Neurologic considerations in propionic acidemia

Coexistence of Two Rare Conditions Complicating the Other's Management: Propionic Acidemia and Apert Syndrome

Introduction

Propionic acidemia (PA) is an inborn error of organic acid metabolism inherited in an autosomal recessive manner. The neonatal-onset disease may present with feeding difficulties and vomiting; seizures, coma, and death may occur if untreated. In addition, catabolic processes such as infections and surgical procedures could cause metabolic decompensation, so patients with organic acidemia should be followed closely.

Case Presentation

Here, a patient diagnosed with PA and Apert syndrome in the neonatal period and the complications caused by the coexistence of the two entities are mentioned. The difficulties precipitated by the coexistence of Apert syndrome and PA make this case unique. She has had prolonged hospitalizations due to metabolic decompensations after cranioplasty and inguinal hernia repair, both triggered by nosocomial respiratory infections, complicating both the surgical treatment of Apert syndrome and the management of PA.

Conclusion

Coexistence of these two serious disorders mandates a more prudent clinical management as Apert syndrome patients undergo several surgical procedures, rendering them susceptible to catabolic decompensations.

Pathophysiological mechanisms of complications associated with propionic acidemia

Propionic acidemia (PA) is a genetic metabolic disorder caused by mutations in the mitochondrial enzyme, propionyl-CoA carboxylase (PCC), which is responsible for converting propionyl-CoA to methylmalonyl-CoA for further metabolism in the tricarboxylic acid cycle. When this process is disrupted, propionyl-CoA and its metabolites accumulate, leading to a variety of complications including life-threatening cardiac diseases and other metabolic strokes. While the clinical symptoms and diagnosis of PA are well established, the underlying pathophysiological mechanisms of PA-induced diseases are not fully understood. As a result, there are currently few effective therapies for PA beyond dietary restriction. This review focuses on the pathophysiological mechanisms of the various complications associated with PA, drawing on extensive research and clinical reports. Most research suggests that propionyl-CoA and its metabolites can impair mitochondrial energy metabolism and cause cellular damage by inducing oxidative stress. However, direct evidence from in vivo studies is still lacking. Additionally, elevated levels of ammonia can be toxic, although not all PA patients develop hyperammonemia. The discovery of pathophysiological mechanisms underlying various complications associated with PA can aid in the development of more effective therapeutic treatments. The consequences of elevated odd-chain fatty acids in lipid metabolism and potential gene expression changes mediated by histone propionylation also warrant further investigation.

Human forebrain organoid-based multi-omics analyses of PCCB as a schizophrenia associated gene linked to GABAergic pathways

Identifying genes whose expression is associated with schizophrenia (SCZ) risk by transcriptome-wide association studies (TWAS) facilitates downstream experimental studies. Here, we integrated multiple published datasets of TWAS, gene coexpression, and differential gene expression analysis to prioritize SCZ candidate genes for functional study. Convergent evidence prioritized Propionyl-CoA Carboxylase Subunit Beta (PCCB), a nuclear-encoded mitochondrial gene, as an SCZ risk gene. However, the PCCB's contribution to SCZ risk has not been investigated before. Using dual luciferase reporter assay, we identified that SCZ-associated SNPs rs6791142 and rs35874192, two eQTL SNPs for PCCB, showed differential allelic effects on transcriptional activities. PCCB knockdown in human forebrain organoids (hFOs) followed by RNA sequencing analysis revealed dysregulation of genes enriched with multiple neuronal functions including gamma-aminobutyric acid (GABA)-ergic synapse. The metabolomic and mitochondrial function analyses confirmed the decreased GABA levels resulted from inhibited tricarboxylic acid cycle in PCCB knockdown hFOs. Multielectrode array recording analysis showed that PCCB knockdown in hFOs resulted into SCZ-related phenotypes including hyper-neuroactivities and decreased synchronization of neural network. In summary, this study utilized hFOs-based multi-omics analyses and revealed that PCCB downregulation may contribute to SCZ risk through regulating GABAergic pathways, highlighting the mitochondrial function in SCZ.

Identification and characterization of the largest deletion in the PCCA gene causing severe acute early-onset form of propionic acidemia

Whole-exome sequencing (WES) is an excellent method for the diagnosis of diseases of uncertain or heterogeneous genetic origin. However, it has limitations for detecting structural variations such as InDels, which the bioinformatics analyzers must be aware of. This study aimed at using WES to evaluate the genetic cause of the metabolic crisis in a 3-day-old neonate admitted to the neonatal intensive care unit (NICU) and deceased after a few days. Tandem mass spectrometry (MS/MS) showed a significant increase in propionyl carnitine (C3), proposing methylmalonic acidemia (MMA) or propionic acidemia (PA). WES demonstrated a homozygous missense variant in exon 4 of the BTD gene (NM_000060.4(BTD):c.1330G > C), responsible for partial biotinidase deficiency. Segregation analysis of the BTD variant revealed the homozygous status of the asymptomatic mother. Furthermore, observation of the bam file, around genes responsible for PA or MMA, by Integrative Genomics Viewer (IGV) software displayed a homozygous large deletion in the PCCA gene. Comprehensive confirmatory studies identified and segregated a novel outframe deletion of 217,877 bp length, "NG_008768.1:g.185211_403087delinsTA", extended from intron 11 to 21 of the PCCA, inducing a premature termination codon and activation of nonsense-mediated mRNA decay (NMD). Homology modeling of the mutant PCCA demonstrated eliminating the protein's active site and critical functional domains. Thereupon, this novel variant is suggested as the largest deletion in the PCCA gene, causing an acute early-onset PA. These results could expand the PCCA variants spectrum, and improve the existing knowledge on the molecular basis of PA, as well as provide new evidence of pathogenicity of the variant (NM_000060.4(BTD):c.1330G > C.

Human forebrain organoids-based multi-omics analyses reveal PCCB's regulation on GABAergic system contributing to schizophrenia

Identifying genes whose expression is associated with schizophrenia (SCZ) risk by transcriptome-wide association studies (TWAS) facilitates downstream experimental studies. Here, we integrated multiple published datasets of TWAS (including FUSION, PrediXcan, summary-data-based Mendelian randomization (SMR), joint-tissue imputation approach with Mendelian randomization (MR-JTI)), gene coexpression, and differential gene expression analysis to prioritize SCZ candidate genes for functional study. Convergent evidence prioritized Propionyl-CoA Carboxylase Subunit Beta ( PCCB ), a nuclear-encoded mitochondrial gene, as an SCZ risk gene. However, the PCCB ’s contribution to SCZ risk has not been investigated before. Using dual luciferase reporter assay, we identified that SCZ-associated SNP rs35874192, an eQTL SNP for PCCB , showed differential allelic effects on transcriptional activities. PCCB knockdown in human forebrain organoids (hFOs) followed by RNA-seq revealed dysregulation of genes enriched with multiple neuronal functions including gamma-aminobutyric acid (GABA)-ergic synapse, as well as genes dysregulated in postmortem brains of SCZ patients or in cerebral organoids derived from SCZ patients. The metabolomic and mitochondrial function analyses confirmed the deceased GABA levels resulted from reduced tricarboxylic acid cycle in PCCB knockdown hFOs. Multielectrode array recording analysis showed that PCCB knockdown in hFOs resulted into SCZ-related phenotypes including hyper-neuroactivities and decreased synchronization of neural network. In summary, this study utilized hFOs-based multi-omics data and revealed that PCCB downregulation may contribute to SCZ risk through regulating GABAergic system, highlighting the mitochondrial function in SCZ.

