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

Mass spectrometry for metabolomics analysis: Applications in neonatal and cancer screening

Chemical analysis by analytical instrumentation has played a major role in disease diagnosis, which is a necessary step for disease treatment. While the treatment process often targets specific organs or compounds, the diagnostic step can occur through various means, including physical or chemical examination. Chemically, the genome may be evaluated to give information about potential genetic outcomes, the transcriptome to provide information about expression actively occurring, the proteome to offer insight on functions causing metabolite expression, or the metabolome to provide a picture of both past and ongoing physiological function in the body. Mass spectrometry (MS) has been elevated among other analytical instrumentation because it can be used to evaluate all four biological machineries of the body. In addition, MS provides enhanced sensitivity, selectivity, versatility, and speed for rapid turnaround time, qualities that are important for instance in clinical procedures involving the diagnosis of a pediatric patient in intensive care or a cancer patient undergoing surgery. In this review, we provide a summary of the use of MS to evaluate biomarkers for newborn screening and cancer diagnosis. As many reviews have recently appeared focusing on MS methods and instrumentation for metabolite analysis, we sought to describe the biological basis for many metabolomic and additional omics biomarkers used in newborn screening and how tandem MS methods have recently been applied, in comparison to traditional methods. Similar comparison is done for cancer screening, with emphasis on emerging MS approaches that allow biological fluids, tissues, and breath to be analyzed for the presence of diagnostic metabolites yielding insight for treatment options based on the understanding of prior and current physiological functions of the body.

Abnormal biochemical indicators of neonatal inherited metabolic disease in carriers

BACKGROUND

Traditional biochemical screening for neonatal inherited metabolic diseases has high false-positive rates and low positive predictive values, which are not conducive to early diagnosis and increase parents' anxiety. This study analysed the relationship between gene variant carriers and their biochemical indicators in traditional biochemical screening, aiming to find explanations for false positives in newborns.

RESULTS

This retrospective study included 962 newborns. Newborns underwent traditional biochemical screening at birth using blood staining and genomic sequencing of their stored blood staining using the NeoSeq Pro panel, which was able to detect 154 pathogenic genes and 86 diseases. A total of 632 newborns were carriers of gene variants. 56% of congenital hypothyroidism carriers had higher thyroid-stimulating hormone levels than normal newborns. Abnormal biochemical indices were detected in 71% of carriers of organic acid metabolic diseases, 69% of carriers of amino acid metabolic diseases, and 85% of carriers of fatty acid β oxidation disorders. In carriers associated with organic acid metabolic diseases, the propionylcarnitine (C3), C3/acetylcarnitine (C2), and methylmalonylcarnitine (C4DC) + 3-hydroxyisovalerylcarnitine (C5OH) levels were higher than those in non-carriers (C3: 4.12 vs. 1.66 µmol/L; C3/C2: 0.15 vs. 0.09; C4DC + C5OH: 0.22 vs. 0.19 µmol/L). In carriers associated with amino acid metabolic diseases, phenylalanine levels were higher than those in non-carriers (68.00 vs. 52.05 µmol/L). For carriers of fatty acid β oxidation disorders, butyrylcarnitine levels were higher than those in non-carriers (0.31 vs. 0.21 µmol/L), while the free carnitine levels were lower than those in non-carriers (14.65 vs. 21.87 µmol/L). There was a higher occurrence of carriers among newborns who received false-positive results for amino acid metabolic diseases compared to those who received negative results (15.52% vs. 6.71%). Similarly, there was a higher occurrence of carriers among newborns who received false-positive results for fatty acid β oxidation disorders compared to those who received negative results (28.30% vs. 7.29%).

CONCLUSIONS

This study showed that the carriers comprised a large number of newborns. Carriers had abnormal biochemical indicators compared with non-carriers, which could explain the false-positive rate for newborns using traditional newborn biochemical screening, especially in amino acid metabolic and fatty acid β oxidation disorders.

Improving the second-tier classification of methylmalonic acidemia patients using a machine learning ensemble method

INTRODUCTION

Methylmalonic acidemia (MMA) is a disorder of autosomal recessive inheritance, with an estimated prevalence of 1:50,000. First-tier clinical diagnostic tests often return many false positives [five false positive (FP): one true positive (TP)]. In this work, our goal was to refine a classification model that can minimize the number of false positives, currently an unmet need in the upstream diagnostics of MMA.

METHODS

We developed machine learning multivariable screening models for MMA with utility as a secondary-tier tool for false positives reduction. We utilized mass spectrometry-based features consisting of 11 amino acids and 31 carnitines derived from dried blood samples of neonatal patients, followed by additional ratio feature construction. Feature selection strategies (selection by filter, recursive feature elimination, and learned vector quantization) were used to determine the input set for evaluating the performance of 14 classification models to identify a candidate model set for an ensemble model development.

RESULTS

Our work identified computational models that explore metabolic analytes to reduce the number of false positives without compromising sensitivity. The best results [area under the receiver operating characteristic curve (AUROC) of 97%, sensitivity of 92%, and specificity of 95%] were obtained utilizing an ensemble of the algorithms random forest, C5.0, sparse linear discriminant analysis, and autoencoder deep neural network stacked with the algorithm stochastic gradient boosting as the supervisor. The model achieved a good performance trade-off for a screening application with 6% false-positive rate (FPR) at 95% sensitivity, 35% FPR at 99% sensitivity, and 39% FPR at 100% sensitivity.

