in clinic.

China nationwide landscape of 16 types inherited metabolic disorders: a retrospective analysis on 372,255 clinical cases

BACKGROUND

Inherited metabolic disorders (IMDs) usually occurs at young age and hence it severely threatening the health and life of young people. While so far there lacks a comprehensive study which can reveals China's nationwide landscape of IMDs. This study aimed to evaluate IMDs incidence and regional distributions in China at a national and province level to guide clinicians and policy makers.

METHODS

The retrospective study conducted from January 2012 to March 2021, we analyzed and characterized 372255 cases' clinical test information and diagnostic data from KingMed Diagnostics Laboratory. The samples were from 32 provincial regions of China, the urine organic acids were detected by gas chromatography-mass spectrometry (GC-MS), amino acids and acylcarnitines in dried blood spots were detected by liquid chromatography-tandem mass spectrometry (LC-MS/MS). We did a statistical analysis of the distribution of the 16 most common IMDs in amino acid disorders and organic acidemias, and then paid special attention to analyze the age and regional distributions of different IMDs. The statistical analyses and visualization analysis were performed with the programming language R (version 4.2.1).

RESULTS

There were 4911 positive cases diagnosed, which was 1.32% of the total sample during the ten-year study period. Most diseases tended to occur at ages younger than 18 year-old. The Ornithine Transcarbamylase Deficiency tended to progress on male infants who were less than 28 days old. While the peak of the positive case number of Citrin Deficiency disease (CD) was at 1-6 months. Different IMDs' had different distribution patterns in China's provinces. Methylmalonic Acidemias and Hyperphenylalaninemia had an imbalanced distribution pattern in China and its positive rate was significantly higher in North China than South China. Conversely, the positive rate of CD was significantly higher in South China than North China.

CONCLUSIONS

Results of this work, such as the differences in distribution pattern of different diseases in terms of age, region, etc. provide important insights and references for clinicians, researchers and healthcare policy makers. The policy makers could optimize the better health screening programs for covering children and infants in specific ages and regions based on our findings.

Clinical, biochemical, and genetic analysis of 28 Chinese patients with holocarboxylase synthetase deficiency

BACKGROUND

This study aimed to describe the clinical, biochemical, and molecular characteristics of Chinese patients with holocarboxylase synthetase (HLCS) deficiency, and to investigate the mutation spectrum of HCLS deficiency as well as their potential correlation with phenotype.

METHODS

A total of 28 patients with HLCS deficiency were enrolled between 2006 and 2021. Clinical and laboratory data were reviewed retrospectively from medical records.

RESULTS

Among the 28 patients, six patients underwent newborn screening, of which only one was missed. Therefore, 23 patients were diagnosed because of disease onset. Among all the patients, 24 showed varying degrees of symptoms such as rash, vomiting, seizures, and drowsiness, while only four cases remained asymptomatic nowadays. The concentration of 3-hydroxyisovalerylcarnitine (C5-OH) in blood and pyruvate, 3-hydroxypropionate, methylcitric acid, 3-hydroxyvaleric acid, 3-methylcrotonylglycine in urine were increased greatly among affected individuals. After prompt supplement of biotin, both the clinical and biochemical symptoms were dramatically resolved and nearly all patients developed normal intelligence and physique on follow-up. DNA sequencing revealed 12 known and 6 novel variants in the HLCS gene of patients. Among them, the variant of c.1522C > T was the most common.

CONCLUSIONS

Our findings expanded the spectrum of phenotypes and genotypes for HLCS deficiency in Chinese populations and suggested that with timely biotin therapy, patients with HLCS deficiency showed low mortality and optimistic prognosis. Newborn screening is crucial for early diagnosis, treatment, and long-term outcomes.

Prenatal Diagnosis of Isovaleric Acidemia From Amniotic Fluid Using Genetic and Biochemical Approaches

Background: Isovaleric acidemia (IVA) is an inborn error of leucine metabolism and different approaches have been applied to its prenatal diagnosis. However, systemic application of a biochemical strategy is rare. To evaluate its reliability and validity, we conducted a retrospective study of our experience with metabolite measurement together with genetic analysis in IVA prenatal diagnosis at a single center.

Methods: A total of eight pregnancies whose probands were diagnosed as IVA were referred to our center for prenatal diagnosis. Prenatal data of genetic analysis and metabolite measurement using tandem mass spectrometry (MS/MS) and gas chromatography/mass spectrometry (GC/MS) in amniotic fluid (AF) samples were retrospectively reviewed.

Results: Genetic and biochemical results were both available in these eight at-risk fetuses. Among them, two fetuses had higher levels of isovalerylcarnitine (C5) and C5/acetylcarnitine (C2) in AF compared with normal reference range and, thus, were determined to be affected, both of whom were found to carry compound heterogeneous mutations according to genetic analysis. The remaining six fetuses were determined to be unaffected based on a normal AF metabolite profile, except one showed slightly elevated C5 and they were found to be carriers according to genetic analysis. However, the level of isovalerylglycine (IVG) could not be detected at all in both groups.

Conclusion: The biochemical analysis, as a quick and convenient method, could be an additional reliable option for the prenatal diagnosis of IVA, especially in families with inconclusive genetic results, and can achieve a more precise diagnosis in conjunction with mutation analysis.

Prevalence of methylmalonic acidemia among newborns and the clinical-suspected population: a meta-analyse

IMPORTANCE

Knowing the scale of rare inborn errors is important for screening and resource allocation. Evidence on the prevalence of methylmalonic acidemia (MMA) among newborns and the clinical-suspected population from large-scale screening programs needs to be systematically synthesized.

OBJECTIVE

To estimate the worldwide prevalence of MMA for newborns and the clinical-suspected population and explore the differences in different regions, periods, and diagnostic technologies.

DATA SOURCES

MEDLINE, Embase, CRD, Cochrane Library, Scopus, CINAHL, and PROSPERO. Study Selection: All studies reporting the epidemiology characteristics of MMA were selected.

DATA EXTRACTION AND SYNTHESIS

Characteristics of study, subjects, and epidemiology were extracted, random-effect models were used for meta-analyses.

MAIN OUTCOME AND MEASURE

Pooled prevalence of MMA.

RESULTS

This study included 111 studies. The pooled prevalence of MMA worldwide was 1.14 per 100,000 newborns (1516/190,229,777 newborns, 95% CI: 0.99-1.29) and 652.11 per 100,000 clinical-suspected patients (1360/4,805,665 clinical-suspected individuals, CI: 544.14-760.07). Asia and Africa got a higher pooled prevalence of MMA. The prevalence of MMA in newborns increased through the years, while that in the clinical-suspected population decreased. Collecting blood ≥ 72 h after birth had a higher pooled prevalence of MMA than collecting during 24 h-72 h after birth. The combining-use of MS/MS and GC/MS had a higher pooled prevalence than the single-use of MS/MS or GC/MS. Prevalence of cbl C, mut, cbl B, cbl A, isolated MMA, combined MMA and homocystinuria, vitamin B12-responsive MMA was synthesized.