Neuropsychological endpoints for clinical trials in methylmalonic acidemia and propionic acidemia: A pilot study

Introduction

This pilot study assessed instruments measuring relatively discrete neuropsychological domains to inform the selection of clinical outcome assessments that may be considered for interventional trials in methylmalonic acidemia (MMA) and propionic acidemia (PA).

Methods

Tests and questionnaires were selected for their possible relevance to MMA and PA and potential sensitivity to modest changes in functioning and behavior.

Results

Twenty-one patients (<18 years, n = 10;>18 years, n = 11) and/or their caregivers responded to video interviews and paper tests. Language deficits and significant motor deficits in some participants impacted scoring, especially in the verbal and processing speed sections of the Wechsler Intelligence Scale for Children, Fifth Edition (WISC-V) and the Wechsler Adult Intelligence Scale, Fourth Edition (WAIS-IV). However, all participants ≥12 years of age were able to complete the Cookie Theft Picture Task. Thus, verbal discourse remains a potentially useful endpoint for participants in this age group. The Vineland Adaptive Behavior Scales (VABS-3) Adaptive Behavior Composite and Communication Scores confirmed delayed or immature functioning in day-to-day activities in these participants. Significant motor deficits prevented completion of some tests. Computerized processing speed tasks, which require pressing a button or tapping a computer screen, may be easier than writing or checking off boxes on paper in this cohort. Sleep characteristics among MMA participants were within normative ranges of the Child and Adolescent Sleep Checklist (CASC), indicating that this measurement would not provide valuable data in a clinical trial. Despite their challenges, responses to the Metabolic Quality of Life Questionnaire indicated these patients and their caregivers perceive an overall high quality of life.

Conclusion

Overall, test and questionnaire results were notably different between participants with MMA and participants with PA. The study demonstrates that pilot studies can detect instruments that may not be appropriate for individuals with language or motor deficits and that may not provide a broad range of scores reflecting disease severity. It also provides a rationale for focusing on discrete neuropsychological domains since some aspects of functioning were less affected than others and some were more closely related to disease severity. When global measures are used, overall scores may mask specific deficits. A pilot study like this one cannot ensure that scores will change over time in response to a specific treatment in a clinical trial. However, it can avert the selection of instruments that do not show associations with severity or biomedical parameters likely to be the target of a clinical trial. A pilot study can also identify when differences in diagnoses and baseline functioning need to be addressed prior to developing the analytical plan for the trial.

Case report: A unusual case of delayed propionic acidemia complicated with subdural hematoma

Background

Propionic acidemia (PA) is an inherited autosomal recessive metabolic disorder that is classified as early-onset or late-onset, depending on the onset time of clinical symptoms. It clinically manifests as numerous lesions in the brain, pancreas, liver, and muscle. Muscle biopsies show myopathic changes, which help to distinguish late-onset propionic acidemia from other metabolic diseases involving muscles.

Case presentation

A 19-year-old Chinese girl was admitted to the hospital because of poor eating and fatigue. Head magnetic resonance imaging suggested metabolic diseases, and we administered symptomatic support treatment. Her symptoms gradually worsened, and she began to show convulsions and disturbances of consciousness. Muscle pathology showed myopathy-like changes. The presence of organic acids in the blood and urine suggested PA. Genetic analyses identified two compound heterozygous mutations in the patient's PCCB gene, confirming the diagnosis of delayed PA.

Conclusions

The muscle pathological examination of late-onset PA provides valuable information that is helpful for distinguishing delayed-onset PA from metabolic diseases. In the absence of a history of trauma, subdural hematoma may be a very rare complication of late-onset PA and can be regarded as a poor prognostic sign; therefore, it is suggested to perform head computed tomography as part of the routine neurological evaluation of PA patients.

Stroke-like Episodes in Inherited Neurometabolic Disorders

Stroke-like episodes (SLEs) are significant clinical manifestations of metabolic disorders affecting the central nervous system. Morphological equivalents presented in neuroimaging procedures are described as stroke-like lesions (SLLs). It is crucial to distinguish SLEs from cerebral infarction or intracerebral hemorrhage, mainly due to the variety in management. Another significant issue to underline is the meaning of the main pathogenetic hypotheses in the development of SLEs. The diagnostic process is based on the patient’s medical history, physical and neurological examination, neuroimaging techniques and laboratory and genetic testing. Implementation of treatment is generally symptomatic and includes L-arginine supplementation and adequate antiepileptic management. The main aim of the current review was to summarize the basic and actual knowledge about the occurrence of SLEs in various inherited neurometabolic disorders, discuss the possible pathomechanism of their development, underline the role of neuroimaging in the detection of SLLs and identification of the electroencephalographic patterns as well as histological abnormalities in inherited disorders of metabolism.

Biomarkers for drug development in propionic and methylmalonic acidemias

There is an unmet need for the development and validation of biomarkers and surrogate endpoints for clinical trials in propionic acidemia (PA) and methylmalonic acidemia (MMA). This review examines the pathophysiology and clinical consequences of PA and MMA that could form the basis for potential biomarkers and surrogate endpoints. Changes in primary metabolites such as methylcitric acid (MCA), MCA:citric acid ratio, oxidation of ¹³ C-propionate (exhaled ¹³ CO₂ ), and propionylcarnitine (C3) have demonstrated clinical relevance in patients with PA or MMA. Methylmalonic acid, another primary metabolite, is a potential biomarker, but only in patients with MMA. Other potential biomarkers in patients with either PA and MMA include secondary metabolites, such as ammonium, or the mitochondrial disease marker, fibroblast growth factor 21. Additional research is needed to validate these biomarkers as surrogate endpoints, and to determine whether other metabolites or markers of organ damage could also be useful biomarkers for clinical trials of investigational drug treatments in patients with PA or MMA. This review examines the evidence supporting a variety of possible biomarkers for drug development in propionic and methylmalonic acidemias.

Pharmacologic modulation of brain metabolism by valproic acid can induce a neuroprotective environment

OBJECTIVE

Traumatic brain injury (TBI) is a leading cause of trauma-related morbidity and mortality. Valproic acid (VPA) has been shown to attenuate brain lesion size and swelling within the first few hours following TBI. Because injured neurons are sensitive to metabolic changes, we hypothesized that VPA treatment would alter the metabolic profile in the perilesional brain tissues to create a neuroprotective environment.

METHODS

We subjected swine to combined TBI (12-mm cortical impact) and hemorrhagic shock (40% blood volume loss and 2 hours of hypotension) and randomized them to two groups (n = 5/group): (1) normal saline (NS; 3× hemorrhage volume) and (2) NS-VPA (NS, 3× hemorrhage volume; VPA, 150 mg/kg). After 6 hours, brains were harvested, and 100 mg of the perilesional tissue was used for metabolite extraction. Samples were analyzed using reversed-phase liquid chromatography-mass spectrometry in positive and negative ion modes, and data were analyzed using MetaboAnalyst software (McGill University, Quebec, Canada).