CONCLUSIONS

The classification results and approach of this research can be utilized by clinicians globally, to improve the overall discovery of MMA in pediatric patients. The improved method, when adjusted to 100% precision, can be used to further inform the diagnostic process journey of MMA and help reduce the burden for patients and their families.

Evaluating a Novel Newborn Screening Methodology: Combined Genetic and Biochemical Screenings

PURPOSE

Analysis of four newborn screening modes using newborn genomic sequencing (nGS) and traditional biochemical screening (TBS).

METHODS

Prospective clinical study with a total of 1,012 newborn samples from retrospective TBS. Three independent groups performed the study under strict double-blind conditions according to the screening modes: independent biochemical (IBS), independent NeoSeq (INS), sequential (SS), and combined (CS) screening. Using targeted sequencing, the NeoSeq panel included 154 pathogenic genes covering 86 diseases.

RESULTS

Of the 1,012 newborns, 120 were diagnosed were diagnosed with genetic diseases Among them, 52 cases were within the scope of TBS and 68 additional cases were identified through nGS. The number of cases detected per screening mode was 50, 113, 56, and 119 for IBS, INS, SS, and CS, respectively. CS was the most satisfactory screening mode, with the detection rate of 99.17%, the specificity and positive predictive value of 100%, and the negative predictive value of 99.89%. In addition, of the 68 cases identified by nGS (96 variants in 31 pathogenic genes), only four participants (5.9%) had clinical manifestations consistent with the disease. The experimental reporting cycles of CS and INS were the shortest.

CONCLUSIONS

CS was the most satisfactory method for newborn screening, which combined nGS with TBS to improve early diagnosis.

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.

Screening of 1.17 million newborns for inborn errors of metabolism using tandem mass spectrometry in Shanghai, China: A 19-year report

BACKGROUND

Inborn errors of metabolism (IEMs) frequently result in progressive and irreversible clinical consequences if not be diagnosed or treated timely. The tandem mass spectrometry (MS/MS)-based newborn screening (NBS) facilitates early diagnosis and treatment of IEMs. The aim of this study was to determine the characteristics of IEMs and the successful deployment and application of MS/MS screening over a 19-year time period in Shanghai, China, to inform national NBS policy.

METHODS

The amino acids and acylcarnitines in dried blood spots from 1,176,073 newborns were assessed for IEMs by MS/MS. The diagnosis of IEMs was made through a comprehensive consideration of clinical features, biochemical performance and genetic testing results. The levels of MS/MS testing parameters were compared between various IEM subtypes and genotypes.

RESULTS

A total of 392 newborns were diagnosed with IEMs from January 2003 to June 2022. There were 196 newborns with amino acid disorders (50.00%, 1: 5910), 115 newborns with organic acid disorders (29.59%, 1: 10,139), and 81 newborns with fatty acid oxidation disorders (20.41%; 1:14,701). Phenylalanine hydroxylase deficiency, methylmalonic acidemia and primary carnitine deficiency were the three most common disorders. Some hotspot variations in eight IEM genes (PAH, SLC22A5, MMACHC, MMUT, MAT1A, MCCC2, ACADM, ACAD8), 35 novel variants and some genotype-biochemical phenotype associations were identified.

CONCLUSIONS

A total of 28 types of IEMs were identified, with an overall incidence of 1: 3000 in Shanghai, China. Our study offered clinical guidance for the implementation of MS/MS-based NBS and genetic counseling for IEMs in this city.

Biochemical and molecular features of chinese patients with glutaric acidemia type 1 from Fujian Province, southeastern China

BACKGROUND

Glutaric acidemia type 1 (GA1) is a rare autosomal recessive inherited metabolic disorder caused by variants in the gene encoding the enzyme glutaryl-CoA dehydrogenase (GCDH). The estimated prevalence of GA1 and the mutational spectrum of the GCDH gene vary widely according to race and region. The aim of this study was to assess the acylcarnitine profiles and genetic characteristics of patients with GA1 in Fujian Province, southeastern China.

RESULTS

From January 2014 to December 2022, a total of 1,151,069 newborns (631,016 males and 520,053 females) were screened using MS/MS in six newborn screening (NBS) centers in Fujian Province and recruited for this study. Through NBS, 18 newborns (13 females and 5 males) were diagnosed with GA1. Thus, the estimated incidence of GA1 was 1 in 63,948 newborns in Fujian province. In addition, 17 patients with GA1 were recruited after clinical diagnosis. All but one patient with GA1 had a remarkable increase in glutarylcarnitine (C5DC) concentrations. The results of urinary organic acid analyses in 33 patients showed that the concentration of glutaric acid (GA) increased in all patients. The levels of C5DC and GA in patients identified via NBS were higher than those in patients identified via clinical diagnosis (P < 0.05). A total of 71 variants of 70 alleles were detected in patients with GA1, with 19 different pathogenic variants identified. The three most prevalent variants represented 73.23% of the total and were c.1244-2 A > C, p.(?) (63.38%), c.1261G > A, p.Ala421Thr (5.63%), and c.406G > T, p.Gly136Cys (4.22%). The most abundant genotype observed was c.[1244-2 A > C]; [1244-2 A > C] (18/35, 52.43%) and its phenotype corresponded to high excretors (HE, GA > 100 mmol/mol Cr).

CONCLUSIONS

In conclusion, we investigated the biochemical and molecular features of 35 unrelated patients with GA1. C5DC concentrations in dried blood spots and urinary GA are effective indicators for a GA1 diagnosis. Our study also identified a GCDH variant spectrum in patients with GA1 from Fujian Province, southeastern China. Correlation analysis between genotypes and phenotypes provides preliminary and valuable information for genetic counseling and management.