CONCLUSIONS AND RELEVANCE

Prevalence of MMA among newborns was extremely low, but considerably high in the clinical-suspected population, indicating the need for more efficient newborn screening strategies and closer monitoring of the high-risk population for the early signs of MMA. Asia and Africa should attach importance to the high prevalence of MMA. Further diagnostic tests were recommended for the combining-use vs single-use of MS/MS and GC/MS and for collecting blood after 72 h vs during 24-72 h after birth.

Clinical and molecular characteristics of 69 Chinese patients with ornithine transcarbamylase deficiency

Background

This study aimed to describe the clinical and biochemical features of Chinese patients with ornithine transcarbamylase deficiency (OTCD), and to investigate the mutation spectrum of OTC gene and their potential correlation with phenotype.

Methods

Sixty-nine patients with OTCD were enrolled between 2004 and 2019. Clinical and laboratory data were reviewed retrospectively from medical records.

Results

Fifteen cases (13 males, 2 females) presented with early onset; 53 cases (21 males, 32 females) had late onset, and one female was asymptomatic. The median onset age was 1.5 years (range 1 day–56 years). Urine orotic acid levels were increased in all patients tested, while only 47.6% of patients showed decreased serum levels of citrulline. The peak plasma ammonia levels were higher in early-onset patients than in late-onset patients (P < 0.01). Fifty-four different mutations of OTC gene were identified and 18 of them were novel. R277W (10.6%) was the most common mutation, followed by G195R (4.6%) and A209V (3.0%). By June 2019, 41 patients had survived, 24 were deceased, and 4 were lost to follow-up. Among the survivors, 13 patients had received liver transplantation at a median age of 3 years, with a one-year survival rate of 100%. The mortality of OTCD is extremely high among patients with early onset (80.0% versus 24.5% in patients with late onset).

Conclusions

The evaluation of serum citrulline level is of limited value in diagnosis of OTCD, while urine orotic acid detection and genetic testing are more helpful.

Incidence of inborn errors of metabolism detected by tandem mass spectrometry in China: A census of over seven million newborns between 2016 and 2017

BACKGROUND

The incidence of inborn errors of metabolism varies widely across countries. Very few studies have analyzed the incidence of these disorders in Mainland China. We aimed to estimate the overall and disease-specific incidences of inborn errors of metabolism in Chinese newborns and investigate the geographical distribution of these disorders.

METHODS

A national cross-sectional survey was conducted to investigate newborn inborn errors of metabolism screening by tandem mass spectroscopy in Mainland China between 2016 and 2017. A total of 246 newborn screening centers were surveyed using a standardized questionnaire. We examined the cumulative and disease-specific incidences of inborn errors of metabolism in Mainland China as a whole and in different geographical locations.

RESULTS

Over 7 million newborns were screened and 2747 were diagnosed with inborn errors of metabolism, yielding an overall incidence of 38.69 per 100,000 births (95% confidence interval: 37.27-40.17). The most common disorders were amino acid disorders (17.14 per 100,000 births, 95% confidence interval: 16.21-18.13), followed by organic acid disorders (12.39 per 100,000 births, 95% confidence interval: 11.60-13.24) and fatty acid oxidation disorders (9.16 per 100,000 births, 95% confidence interval: 8.48-9.89). The overall and disease-specific incidence rates differed significantly across geographical locations (P < 0.001).

CONCLUSIONS

The overall incidence of inborn errors of metabolism in Chinese newborns is relatively high. It is urgent to establish the recommended uniform screening panel for inborn errors of metabolism to guide the national and regional tandem mass spectroscopy newborn screening programs.

Biochemical and genetic approaches to the prenatal diagnosis of propionic acidemia in 78 pregnancies

Background

Propionic acidemia (PA) is a serious metabolic disorder, and different approaches have been applied to its prenatal diagnosis. To evaluate the reliability and validity of a biochemical strategy in the prenatal diagnosis of PA, we conducted a retrospective study of our 11-year experiences at a single center.

Methods

We accumulated data from 78 pregnancies from 58 families referred to our center and provided prenatal diagnosis by directed genetic analysis and/or metabolite measurement using tandem mass spectrometry (MS/MS) and gas chromatography/mass spectrometry (GC/MS) of amniotic fluid (AF) samples.

Results

Sixty-five unaffected fetuses (83.33%) and 13 affected fetuses (16.67%) were confirmed in our study. The characteristic metabolites including propionylcarnitine (C3) level, C3/acetylcarnitine (C2) ratio and 2-methylcitric acid (2MCA) level in unaffected and affected groups showed significant differences (P < 0.0001), while the level of 3-hydroxypropionic acid (3HPA) showed no significant difference between the two groups (P > 0.05).Of the 78 pregnancies, 24 fetuses were found to have either one causative pathogenic variant or were without genetic information in the proband. Three of these fetuses had elevated AF levels of C3, C3/C2 ratio, and 2MCA and, thus, were determined to be affected, while the remaining fetuses were determined to be unaffected based on a normal AF metabolite profile. Our genetic and biochemical results were highly consistent with postnatal follow-up results on all unaffected fetuses.

Conclusions

We conclude that a biochemical approach can serve as a fast and convenient prenatal diagnostic method for pregnancies at an increased risk for PA, which could be used in conjunction with genetic testing for precise prenatal diagnosis of this disorder. In our analysis, the characteristic metabolites C3 level, C3/C2 ratio, and 2MCA level in AF supernatant were dependable biochemical markers for diagnosis, of which the C3/C2 ratio appears to be the most reliable biochemical marker for the prenatal diagnosis of PA.