RESULTS

In untargeted reversed-phase liquid chromatography-mass spectrometry analysis, we detected 3,750 and 1,955 metabolites in positive and negative ion modes, respectively. There were no significantly different metabolites in positive ion mode; however, 167 metabolite features were significantly different (p < 0.05) in the negative ion mode, which included VPA derivates. Pathway analysis showed that several pathways were affected in the treatment group, including the biosynthesis of unsaturated fatty acids (p = 0.001). Targeted amino acid analysis on glycolysis/tricarboxylic acid (TCA) cycle revealed that VPA treatment significantly decreased the levels of the excitotoxic amino acid serine (p = 0.001).

CONCLUSION

Valproic acid can be detected in perilesional tissues in its metabolized form. It also induces metabolic changes in the brains within the first few hours following TBI to create a neuroprotective environment.

Association of microbiota-derived propionic acid and Alzheimer's disease; bioinformatics analysis

PURPOSE

Microbiota-derived metabolites could alter the brain tissue toward the neurodegeneration disease. This study aims to select the genes associated with Propionic acid (PPA) and compromise Alzheimer's disease (AD) to find the possible roles of PPA in AD pathogenesis.

METHODS

Microbiota-derived metabolites could alter the brain tissue toward the neurodegeneration disease. This study aims to select the genes associated with Propionic acid (PPA) and compromise Alzheimer's disease (AD) to find the possible roles of PPA in AD pathogenesis.

RESULTS

Amongst all genes associated with PPA and AD, 284 genes to be shared by searching databases and were subjected to further analysis. AD-PPA genes mainly involved in cancer, bacterial and virus infection, and neurological and non-neurological diseases. Gene Ontology and pathway analysis covered the most AD hallmark, such as amyloid formation, apoptosis, proliferation, inflammation, and immune system. Network analysis revealed hub and bottleneck genes. MCODE analysis also indicated the seed genes represented in the significant subnetworks. ICAM1 and CCND1 were the hub, bottleneck, and seed genes.

CONCLUSIONS

PPA interacted genes implicated in AD act through pathways initiate neuronal cell death. In sum up, AD-PPA shared genes exhibited evidence that supports the idea PPA secreted from bacteria could alter brain physiology toward the emerging AD signs. This idea needs to confirm by more future investigation in animal models.

Propionic and Methylmalonic Acidemias: Initial Clinical and Biochemical Presentation

PA and MAA have numerous nonspecific presentations, potentially leading to delayed diagnosis or misdiagnosis. In this paper, we present the clinical and biochemical characteristics of MMA and PA patients at initial presentation. Results. This is a retrospective review of 20 patients with PA (n = 10) and MMA (n = 10). The most observed symptoms were vomiting (85%) and refusing feeding (70%). Ammonia was 108.75 ± 9.3 μmol/l, showing a negative correlation with pH and bicarbonate and positive correlation with lactate and anion gap. Peak ammonia did not correlate with age of onset (r = 0.11 and p = 0.64) or age at diagnosis (r = 0.39 and p = 0.089), nor did pH (r = 0.01, p = 0.96; r = −0.25, p = 0.28) or bicarbonate (r = 0.07, p = 0.76; r = −0.22, p = 0.34). There was no correlation between ammonia and C3 : C2 (r = 0.1 and p = 0.96) or C3 (r = 0.23 and p = 0.32). The glycine was 386 ± 167.1 μmol/l, and it was higher in PA (p = 0.003). There was a positive correlation between glycine and both pH (r = 0.56 and p = 0.01) and HCO₃ (r = 0.49 and p = 0.026). There was no correlation between glycine and ammonia (r = −0.435 and p = 0.055) or lactate (r = 0.32 and p = 0.160). Conclusion. Clinical presentation of PA and MMA is nonspecific, though vomiting and refusing feeding are potential markers of decompensation. Blood gas, lactate, and ammonia levels are also good predictors of decompensation, though increasing levels of glycine may not indicate metabolic instability.

Clinical Course and Nutritional Management of Propionic and Methylmalonic Acidemias

Propionic and methylmalonic acidemias result in multiple health problems including increased risk for neurological and intellectual disabilities. Knowledge regarding factors that correlate to poor prognosis and long-term outcomes is still limited. In this study, we aim to provide insight concerning clinical course and long-term complications by identifying possible correlating factors to complications. Results. This is a retrospective review of 20 Egyptian patients diagnosed with PA (n = 10) and MMA (n = 10) in the years 2014–2018. PA patients had lower DQ/IQ and were more liable to hypotonia and developmental delay. The DQ/IQ had a strong negative correlation with length of hospital stay, frequency of PICU admissions, time delay until diagnosis, and the mode ammonia level. However, DQ/IQ did not correlate with age of onset of symptoms or the peak ammonia level at presentation. Both the growth percentiles and albumin levels had a positive correlation with natural protein intake and did not correlate with the total protein intake. Additionally, patients on higher amounts of medical formula did not necessarily show an improvement in the frequency of decompensation episodes. Conclusion. Our findings indicate that implementation of NBS, vigilant and proactive management of decompensation episodes, and pursuing normal ammonia levels during monitoring can help patients achieve a better neurological prognosis. Furthermore, patients can have a better outcome on mainly natural protein; medical formula should only be used in cases where patients do not meet 100–120% of their DRI from natural protein.

Identification of genes involved in the evolution of human intelligence through combination of inter-species and intra-species genetic variations

Understanding the evolution of human intelligence is an important undertaking in the science of human genetics. A great deal of biological research has been conducted to search for genes which are related to the significant increase in human brain volume and cerebral cortex complexity during hominid evolution. However, genetic changes affecting intelligence in hominid evolution have remained elusive. We supposed that a subset of intelligence-related genes, which harbored intra-species variations in human populations, may also be evolution-related genes which harbored inter-species variations between humans (Homo sapiens) and great apes (including Pan troglodytes and Pongo abelii). Here we combined inter-species and intra-species genetic variations to discover genes involved in the evolution of human intelligence. Information was collected from published GWAS works on intelligence and a total of 549 genes located within the intelligence-associated loci were identified. The intelligence-related genes containing human-specific variations were detected based on the latest high-quality genome assemblies of three human's closest species. Finally, we identified 40 strong candidates involved in human intelligence evolution. Expression analysis using RNA-Seq data revealed that most of the genes displayed a relatively high expression in the cerebral cortex. For these genes, there is a distinct expression pattern between humans and other species, especially in neocortex tissues. Our work provided a list of strong candidates for the evolution of human intelligence, and also implied that some intelligence-related genes may undergo inter-species evolution and contain intra-species variation.

Liver Transplantation for Propionic Acidemia: A Multicenter-linked Database Analysis

OBJECTIVES

Propionic acidemia (PA) is a rare inborn error of metabolism resulting from deficiency in the enzyme necessary for catabolism of branched-chain amino acids, some odd chain fatty acids and cholesterol. Despite optimal medical management, PA often leads to acute and progressive neurological injury. Reports on liver transplantation (LT) as a cellular therapy are limited and varied. The objective of this study was to examine the largest collection of patients who underwent LT for PA.

METHODS

Examining the Scientific Registry of Transplant Recipients and the Pediatric Health Information System administrative billing databases, we performed a multicenter, retrospective analysis of LT over a 16-year period. During this period, 4849 pediatric LT were performed out of which 23 were done for PA at 10 different centers.