A multicenter prospective study of next-generation sequencing-based newborn screening for monogenic genetic diseases in China

BACKGROUND

Newborn screening (NBS) is an important and successful public health program that helps improve the long-term clinical outcomes of newborns by providing early diagnosis and treatment of certain inborn diseases. The development of next-generation sequencing (NGS) technology provides new opportunities to expand current newborn screening methodologies.

METHODS

We designed a a newborn genetic screening (NBGS) panel targeting 135 genes associated with 75 inborn disorders by multiplex PCR combined with NGS. With this panel, a large-scale, multicenter, prospective multidisease analysis was conducted on dried blood spot (DBS) profiles from 21,442 neonates nationwide.

RESULTS

We presented the positive detection rate and carrier frequency of diseases and related variants in different regions; and 168 (0.78%) positive cases were detected. Glucose-6-Phosphate Dehydrogenase deficiency (G6PDD) and phenylketonuria (PKU) had higher prevalence rates, which were significantly different in different regions. The positive detection of G6PD variants was quite common in south China, whereas PAH variants were most commonly identified in north China. In addition, NBGS identified 3 cases with DUOX2 variants and one with SLC25A13 variants, which were normal in conventional NBS, but were confirmed later as abnormal in repeated biochemical testing after recall. Eighty percent of high-frequency gene carriers and 60% of high-frequency variant carriers had obvious regional differences. On the premise that there was no significant difference in birth weight and gestational age, the biochemical indicators of SLC22A5 c.1400C > G and ACADSB c.1165A > G carriers were significantly different from those of non-carriers.

CONCLUSIONS

We demonstrated that NBGS is an effective strategy to identify neonates affected with treatable diseases as a supplement to current NBS methods. Our data also showed that the prevalence of diseases has significant regional characteristics, which provides a theoretical basis for screening diseases in different regions.

Clinical and Gene Analysis of Fatty Acid Oxidation Disorders Found in Neonatal Tandem Mass Spectrometry Screening

Objective

To investigate the clinical and gene mutation characteristics of fatty acid oxidative metabolic diseases found in neonatal screening.

Methods

A retrospective analysis was performed on 29,948 neonatal blood tandem mass spectrometry screening samples from January 2018 to December 2021 in our neonatal screening centre. For screening positive, recall review is still suspected of fatty acid oxidation metabolic disorders in children as soon as possible to improve the genetic metabolic disease-related gene detection package to confirm the diagnosis. All diagnosed children were followed up to the deadline.

Results

Among 29,948 neonates screened by tandem mass spectrometry, 14 cases of primary carnitine deficiency, six cases of short-chain acyl coenzyme A dehydrogenase deficiency, two cases of carnitine palmitoyltransferase-I deficiency and one case of multiple acyl coenzyme A dehydrogenase deficiency were recalled. Except for two cases of multiple acyl coenzyme A dehydrogenase deficiency that exhibited [manifestations], the other 21 cases were diagnosed pre-symptomatically. Eight mutations of SLC22A5 gene were detected, including c.51C>G, c.403G>A, c.506G>A, c.1400C>G, c.1085C>T, c.706C>T, c.1540G>C and c.338G>A. Compound heterozygous mutation of CPT1A gene c.2201T>C, c.1318G>A, c.2246G>A, c.2125G>A and ETFA gene c.365G>A and c.699_701delGTT were detected, and new mutation sites were found.

Conclusion

Neonatal tandem mass spectrometry screening is an effective method for identifying fatty acid oxidative metabolic diseases, but it should be combined with urine gas chromatography-mass spectrometry and gene sequencing technology. Our findings enrich the gene mutation profile of fatty acid oxidative metabolic disease and provide evidence for genetic counselling and prenatal diagnosis in families.

Molecular genetic screening of full-term small for gestational age

OBJECTIVE

To examine the clinical application of genomic screening in newborns small for gestational age (SGA), hoping to provide an efficient technique for early discovery of neonatal diseases, which is necessary to elevate survival rates and the quality of life in infants.

METHODS

Totally 93 full-term SGA newborns were assessed. Dried blood spot (DBS) samples were obtained at 72 h after birth, and tandem mass spectrometry (TMS) and Angel Care genomic screening (GS, using Targeted next generation sequencing) were carried out.

RESULTS

All 93 subjects were examined by Angel Care GS and TMS. No children showing inborn errors of metabolism (IEM) were detected by TMS, while 2 pediatric cases (2.15%, 2/93) were confirmed as thyroid dyshormonogenesis 6 (TDH6) by Angel Care GS. Additionally, 45 pediatric cases (48.4%) had one or more variants conferring a carrier status for recessive childhood-onset disorders, with 31 genes and 42 variants associated with 26 diseases. The top three gene-related diseases with carrier status were autosomal recessive deafness (DFNB), abnormal thyroid hormone and Krabbe disease.

CONCLUSIONS

SGA is tightly associated with genetic variation. Molecular Genetic Screening allows early detection of congenital hypothyroidism and may be a potent genomic sequencing technique for screening newborns.

Newborn screening for inborn errors of metabolism in a northern Chinese population

OBJECTIVES

Newborn screening (NBS) for inborn errors of metabolism (IEMs) has been successfully implemented in China. However, the data on the IEM profiles in many regions are lacking. This study aimed to report the incidence, disease spectrum, and genetic profile of IEMs in northern China.

METHODS

A total of 36,590 newborns were screened using tandem mass spectrometry between January 2016 and April 2022. Newborns with positive results were referred for confirmatory testing.

