Impact of selected inborn errors of metabolism on prenatal and neonatal development

Fetal Brain MRI Abnormalities in Pyruvate Dehydrogenase Complex Deficiency

BACKGROUND AND OBJECTIVES

Pyruvate dehydrogenase complex deficiency (PDCD) is a disorder of mitochondrial metabolism that is caused by pathogenic variants in multiple genes, including PDHA1. Typical neonatal brain imaging findings have been described, with a focus on malformative and encephaloclastic features. Fetal brain MRI in PDCD has not been comprehensively described. The aims of this study were (1) to further characterize the fetal brain MRI findings in PDCD using comprehensive fetal imaging and genetic testing and (2) to determine whether markers of diagnosis of PDCD could be identified on prenatal imaging.

METHODS

Fetuses with a diagnosis of PDCD related to a genetic etiology that had undergone fetal MRI were included. Fetuses were identified retrospectively from local databases of 4 fetal diagnostic clinics within tertiary pediatric health care centers. Electronic medical records were reviewed retrospectively: demographics, maternal and pregnancy history, fetal outcomes, and neonatal outcomes (if available) were reviewed and recorded. Fetal and neonatal imaging reports were reviewed; source fetal and neonatal brain MRI scans were reviewed by a single pediatric neuroradiologist (J.W.S.) for consistency. Genetic testing strategies and results including variant type, zygosity, inheritance pattern, and pathogenicity were recorded. Deidentified data were combined and reported descriptively.

RESULTS

A total of 10 fetuses with a diagnosis of PDCD were included. 8 fetuses had corpus callosum dysgenesis, 6 had an abnormal gyration pattern, 10 had reduced brain volumes, and 9 had cystic lesions. 1 fetus had intraventricular hemorrhages. 1 fetus had a midbrain malformation with aqueductal stenosis and severe hydrocephalus. 6 fetuses imaged in the second trimester had cystic lesions involving the ganglionic eminences (GEs) while GE cysts were not present in the 4 fetuses imaged in the third trimester.

DISCUSSION

Fetuses with PDCD have similar brain MRI findings to neonates described in the literature, although some of these findings are subtle early in pregnancy. Additional features, such as cystic lesions of the GEs, are noted in the second trimester in fetuses with PDCD. These may represent an early diagnostic marker of PDCD, although more data are needed to validate this association. Early diagnosis of PDCD using fetal MRI may inform genetic counseling, pregnancy decision making, and neonatal care planning.

Historic obstacles and emerging opportunities in the field of developmental metabolism - lessons from Heidelberg

The field of developmental metabolism is experiencing a technological revolution that is opening entirely new fields of inquiry. Advances in metabolomics, small-molecule sensors, single-cell RNA sequencing and computational modeling present new opportunities for exploring cell-specific and tissue-specific metabolic networks, interorgan metabolic communication, and gene-by-metabolite interactions in time and space. Together, these advances not only present a means by which developmental biologists can tackle questions that have challenged the field for centuries, but also present young scientists with opportunities to define new areas of inquiry. These emerging frontiers of developmental metabolism were at the center of a highly interactive 2023 EMBO workshop 'Developmental metabolism: flows of energy, matter, and information'. Here, we summarize key discussions from this forum, emphasizing modern developmental biology's challenges and opportunities.

Characteristic Fetal Brain MRI Abnormalities in Pyruvate Dehydrogenase Complex Deficiency

Pyruvate dehydrogenase complex deficiency (PDCD) is a disorder of mitochondrial metabolism that is caused by pathogenic variants in multiple genes, including PDHA1. Typical neonatal brain imaging findings in PDCD have been described, with a focus on malformative features and chronic encephaloclastic changes. However, fetal brain MRI imaging in confirmed PDCD has not been comprehensively described. We sought to demonstrate the prenatal neurological and systemic manifestations of PDCD determined by comprehensive fetal imaging and genomic sequencing. All fetuses with a diagnosis of genetic PDCD who had undergone fetal MRI were included in the study. Medical records, imaging data, and genetic testing results were reviewed and reported descriptively. Ten patients with diagnosis of PDCD were included. Most patients had corpus callosum dysgenesis, abnormal gyration pattern, reduced brain volumes, and periventricular cystic lesions. One patient had associated intraventricular hemorrhages. One patient had a midbrain malformation with aqueductal stenosis and severe hydrocephalus. Fetuses imaged in the second trimester were found to have enlargement of the ganglionic eminences with cystic cavitations, while those imaged in the third trimester had germinolytic cysts. Fetuses with PDCD have similar brain MRI findings to neonates described in the literature, although some of these findings may be subtle early in pregnancy. Additional features, such as cystic cavitations of the ganglionic eminences, are noted in the second trimester in fetuses with PDCD, and these may represent a novel early diagnostic marker for PDCD. Using fetal MRI to identify these radiological hallmarks to inform prenatal diagnosis of PDCD may guide genetic counseling, pregnancy decision-making, and neonatal care planning.

