Fatty acid oxidation disorders (FAODs) are a family of rare, genetic disorders that affect any part of the fatty acid oxidation pathway. Patients present with severe phenotypes, such as hypoketotic hypoglycemia, cardiomyopathy, and rhabdomyolysis, and currently manage these symptoms by the avoidance of fasting and maintaining a low-fat, high-carbohydrate diet. Because knowledge about FAODs is limited due to the small number of patients, rodent models have been crucial in learning more about these disorders, particularly in studying the molecular mechanisms involved in different phenotypes and in evaluating treatments for patients. The purpose of this review is to present the different FAOD mouse models and highlight the benefits and limitations of using these models. Specifically, we discuss the phenotypes of the available FAOD mouse models, the potential molecular causes of prominent FAOD phenotypes that have been studied using FAOD mouse models, and how FAOD mouse models have been used to evaluate treatments for patients.

BACKGROUND: Type B lactic acidosis and hypoglycemia can occur in various pediatric conditions. In young children with a history of fasting preceding these metabolic derangements, inborn errors of metabolism should be primarily considered. However, the Warburg effect, a rare metabolic complication, can also manifest in children with hematologic malignancies. Only a few reports of this condition in children have been published in the literature.
OBJECTIVE: To identify the clinical course, treatment strategies, and outcomes of childhood hematologic malignancies with type B lactic acidosis.
METHODS: We performed a comprehensive search of the PubMed, Scopus, and Cochrane databases without any time restriction but limited to English language articles. The databases were last accessed on July 1st, 2023.
RESULTS: A total of 20 publications were included in the analysis, all of which were case reports or case series. No higher quality evidence was available. Among children with hematologic malignancies and Warburg effect, there were 14 cases of acute lymphoblastic leukemia and 6 cases of non-Hodgkin\'s lymphoma including our illustrative case. Lactic acidosis occurred in 55% of newly diagnosed cases and 45% of relapsed cases. The mean age was 10.3 ± 4.5 years, and 80% of cases were male. The mean serum lactate was 16.9 ± 12.6 mmol/L, and 43.8% of the cases had concomitant hypoglycemia. Lactic acidosis initially subsided in 80% of patients receiving chemotherapy compared to 60% in the contrast group. The mortality rate of newly diagnosed cases was 45.5%, while the relapsed cases represented a 100% mortality rate. All 8 patients reported before 2001 died from disease-related complications. However, patients described in reports published between 2003 and 2023 had a 54.5% rate of complete remission.
CONCLUSIONS: This complication has historically led to fatal outcome; however, patients who received chemotherapy showed a more favorable response. Therefore, it is crucial to promptly initiate specific treatment in this context.

Inborn errors of metabolism (IEMs) comprise a diverse group of monogenic disorders caused by enzyme deficiencies that result either in a toxic accumulation of metabolic intermediates or a shortage of essential end-products. Certain IEMs, like phenylketonuria (PKU), necessitate stringent dietary intervention that could lead to microbiome dysbiosis, thereby exacerbating the clinical phenotype. The objective of this systematic review was to examine the impact of PKU therapies on the intestinal microbiota. This research was conducted following the PRISMA Statement, with data from PubMed, Scopus, ScienceDirect, and Web of Science. A total of 18 articles meeting the inclusion criteria were published from 2011 to 2022. Significant reductions in several taxonomic groups in individuals with PKU when compared to the control group were detected in a quantitative analysis conducted across seven studies. The meta-analysis synthesis indicates a contrast in biodiversity between PKU subjects and the control population. Additionally, the meta-regression results, derived from the Bacillota/Bacteroidota ratio data, suggest a potential influence of diet in adult PKU populations (p = 0.004). It is worth noting that the limited number of studies calls for further research and analysis in this area. Our findings indicate the necessity of enhancing understanding of microbiota variability in reaction to treatments among PKU subjects to design tailored therapeutic and nutritional interventions to prevent complications resulting from microbiota disruption.

BACKGROUND: Persistent pulmonary hypertension of the newborn manifesting with refractory and severe cyanosis is the consequence of high pulmonary vascular resistance causing extrapulmonary right-to-left shunt. Acidosis and hypoxemia produce pulmonary vasoconstriction. Persistent pulmonary hypertension of the newborn occurs due to numerous disorders and has been rarely reported as a manifestation of methylmalonic acidemia. We report a newborn with methylmalonic acidemia who presented with persistent pulmonary hypertension of the newborn.
METHODS: A 1-day-old Iranian girl presented with respiratory distress and refractory metabolic acidosis. She was born at 39 + 5 weeks gestational age with Apgar scores of 8 and 9 in the 1st and 5th minutes, respectively, and was in good condition up to 10 hours of life. After that, she presented with cyanosis, tachypnea, retraction, and hypotonia. Despite receiving oxygen, she had low oxygen saturation. Echocardiography revealed severe pulmonary hypertension and right-to-left shunt through patent ductus arteriosus and foramen ovale. Her acidosis worsened despite receiving full support and medical therapy. So, she was started on peritoneal dialysis. Unfortunately, she did not respond to treatment, and after she had died, biochemical tests confirmed methylmalonic acidemia.
CONCLUSIONS: Persistent pulmonary hypertension of the newborn is a very rare manifestation of methylmalonic acidemia. Severe inborn errors of metabolism may cause irreversible damage with adverse lifelong morbidity, and early diagnosis may help to prevent such complications. Furthermore, diagnosis of these disorders aids in prenatal diagnosis through the use of cultured amniocytes or chorionic villi to detect gene mutations, as well as biochemical analyses of amniotic fluid for subsequent pregnancies.