RESULTS

Ten patients were confirmed to have IEMs, with an overall incidence of 1:3,539 in the Rizhao region. Five types of IEMs were detected, including four patients with propionic acidemia (PA), three patients with methylmalonic acidemia (MMA), one of each with citrin deficiency, primary carnitine deficiency, and isobutyryl-CoA dehydrogenase deficiency. PA was the most common IEM, with an unexpectedly high incidence of 1:8,848, followed by MMA, with an incidence rate of 1:11,797. All patients had abnormal screening markers and harbored biallelic variants in their respective causative genes. Two novel PCCB variants (c.505G>A and c.1123_1124insG) were identified in patients with PA. In silico analyses predicted that these two variants were potentially pathogenic.

CONCLUSIONS

This study preliminarily clarified the incidence, disease spectrum, and genetic profile of IEMs in the Rizhao region. PA is the most common IEM and MMA is the second most common in our region. The two novel identified PCCB variants further expand the variant spectrum of PA. More attention should be paid to NBS, early diagnosis, and management of PA and MA.

Incidence and genetic variants of inborn errors of metabolism identified through newborn screening: A 7-year study in eastern coastal areas of China

BACKGROUND

The incidence of inborn errors of metabolism (IEM) varies across countries and areas. Currently, there are no studies on IEM using newborn screening (NBS) in eastern coastal areas of China. We aimed to estimate the incidence and genetic variants of IEM and understand the spectrum of diseases caused by IEM and variants among them in this area.

METHODS

The NBS performed by tandem mass spectrometry (MS/MS) from 2016 to 2021 was retrospectively reviewed. Heel blood was collected from all newborns 72 h after birth. Targeted massively parallel sequencing was performed for genetic analysis.

RESULTS

Among 245,194 newborns, 95 were diagnosed with IEM, the overall incidence observed was-IEM: 1/2581; amino acid metabolism disorder: 1/4715; organic acid metabolism disorder: 1/11676; and fatty acid metabolism disorder: 1/11145. The incidence of different IEM was in the range of 1/245194 to 1/6452. Phenylketonuria (PKU, 1/7211) was the most common IEM, followed by methylmalonic acidemia (MMA, 1/27244), short-chain acyl-CoA dehydrogenase deficiency (SCADD, 1/30649), and citrin deficiency (CD, 1/35028). For genetic variants, the common hotspot variants found were-PAH gene for PKU: c.728G > A, c.442-1G > A, c.611A > G, c.721C > T; PTS gene for non-classical PKU: c.259C > T; MMACHC gene for MMA: c.658_660delAAG, c.609G > A; MMUT gene for MMA: c.1663G > A; ACADS gene for SCADD: c.1031A > G and c.1130C > T; and SLC25A13 gene for CD: c.1638_1660dup, c.852_855del.

CONCLUSION

This study displayed the diseases and varied spectrum of IEM in eastern coastal areas of China. Implementing NBS for IEM by MS/MS combined with massively parallel sequencing can offer an improved plan for NBS to detect IEM.

Metabolic Engineering: Methodologies and Applications

Metabolic engineering aims to improve the production of economically valuable molecules through the genetic manipulation of microbial metabolism. While the discipline is a little over 30 years old, advancements in metabolic engineering have given way to industrial-level molecule production benefitting multiple industries such as chemical, agriculture, food, pharmaceutical, and energy industries. This review describes the design, build, test, and learn steps necessary for leading a successful metabolic engineering campaign. Moreover, we highlight major applications of metabolic engineering, including synthesizing chemicals and fuels, broadening substrate utilization, and improving host robustness with a focus on specific case studies. Finally, we conclude with a discussion on perspectives and future challenges related to metabolic engineering.

Challenges of genetic diagnosis of inborn errors of metabolism in a major tertiary care center in Lebanon

Background: Inborn errors of metabolism are rare genetic disorders; however, these are prevalent in countries with high consanguinity rates, like Lebanon. Patients are suspected, based on a combination of clinical and biochemical features; however, the final confirmation relies on genetic testing. Using next generation sequencing, as a new genetic investigational tool, carries several challenges for the physician, the geneticist, and the families. Methods: In this retrospective study, we analyzed the clinical, biochemical, and genetic profile of inborn errors of metabolism suspected patients, seen at a major tertiary care center in Lebanon, between 2015 and 2018. Genetic testing was performed using next generation sequencing. Genotype-phenotype correlation and diagnostic yield of each testing modality were studied. Results: Out of 211 patients genetically tested, 126 were suspected to have an inborn error of metabolism. The diagnostic yield of next generation sequencing reached 64.3%. Single gene testing was requested in 53%, whole exome sequencing in 36% and gene panels in 10%. Aminoacid disorders were mostly diagnosed followed by storage disorders, organic acidemias and mitochondrial diseases. Targeted testing was performed in 77% of aminoacid and organic acid disorders and half of suspected storage disorders. Single gene sequencing was positive in 75%, whereas whole exome sequencing diagnostic yield for complex cases, like mitochondrial disorders, reached 49%. Good clinical and biochemical correlation allowed the interpretation of variants of unknown significance and negative mutations as well as therapeutic management of most patients. Conclusion: Tailoring the choice of test modality, by next generation sequencing, to the category of suspected inborn errors of metabolism may lead to rapid diagnosis, shortcutting the cost of repeated testing. Whole exome sequencing as a first-tier investigation may be considered mainly for suspected mitochondrial diseases, whereas targeted sequencing can be offered upon suspicion of a specific enzyme deficiency. Timing and modality of gene test remain challenging, in view of the cost incurred by families.