Characterization of pregnancy outcome of women with an offspring with inborn errors of metabolism: A population-based study

Introduction: Inborn errors of metabolism (IEM) are scarce, and their diagnosis is often made after birth. This has led to the perception that most fetuses affected by these disorders do not become clinically apparent during pregnancy. Our aim was to determine the obstetrical characteristics of women with an offspring affected by IEM.

Methods: This population-based retrospective cohort study included all women who delivered at the Soroka University Medical Center (SUMC) from 1988 to 2017 who met the inclusion criteria. Mothers who had an offspring with IEM were included in the study group, and those who had offsprings without IEM comprised the comparison group.

Results: A total of 388,813 pregnancies were included in the study, and 184 of them were complicated by a fetus with IEM. The number of Bedouin women was higher in the IEM-affected infant group than in the comparison group (90.8% vs. 53.3%, p < 0.001); women who had a fetus with IEM had a higher rate of polyhydramnios (7.1% vs. 3.2%, p = 0.005), HELLP syndrome (3.3% vs. 1.1%, p = 0.014), and preterm birth (20.7% vs. 10.1%, p < 0.001); neonates with IEM had lower mean birth weight (p < 0.001), lower Apgar scores at 1′ and 5′ minutes (p < 0.001), and a higher rate of fetal growth restriction (FGR) (p < 0.001), postpartum death <28 days (p < 0.001), and neonatal death (p < 0.001) than those in the comparison group. Pregnancies with IEM fetuses were independently associated with preterm birth (OR 2.00; CI 1.4–3), polyhydramnios (OR 2.08; CI 1.17–3.71), and FGR (OR 2.24; CI 1.2–4.19). Each family of metabolic diseases is independently associated with specific pregnancy complications (i.e., mitochondrial diseases are associated with HELLP syndrome (OR 5.6; CI 1.8–17), and lysosomal storage disease are associated with nonimmune hydrops fetalis (OR 26.4; CI 3.39–206).

Conclusion: This study reports for the first time, an independent association of IEM with specific complications of pregnancy. This observation has clinical implications, as the identification of specific pregnancy complications in a population at risk for IEM can assist in the prenatal diagnosis of an affected fetus.

Cost-effectiveness analysis of newborn screening by tandem mass spectrometry in Shenzhen, China: value and affordability of new screening technology

BACKGROUND

Newborn screening (NBS) can prevent inborn errors of metabolism (IEMs), which may cause long-term disability and even death in newborns. However, in China, tandem mass spectrometry (MS/MS) screening has just started. This study aimed to assess the cost-effectiveness of NBS using MS/MS in Shenzhen under the nationally recommended program, as well as evaluate the value and affordability of introducing this new screening technology.

METHODS

A Markov model was built to estimate the cost and quality-adjusted life-years (QALYs) of different screening programs. We compared PKU screening using traditional immunofluorescence (IF) with the other 11 IEMs not screened and all 12 IEMs screened using MS/MS, and the programs detecting different numbers of IEMs chosen from the national recommended program were also compared. A sensitivity analysis and budget impact analysis (BIA) were performed.

RESULTS

The incremental cost-effectiveness ratio (ICER) of detecting all 12 IEMs in the national program is 277,823 RMB per QALY, below three times per capita GDP in Shenzhen. MS/MS screening in Shenzhen can be cost-effective only if at least three diseases (PKU, PCD and MMA) are covered and when the screening program covers five diseases (PKU, PCD, MMA, MSUD, IVA), the ICER closely approaches its critical threshold. The BIA indicated the implementation cost of the national program to be around 490 million RMB over 10 years and showed no difference in budget between programs detecting different numbers of IEMs.