Prenatal Diagnosis of Glutaric Acidemia I Based on Amniotic Fluid Samples in 42 Families Using Genetic and Biochemical Approaches

Direct mutation analysis is the major method for glutaric acidemia I (GA-I) prenatal diagnosis, while systemic application of a biochemical strategy is rare. We describe our experiences with metabolite measurement together with mutation analysis in GA-I prenatal diagnosis at a single center over 10 years. The data of genetic analysis and metabolite measurement using gas chromatography/mass spectrometry(GC/MS) and tandem mass spectrometry(MS/MS) in amniotic fluid samples of 44 fetuses from 42 GA-I families referred to our center from 2009 to 2019 were retrospectively analyzed. Among these 44 fetuses, genetic and biochemical results were both available in 39 fetuses. Of these, 6 fetuses were judged as affected and 33 fetuses as unaffected by mutation analysis. The levels of glutarylcarnitine (C5DC), C5DC/octanoylcarnitine (C8), and glutaric acid in the supernatant of amniotic fluid from affected fetuses were significantly higher than those in unaffected fetuses [1.73μmol/L (0.89–4.19) vs. 0.16μmol/L (0.06–0.37), 26.26 (12.4–55.55) vs. 2.23 (1.04–8.44), and 103.94 mmol/mol creatinine (30.37–148.31) vs. 1.01mmol/mol creatinine (0–9.81), respectively; all P < 0.0001]. Among all families, two were found to have one causative mutation in the proband, in four pregnancies from these two families, three fetuses were judged as “unaffected” and one was judged as “affected” according to metabolites results. Postnatal follow-up showed a normal phenotype in all unaffected fetuses judged by mutation or metabolite analysis. C5DC, C5DC/C8, and glutaric acid levels in the supernatant of amniotic fluid showed significant differences and no overlap between the affected and unaffected fetuses. Biochemical strategy could be implemented as a quick and convenient method for the prenatal diagnosis of GA-I.

Expanded newborn screening for inborn errors of metabolism by tandem mass spectrometry in newborns from Xinxiang city in China

Background

Tandem mass spectrometry is a powerful technology available in China over the last 15 years. The development of tandem mass spectrometry had made it possible to rapidly screen newborns for inborn errors of metabolism. The aim of this study was to determine the birth incidence of inborn errors of metabolism through expanded screening of newborns by tandem mass spectrometry in Xinxiang area.

Methods

Dried blood spots from 50 112 newborns were assessed for inborn errors of metabolism by tandem mass spectrometry. The diagnoses were confirmed based on the clinical features, conventional laboratory tests, and the organic acid levels tested in urine by gas chromatography‐mass spectrometry.

Results

The study findings revealed that 31 newborns were diagnosed with inborn errors of metabolism. The total incidence rate of inborn errors of metabolism was 1/1617, and these included 16 cases of amino acid disorders (51.6%), nine cases of organic acid disorders (29.0%), and 6 (19.4%) cases of fatty acid beta‐oxidation disorders.

Conclusions

The screening for the incidence of inborn errors of metabolism in Xinxiang area showed that the rate was higher than previously reported. This study provides valuable data which may be useful in facilitating improvements in the expansion of screening to enable early diagnosis and treatment of inborn errors of metabolism before the onset of symptoms.

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.

Prenatal diagnosis of methylmalonic aciduria from amniotic fluid using genetic and biochemical approaches

OBJECTIVES

This study reported the clinical prenatal diagnosis experience of families affected by methylmalonic acidemia (MMA) evaluated at a single prenatal diagnosis center over 8 years, and the reliability of a biochemical approach for prenatal diagnosis was analyzed.

METHODS

Prenatal diagnosis data for 187 MMA families referred to our center from 2009 to 2016 were reviewed retrospectively. The results of the genetic analysis and biochemical approach were compared.

RESULTS

A total of 41 MMA-affected pregnancies (21%) were identified. The biochemical analysis could identify the true status of 99.5% of fetuses. The diagnostic sensitivities of the propionylcarnitine (C3) level, the C3 to acetylcarnitine (C2) ratio (C3/C2), the methylmalonic acid, and methylcitrate levels in the amniotic fluid were 95.1%, 100%, 100%, and 82.9%, respectively, and the specificities were 98.7%, 99.3%, 97.4%, and 96.7%, respectively.

CONCLUSIONS

The biochemical analysis could be optionally used in the prenatal diagnosis of MMA, especially in cases where the genetic results are inconclusive. Among the four tested biochemical markers, C3/C2 appeared to be the most reliable.

Two Infants With Beta-Ketothiolase Deficiency Identified by Newborn Screening in China

Beta-ketothiolase deficiency (BKTD) is an autosomal recessive disease caused by a defect of mitochondrial acetoacetyl-CoA thiolase. Beginning in 2014, we carried out newborn screening by tandem mass spectrometry (MS/MS) followed by next-generation sequencing (NGS) and identified two infants with BKTD among 203,750 newborns born in Jiangsu Province, China. Both infants showed the characteristic chemical abnormalities of BKTD. We used NGS to confirm variants in the ACAT1. Patient 1 had the compound heterozygous variants c.721dupA and c.928G > C. Patient 2 had compound heterozygosity for the c.238+1G > A and c.1163G > T variants. c.721dupA, c.928G > C and c.1163G > T were suspected to be likely pathogenic, whereas c.238+1G > A was determined to be pathogenic. None of the four variants have been reported in the literature. Patient 1 presented with onset of metabolic acidosis and neonatal hypoglycemia 8 days after birth, whereas patient 2 was detected through neonatal disease screening but had no clinical manifestations. These findings contribute to our understanding of the clinical characteristics and genetic basis of BKTD.

Application of Next-Generation Sequencing Following Tandem Mass Spectrometry to Expand Newborn Screening for Inborn Errors of Metabolism: A Multicenter Study

This study explored the effectiveness of expanding newborn screening (NBS) by tandem mass spectrometry (TMS) and gene diagnosis by next-generation sequencing (NGS). First, we described the characteristics of gene variants in Jiangsu Province. We collected clinical data from three NBS centers. All infants followed a unified screening and diagnosis process. After obtaining informed consent, dried blood spots (DBSs) were collected and analyzed by TMS. If the results fell outside of the cut-off value, repeat analysis was performed. If the re-test results remained abnormal, the infant was recalled for further assessment. We performed targeted sequencing using the extended edition panel of inborn errors of metabolism (IEM) to detect 306 genes using the Illumina HiSeq 2500 platform. A total of 536,008 babies underwent NBS by TMS in three NBS centres. In total, 194 cases were eventually diagnosed with various types of inherited metabolic diseases, with an overall incidence of 1/2763. There were 23 types of diseases, including ten amino acid disorders (43.5%), eight organic acidaemias (34.8%) and five fatty acid oxidation defects (21.7%). In these infants, we clearly identified variants of disease-causing genes by next-generation sequencing (NGS). Most had two variants and others had one or three variants: 88% of gene variants were heterozygous and 12% were homozygous. There is a certain incidence of IEM in Jiangsu Province and it is necessary to carry out screening for 27 diseases. Meanwhile, NGS combined with TMS offers an enhanced plan for NBS for IEM.