Newborn screening for genetic disorders: Current status and prospects for the future

Newborn screening (NBS) is a public health service aimed at identifying infants with severe genetic disorders, thus providing effective treatment early enough to prevent or ameliorate the onset of symptoms. Current NBS uses biochemical analysis of dried blood spots, predominately with time-resolved fluorescence immunoassay and tandem mass spectrometry, which produces some false positives and false negatives. The application of enzymatic activity-based testing technology provides a reliable screening method for some disorders. Genetic testing is now commonly used for secondary or confirmatory testing after a positive result in some NBS programs. Recently, next-generation sequencing (NGS) has emerged as a robust tool that enables large panels of genes to be scanned together rapidly. Rapid advances in NGS emphasize the potential for genomic sequencing to improve NBS programs. However, some challenges still remain and require solution before this is applied for population screening.

Molecular Genetic Screening of Neonatal Intensive Care Units: Hyperbilirubinemia as an Example

Objective

To explore the clinical value of newborn genomic screening (nGS) for neonatal intensive care units (NICU) infants (taking neonatal hyperbilirubinemia as an example).

Methods

Dried blood spots (DBSs) were collected after 72 hours of birth. The tandem mass spectrometry (TMS) screening and Angel Care genomic screening (GS, based on Targeted next-generation sequencing) were performed at the same time.

Results

Ninety-six hyperbilirubinemia newborns were enrolled in this study and none was identified with inborn errors of metabolism (IEM) by TMS, while 6 infants (6.25%, 6/96) were suspected to have a genetic disorder by Angel Care, including 2 cases of glucose-6-phosphate dehydrogenase deficiency (G6PD), and 1 case of maple syrup urine disease type 1B (MSUD1B), autosomal recessive deafness 1A (DFNB1A), Leber hereditary optic neuropathy (LHON), thyroid dyshormonogenesis 6 (TDH6) each. In addition, 44 infants (45.8%) were detected having at least one variant which conferred a carrier status for a recessive childhood-onset disorder. A total of 33 out of 60 variants (55.0%) reported for carrier status were pathogenic (P), 24 (40.0%) were likely pathogenic (LP), and 3 variants were variant of uncertain significance (VUS). Top six common genes of carrier status were GJB2, DUOX2, PRODH, ATP7B, SLC12A3, SLC26A4. Two newborns showed abnormalities in elementary screening of TMS, but were confirmed as false positive after recall. Their results of Angel Care did not found abnormality.

Conclusion

Using neonatal hyperbilirubinemia as an example, genome sequencing screening can find more evidence of genetic variation in NICU newborns, and “Angel Care” is an effective method.

Application of a next-generation sequencing (NGS) panel in newborn screening efficiently identifies inborn disorders of neonates

Background

Newborn screening (NBS) has been implemented for neonatal inborn disorders using various technology platforms, but false-positive and false-negative results are still common. In addition, target diseases of NBS are limited by suitable biomarkers. Here we sought to assess the feasibility of further improving the screening using next-generation sequencing technology.

Methods

We designed a newborn genetic sequencing (NBGS) panel based on multiplex PCR and next generation sequencing to analyze 134 genes of 74 inborn disorders, that were validated in 287 samples with previously known mutations. A retrospective cohort of 4986 newborns was analyzed and compared with the biochemical results to evaluate the performance of this panel.

Results

The accuracy of the panel was 99.65% with all samples, and 154 mutations from 287 samples were 100% detected. In 4986 newborns, a total of 113 newborns were detected with biallelic or hemizygous mutations, of which 36 newborns were positive for the same disorder by both NBGS and conventional NBS (C-NBS) and 77 individuals were NBGS positive/C-NBS negative. Importantly, 4 of the 77 newborns were diagnosed currently including 1 newborn with methylmalonic acidemia, 1 newborn with primary systemic carnitine deficiency and 2 newborns with Wilson’s disease. A total of 1326 newborns were found to be carriers with an overall carrier rate of 26.6%.

Conclusion

Analysis based on next generation sequencing could effectively identify neonates affected with more congenital disorders. Combined with C-NBS, this approach may improve the early and accurate identification of neonates with inborn disorders. Our study lays the foundation for prospective studies and for implementing NGS-based analysis in NBS.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02231-x.

The Editor's Choice for Issue 3, Volume 7

Dear Readers: Choosing one paper from a total of 28 papers published in the third issue of Volume 7 was quite a challenge [...].

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.

NeoSeq: a new method of genomic sequencing for newborn screening

Objective

To explore the clinical application of NeoSeq in newborn screening.

Methods

Based on the results obtained from traditional newborn screening (NBS) with tandem mass spectrometry (TMS), three cohorts were recruited into the present study: 36 true positive cases (TPC), 60 false-positive cases (FPC), and 100 negative cases. The dried blood spots of the infants were analyzed with NeoSeq, which is based on multiplex PCR amplicon sequencing.

Results

Overall, the sensitivity of NeoSeq was 55.6% (20/36) in the detection of TPC. NeoSeq detected disease-related genes in 20 of 36 TPC infants, while it could not identify these genes in eight children. Five cases (3.1%) with disease risk were additionally found in the FPC and NC cohorts. There was a significant difference in the diagnostic time between the two methods—10 days for NeoSeq vs. 43 days for traditional NBS.

Conclusions

NeoSeq is an economic genomic screening test for newborn screening. It can detect most inborn errors of metabolism, reduce the rate of false positive results, shorten the porting cycles, and reduce the screening cost. However, it is still necessary to further optimize the panel design and add more clinically relevant genomic variants to increase its sensitivity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-02116-5.