RESULTS

The majority of recipients were 5 years of age or younger and had status 1b exception points at the time of transplant. The 1-, 3-, and 5-year graft survival for PA LT recipients was 84.6% and the 1-, 3, and 5-year patient survival was 89.5%. There was no significant difference in graft or patient survival between PA and non-PA LT recipients. Despite historical data to the contrary, we did not find an increased incidence of hepatic arterial thrombosis in patients undergoing LT for PA. Patients in the PA LT group, however, had a significantly higher postoperative rate of readmission compared with the non-PA LT group (90.5% vs 72.8%, P = 0.021).

CONCLUSION

LT for children with PA is a viable treatment option with acceptable outcomes.

High prevalence of self-reported autism spectrum disorder in the Propionic Acidemia Registry

Propionic Acidemia (PA) is characterized by the accumulation of propionic acid (PPA), its toxic derivatives, and ammonia. The disease causes multiorgan damage, especially in heart, pancreas, and brain; seizures and intellectual disability are often described. Some PA children also show autism spectrum disorders (ASD). In this study, we have compiled data from 62 individuals from the Propionic Acidemia International Patient Registry and compared it to the published literature on the prevalence of autism in PA. The PA registry shows a significant proportion of ASD diagnoses that is consistent with the combined prevalence reported in the literature. It also shows that ASD in PA is gender balanced and it is diagnosed at older ages (median age 8 years) than in the national registry for autism (median age 4.3 years), which raises the possibility, among others, of PA specific risk factors affecting the natural history of ASD. Data from patient registries provide valuable information on studying the mechanisms involved in a rare disease, although more outreach effort must be done to increase participation and consistency in data entry.

Metabolic Strokes in Propionic Acidemia: Transient Hemiplegic Events Without Encephalopathy

Metabolic strokes are a notable feature associated with acute catabolic crises in patients with propionic acidemia. Despite their importance, these events are not well characterized. Here, we present the clinical history of a patient with propionic acidemia who developed 5 episodes of acute hemiparesis between 3 and 11 years of age. The clinical finding of hemiparesis associated with 4 of these 5 events were shorted lived (2-5 days). Neuroimaging showed signal changes in the basal ganglia manifesting many years following the initial episode. Two of the episodes were accompanied by definite seizures. Based on these factors, the hemiparetic events were most consistent with metabolic strokes, though what is distinctive is that most of the events occurred without evidence of metabolic decompensation; brain magnetic resonance imaging findings were not suggestive in the acute setting. We present a framework for evaluating suspected metabolic stroke in propionic acidemia, in light of the sometimes perplexing clinical heterogeneity underlining these events.

Pathophysiology of propionic and methylmalonic acidemias. Part 1: Complications

Over the last decades, advances in clinical care for patients suffering from propionic acidemia (PA) and isolated methylmalonic acidemia (MMA) have resulted in improved survival. These advances were possible thanks to new pathophysiological insights. However, patients may still suffer from devastating complications which largely determine the unsatisfying overall outcome. To optimize our treatment strategies, better insight in the pathophysiology of complications is needed. Here, we perform a systematic data-analysis of cohort studies and case-reports on PA and MMA. For each of the prevalent and rare complications, we summarize the current hypotheses and evidence for the underlying pathophysiology of that complication. A common hypothesis on pathophysiology of many of these complications is that mitochondrial impairment plays a major role. Assuming that complications in which mitochondrial impairment may play a role are overrepresented in monogenic mitochondrial diseases and, conversely, that complications in which mitochondrial impairment does not play a role are underrepresented in mitochondrial disease, we studied the occurrence of the complications in PA and MMA in mitochondrial and other monogenic diseases, using data provided by the Human Phenotype Ontology. Lastly, we combined this with evidence from literature to draw conclusions on the possible role of mitochondrial impairment in each complication. Altogether, this review provides a comprehensive overview on what we, to date, do and do not understand about pathophysiology of complications occurring in PA and MMA and about the role of mitochondrial impairment herein.

Epilepsy in Propionic Acidemia: Case Series of 14 Saudi Patients

Propionic acidemia is an inborn error of metabolism that is inherited in an autosomal recessive manner. It is characterized by a deficient propionyl-CoA carboxylase due to mutations in either of its beta or alpha subunits. In the literature, there is a clear association between propionic acidemia and epilepsy. In this cohort, we retrospectively reviewed the data of 14 propionic acidemia patients in Saudi Arabia and compared the findings to those of former studies. Six of the 14 (43%) patients developed epileptic seizure, mainly focal seizures. All patients were responsive to conventional antiepileptic drugs as their seizures are controlled. The predominant electroencephalographic (EEG) findings were diffuse slowing in 43% and multifocal epileptiform discharges in 14% of the patients. In 1 patient, burst suppression pattern was detected, a pattern never before reported in patients with propionic acidemia. Brain magnetic resonance imaging (MRI) findings mainly consisted of signal changes of the basal ganglia (36%), generalized brain atrophy (43%), and delayed myelination (43%).The most common genotype in our series is the homozygous missense mutation in the PCCA gene (c.425G>A; p. Gly142Asp). However, there is no clear genotype-seizure correlation. We conclude that seizure is not an uncommon finding in patients with propionic acidemia and not difficult to control. Additional studies are needed to further elaborate on genotype-seizure correlation.

Metabolic etiologies in West syndrome

West syndrome (WS) is an early life epileptic encephalopathy associated with infantile spasms, interictal electroencephalography (EEG) abnormalities including high amplitude, disorganized background with multifocal epileptic spikes (hypsarrhythmia), and often neurodevelopmental impairments. Approximately 64% of the patients have structural, metabolic, genetic, or infectious etiologies and, in the rest, the etiology is unknown. Here we review the contribution of etiologies due to various metabolic disorders in the pathology of WS. These may include metabolic errors in organic molecules involved in amino acid and glucose metabolism, fatty acid oxidation, metal metabolism, pyridoxine deficiency or dependency, or acidurias in organelles such as mitochondria and lysosomes. We discuss the biochemical, clinical, and EEG features of these disorders as well as the evidence of how they may be implicated in the pathogenesis and treatment of WS. The early recognition of these etiologies in some cases may permit early interventions that may improve the course of the disease.

Dietary Considerations in Autism Spectrum Disorders: The Potential Role of Protein Digestion and Microbial Putrefaction in the Gut-Brain Axis

Children with autism spectrum disorders (ASD), characterized by a range of behavioral abnormalities and social deficits, display high incidence of gastrointestinal (GI) co-morbidities including chronic constipation and diarrhea. Research is now increasingly able to characterize the “fragile gut” in these children and understand the role that impairment of specific GI functions plays in the GI symptoms associated with ASD. This mechanistic understanding is extending to the interactions between diet and ASD, including food structure and protein digestive capacity in exacerbating autistic symptoms. Children with ASD and gut co-morbidities exhibit low digestive enzyme activity, impaired gut barrier integrity and the presence of antibodies specific for dietary proteins in the peripheral circulation. These findings support the hypothesis that entry of dietary peptides from the gut lumen into the vasculature are associated with an aberrant immune response. Furthermore, a subset of children with ASD exhibit high concentrations of metabolites originating from microbial activity on proteinaceous substrates. Taken together, the combination of specific protein intakes poor digestion, gut barrier integrity, microbiota composition and function all on a background of ASD represents a phenotypic pattern. A potential consequence of this pattern of conditions is that the fragile gut of some children with ASD is at risk for GI symptoms that may be amenable to improvement with specific dietary changes. There is growing evidence that shows an association between gut dysfunction and dysbiosis and ASD symptoms. It is therefore urgent to perform more experimental and clinical research on the “fragile gut” in children with ASD in order to move toward advancements in clinical practice. Identifying those factors that are of clinical value will provide an evidence-based path to individual management and targeted solutions; from real time sensing to the design of diets with personalized protein source/processing, all to improve GI function in children with ASD.