Age-Specific Cut-off Values of Amino Acids and Acylcarnitines for Diagnosis of Inborn Errors of Metabolism Using Liquid Chromatography Tandem Mass Spectrometry

Liquid Chromatography tandem mass spectrometry (LC-MS/MS) is used for the diagnosis of more than 30 inborn errors of metabolisms (IEMs). Accurate and reliable diagnosis of IEMs by quantifying amino acids (AAs) and acylcarnitines (ACs) using LC-MS/MS systems depend on the establishment of age-specific cut-offs of the analytes. This study aimed to (1) determine the age-specific cut-off values of AAs and ACs in Bangladesh and (2) validate the LC-MS/MS method for diagnosis of the patients with IEMs. A total of 570 enrolled healthy participants were divided into 3 age groups, namely, (1) newborns (1-7 days), (2) 8 days–7 years, and (3) 8–17 years, to establish the age-specific cut-offs for AAs and ACs. Also, 273 suspected patients with IEMs were enrolled to evaluate the reliability of the established cut-off values. Quantitation of AAs and ACs was performed on an automated LC-MS/MS system using dried blood spot (DBS) cards. Then the specimens of the enrolled clinically suspected patients were analyzed by the established method. Nine patients came out as screening positive for different IEMs, including two borderline positive cases of medium-chain acyl-CoA dehydrogenase deficiency (MCAD). A second-tier test for confirmation of the screening positive cases was conducted by urinary metabolic profiling using gas chromatography- mass spectrometry (GC-MS). Out of 9 cases that came out as screening positive by LC-MS/MS, seven cases were confirmed by urinary GC-MS analysis including 3 cases with phenylketonuria, 1 with citrullinemia type II, 1 with methylmalonic acidemia, 1 with isovaleric acidemia and 1 with carnitine uptake defect. Two borderline positive cases with MCAD were found negative by urinary GC-MS analysis. In conclusion, along with establishment of a validated LC-MS/MS method for quantitation of AAs and ACs from the DBS cards, the study also demonstrates the presence of predominantly available IEMs in Bangladesh.

Global birth prevalence and mortality from inborn errors of metabolism: a systematic analysis of the evidence

Background

Inborn errors of metabolism (IEM) are a group of over 500 heterogeneous disorders resulting from a defect in functioning of an intermediate metabolic pathway. Individually rare, their cumulative incidence is thought to be high, but it has not yet been estimated globally. Although outcomes can often be good if recognised early, IEM carry a high fatality rate if not diagnosed. As a result, IEM may contribute significantly to the burden of non-communicable childhood morbidity.

Methods

We conducted a systematic literature review of birth prevalence and case fatality of IEM globally, with search dates set from 1980 to 2017. Using random-effects meta-analysis, we estimated birth prevalence of separate classes of IEM and all-cause IEM, split by geographical region. We also estimated levels of parental consanguinity in IEM cases and global case fatality rates and resultant child deaths from all-cause IEM.

Findings

49 studies met our selection criteria. We estimate the global birth prevalence of all-cause IEM to be 50.9 per 100 000 live births (95% confidence intervals (CI) = 43.4-58.4). Regional pooled birth prevalence rates showed the highest rates of IEM to be in the Eastern Mediterranean region (75.7 per 100 000 live births, 95% CI = 50.0-101.4), correlating with a higher observed rate of parental consanguinity in studies from this area. We estimate case fatality rates to be 33% or higher in low- and middle-income countries (LMICs), resulting in a minimum of 23 529 deaths from IEM per year globally (95% CI = 20 382-27 427), accounting for 0.4% of all child deaths worldwide.

Conclusions

IEM represent a significant cause of global child morbidity and mortality, comprising a notable proportion of child deaths currently not delineated in global modelling efforts. Our data highlight the need for policy focus on enhanced laboratory capacity for screening and diagnosis, community interventions to tackle parental consanguinity, and increased awareness and knowledge regarding management of IEM, particularly in LMICs.

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.

Diagnosis and therapeutic monitoring of inborn errors of metabolism in 100,077 newborns from Jining city in China

BACKGROUND

Mandatory newborn screening for metabolic disorders has not been implemented in most parts of China. Newborn mortality and morbidity could be markedly reduced by early diagnosis and treatment of inborn errors of metabolism (IEM). Methods of screening for IEM by tandem mass spectrometry (MS/MS) have been developed, and their advantages include rapid testing, high sensitivity, high specificity, high throughput, and low sample volume (a single dried blood spot).

METHODS

Dried blood spots of 100,077 newborns obtained from Jining city in 2014-2015 were screened by MS/MS. The screening results were further confirmed by clinical symptoms and biochemical analysis in combination with the detection of neonatal deficiency in organic acid, amino acid, or fatty acid metabolism and DNA analysis.

RESULTS

The percentages of males and females among the 100,077 infants were 54.1% and 45.9%, respectively. Cut-off values were established by utilizing the percentile method. The screening results showed that 98,764 newborns were healthy, and 56 out of the 1313 newborns with suspected IEM were ultimately diagnosed with IEM. Among these 56 newborns, 19 (1:5267) had amino acid metabolism disorders, 26 (1:3849) had organic acid metabolism disorders, and 11 (1:9098) had fatty acid oxidation disorders. In addition, 54 patients with IEM were found to carry mutations, and the other 2 patients had argininemia.

CONCLUSIONS

Fifty-six cases of metabolic disorders in Jining were confirmed via newborn screening (NBS) by MS/MS. Early diagnosis and treatment are crucial for the survival and well-being of affected children. A nationwide NBS program using MS/MS is recommended, especially in poor areas of China.

Frequency of inborn errors of metabolism screening for children with unexplained acute encephalopathy at an emergency department

OBJECTIVE

Our study aimed to estimate the frequency of inborn errors of metabolism (IEMs) in patients presenting with acute encephalopathy-like picture at an emergency department (ED).

SUBJECTS AND METHODS

Our study was a prospective observational study conducted on 30 patients admitted to the pediatric ED with unexplained acute encephalopathy. The study included 30 children with an age ranging from 1 month to 5 years. All patients were subjected to full history taking, thorough clinical examination, and laboratory investigations including serum ammonia, serum lactate, arterial blood gases, tandem mass spectroscopy, organic acid of urine, cerebrospinal fluid examination to exclude central nervous system infection plus the routine laboratory tests (kidney functions, liver functions, random blood glucose, complete blood picture), and brain imaging computed tomography and/or magnetic resonance imaging brain.

RESULTS

Thirty children presented with acute encephalopathy at the ED. All were screened for suspected IEMs. Ten (33.3%) of them was positive in the initial screening test. There were four (13.3%) patients with possible mitochondrial diseases, four (13.3%) patients with possible organic acidemia, one (3.3%) patient with possible urea cycle defect, and one (3.3%) patient with possible nonketotic hyperglycinemia.

CONCLUSION

Any case of unexplained acute encephalopathy presenting to the ED should be investigated for suspected IEM, especially in high-risk families, as early interventions will lead to improved outcome.