Different mutations in the MMUT gene are associated with the effect of vitamin B12 in a cohort of 266 Chinese patients with mut-type methylmalonic acidemia: A retrospective study

BACKGROUND

To summarize the relationship between different MMUT gene mutations and the response to vitamin B12 in MMA.

METHODS

This was a retrospective study of patients diagnosed with mut-type MMA. All patients with mut-type MMA were tested for responsiveness to vitamin B12.

RESULTS

There were 81, 27, and 158 patients in the completely responsive, partially responsive, and nonresponsive groups, respectively, and the proportions of symptom occurrence were 30/81 (37.0%), 21/27 (77.8%), and 131/158 (82.9%), respectively (p < .001). The median levels of posttreatment propionyl carnitine (C3), C3/acetyl carnitine (C2) ratio in the blood, and methylmalonic acid in the urine were all lower than pretreatment, and the median level of C3/C2 ratio in the completely responsive group was within the normal range. In 266 patients, 144 different mutations in the MMUT gene were identified. Patients with the mutations of c.1663G>A, c.2080C>T, c.1880A>G, c.1208G>A, etc. were completely responsive and with the mutations of c.1741C>T, c.1630_1631GG>TA, c.599T>C, etc. were partially responsive. The proportions of healthy/developmental delay outcomes in the three groups were 63.0%/23.5%, 33.3%/40.7%, and 13.3%/60.1%, respectively (p < .001).

CONCLUSION

Different mutations in the MMUT gene are associated with the effect of vitamin B12 treatment.

Biochemical and molecular features of Chinese patients with glutaric acidemia type 1 detected through newborn screening

Background

Glutaric acidemia type 1 (GA1) is a treatable disorder affecting cerebral organic acid metabolism caused by a defective glutaryl-CoA dehydrogenase (GCDH) gene. GA1 diagnosis reports following newborn screening (NBS) are scarce in the Chinese population. This study aimed to assess the acylcarnitine profiles and genetic characteristics of patients with GA1 identified through NBS.

Results

From January 2014 to September 2020, 517,484 newborns were screened by tandem mass spectrometry, 102 newborns with elevated glutarylcarnitine (C5DC) levels were called back. Thirteen patients were diagnosed with GA1, including 11 neonatal GA1 and two maternal GA1 patients. The incidence of GA1 in the Quanzhou region was estimated at 1 in 47,044 newborns. The initial NBS results showed that all but one of the patients had moderate to markedly increased C5DC levels. Notably, one neonatal patient with low free carnitine (C0) level suggest primary carnitine deficiency (PCD) but was ultimately diagnosed as GA1. Nine neonatal GA1 patients underwent urinary organic acid analyses: eight had elevated GA and 3HGA levels, and one was reported to be within the normal range. Ten distinct GCDH variants were identified. Eight were previously reported, and two were newly identified. In silico prediction tools and protein modeling analyses suggested that the newly identified variants were potentially pathogenic. The most common variant was c.1244-2 A>C, which had an allelic frequency of 54.55% (12/22), followed by c.1261G>A (p.Ala421Thr) at 9.09% (2/22).

Conclusions

Neonatal GA1 patients with increased C5DC levels can be identified through NBS. Maternal GA1 patients can also be detected using NBS due to the low C0 levels in their infants. Few neonatal GA1 patients may have atypical acylcarnitine profiles that are easy to miss during NBS; therefore, multigene panel testing should be performed in newborns with low C0 levels. This study indicates that the GCDH variant spectra were heterogeneous in this southern Chinese cohort.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-01964-5.

[New Inborn Errors of Metabolism added in the French program of neonatal screening]

Inborn Errors of Metabolism (IEM) are rare and heterogenous disorders. For most IEMs, clinical signs are non-specific or belated. Late diagnosis is frequent, leading to death or severe sequelae. Some IEM induce intermediate metabolites circulating in the blood. They may be detected by tandem mass spectrometry. This method allows the simultaneous detection of many IEM in different metabolic pathways. In France, newborn screening (NBS) program for IEM, limited to phenylketonuria for decades, has been recently extended to medium chain acyl-CoA dehydrogenase deficiency. Rationale, methodology and organization of this new NBS program are described. Seven other IEM (maple syrup urine disease, homocystinuria, tyrosinemia type I, glutaric aciduria type I, isovaleric acidemia, long chain hydroxy-acyl-CoA dehydrogenase deficiency, carnitine uptake disorder) should be screened in the next program extension. Efforts are needed to fully understand the predictive value of each abnormal testing at birth, decrease the false positive rate, and develop the adequate management strategies.

Increased detection of primary carnitine deficiency through second-tier newborn genetic screening

BACKGROUND

Newborn screening for primary carnitine deficiency (NBS) is commonly implemented worldwide; however, it has poor sensitivity. This study aimed to evaluate the feasibility of improving screening by including a second-tier genetic assay.

RESULTS

An Agena iPLEX assay was developed to identify 17 common SLC22A5 mutations in Chinese populations and was applied in NBS as a second-tier screening. From January 2017 to December 2018, 204,777 newborns were screened for PCD using tandem mass spectrometry. A total of 316 (0.15%) residual NBS-positive specimens with low free carnitine (C0) levels were subjected to this second-tier screening. The screening identified 20 screen-positive newborns who harboured biallelic mutations in theSLC22A5 gene, 99 carriers with one mutation, and 197 screen-negative newborns with no mutations. Among the 99 carriers, four newborns were found to have a second disease-causing SLC22A5mutation by further genetic analysis. Among the 197 screen-negatives were four newborns with persistently low C0 levels, and further genetic analysis revealed that one newborn had two novel SLC22A5 pathogenic variants. In total, 25 newborns were diagnosed with PCD, for a positive predictive value of 7.91% (25/316). Based on these data, we estimate the incidence of PCD in Quanzhou is estimated to be 1:8191.Thirteen distinct SLC22A5 variants were identified, and the most common was c.760C > T, with an allelic frequency of 32% (16/50), followed by c.1400C > G (7/50, 14%), and c.51C > G (7/50, 14%).