CONCLUSIONS

We conclude that the newborn screening using MS/MS in Shenzhen is cost-effective, and the budget affordable for the Shenzhen government. Two concepts for selecting the IEMs to be detected are also presented. One is to choose the most cost-effective screening programs detecting highest number of IEMs to achieve a minimal ICER. The other considers the curability and affordability of the disease as the basis of healthcare decisions to screen suitable IEMs, achieving an ICER under the threshold and close to the minimum value.

Inborn Errors of Metabolism-Approach to Diagnosis and Management in Neonates

Inborn errors of metabolism (IEM), otherwise known as inherited metabolic disorders (IMD), are individually rare, but collectively common. IEM pose a challenge to diagnosis, as neonates present with nonspecific signs. A high index of suspicion is essential. Knowledge on clinical presentation may be life saving, especially for conditions that are treatable. It is important for the first-line physicians not to miss treatable disorders. Simplified classification and algorithmic approach help in the clinical setting. This article describes the classification of IEM into three groups, namely group 1 - intoxication disorders, group 2 - energy defects, and group 3 - storage disorders. Clinical presentations of IEM in the neonatal period, a quick guide to the diagnosis with the help of baseline investigations (glucose, arterial blood gas, lactate, ammonia, and ketone abbreviated as GALAK), a tabulated guide to the diagnosis with the help of tandem mass spectrometry (TMS), and gas chromatography and mass spectrometry (GCMS) are summarized in this article. Four principles of therapy that include substrate reduction, provision of deficient metabolites, disposal of toxic metabolites, and increase in enzyme activity are elaborated with particular stress to the diet management. In addition, a list of medications used in the treatment of different disorders classified according to Society for the Study of IEM (SSIEM) is presented.

The role of next-generation sequencing in the investigation of ultrasound-identified fetal structural anomalies

Fetal structural anomalies have an impact on fetal mortality and morbidity. Next-generation sequencing (NGS) may be incorporated into clinical pathways for investigation of paediatric morbidity but can also be used to delineate the prognosis of fetal anomalies. This paper reviews the role of NGS in the investigation of fetal malformations, the literature defining the clinical utility, the technique most commonly used and potential promise and challenges for implementation into clinical practice. Prospective case selection with informative pre-test counselling by multidisciplinary teams is imperative. Regulated laboratory sequencing, bioinformatic pathways with potential variant identification and conservative matching with the phenotype is important. TWEETABLE ABSTRACT: Prenatal exome sequencing in fetal structural anomalies yields diagnostic information in up to 20% of cases.

A proposed nosology of inborn errors of metabolism

Purpose

We propose a nosology for inborn errors of metabolism that builds on their recent redefinition.

Methods

We established a strict definition of criteria in order to develop a self-consistent schema for inclusion of a disorder into the nosology.

Results

We identified 1,015 well-characterized inborn errors of metabolism described in the literature. In addition, there are 111 less well-characterized conditions that may be inborn errors but do not meet strict criteria for inclusion in the current nosology.

Conclusion

We provide a master list of all currently recognized inborn errors of metabolism grouped according to their pathophysiological basis, with the hope of setting a standard against which new errors should be defined, as well as to promote awareness and foster collaboration in the area. With the rapid advances in the field of genetics in recent years, it is likely that this nosology will need to be updated in the near future, a process that will benefit from broader input and collaboration of experts in the field in order to improve future versions of the proposed classification.

The role of the clinician in the multi-omics era: are you ready?