Atypical hemolytic uremic syndrome induced by CblC subtype of methylmalonic academia: A case report and literature review

RATIONALE

Methylmalonic acidemia (MMA) is a common organic acidemia, mainly due to methylmalonyl-CoA mutase (MCM) or its coenzyme cobalamin (VitB12) metabolic disorders. Cobalamin C (CblC) type is the most frequent inborn error of cobalamin metabolism; it can develop symptoms in childhood and often combine multisystem damage, which leads to methylmalonic acid, propionic acid, methyl citrate, and other metabolites abnormal accumulation, causing nerve, liver, kidney, bone marrow, and other organ damage.

PATIENT CONCERNS

A 4-year-old girl presented with paleness, fatigue, severe normochromic anemia, and acute kidney injury.

DIAGNOSIS

Based on severe normochromic anemia and acute kidney injury, renal biopsy showed membranous proliferative glomerular lesions and thrombotic microvascular disease, supporting the diagnosis of aHUS. Although the serum vitamin B12 was normal, further investigation found the concentration of urinary methylmalonic acid and serum homocysteine increased obviously, genetic analysis revealed a heterozygous MMACHC mutation (exonl: c. 80A >G, c. 609G >A). The final diagnosis was aHUS induced by inherited methylmalonic acidemia (MMACHC heterozygous mutation exonl: c. 80A >G, c. 609G >A).

INTERVENTIONS

The patient was treated with a 1mg vitamin B12 intramuscular injection daily for 4 days after which the dose was then adjusted to a 1mg intramuscular injection twice a week. At the same time, the girl was given levocarnitine, betaine, folic acid, along with supportive treatment.

OUTCOMES

After treated by vitamin B12 for 10 days, the patient condition significantly improved, Follow-up results showed complete recovery of hemoglobin and renal function.

LESSONS

Although the majority of MMA onset from neurological damage, our case illustrates that partial CblC-type MMA can onset with severe metabolic aHUS. On the basis of chronic thrombotic microangiopathy (TMA)-induced renal damage, it can be complicated by acute hemolytic lesions. MMA should be considered in those patients with unclear microangiopathic hemolytic anemia accompany significant megaloblastic degeneration in bone marrow. We should pay attention to the causes and adopt a reasonable treatment strategy.

Applying targeted next generation sequencing to dried blood spot specimens from suspicious cases identified by tandem mass spectrometry-based newborn screening

BACKGROUND

Tandem mass spectrometry (TMS)-based newborn screening has been proven successful as one of the public healthcare programs, although the practicability has not yet been specifically addressed.

METHODS

Sixty residual dried blood spot (DBS) specimens from confirmation/diagnosis-insufficient cases discovered by TMS screening were analyzed by targeted next generation sequencing (TNGS) assay.

RESULTS

In total, 26, 11, 9, and 14 cases were diagnosed as positive, high risk, low risk, and negative, respectively.

CONCLUSIONS

Applying the DBS-based TNGS assay for the accurate and rapid diagnosis of inborn errors of metabolism (IEMs) is feasible, competent, and advantageous, enabling a simplified TMS screening-based, TNGS assay-integrated newborn screening scheme highlighting an efficient, executable, and one-step screening-to-diagnosis workflow.

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

BACKGROUND

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is a representative disorder of fatty acid oxidation and is one of the most prevalent inborn errors of metabolism among Caucasian populations. In Japan, however, it was as late as 2000 when the first patient was found, and enzymatic and genetic evaluation of MCAD deficiency began.

METHODS

We measured octanoyl-CoA dehydrogenase activity in lymphocytes of symptomatic children and newborn screening (NBS)-positive subjects who showed elevated levels of C8-acylcarnitine in blood. The results were further confirmed by direct sequencing of the ACADM gene.

RESULTS

The disease was diagnosed in 9 out of 18 symptomatic children. The affected patients showed residual activities from 0% to 3% of the normal average value, except for one patient with 10% activity. Concerning 50 NBS-positive subjects, 18 with enzymatic activities around 10% or lower and 14 with activities ranging from 13% to 30% were judged to be affected patients, and biallelic variants were detected in most of the cases tested. Newborns with higher enzymatic activities were estimated to be heterozygous carriers or healthy subjects, though biallelic variants were detected in 5 of them. Genetic analysis detected 22 kinds of variant alleles. The most prevalent was c.449_452delCTGA (p.T150Rfs), which was followed by c.50G>A (p.R17H), c.1085G>A (p.G362E), c.157C>T (p.R53C), and c.843A>T (p.R281S); these five variants accounted for approximately 60% of all the alleles examined.

CONCLUSION

Our study has revealed the unique genetic backgrounds of MCAD deficiency among Japanese, based on the largest series of non-Caucasian cases. A continuous spectrum of severity was also observed in our series of NBS-positive cases, suggesting that it is essential for every nation and ethnic group to accumulate its own information on gene variants, together with their enzymatic evaluation, in order to establish an efficient NBS system for MCAD deficiency.

Mutation analysis of methylmalonyl CoA mutase gene exon 2 in Egyptian families: Identification of 25 novel allelic variants

Methylmalonic aciduria (MMA) is an autosomal recessive disorder of methylmalonate and cobalamin (cbl; vitamin B₁₂) metabolism. It is an inborn error of organic acid metabolism which commonly results from a defect in the gene encoding the methylmalonyl-CoA mutase (MCM) apoenzyme. Here we report the results of mutation study of exon 2 of the methylmalonyl CoA mutase (MUT) gene, coding MCM residues from 1 to 128, in ten unrelated Egyptian families affected with methylmalonic aciduria. Patients were presented with a wide-anion gap metabolic acidosis. The diagnosis has established by the measurement of C3 (propionylcarnitine) and C3:C2 (propionylcarnitine/acetylcarnitine) in blood by using liquid chromatography–tandem mass spectrometry (LC/MS–MS) and was confirmed by the detection of an abnormally elevated level of methylmalonic acid in urine by using gas chromatography–mass spectrometry (GC/MS) and isocratic cation exchange high-performance liquid-chromatography (HPLC). Direct sequencing of gDNA of the MUT gene exon 2 has revealed a total of 26 allelic variants: ten of which were intronic, eight were located upstream to the exon 2 coding region, four were novel modifications predicted to affect the splicing region, three were novel mutations within the coding region: c.15G > A (p.K5K), c.165C > A (p.N55K) and c.7del (p.R3EfsX14), as well as the previously reported mutation c.323G > A (p.R108H).