CONCLUSION

Data from this study revealed that 24% (6/25) of PCD cases would have been missed by conventional NBS. This high-throughput iPLEX assay is a powerful tool for PCD genotyping. The addition of this second-tier genetic screening to the current NBS program could identify missed PCD cases, thereby increasing PCD detection. However, further studies are needed to optimise the workflow of the new screening algorithm and to evaluate the cost-effectiveness of this screening approach.

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.

Molecular and biochemical investigations of inborn errors of metabolism-altered redox homeostasis in branched-chain amino acid disorders, organic acidurias, and homocystinuria

India, resembling other developing nations, is confronting a hastening demographic switch to non-communicable diseases. Inborn errors of metabolism (IEM) constitute a varied heterogeneous group of disorders with variable clinical appearance, primarily in the pediatric populace. Congenital deformities and genetic disorders are significant for mortality throughout the world, and the Indian scenario is not very different. IEMs are a group of monogenic issues described by dysregulation of the metabolic networks that bring about development and homeostasis. Incipient evidence focuses on oxidative stress and mitochondrial dysfunction as significant contributors to the multiorgan modifications are detected in a few IEMs. The amassing of toxic metabolites in organic acidurias, respiratory chain, and fatty acid oxidation ailments inhibit mitochondrial enzymes and processes, bringing about elevated levels of reactive oxygen species (ROS). In different IEMs, as in homocystinuria, various sources of ROS have been suggested. In patients' samples along with cellular and experimental animal models, a few investigations have recognized substantial increments in ROS levels alongside diminishes in antioxidant defenses, relating with oxidative damage to proteins, lipids as well as DNA. Elevated ROS levels interrupt redox signaling pathways controlling biological processes such as cell development, differentiation, or apoptosis; however, few investigations explore these processes in IEMs. This review depicts the mitochondrial dysfunction, oxidative stress, redox signaling in branched-chain amino acid disorders, further organic acidurias, and homocystinuria, alongside the latest research investigating the proficiency of antioxidants in addition to mitochondria-targeted therapies as therapeutic components in these diseases.

Second-Tier Next Generation Sequencing Integrated in Nationwide Newborn Screening Provides Rapid Molecular Diagnostics of Severe Combined Immunodeficiency

Severe combined immunodeficiency (SCID) and other T cell lymphopenias can be detected during newborn screening (NBS) by measuring T cell receptor excision circles (TRECs) in dried blood spot (DBS) DNA. Second tier next generation sequencing (NGS) with an amplicon based targeted gene panel using the same DBS DNA was introduced as part of our prospective pilot research project in 2015. With written parental consent, 21 000 newborns were TREC-tested in the pilot. Three newborns were identified with SCID, and disease-causing variants in IL2RG, RAG2, and RMRP were confirmed by NGS on the initial DBS DNA. The molecular findings directed follow-up and therapy: the IL2RG-SCID underwent early hematopoietic stem cell transplantation (HSCT) without any complications; the leaky RAG2-SCID received prophylactic antibiotics, antifungals, and immunoglobulin infusions, and underwent HSCT at 1 year of age. The child with RMRP-SCID had complete Hirschsprung disease and died at 1 month of age. Since January 2018, all newborns in Norway have been offered NBS for SCID using 1st tier TRECs and 2nd tier gene panel NGS on DBS DNA. During the first 20 months of nationwide SCID screening an additional 88 000 newborns were TREC tested, and four new SCID cases were identified. Disease-causing variants in DCLRE1C, JAK3, NBN, and IL2RG were molecularly confirmed on day 8, 15, 8 and 6, respectively after birth, using the initial NBS blood spot. Targeted gene panel NGS integrated into the NBS algorithm rapidly delineated the specific molecular diagnoses and provided information useful for management, targeted therapy and follow-up i.e., X rays and CT scans were avoided in the radiosensitive SCID. Second tier targeted NGS on the same DBS DNA as the TREC test provided instant confirmation or exclusion of SCID, and made it possible to use a less stringent TREC cut-off value. This allowed for the detection of leaky SCIDs, and simultaneously reduced the number of control samples, recalls and false positives. Mothers were instructed to stop breastfeeding until maternal cytomegalovirus (CMV) status was determined. Our limited data suggest that shorter time-interval from birth to intervention, may prevent breast milk transmitted CMV infection in classical SCID.