Population-specific variation database of inborn errors of metabolism (IEMs) is essential for precise genetic diagnosis and disease prevention. Here we presented a systematic review of clinically relevant variants of 13 IEMs genes reported among Chinese patients.
A systematic search of the following electronic databases for 13 IEMs genes was conducted: PubMed-NCBI, China national knowledge infrastructure and Wanfang databases. Patient data was extracted from articles eligible for inclusion and recorded in Excel electronic form using a case-by-case approach.
A total of 218 articles, 93 published in English and 125 in Chinese, were retrieved. After variant annotation and deduplication, 575 unique patients (241 from articles published in Chinese) were included in the population-specific variation database. Patients identified by newborn screening and symptomatic presentation were 231 (40.17%) and 344 (59.83%), respectively. Biallelic variants were observed in 525/575 (91.3%). Among the 581 unique variants identified, 83 (14.28%) were described ≥ 3 times and 97 (16.69%) were not recorded in Clinvar or HGMD. Four variants were reclassified as benign and dozens of confusing variants deserved further research.
This review provides a unique resource of the well-characterized diseases and causative variants that have accumulated in Chinese population and is a preliminary attempt to build the Chinese genetic variation database of IEMs.

Heart failure (HF) is a progressive chronic disease that remains a primary cause of death worldwide, affecting over 64 million patients. HF can be caused by cardiomyopathies and congenital cardiac defects with monogenic etiology. The number of genes and monogenic disorders linked to development of cardiac defects is constantly growing and includes inherited metabolic disorders (IMDs). Several IMDs affecting various metabolic pathways have been reported presenting cardiomyopathies and cardiac defects. Considering the pivotal role of sugar metabolism in cardiac tissue, including energy production, nucleic acid synthesis and glycosylation, it is not surprising that an increasing number of IMDs linked to carbohydrate metabolism are described with cardiac manifestations. In this systematic review, we offer a comprehensive overview of IMDs linked to carbohydrate metabolism presenting that present with cardiomyopathies, arrhythmogenic disorders and/or structural cardiac defects. We identified 58 IMDs presenting with cardiac complications: 3 defects of sugar/sugar-linked transporters (GLUT3, GLUT10, THTR1); 2 disorders of the pentose phosphate pathway (G6PDH, TALDO); 9 diseases of glycogen metabolism (GAA, GBE1, GDE, GYG1, GYS1, LAMP2, RBCK1, PRKAG2, G6PT1); 29 congenital disorders of glycosylation (ALG3, ALG6, ALG9, ALG12, ATP6V1A, ATP6V1E1, B3GALTL, B3GAT3, COG1, COG7, DOLK, DPM3, FKRP, FKTN, GMPPB, MPDU1, NPL, PGM1, PIGA, PIGL, PIGN, PIGO, PIGT, PIGV, PMM2, POMT1, POMT2, SRD5A3, XYLT2); 15 carbohydrate-linked lysosomal storage diseases (CTSA, GBA1, GLA, GLB1, HEXB, IDUA, IDS, SGSH, NAGLU, HGSNAT, GNS, GALNS, ARSB, GUSB, ARSK). With this systematic review we aim to raise awareness about the cardiac presentations in carbohydrate-linked IMDs and draw attention to carbohydrate-linked pathogenic mechanisms that may underlie cardiac complications.

Cerebrotendinous Xanthomatosis represents a rare and underdiagnosed inherited neurometabolic disorder due to homozygous or compound heterozygous variants involving the CYP27A1 gene. This bile acid metabolism disorder represents a key potentially treatable neurogenetic condition due to the wide spectrum of neurological presentations in which it most commonly occurs. Cerebellar ataxia, peripheral neuropathy, spastic paraparesis, epilepsy, parkinsonism, cognitive decline, intellectual disability, and neuropsychiatric disturbances represent some of the most common neurological signs observed in this condition. Despite representing key features to increase diagnostic index suspicion, multisystemic involvement does not represent an obligatory feature and can also be under evaluated during diagnostic work-up. Chenodeoxycholic acid represents a well-known successful therapy for this inherited metabolic disease, however its unavailability in several contexts, high costs and common use in patients at late stages of disease course limit more favorable neurological outcomes for most individuals. This review article aims to discuss and highlight the most recent and updated knowledge regarding clinical, pathophysiological, neuroimaging, genetic and therapeutic aspects related to Cerebrotendinous Xanthomatosis.