Since Garrod's first description of alkaptonuria in 1902, and newborn screening for phenylketonuria introduced in the 1960s, P4 medicine (preventive, predictive, personalized, and participatory) has been a reality for the clinician serving patients with inherited metabolic diseases. The era of high-throughput technologies promises to accelerate its scale dramatically. Genomics, transcriptomics, epigenomics, proteomics, glycomics, metabolomics, and lipidomics offer an amazing opportunity for holistic investigation and contextual pathophysiologic understanding of inherited metabolic diseases for precise diagnosis and tailored treatment. While each of the -omics technologies is important to systems biology, some are more mature than others. Exome sequencing is emerging as a reimbursed test in clinics around the world, and untargeted metabolomics has the potential to serve as a single biochemical testing platform. The challenge lies in the integration and cautious interpretation of these big data, with translation into clinically meaningful information and/or action for our patients. A daunting but exciting task for the clinician; we provide clinical cases to illustrate the importance of his/her role as the connector between physicians, laboratory experts and researchers in the basic, computer, and clinical sciences. Open collaborations, data sharing, functional assays, and model organisms play a key role in the validation of -omics discoveries. Having all the right expertise at the table when discussing the diagnostic approach and individualized management plan according to the information yielded by -omics investigations (e.g., actionable mutations, novel therapeutic interventions), is the stepping stone of P4 medicine. Patient participation and the adjustment of the medical team's plan to his/her and the family's wishes most certainly is the capstone. Are you ready?

Promises, pitfalls and practicalities of prenatal whole exome sequencing

Prenatal genetic diagnosis provides information for pregnancy and perinatal decision-making and management. In several small series, prenatal whole exome sequencing (WES) approaches have identified genetic diagnoses when conventional tests (karyotype and microarray) were not diagnostic. Here, we review published prenatal WES studies and recent conference abstracts. Thirty-one studies were identified, with diagnostic rates in series of five or more fetuses varying between 6.2% and 80%. Differences in inclusion criteria and trio versus singleton approaches to sequencing largely account for the wide range of diagnostic rates. The data suggest that diagnostic yields will be greater in fetuses with multiple anomalies or in cases preselected following genetic review. Beyond its ability to improve diagnostic rates, we explore the potential of WES to improve understanding of prenatal presentations of genetic disorders and lethal fetal syndromes. We discuss prenatal phenotyping limitations, counselling challenges regarding variants of uncertain significance, incidental and secondary findings, and technical problems in WES. We review the practical, ethical, social and economic issues that must be considered before prenatal WES could become part of routine testing. Finally, we reflect upon the potential future of prenatal genetic diagnosis, including a move towards whole genome sequencing and non-invasive whole exome and whole genome testing. © 2017 John Wiley & Sons, Ltd.

Comparative analysis of cytosolic and mitochondrial ATP synthesis in embryonic and postnatal hippocampal neuronal cultures

ATP in neurons is commonly believed to be synthesized mostly by mitochondria via oxidative phosphorylation. Neuronal mitochondria have been studied primarily in culture, i.e., in neurons isolated either from embryos or from neonatal pups. Although it is generally assumed that both embryonic and postnatal cultured neurons derive their ATP from mitochondrial oxidative phosphorylation, this has never been tested experimentally. We expressed the FRET-based ATP sensor AT1.03 in cultured hippocampal neurons isolated either from E17 to E18 rat embryos or from P1 to P2 rat pups and monitored [ATP]c simultaneously with mitochondrial membrane potential (ΔΨm; TMRM) and NAD(P)H autofluorescence. In embryonic neurons, transient glucose deprivation induced a near-complete decrease in [ATP]c, which was partially reversible and was accelerated by inhibition of glycolysis with 2-deoxyglucose. In the absence of glucose, pyruvate did not cause any significant increase in [ATP]c in 84% of embryonic neurons, and inhibition of mitochondrial ATP synthase with oligomycin failed to decrease [ATP]c. Moreover, ΔΨm was significantly reduced by oligomycin, indicating that mitochondria acted as consumers rather than producers of ATP in embryonic neurons. In sharp contrast, in postnatal neurons pyruvate added during glucose deprivation significantly increased [ATP]c (by 54 ± 8%), whereas oligomycin induced a sharp decline in [ATP]c and increased ΔΨm. These signs of oxidative phosphorylation were observed in all tested P1-P2 neurons. Measurement of ΔΨm with the potential-sensitive probe JC-1 revealed that neuronal mitochondrial membrane potential was significantly reduced in embryonic cultures compared to the postnatal ones, possibly due to increased proton permeability of inner mitochondrial membrane. We conclude that, in embryonic, but not postnatal neuronal cultures, ATP synthesis is predominantly glycolytic and the oxidative phosphorylation-mediated synthesis of ATP by mitochondrial F1Fo-ATPase is insignificant.