Inborn errors of metabolism detectable by tandem mass spectrometry in Beijing

Background Individual inborn errors of metabolism (IEMs) are rare disorders. Expanded newborn screening for IEMs by tandem mass spectrometry (TMS) is an efficient approach for early diagnosis. Here we provide the newborn screening program for the application of this approach (between July 2014 and March 2019) to the identification of newborns in Beijing at risk of developing a potentially fatal disease. Methods The amino acids and acylcarnitines in dried blood spots were analyzed by TMS. Diagnoses of newborns with elevated metabolites were confirmed by gas chromatography-mass spectrometry, biochemical studies, and genetic analysis. Results Among the healthy newborns, 16 metabolic disorder cases were confirmed, giving a total birth prevalence of 1:3666 live births. Organic acidemia (OA) was the most common (9/16 patients; 56%), and methylmalonic acidemia was the most frequently observed OA (7/9 patients; 89%). Five infants were diagnosed with methylmalonic acidemia with homocystinuria type CblC, two with isolated methylmalonic acidemia, one with propionic acidemia, and one with isovaleric acidemia. Four patients (4/16, 25%) were diagnosed with hyperphenylalaninemia. One suffered with medium-chain acyl CoA dehydrogenase deficiency, one with carnitine uptake deficiency, and one with citrin deficiency. Eleven cases underwent genetic analysis. Seventeen mutations in eight IEM-associated genes were identified in 11 confirmed cases. Symptoms were already present within 2 days after birth in 44% (7/16) cases. The infant with propionic acidemia died at 7 days after birth. The other cases received timely diagnosis and treatment, and most of them grew well. Conclusions The results illustrate challenges encountered in disease management highlighting the importance of newborn screening for inherited metabolic disorders, which is not yet nationally available in our country. Regional newborn screening programs will provide a better estimation of the incidence of IEM.

Screening 3.4 million newborns for primary carnitine deficiency in Zhejiang Province, China

Testing for primary carnitine deficiency (PCD) has been implemented in many newborn screening (NBS) programs, but few large-scale studies on NBS for PCD have been reported in China. This study aimed to assess the incidence and biochemical, clinical, and genetic characteristics of PCD discovered by NBS. Dried blood spots from newborns were analyzed by tandem mass spectrometry (MS/MS) and suspected positive patients were further tested using molecular genetic analysis. Infants who carried two variants in SLC22A5 or those with extremely low free carnitine levels during recall were referred for follow-up and treatment. Over 3.4 million newborns were screened and 113 newborns were diagnosed with PCD, yielding a positive predictive value of 1.93%. In addition, 63 mothers with PCD were identified. The incidence of PCD in newborns and mothers in Zhejiang was 1:30,182 and 1:54,137, respectively. Thirty-seven distinct variants were identified in SLC22A5 of which 10 were novel. c.1400C > G (p.S467C) was the most prevalent variant in both newborns and mothers with PCD, while c.760C > T (p.R254*), which is reportedly common in other Chinese regions, was rarely detected in maternal PCD patients. This study reports the largest series of patients with PCD detected by NBS and identifies 10 novel variants, expanding the variant spectrum of SLC22A5.

Newborn screening and diagnosis of inborn errors of metabolism: A 5-year study in an eastern Chinese population

Inborn errors of metabolism (IEMs) can cause intellectual disability or even death in children. To evaluate the disease spectrum and genetic characteristics of IEMs in Jining City of Shandong Province in East China, we used tandem mass spectrometry (MS/MS) technology for IEMs screening combined with genetic analysis. Newborns were screened from July 14, 2014, to December 31, 2018. Amino acid and carnitine contents were detected by MS/MS. According to the results for normal newborns, the reference range of our laboratory was established with the percentile method. The suspected positive newborns were further diagnosed using next-generation sequencing. A total of 514,234 newborns were screened, and 265 were diagnosed with IEMs, with a detection rate of 1:1941. Of the 265 patients, 130 (49.06%) had organic acid disorders, 83 (31.32%) had amino acid disorders, 34 (12.83%) had fatty acid oxidation disorders, and 18 (6.79%) had urea circulatory disorders. PAHD and MMA were the two most common disorders. IEMs-associated genes were identified in 233 patients. Our data indicated that IEMs are never uncommon in Jining, and the disease spectrum and genetic background were clearly elucidated, contributing to the treatment and prenatal genetic counseling of these disorders in the region.

Biochemical Screening of Intellectually Disabled Patients: A Stepping Stone to Initiate a Newborn Screening Program in Pakistan

Inborn errors of metabolism (IEMs) are rare group of genetic disorders comprising of more than 1,000 different types. Around 200 of IEMs are potentially treatable through diet, pharmacological and other therapies, if diagnosed earlier in life. IEMs can be diagnosed early through newborn screening (NBS) programs, which are in place in most of the developed countries. However, establishing a NBS in a developing country is a challenging task due to scarcity of disease related data, large population size, poor economy, and burden of other common disorders. Since, not enough data is available for the prevalence of IEMs in Pakistan; therefore, in this study, we set out to find the prevalence of various treatable IEMs in a cohort of intellectually disabled patients suspected for IEMs, which will help us to initiate a NBS program for the most frequent IEMs in Pakistan. Therefore, a total of 429 intellectually disabled (IQ <70) patient samples were collected from Pakistan. A subset of 113 patient samples was selected based on the clinical information for the detailed biochemical screening. Advance analytical techniques like, Amino Acid Analyzer, GC-MS, UHPLC-MS, and MS/MS were used to screen for different treatable IEMs like aminoacidopathies, fatty acid β-oxidation disorders and mucopolysaccharidoses (MPS) etc. A total of 14 patients were diagnosed with an IEM i.e., 9 with homocystinuria, 2 with MPS, 2 with Guanidinoacetate methyltransferase (GAMT) deficiency and 1 with sitosterolemia. These IEMs are found frequent in the collected patient samples from Pakistan. Thus, present study can help to take an initiative step to start a NBS program in Pakistan, especially for the homocystinuria having highest incidence among aminoacidopathies in the studied patients, and which is amenable to treatment. This endeavor will pave the way for a healthier life of affected patients and will lessen the burden on their families and society.

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.

Mitochondrial Genetic Disorders: Cell Signaling and Pharmacological Therapies

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