Propionyl-CoA carboxylase - A review

Propionyl-CoA carboxylase (PCC) is the enzyme which catalyzes the carboxylation of propionyl-CoA to methylmalonyl-CoA and is encoded by the genes PCCA and PCCB to form a hetero-dodecamer. Dysfunction of PCC leads to the inherited metabolic disorder propionic acidemia, which can result in an affected individual presenting with metabolic acidosis, hyperammonemia, lethargy, vomiting and sometimes coma and death if not treated. Individuals with propionic acidemia also have a number of long term complications resulting from the dysfunction of the PCC enzyme. Here we present an overview of the current knowledge about the structure and function of PCC. We review an updated list of human variants which are published and provide an overview of the disease.

Irritable bowel syndrome: a gut microbiota-related disorder?

Irritable bowel syndrome (IBS) is one of the most common gastrointestinal (GI) disorders. Despite its prevalence, the pathophysiology of IBS is not well understood although multiple peripheral and central factors are implicated. Recent studies suggest a role for alterations in gut microbiota in IBS. Significant advances in next-generation sequencing technology and bioinformatics and the declining cost have now allowed us to better investigate the role of gut microbiota in IBS. In the following review, we propose gut microbiota as a unifying factor in the pathophysiology of IBS. We first describe how gut microbiota can be influenced by factors predisposing individuals to IBS such as host genetics, stress, diet, antibiotics, and early life experiences. We then highlight the known effects of gut microbiota on mechanisms implicated in the pathophysiology of IBS including disrupted gut brain axis (GBA), visceral hypersensitivity (VH), altered GI motility, epithelial barrier dysfunction, and immune activation. While there are several gaps in the field that preclude us from connecting the dots to establish causation, we hope this overview will allow us to identify and fill in the voids.

Methylmalonic and propionic acidemias: clinical management update

PURPOSE OF REVIEW

Recent clinical studies and management guidelines for the treatment of the organic acidopathies methylmalonic acidemia (MMA) and propionic acidemia address the scope of interventions to maximize health and quality of life. Unfortunately, these disorders continue to cause significant morbidity and mortality due to acute and chronic systemic and end-organ injury.

RECENT FINDINGS

Dietary management with medical foods has been a mainstay of therapy for decades, yet well controlled patients can manifest growth, development, cardiac, ophthalmological, renal, and neurological complications. Patients with organic acidopathies suffer metabolic brain injury that targets specific regions of the basal ganglia in a distinctive pattern, and these injuries may occur even with optimal management during metabolic stress. Liver transplantation has improved quality of life and metabolic stability, yet transplantation in this population does not entirely prevent brain injury or the development of optic neuropathy and cardiac disease.

SUMMARY

Management guidelines should identify necessary screening for patients with methylmalonic acidemia and propionic acidemia, and improve anticipatory management of progressive end-organ disease. Liver transplantation improves overall metabolic control, but injury to nonregenerative tissues may not be mitigated. Continued use of medical foods in these patients requires prospective studies to demonstrate evidence of benefit in a controlled manner.

Expansion of the Phenotypic Spectrum of Propionic Acidemia with Isolated Elevated Propionylcarnitine

We report three patients with elevations of propionylcarnitine (C3), one without elevations of 2-methylcitrate and 3-hydroxypropionate in urine organic acid analysis, and the other two showing only mild elevations, all of whom were subsequently confirmed to have propionic acidemia by molecular analysis of PCCA and PCCB genes. To date, they have had a mild clinical course. These cases illustrate the importance of considering high C3 as the only biochemical abnormality in a diagnosis of propionic acidemia. Since mild C3 elevations may be overlooked and considered non-diagnostic in isolation, we advise considering a diagnosis of propionic acidemia even in the absence of significant elevations 2-methylcitrate or 3-hydroxypropionate in urine organic acid analysis.

In vivo evidence of mitochondrial dysfunction and altered redox homeostasis in a genetic mouse model of propionic acidemia: Implications for the pathophysiology of this disorder

Accumulation of toxic metabolites has been described to inhibit mitochondrial enzymes, thereby inducing oxidative stress in propionic acidemia (PA), an autosomal recessive metabolic disorder caused by the deficiency of mitochondrial propionyl-CoA carboxylase. PA patients exhibit neurological deficits and multiorgan complications including cardiomyopathy. To investigate the role of mitochondrial dysfunction in the development of these alterations we have used a hypomorphic mouse model of PA that mimics the biochemical and clinical hallmarks of the disease. We have studied the tissue-specific bioenergetic signature by Reverse Phase Protein Microarrays and analysed OXPHOS complex activities, mtDNA copy number, oxidative damage, superoxide anion and hydrogen peroxide levels. The results show decreased levels and/or activity of several OXPHOS complexes in different tissues of PA mice. An increase in mitochondrial mass and OXPHOS complexes was observed in brain, possibly reflecting a compensatory mechanism including metabolic reprogramming. mtDNA depletion was present in most tissues analysed. Antioxidant enzymes were also found altered. Lipid peroxidation was present along with an increase in hydrogen peroxide and superoxide anion production. These data support the hypothesis that oxidative damage may contribute to the pathophysiology of PA, opening new avenues in the identification of therapeutic targets and paving the way for in vivo evaluation of compounds targeting mitochondrial biogenesis or reactive oxygen species production.

Impact of age at onset and newborn screening on outcome in organic acidurias

BACKGROUND AND AIM

To describe current diagnostic and therapeutic strategies in organic acidurias (OADs) and to evaluate their impact on the disease course allowing harmonisation.

METHODS

Datasets of 567 OAD patients from the E-IMD registry were analysed. The sample includes patients with methylmalonic (MMA, n = 164), propionic (PA, n = 144) and isovaleric aciduria (IVA, n = 83), and glutaric aciduria type 1 (GA1, n = 176). Statistical analysis included description and recursive partitioning of diagnostic and therapeutic strategies, and odds ratios (OR) for health outcome parameters. For some analyses, symptomatic patients were divided into those presenting with first symptoms during (i.e. early onset, EO) or after the newborn period (i.e. late onset, LO).

RESULTS

Patients identified by newborn screening (NBS) had a significantly lower median age of diagnosis (8 days) compared to the LO group (363 days, p < 0.001], but not compared to the EO group. Of all OAD patients 71 % remained asymptomatic until day 8. Patients with cobalamin-nonresponsive MMA (MMA-Cbl(-)) and GA1 identified by NBS were less likely to have movement disorders than those diagnosed by selective screening (MMA-Cbl(-): 10 % versus 39 %, p = 0.002; GA1: 26 % versus 73 %, p < 0.001). For other OADs, the clinical benefit of NBS was less clear. Reported age-adjusted intake of natural protein and calories was significantly higher in LO patients than in EO patients reflecting different disease severities. Variable drug combinations, ranging from 12 in MMA-Cbl(-) to two in isovaleric aciduria, were used for maintenance treatment. The effects of specific metabolic treatment strategies on the health outcomes remain unclear because of the strong influences of age at onset (EO versus LO), diagnostic mode (NBS versus selective screening), and the various treatment combinations used.