Inherited metabolic diseases in the Southern Chinese population: spectrum of diseases and estimated incidence from recurrent mutations

Inherited metabolic diseases (IMDs) are a large group of rare genetic diseases. The spectrum and incidences of IMDs differ among populations, which has been well characterised in Caucasians but much less so in Chinese. In a setting of a University Hospital Metabolic Clinic in Hong Kong, over 100 patients with IMDs have been seen during a period of 13 years (from 1997 to 2010). The data were used to define the spectrum of diseases in the Southern Chinese population. Comparison with other populations revealed a unique spectrum of common IMDs. Furthermore, the incidence of the common IMDs was estimated by using population carrier frequencies of known recurrent mutations. Locally common diseases (their estimated incidence) include (1) glutaric aciduria type 1 (∼1/60,000), (2) multiple carboxylase deficiency (∼1/60,000), (3) primary carnitine deficiency (∼1/60,000), (4) carnitine-acylcarnitine translocase deficiency (∼1/60,000), (5) glutaric aciduria type 2 (∼1/22,500), (6) citrin deficiency (∼1/17,000), (7) tetrahydrobiopterin-deficient hyperphenylalaninaemia due to 6-pyruvoyl-tetrahydropterin synthase deficiency (∼1/60,000), (8) glycogen storage disease type 1 (∼1/150,000). In addition, ornithine carbamoyltransferase deficiency and X-linked adrenoleukodystrophy are common X-linked diseases. Findings of the disease spectrum and treatment outcome are summarised here which may be useful for clinical practice. In addition, data will also be useful for policy makers in planning of newborn screening programs and resource allocation.

Analysis of genetic mutations in Chinese patients with systemic primary carnitine deficiency

Systemic primary carnitine deficiency (CDSP) is caused by mutations in SLC22A5 gene, which encodes organic cation transporter 2(OCTN2). CDSP leads to skeletal or cardiac myopathy and hepatic encephalopathy. The present study aimed to identify SLC22A5 gene mutations and analyze the potential relationship between genotype and clinical symptoms in 20 Chinese patients with CDSP. The complete coding region of the SLC22A5 gene including intron-exon boundaries were amplified and sequenced in all patients. Eighteen different mutations were found; of which, nine were novel. The mutations clustering in exons 1 and 4 accounted for 66.7% of all mutant alleles (26/39). The c.760C>T (p. R254X) was the most frequent mutation (25.6%, 10/39), suggesting it as an ethnic founder mutation. The relationship between genotype and phenotype was investigated in patients carrying the R254X mutation. Homozygous patients with R254X were late-onset cases who presented with dilated cardiomyopathy and muscle weakness after 1 year of age. Compound heterozygous patients carrying R254X, combined with other missense mutations occurred in very specific positions, dramatically altered OCTN2 protein function. Based on the analysis of case studies, a clear relationship between free carnitine (C0) level in plasma and OCTN2 genotype was not found in the present work, however, the low plasma C0 level could not indicate disease severity or genotype. Further functional studies with a large sample size are required to understand the relationship between R254X mutation and CDSP.

Inborn errors of metabolism and expanded newborn screening: review and update

Inborn errors of metabolism (IEM) are a phenotypically and genetically heterogeneous group of disorders caused by a defect in a metabolic pathway, leading to malfunctioning metabolism and/or the accumulation of toxic intermediate metabolites. To date, more than 1000 different IEM have been identified. While individually rare, the cumulative incidence has been shown to be upwards of 1 in 800. Clinical presentations are protean, complicating diagnostic pathways. IEM are present in all ethnic groups and across every age. Some IEM are amenable to treatment, with promising outcomes. However, high clinical suspicion alone is not sufficient to reduce morbidities and mortalities. In the last decade, due to the advent of tandem mass spectrometry, expanded newborn screening (NBS) has become a mandatory public health strategy in most developed and developing countries. The technology allows inexpensive simultaneous detection of more than 30 different metabolic disorders in one single blood spot specimen at a cost of about USD 10 per baby, with commendable analytical accuracy and precision. The sensitivity and specificity of this method can be up to 99% and 99.995%, respectively, for most amino acid disorders, organic acidemias, and fatty acid oxidation defects. Cost-effectiveness studies have confirmed that the savings achieved through the use of expanded NBS programs are significantly greater than the costs of implementation. The adverse effects of false positive results are negligible in view of the economic health benefits generated by expanded NBS and these could be minimized through increased education, better communication, and improved technologies. Local screening agencies should be given the autonomy to develop their screening programs in order to keep pace with international advancements. The development of biochemical genetics is closely linked with expanded NBS. With ongoing advancements in nanotechnology and molecular genomics, the field of biochemical genetics is still expanding rapidly. The potential of tandem mass spectrometry is extending to cover more disorders. Indeed, the use of genetic markers in T-cell receptor excision circles for severe combined immunodeficiency is one promising example. NBS represents the highest volume of genetic testing. It is more than a test and it warrants systematic healthcare service delivery across the pre-analytical, analytical, and post-analytical phases. There should be a comprehensive reporting system entailing genetic counselling as well as short-term and long-term follow-up. It is essential to integrate existing clinical IEM services with the expanded NBS program to enable close communication between the laboratory, clinicians, and allied health parties. In this review, we will discuss the history of IEM, its clinical presentations in children and adult patients, and its incidence among different ethnicities; the history and recent expansion of NBS, its cost-effectiveness, associated pros and cons, and the ethical issues that can arise; the analytical aspects of tandem mass spectrometry and post-analytical perspectives regarding result interpretation.

Cost-benefit analysis of Hyperphenylalaninemia Due to 6-Pyruvoyl-Tetrahydropterin Synthase (PTPS) Deficiency: For Consideration of Expanded Newborn Screening in Hong Kong

Objectives

To evaluate the cost-benefit of implementing an expanded newborn screening programme for hyperphenylalaninemias due to 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency in Hong Kong.

Setting

Regional public hospitals in Hong Kong providing care for cases of inborn errors of metabolism.

Methods

Implementational and operational costs of a new expanded mass spectrometry-based newborn screening programme were estimated. Data on various medical expenditures for the mild and severe phenotypic subtypes were gathered from a case cohort diagnosed with PTPS deficiency from 2001 to 2009. Local incidence from a previously published study was used.

Results

Implementation and operational costs of an expanded newborn screening programme in Hong Kong were estimated at HKD 10,473,848 (USD 1,342,801) annually. Assuming a birthrate of 50,000 per year and an incidence of 1 in 29,542 live births, the medical costs and adjusted loss of workforce per year would be HKD 20,773,207 (USD 2,663,232). Overall the annual savings from implementing the programme would be HKD 9,632,750 (USD 1,234,968).

Conclusions

Our estimates show that implementation of an expanded newborn screening programme in Hong Kong is cost-effective, with a significant annual saving for public expenditure.

Spectrum analysis of common inherited metabolic diseases in Chinese patients screened and diagnosed by tandem mass spectrometry

BACKGROUND

Information concerning inherited metabolic diseases in China is scarce. We investigated the prevalence and age distributions of amino acid, organic acid, and fatty acid oxidation disorders in Chinese patients.