Inborn errors of metabolism (IEMs) are characterized by deficits in metabolic enzymes as a result of an inherited disease, leading to the accumulation or decreased excretion of proteins, carbohydrates and lipids. Although IEMs are often diagnosed during childhood, adolescent and adult onset variants may be accompanied by less somatic and more psychiatric manifestations, which often hampers recognition by psychiatrists of the distinction between a primary and secondary psychiatric disorder. To help clinicians in the diagnostic process, we aimed to provide an overview of psychiatric manifestations in IEMs. Our literature search yielded 4380 records in total, of which 88 studies were included in the qualitative synthesis. Reported psychiatric disorders in adolescent and adult IEMs included depression, anxiety disorder, psychosis, attention deficit hyperactivity disorder, autism spectrum disorder, bipolar disorder and obsessive-compulsive disorder as assessed by semi-structured diagnostic interviews and validated questionnaires. A diagnostic screener and multidisciplinary IEM clinics are proposed to help clinicians during the diagnostic process, to prevent diagnostic delay and to raise awareness of the psychiatric manifestations among IEMs.

Fatty acid oxidation disorders (FAODs) are inborn errors of metabolism (IEMs) caused by defects in the fatty acid (FA) mitochondrial β-oxidation. The most common FAODs are characterized by the accumulation of medium-chain FAs and long-chain (3-hydroxy) FAs (and their carnitine derivatives), respectively. These deregulations are associated with lipotoxicity which affects several organs and potentially leads to life-threatening complications and comorbidities. Changes in the lipidome have been associated with several diseases, including some IEMs. In FAODs, the alteration of acylcarnitines (CARs) and FA profiles have been reported in patients and animal models, but changes in polar and neutral lipid profile are still scarcely studied. In this review, we present the main findings on FA and CAR profile changes associated with FAOD pathogenesis, their correlation with oxidative damage, and the consequent disturbance of mitochondrial homeostasis. Moreover, alterations in polar and neutral lipid classes and lipid species identified so far and their possible role in FAODs are discussed. We highlight the need of mass-spectrometry-based lipidomic studies to understand (epi)lipidome remodelling in FAODs, thus allowing to elucidate the pathophysiology and the identification of possible biomarkers for disease prognosis and an evaluation of therapeutic efficacy.

BACKGROUND: Arginase 1 Deficiency (ARG1-D) is a rare, progressive, metabolic disorder that is characterized by devastating manifestations driven by elevated plasma arginine levels. It typically presents in early childhood with spasticity (predominately affecting the lower limbs), mobility impairment, seizures, developmental delay, and intellectual disability. This systematic review aims to identify and describe the published evidence outlining the epidemiology, diagnosis methods, measures of disease progression, clinical management, and outcomes for ARG1-D patients.
METHODS: A comprehensive literature search across multiple databases such as MEDLINE, Embase, and a review of clinical studies in ClinicalTrials.gov (with results reported) was carried out per PRISMA guidelines on 20 April 2020 with no date restriction. Pre-defined eligibility criteria were used to identify studies with data specific to patients with ARG1-D. Two independent reviewers screened records and extracted data from included studies. Quality was assessed using the modified Newcastle-Ottawa Scale for non-comparative studies.
RESULTS: Overall, 55 records reporting 40 completed studies and 3 ongoing studies were included. Ten studies reported the prevalence of ARG1-D in the general population, with a median of 1 in 1,000,000. Frequently reported diagnostic methods included genetic testing, plasma arginine levels, and red blood cell arginase activity. However, routine newborn screening is not universally available, and lack of disease awareness may prevent early diagnosis or lead to misdiagnosis, as the disease has overlapping symptomology with other diseases, such as cerebral palsy. Common manifestations reported at time of diagnosis and assessed for disease progression included spasticity (predominately affecting the lower limbs), mobility impairment, developmental delay, intellectual disability, and seizures. Severe dietary protein restriction, essential amino acid supplementation, and nitrogen scavenger administration were the most commonly reported treatments among patients with ARG1-D. Only a few studies reported meaningful clinical outcomes of these interventions on intellectual disability, motor function and adaptive behavior assessment, hospitalization, or death. The overall quality of included studies was assessed as good according to the Newcastle-Ottawa Scale.
CONCLUSIONS: Although ARG1-D is a rare disease, published evidence demonstrates a high burden of disease for patients. The current standard of care is ineffective at preventing disease progression. There remains a clear need for new treatment options as well as improved access to diagnostics and disease awareness to detect and initiate treatment before the onset of clinical manifestations to potentially enable more normal development, improve symptomatology, or prevent disease progression.