CONCLUSIONS

NBS is an effective intervention to reduce time until diagnosis especially for LO patients and to prevent irreversible cerebral damage in GA1 and MMA-Cbl(-). Huge diversity of therapeutic interventions hampers our understanding of optimal treatment.

In Vivo NMR Studies of the Brain with Hereditary or Acquired Metabolic Disorders

Metabolic disorders, whether hereditary or acquired, affect the brain, and abnormalities of the brain are related to cellular integrity; particularly in regard to neurons and astrocytes as well as interactions between them. Metabolic disturbances lead to alterations in cellular function as well as microscopic and macroscopic structural changes in the brain with diabetes, the most typical example of metabolic disorders, and a number of hereditary metabolic disorders. Alternatively, cellular dysfunction and degeneration of the brain lead to metabolic disturbances in hereditary neurological disorders with neurodegeneration. Nuclear magnetic resonance (NMR) techniques allow us to assess a range of pathophysiological changes of the brain in vivo. For example, magnetic resonance spectroscopy detects alterations in brain metabolism and energetics. Physiological magnetic resonance imaging (MRI) detects accompanying changes in cerebral blood flow related to neurovascular coupling. Diffusion and T1/T2-weighted MRI detect microscopic and macroscopic changes of the brain structure. This review summarizes current NMR findings of functional, physiological and biochemical alterations within a number of hereditary and acquired metabolic disorders in both animal models and humans. The global view of the impact of these metabolic disorders on the brain may be useful in identifying the unique and/or general patterns of abnormalities in the living brain related to the pathophysiology of the diseases, and identifying future fields of inquiry.

Gastrointestinal symptoms and autism spectrum disorder: links and risks - a possible new overlap syndrome

Autism spectrum disorder (ASD) is a genetically determined neurodevelopmental brain disorder presenting with restricted, repetitive patterns of behaviors, interests, and activities, or persistent deficits in social communication and social interaction. ASD is characterized by many different clinical endophenotypes and is potentially linked with certain comorbidities. According to current recommendations, children with ASD are at risk of having alimentary tract disorders - mainly, they are at a greater risk of general gastrointestinal (GI) concerns, constipation, diarrhea, and abdominal pain. GI symptoms may overlap with ASD core symptoms through different mechanisms. These mechanisms include multilevel pathways in the gut-brain axis contributing to alterations in behavior and cognition. Shared pathogenetic factors and pathophysiological mechanisms possibly linking ASD and GI disturbances, as shown by most recent studies, include intestinal inflammation with or without autoimmunity, immunoglobulin E-mediated and/or cell-mediated GI food allergies as well as gluten-related disorders (celiac disease, wheat allergy, non-celiac gluten sensitivity), visceral hypersensitivity linked with functional abdominal pain, and dysautonomia linked with GI dysmotility and gastroesophageal reflux. Dysregulation of the gut microbiome has also been shown to be involved in modulating GI functions with the ability to affect intestinal permeability, mucosal immune function, and intestinal motility and sensitivity. Metabolic activity of the microbiome and dietary components are currently suspected to be associated with alterations in behavior and cognition also in patients with other neurodegenerative diseases. All the above-listed GI factors may contribute to brain dysfunction and neuroinflammation depending upon an individual patient's genetic vulnerability. Due to a possible clinical endophenotype presenting as comorbidity of ASD and GI disorders, we propose treating this situation as an "overlap syndrome". Practical use of the concept of an overlap syndrome of ASD and GI disorders may help in identifying those children with ASD who suffer from an alimentary tract disease. Unexplained worsening of nonverbal behaviors (agitation, anxiety, aggression, self-injury, sleep deprivation) should alert professionals about this possibility. This may shorten the time to diagnosis and treatment commencement, and thereby alleviate both GI and ASD symptoms through reducing pain, stress, or discomfort. Furthermore, this may also protect children against unnecessary dietary experiments and restrictions that have no medical indications. A personalized approach to each patient is necessary. Our understanding of ASDs has come a long way, but further studies and more systematic research are warranted.

Deconstructing Black Swans: An Introductory Approach to Inherited Metabolic Disorders in the Neonate

BACKGROUND

Inherited metabolic disorders (IMDs) are individually rare but collectively common disorders that frequently require rapid or urgent therapy.

PURPOSE

This article provides a generalized approach to IMDs, as well as some investigations and safe therapies that may be initiated pending the metabolic consult.

METHODS/SEARCH STRATEGY

An overview of the research supporting management strategies is provided. In addition, the newborn metabolic screen is reviewed.

FINDINGS/RESULTS

Caring for infants with IMDs can seem difficult because each of the types is rarely seen; however, collectively the management can be seen as similar.

IMPLICATIONS FOR PRACTICE

When an IMD is suspected, a metabolic specialist should be consulted for expert advice regarding appropriate laboratory investigations and management. Because rapid intervention of IMDs before the onset of symptoms may prevent future irreversible sequelae, each abnormal newborn screen must be addressed promptly.

IMPLICATIONS FOR RESEARCH

Management can be difficult. Research in this area is limited and can be difficult without multisite coordination since sample sizes of any significance are difficult to achieve.

Propionic acidemia in the Arab World

The autosomal recessive disease propionic acidemia (PA) is an inborn error of metabolism with highly variable clinical manifestations, caused by a deficiency of propionyl-CoA carboxylase (PCC) enzyme, due to mutations in either PCCA or PCCB genes, which encode the alpha and beta subunits of the PCC enzyme, respectively. The classical clinical presentation consists of poor feeding, vomiting, metabolic acidosis, hyperammonemia, lethargy, neurological problems, and developmental delay. PA seems to be a prevalent disease in the Arab World. Arab patients with PA seem to have the same classical clinical picture for PA with distinctive associated complications and other diseases. Most of the mutations found in Arab patients seem to be specific to the Arab population, and not observed in other ethnic groups. In this review, I will discuss in details the clinical and molecular profile of Arab patients with PA.

Proposed guidelines for the diagnosis and management of methylmalonic and propionic acidemia

Methylmalonic and propionic acidemia (MMA/PA) are inborn errors of metabolism characterized by accumulation of propionic acid and/or methylmalonic acid due to deficiency of methylmalonyl-CoA mutase (MUT) or propionyl-CoA carboxylase (PCC). MMA has an estimated incidence of ~ 1: 50,000 and PA of ~ 1:100’000 -150,000. Patients present either shortly after birth with acute deterioration, metabolic acidosis and hyperammonemia or later at any age with a more heterogeneous clinical picture, leading to early death or to severe neurological handicap in many survivors. Mental outcome tends to be worse in PA and late complications include chronic kidney disease almost exclusively in MMA and cardiomyopathy mainly in PA. Except for vitamin B₁₂ responsive forms of MMA the outcome remains poor despite the existence of apparently effective therapy with a low protein diet and carnitine. This may be related to under recognition and delayed diagnosis due to nonspecific clinical presentation and insufficient awareness of health care professionals because of disease rarity.