METHODS

Blood levels of amino acids and acylcarnitines (tandem mass spectrometry) were measured in 18,303 patients with suspected inherited metabolic diseases. Diagnosis was based on clinical features, blood levels of amino acids or acylcarnitines, urinary organic acid levels (gas chromatography-mass spectrometry), and (in some) gene mutation tests.

RESULTS

Inherited metabolic diseases were confirmed in 1,135 patients (739 males, 396 females). Median age was 12 months (1 day to 59 years). There were 28 diseases: 12 amino acid disorders (580 patients, 51.1%), with hyperphenylalaninemia (HPA) being the most common; nine organic acidemias (408 patients, 35.9%), with methylmalonic acidemia (MMA) as the most common; and seven fatty acid oxidation defects (147 patients, 13.0%), with multiple acyl-coenzyme A dehydrogenase deficiency (MADD) being the most common. Onset was mainly at 1-6 months for citrin deficiency, 0-6 months for MMA, and in newborns for ornithine transcarbamylase deficiency (OTCD). HPA was common in patients aged 1-3 years, and MADD was common in patients >18 years.

CONCLUSIONS

In China, HPA, citrin deficiency, MMA, and MADD are the most common inherited disorders, particularly in newborns/infants.

Clinical features and mutations in seven Chinese patients with very long chain acyl-CoA dehydrogenase deficiency

BACKGROUND

Very long chain acyl-CoA dehydrogenase deficiency (VLCADD) is an inherited metabolic disease caused by deleterious mutations in the ACADVL gene that encodes very long chain acyl-CoA dehydrogenase (VLCAD), and which can present as cardiomyopathy in neonates, as hypoketotic hypoglycemia in infancy, and as myopathy in late-onset patients. Although many ACADVL mutations have been described, no prevalent mutations in the ACADVL gene have been associated with VLCADD. Herein, we report the clinical course of the disease and explore the genetic mutation spectrum in seven Chinese patients with VLCADD.

METHODS

Seven Chinese patients, from newborn to 17 years old, were included in this study. Tandem mass spectrometry was performed to screen for VLCAD deficiency. All exons and flanking introns of the ACADVL gene were analyzed using polymerase chain reaction and direct sequencing. Online analysis tools were used to predict the impact of novel mutations.

RESULTS

All cases had elevated serum levels of tetradecanoylcarnitine (C14:1) which is the characteristic biomarker for VLCADD. The phenotype of VLCADD is heterogeneous. Two patients were hospitalized for hypoactivity and hypoglycemia shortly after birth. Three patients showed hepatomegaly and hypoglycemia in infancy. The other two adolescent patients showed initial manifestations of exercise intolerance or rhabdomyolysis. Three of the patients died at the age of 6-8 months. Eleven different mutations in the ACADVL gene in the 7 patients were identified, including seven reported mutations (p.S22X, p.W427X, p.A213T, p.G222R, p.R450H, c.296-297delCA, c.1605+1G>T) and four novel mutations (p.S72F, p.Q100X, p.M437T, p.D466Y). The p.R450H and p.D466Y (14.28%, 2/14 alleles) mutations were identified in two alleles respectively.

CONCLUSIONS

The clinical manifestations were heterog-eneous and ACADVL gene mutations were heterozygous in the seven VLCADD Chinese patients. R450H may be a relatively common mutation in Asian populations. The genotype and phenotype had a certain correlation in our patients.

Separation and identification of underivatized plasma acylcarnitine isomers using liquid chromatography-tandem mass spectrometry for the differential diagnosis of organic acidemias and fatty acid oxidation defects

A simple HPLC-MS/MS method has been established to separate and identify underivatized acylcarnitine isomers. Human plasma samples were deproteinized and concentrated. Acylcarnitines were separated on a reverse phase column and detected with triple quadrupole linear ion trap mass spectrometry. Deuterium-labeled internal standards were used for quantitation. To identify acylcarnitines without pure standards, information-dependent acquisition linking to enhanced product ion scan mode was used. 112 acylcarnitines, including stereoisomers, were found in samples of patients. Dicarboxylic acylcarnitines, such as methylmalonylcarnitine and glutarylcarnitine, were detected with high sensitivity. Three stereoisomers of (R,S)2-methyl-3-hydroxy butyrylcarnitine were detected in samples of patients with β-ketothiolase deficiency. Validation results revealed excellent precision and accuracy of the method. In general the within- and between-run coefficients of variation (CV%) were less than 15%, and recoveries were in the range of 92.7-117.5%. In addition, the reference intervals of acylcarnitines for children aged 3-day to13-year old were established. Using the new method and reference intervals, we have correctly diagnosed 49 patients with fatty acid oxidation defects or organic acidemias in 176 high-risk patients.

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.

Impact of inborn errors of metabolism on admission in a neonatal intensive care unit: a 4-year report

Inborn errors of metabolism (IEM) have greater repercussions in neonatology units. The aim of our study was to evaluate the impact of IEM in a neonatal intensive care unit (NICU) and the resources required to care for these neonates. All patients with IEM admitted in our unit during a 4-year period were evaluated for specific diagnosis, demographic data, clinical features, biochemical characteristics at admission, need for mechanical ventilation, use of extracorporeal removal therapy, and outcome at NICU discharge. The study group comprised 2742 infants, 39 of which required admission to the NICU (1.42% of admissions) because of severe symptoms and/or newborn screening. Five of the 39 had an earlier diagnosis and treatment because of expanded newborn screening. The average age at admission was 5 days [interquartile range (IQR, 3-9 days)] and the median length of stay in the NICU for the study population was 5 days (IQR, 3-12 days). Aggressive support was often necessary (extracorporeal removal therapy, mechanical ventilation). Ten patients died; thus the death rate was 25.6%. Overall mortality in the NICU was 10.4% during the study period. These observations shown that IEM may be very common in our population. Most patients with IEM admitted to a NICU require aggressive support (including mechanical ventilation and extracorporeal removal therapies), and consume significant resources for relatively shorter stays.

Analysis of gene mutations in Chinese patients with maple syrup urine disease

OBJECTIVE

Maple syrup urine disease (MSUD) is predominantly caused by mutations in the BCKDHA, BCKDHB and DBT genes, which encode for the E1α, E1β and E2 subunits of the branched-chain α-keto acid dehydrogenase complex, respectively. The aim of this study was to screen DNA samples from 16 Chinese MSUD patients and assess a potential correlation between genotype and phenotype.

METHODS

BCKDHA, BCKDHB and DBT genes were analyzed by polymerase chain reaction (PCR) and direct sequencing. Segments bearing novel mutations were identified by PCR-restriction fragment length polymorphism (PCR-RFLP) analysis.