These guidelines aim to provide a trans-European consensus to guide practitioners, set standards of care and to help to raise awareness. To achieve these goals, the guidelines were developed using the SIGN methodology by having professionals on MMA/PA across twelve European countries and the U.S. gather all the existing evidence, score it according to the SIGN evidence level system and make a series of conclusive statements supported by an associated level of evidence. Although the degree of evidence rarely exceeds level C (evidence from non-analytical studies like case reports and series), the guideline should provide a firm and critical basis to guide practice on both acute and chronic presentations, and to address diagnosis, management, monitoring, outcomes, and psychosocial and ethical issues. Furthermore, these guidelines highlight gaps in knowledge that must be filled by future research. We consider that these guidelines will help to harmonize practice, set common standards and spread good practices, with a positive impact on the outcomes of MMA/PA patients.

Metabolic encephalopathy in beta-ketothiolase deficiency: the first report from India

Beta-ketothiolase deficiency, or mitochondrial acetoacetyl-CoA thiolase (T2) deficiency, is a rare autosomal recessive disorder affecting isoleucine catabolism and ketone body metabolism. A patient from South India presented with acute ketoacidosis at 11 months of age. During the acute crisis the C5OH (2-methyl-3-hydroxybutyryl) carnitine and C5:1 (tiglyl) carnitine were elevated and large amounts of 2-methyl-3-hydroxybutyrate, tiglylglycine, and 2-methylacetoacetate were excreted. Brain CT showed bilateral basal ganglia lesions. Potassium ion-activated acetoacetyl-CoA thiolase activity was deficient in the patient's fibroblasts. The patient is a homozygote for a novel c.578T>G (M193R) mutation. This is the first report of T2 deficiency confirmed by enzyme and molecular analysis from India.

Concurrent non-ketotic hyperglycinemia and propionic acidemia in an eight year old boy

This is the first reported case of a patient with both non-ketotic hyperglycinemia and propionic acidemia. At 2 years of age, the patient was diagnosed with non-ketotic hyperglycinemia by elevated glycine levels and mutations in the GLDC gene (paternal allele: c.1576_1577insC delT and c.1580delGinsCAA; p.S527Tfs*13, and maternal allele: c.1819G>A; p.G607S). At 8 years of age after having been placed on ketogenic diet, he became lethargic and had severe metabolic acidosis with ketonuria. Urine organic acid analysis and plasma acylcarnitine profile were consistent with propionic acidemia. He was found to have an apparently homozygous mutation in the PCCB gene: c.49C>A; p.Leu17Met. The patient was also treated with natural protein restriction, carnitine, biotin, and thiamine and had subjective and biochemical improvement.

Disruption of redox homeostasis and brain damage caused in vivo by methylmalonic acid and ammonia in cerebral cortex and striatum of developing rats

Hyperammonemia is a common finding in children with methylmalonic acidemia and propionic acidemia, but its contribution to the development of the neurological symptoms in the affected patients is poorly known. Considering that methylmalonic acid (MMA) and propionic acid (PA) predominantly accumulate in these disorders, we investigated the effects of hyperammonemia induced by urease treatment in 30-day-old rats receiving an intracerebroventricular (ICV) injection of MMA or PA on important parameters of redox homeostasis in cerebral cortex and striatum. We evaluated glutathione (GSH) concentrations, sulfhydryl content, nitrate and nitrite concentrations, 2',7'-dichlorofluorescein (DCFH) oxidation, and the activity of antioxidant enzymes. MMA decreased GSH concentrations and sulfhydryl content and increased nitrate and nitrite concentrations in cerebral cortex and striatum from hyperammonemic rats, whereas MMA or ammonia per se did not alter these parameters. MMA plus hyperammonemia also decreased glutathione reductase activity in rat cerebral cortex, but did not affect catalase, superoxide dismutase and glutathione peroxidase activities, neither DCFH oxidation. Furthermore, ICV PA administration alone or combined with hyperammonemia did not alter any of the evaluated parameters. We also found that pre-treatment with antioxidants prevented GSH reduction and sulfhydryl oxidation, whereas N(ω)-nitro-L-arginine methyl ester (L-NAME) prevented the increased nitrate and nitrite concentrations provoked by MMA plus ammonia treatments. Histological alterations, including vacuolization, ischemic neurons, and pericellular edema, were observed in brain of hyperammonemic rats injected with MMA. The data indicate a synergistic effect of MMA and ammonia disturbing redox homeostasis and causing morphological brain abnormalities in rat brain.

Acute psychosis in propionic acidemia: 2 case reports

Propionic acidemia is an inborn deficiency of propionyl-coenzyme A (CoA) carboxylase activity, which leads to mitochondrial accumulation of propionyl-CoA and its by-products. Neurologic complications are frequent, but only a few cases presenting with psychiatric symptoms have been reported so far. We report 2 cases of children with chronic psychiatric symptoms who presented with an acute psychotic episode as teenagers. Both patients had hallucinations, panic and grossly disorganized behavior, for several weeks to several months. They had signs of moderate metabolic decompensation at the beginning of the episode, although the psychiatric symptoms lasted longer than the metabolic imbalance. We propose that these episodes were at least partially imputable to propionic acidemia. Such episodes require psychiatric examination and antipsychotic treatment, which may have to be adapted in case of cardiomyopathy or long QT syndrome.

Mechanism of metabolic stroke and spontaneous cerebral hemorrhage in glutaric aciduria type I

Background

Metabolic stroke is the rapid onset of lasting central neurological deficit associated with decompensation of an underlying metabolic disorder. Glutaric aciduria type I (GA1) is an inherited disorder of lysine and tryptophan metabolism presenting with metabolic stroke in infancy. The clinical presentation includes bilateral striatal necrosis and spontaneous subdural and retinal hemorrhages, which has been frequently misdiagnosed as non-accidental head trauma. The mechanisms underlying metabolic stroke and spontaneous hemorrhage are poorly understood.

Results

Using a mouse model of GA1, we show that metabolic stroke progresses in the opposite sequence of ischemic stroke, with initial neuronal swelling and vacuole formation leading to cerebral capillary occlusion. Focal regions of cortical followed by striatal capillaries are occluded with shunting to larger non-exchange vessels leading to early filling and dilation of deep cerebral veins. Blood–brain barrier breakdown was associated with displacement of tight-junction protein Occludin.

Conclusion

Together the current findings illuminate the pathophysiology of metabolic stroke and vascular compromise in GA1, which may translate to other neurometabolic disorders presenting with stroke.

Clinical spectrum of propionic acidaemia

Objectives. To evaluate the clinical features, physical findings, diagnosis, and laboratory parameters of the patients with propionic acidaemia (PA). Methods. The records of diagnosed cases of propionic acidaemia were reviewed, retrospectively. Results. Twenty-six patients with PA had 133 admissions. The majority (85%) of the patients exhibited clinical manifestations in the 1st week of life. Regarding clinical features, lethargy, fever, poor feeding, vomiting, dehydration, muscular hypotonia, respiratory symptoms, encephalopathy, disturbance of tone and reflexes, and malnutrition were observed in 51–92% admissions. Metabolic crises, respiratory diseases, hyperammonaemia, metabolic acidosis, hypoalbuminaemia, and hypocalcaemia were observed in 30–96% admissions. Pancytopenia, ketonuria, hypoproteinemia, hypoglycaemia, and mildly disturbed liver enzymes were found in 12–41% admissions. Generalised brain oedema was detected in 17% and cerebral atrophy in 25% admissions. Gender-wise odd ratio analysis showed value of 1.9 for lethargy, 1.99 for respiratory diseases, 0.55 for anaemia, and 1.82 for hypocalcaemia. Conclusion. Propionic acidaemia usually presents with wide spectrum of clinical features and disturbances of laboratory parameters in early neonatal age. It is associated with significant complications which deteriorate the patients' quality of life. Perhaps with early diagnosis of the disease and in time intervention, these may be preventable.

Long-term neurological outcome of a cohort of 80 patients with classical organic acidurias

Background

Classical organic acidurias including methylmalonic aciduria (MMA), propionic aciduria (PA) and isovaleric aciduria (IVA) are severe inborn errors of the catabolism of branched-chain amino acids and odd-numbered chain fatty acids, presenting with severe complications.

Methods

This study investigated the long-term outcome of 80 patients with classical organic aciduria (38 with MMA, 24 with PA and 18 with IVA) by integrating clinical, radiological, biochemical and genetic data.

Results

Patients were followed-up for a mean of 14 years [age 3.3-46.3 years]. PA included a greater number of patients with abnormal neurological examination (37% in PA, 24% in MMA and 0% in IVA), lower psychometric scores (abnormal evaluation at age 3 years in 61% of patients with PA versus 26% in MMA and 18% in IVA) and more frequent basal ganglia lesions (56% of patients versus 36% in MMA and 17% in IVA). All patients with IVA presented a normal neurological examination and only 1/3 presented cognitive troubles. Prognosis for MMA was intermediate. Biochemical metabolite analysis excluding acute decompensations revealed significant progressive increases of glycine, alanine and glutamine particularly in PA and possibly in MMA but no correlation with neurological outcome. A significant increase of plasma methylmalonic acid was found in MMA patients with intellectual deficiency (mean level of 199 μmol/L versus 70 μmol/L, p < 0.05), with an estimated significant probability of severe outcome for average levels between birth and age 6 years above 167 μmol/L. Urinary 3-hydroxypropionate (3-HP) levels were significantly higher in PA patients with intellectual deficiency (mean level of 68.9 μmol/mmol of creatinine versus 34.6 μmol/mmol of creatinine, p < 0.01), with an estimated significant probability of severe outcome for average levels between birth and age 6 years above 55 μmol/mmol. As for molecular analysis, prognosis of MMA patients with mutations involving the MMAA gene was better compared to patients with mutations involving the MUT gene.

Conclusion

Propionic aciduria had the most severe neurological prognosis. Our radiological and biochemical data are consistent with a mitochondrial toxicity mechanism. Follow-up plasma MMA and urinary 3-HP levels may have prognostic significance calling for greater efforts to optimize long-term management in these patients.

Propionic acidemia and optic neuropathy: a report of two cases

INTRODUCTION

Propionic acidemia is a metabolic disease produced by a deficiency of the enzyme propionyl-CoA carboxylase. It can lead to coma, with severe neurologic encephalopathy or present later in life with vomiting, hypotonia, and seizures. An early diagnosis with adequate treatment helps to prevent the sequelae. Among the described complications is optic neuropathy, although not commonly reported, it is very disabling.

OBJECTIVES

To describe two patients with propionic acidemia and optic neuropathy.

PATIENTS AND METHODS

Patient 1: 16 years old, male, parents without consanguinity. He was diagnosed at 5 months of age because of hypotonia and seizures. Until the age of 9 years, he evolved satisfactorily; therefore, he stopped treatment. At 13 years, he presented bilateral optic neuropathy. Patient 2: 20 years, female, parents without consanguinity. She was diagnosed with PA at 11 months of age because of hypotonia and seizures. She evolved satisfactorily until the age of 9 years when she presented a metabolic decompensation followed by a bad metabolic control. At 18 years, she presented bilateral progressive optic neuropathy.

RESULTS

Both patients have psychometric scores with borderline IQ 84-75 (WISC-R) beside optic neuropathy. They were evaluated by an ophthalmologist and also by neuroimaging (MRI of optic pathway).

CONCLUSIONS

Pathophysiology of optic neuropathy is not completely understood. There is evidence that the damage is due to an accumulation of neurotoxic compounds secondary to the metabolic block increasing the oxidative stress. We suggest an annual ophthalmologic evaluation in the long-term follow-up of organic acidurias with visual loss, in order to detect this disabling sequela at an earlier stage.

Short-chain fatty acid fermentation products of the gut microbiome: implications in autism spectrum disorders

Recent evidence suggests potential, but unproven, links between dietary, metabolic, infective, and gastrointestinal factors and the behavioral exacerbations and remissions of autism spectrum disorders (ASDs). Propionic acid (PPA) and its related short-chain fatty acids (SCFAs) are fermentation products of ASD-associated bacteria (Clostridia, Bacteriodetes, Desulfovibrio). SCFAs represent a group of compounds derived from the host microbiome that are plausibly linked to ASDs and can induce widespread effects on gut, brain, and behavior. Intraventricular administration of PPA and SCFAs in rats induces abnormal motor movements, repetitive interests, electrographic changes, cognitive deficits, perseveration, and impaired social interactions. The brain tissue of PPA-treated rats shows a number of ASD-linked neurochemical changes, including innate neuroinflammation, increased oxidative stress, glutathione depletion, and altered phospholipid/acylcarnitine profiles. These directly or indirectly contribute to acquired mitochondrial dysfunction via impairment in carnitine-dependent pathways, consistent with findings in patients with ASDs. Of note, common antibiotics may impair carnitine-dependent processes by altering gut flora favoring PPA-producing bacteria and by directly inhibiting carnitine transport across the gut. Human populations that are partial metabolizers of PPA are more common than previously thought. PPA has further bioactive effects on neurotransmitter systems, intracellular acidification/calcium release, fatty acid metabolism, gap junction gating, immune function, and alteration of gene expression that warrant further exploration. These findings are consistent with the symptoms and proposed underlying mechanisms of ASDs and support the use of PPA infusions in rats as a valid animal model of the condition. Collectively, this offers further support that gut-derived factors, such as dietary or enteric bacterially produced SCFAs, may be plausible environmental agents that can trigger ASDs or ASD-related behaviors and deserve further exploration in basic science, agriculture, and clinical medicine.

Autism spectrum disorder in a child with propionic acidemia

Autism is a neurodevelopmental disorder characterized by a combination of reciprocal social deficits, communication impairment, and rigid ritualistic interests. While autism does not have an identifying cause in most of the cases, it is associated with known medical conditions in at least 10% of cases. Although uncommon, cases of autism have also been reported in association with metabolic disorders. In this brief report, we describe the occurrence of autism in a 7-year-old girl with propionic acidemia (PA), a common form of organic aciduria resulting from the deficiency of propionyl-CoA carboxylase and characterized by frequent and potentially lethal episodes of metabolic acidosis often accompanied by hyperammonemia. It is particularly common in countries with high rates of consanguinity. Early diagnosis of autism in patients with metabolic disorders is important since autistic features are sometimes the most disruptive of all the child's problems. This facilitates providing the needed behavioral services not otherwise available for children with metabolic disorders.