RESULTS

Within the variant alleles, 28 mutations (28/32, 87.5%), were detected in 15 patients, while one patient displayed no mutations. Mutations were comprised of 20 different: 6 BCKDHA gene mutations in 4 cases, 10 BCKDHB gene mutations in 8 cases and 4 DBT gene mutations in 3 cases. From these, 14 were novel, which included 3 mutations in the BCKDHA gene, 7 in the BCKDHB gene and 4 in the DBT gene. Only two patients with mutations in the BCKDHB and DBT genes were thiamine-responsive and presented a better clinical outcome.

CONCLUSION

We identified 20 different mutations within the BCKDHA, BCKDHB and DBT genes among 16 Chinese MSUD patients, including 14 novel mutations. The majority were non-responsive to thiamine, associating with a worse clinical outcome. Our data provide the basis for further genotype-phenotype correlation studies in these patients, which will be beneficial for early diagnosis and in directing the approach to clinical intervention.

Impact of inborn errors of metabolism on admission in a neonatal intensive care unit--a prospective cohort study

OBJECTIVE

To estimate the incidence of Inborn errors of metobolism (IEM) in Neonatal intensive care unit (NICU) using tandem mass spectrometry and to determine the impact that these disorders have on NICU resources.

METHODS

During the period of study, 724 (81% eligible cases) dried blood filter-paper samples were collected from a NICU. The samples were analysed using tandem mass spectrometry. The diagnosis was further confirmed through clinical symptoms and by gas chromatography-mass spectrometry. The results were also confirmed by clinical follow-up of all positive patients in an overall interval of 1 year. The mean observation period was 11 months per neonate.

RESULTS

In total, 22 cases were screen positive and 8 cases of inborn errors of metabolism were detected. The incidence of IEM in the population of patients admitted to the authors' NICU was 1.1%. The most common inborn error found was methylmalonic acidemia (3 cases, 37.5%), and all of the cases needed aggressive treatment and invasive mechanical ventilation. There were two cases of Tyrosinemia type 1, one case each of Maple Syrup Urine Disease, Propionic Acidemia, and Multiple Acyl-CoA dehydrogenase deficiency (MADD). Five of the eight patients required invasive mechanical ventilation. The median length of NICU stay was 3 days (1~7 days) and early therapeutic intervention was effective for four of them and other four patients (50%) died.

CONCLUSIONS

The incidence of IEM in NICU was 1.1%, indicating an underestimation of the incidence of metabolic disorders prior to implementing screening. Most patients with IEM in the NICU required invasive mechanical ventilation and the mortality was increased due to underlying IEM.

Screening for inborn errors of metabolism in high-risk children: a 3-year pilot study in Zhejiang Province, China

BACKGROUND

Tandem mass spectrometry (MS/MS) has been available in China for 8 years. This technique makes it possible to screen for a wide range of previously unscreened inborn errors of metabolism (IEM) using a single test. This 3-year pilot study investigated the screening, diagnosis, treatment and outcomes of IEM in symptomatic infants and children.

METHODS

All children encountered in the Newborn Screening Center of Zhejiang Province during a 3-year period with symptoms suspicious for IEM were screened for metabolic diseases. Dried blood spots were collected and analyzed by tandem mass spectrometry. The diagnoses were further confirmed by clinical symptoms and biochemical analysis. Neonatal intrahepatic cholestasis caused by citrin deficiency, ornithine transcarbamylase deficiency and primary carnitine deficiency were confirmed by DNA analysis.

RESULTS

A total of 11,060 symptomatic patients (6,720 boys, 4,340 girls) with a median age of 28.8 months (range: 0.04-168.2 months) were screened. Among these, 62 were diagnosed with IEM, with a detection rate of 0.56%. Thirty-five were males and 27 females and the median age was 3.55 months (range 0.07-143.9 months). Of the 62 patients, 27 (43.5%) had aminoacidemias, 26 (41.9%) had organic acidemias and nine (14.5%) had fatty acid oxidation disorders.

CONCLUSIONS

Because most symptomatic patients are diagnosed at an older age, mental retardation and motor delay are difficult to reverse. Additionally, poor medication compliance reduces the efficacy of treatment. More extensive newborn screening is thus imperative for ensuring early diagnosis and enhancing the treatment efficacy of IEM.

Organic acidurias: an updated review

Organic acidurias are an important class of inherited metabolic disorders arising due to defect in intermediary metabolic pathways of carbohydrate, amino acids and fatty acid oxidation. This review summarizes the current knowledge about the important organic acidurias in the Indian population. Specifically, diagnosis and principles of treatment of organic acidurias are covered. The salient features of common organic acidurias as well as their prevalence in various parts of the world are reviewed in some detail.

Epilepsy in children with methylmalonic acidemia: electroclinical features and prognosis

OBJECTIVE

To summarize the electroclinical features and prognosis of epilepsy in children with methylmalonic acidemia (MMA).

METHODS

The medical records of hospitalized MMA patients associated with epilepsy were retrospectively reviewed. The clinical manifestations, laboratory examination results, and treatment modalities were analyzed.

RESULTS

From 63 pediatric inpatients diagnosed as MMA in Peking University First Hospital from June 1996 to December 2009, 27 children (42.9%) associated with epilepsy were enrolled in this study. These 27 patients were also accompanied with other neurological manifestations including mental retardation or regression (n=22), lethargy (n=10), increased muscle tone (n=8), muscle hypotonia (n=8), recurrent vomiting (n=4), tremor (n=2), ataxia (n=2), and abnormal posture (n=1).The onset age of seizure ranged from 8 days to 11 years. The seizure types included partial seizure (n=21), generalized tonic-clonic seizure (n=5), tonic seizure (n=3), myoclonic seizure (n=3), and epileptic spasms (n=2). Five patients had two or three seizure types. Nine patients (33.3%) had a history of status epilepticus. EEG showed slow background activity in 17 patients, focal or multifocal paroxysmal discharges in 16 patients, generalized paroxysmal discharges in four patients, hypsarrythmia in two patients, and suppression-burst pattern in one patient. Cranial MRI scans showed bilateral cerebral atrophy (n=14), increased T2 signal intensities in white matter (n=12), agenesis of corpus callosum (n=2), bilateral increased T2 signal intensities or necrosis in basal ganglia (n=2), and cerebellar atrophy (n=1). Twenty one patients were MMA combined with homocysteinemia. Seventeen patients were confirmed with cobalamin C disease and one with partial mutase deficiency (mut(-)). Vitamin B12-responsive patients had a better outcome compared with vitamin B12-unresponsive patients.

CONCLUSIONS

Epilepsy is a common manifestation of patients with MMA. Partial seizure is more common than other seizure types. Urine organic acid analysis should be performed for children with unknown cause of epilepsy combined with other neurological manifestations, so as to promptly identify the etiology and improve the prognosis.