Propionic acidemia mimicking diabetic ketoacidosis

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.

Metabolome Profiling and Pathway Analysis in Metabolically Healthy and Unhealthy Obesity among Chinese Adolescents Aged 11-18 Years

The underlying mechanisms of the development of unhealthy metabolic phenotypes in obese children and adolescents remain unclear. We aimed to screen the metabolomes of individuals with the unhealthy obesity phenotype and identify the potential metabolic pathways that could regulate various metabolic profiles of obesity in Chinese adolescents. A total of 127 adolescents aged 11-18 years old from China were investigated using a cross-sectional study. The participants were classified as having metabolically healthy obesity (MHO) or metabolically unhealthy obesity (MUO) based on the presence/absence of metabolic abnormalities defined by metabolic syndrome (MetS) and body mass index (BMI). Serum-based metabolomic profiling using gas chromatography-mass spectrometry (GC-MS) was undertaken on 67 MHO and 60 MUO individuals. ROC analyses showed that palmitic acid, stearic acid, and phosphate could predict MUO, and that glycolic acid, alanine, 3-hydroxypropionic acid, and 2-hydroxypentanoic acid could predict MHO (all p < 0.05) from selected samples. Five metabolites predicted MUO, 12 metabolites predicted MHO in boys, and only two metabolites predicted MUO in girls. Moreover, several metabolic pathways may be relevant in distinguishing the MHO and MUO groups, including the fatty acid biosynthesis, fatty acid elongation in mitochondria, propanoate metabolism, glyoxylate and dicarboxylate metabolism, and fatty acid metabolism pathways. Similar results were observed for boys except for phenylalanine, tyrosine and tryptophan biosynthesis, which had a high impact [0.098]. The identified metabolites and pathways could be efficacious for investigating the underlying mechanisms of the development of different metabolic phenotypes in obese Chinese adolescents.

Transient Insulin Resistance in Propionic Acidaemia: Knowing is half the battle

Propionic acidaemia (PPA) is a disorder of amino acid and odd-chain fatty acid metabolism. Hypoglycaemia is a more commonly described finding rather than hyperglycaemia during metabolic decompensation of PPA. There is a high mortality rate in patients with organic acidaemias having severe insulin-resistant hyperglycaemia. We report a nine-month-old boy with PPA who was admitted to tertiary care hospital in Muscat, Oman, in 2018 with metabolic decompensation, persistent hyperglycaemia and transient insulin resistance. Hyperglycaemia did not respond to high insulin infusion. Plasma glucose only improved when glucose infusion rate (GIR) reached 7 mg/kg/min. The patient has full recovery and was discharged, with follow up plan. It is important to balance the GIR to achieve the targeted insulin level, beyond which the risks of hyperglycaemia start to outweigh the potential anabolic benefits of additional insulin secretion. Timely clinical attention should be given to achieve adequate caloric delivery through alternative sources other than high GIR to permit better glycaemic control, especially when insulin-resistant hyperglycaemia is present.

REVIEW: Practical strategies to maintain anabolism by intravenous nutritional management in children with inborn metabolic diseases

One of the most vital elements of management for patients with inborn errors of intermediary metabolism is the promotion of anabolism, the state in which the body builds new components, and avoidance of catabolism, the state in which the body breaks down its own stores for energy. Anabolism is maintained through the provision of a sufficient supply of substrates for energy, as well as critical building blocks of essential amino acids, essential fatty acids, and vitamins for synthetic function and growth. Patients with metabolic diseases are at risk for decompensation during prolonged fasting, which often occurs during illnesses in which enteral intake is compromised. During these times, intravenous nutrition must be supplied to fully meet the specific nutritional needs of the patient. We detail our approach to intravenous management for metabolic patients and its underlying rationale. This generally entails a combination of intravenous glucose and lipid as well as early introduction of protein and essential vitamins. We exemplify the utility of our approach in case studies, as well as scenarios and specific disorders which require a more careful administration of nutritional substrates or a modification of macronutrient ratios.

Cardiometabolic risk factor clustering in patients with deficient branched-chain amino acid catabolism: A case-control study

Classical organic acidemias (OAs) result from defective mitochondrial catabolism of branched-chain amino acids (BCAAs). Abnormal mitochondrial function relates to oxidative stress, ectopic lipids and insulin resistance (IR). We investigated whether genetically impaired function of mitochondrial BCAA catabolism associates with cardiometabolic risk factors, altered liver and muscle energy metabolism, and IR. In this case-control study, 31 children and young adults with propionic acidemia (PA), methylmalonic acidemia (MMA) or isovaleric acidemia (IVA) were compared with 30 healthy young humans using comprehensive metabolic phenotyping including in vivo ³¹ P/¹ H magnetic resonance spectroscopy of liver and skeletal muscle. Among all OAs, patients with PA exhibited abdominal adiposity, IR, fasting hyperglycaemia and hypertriglyceridemia as well as increased liver fat accumulation, despite dietary energy intake within recommendations for age and sex. In contrast, patients with MMA more frequently featured higher energy intake than recommended and had a different phenotype including hepatomegaly and mildly lower skeletal muscle ATP content. In skeletal muscle of patients with PA, slightly lower inorganic phosphate levels were found. However, hepatic ATP and inorganic phosphate concentrations were not different between all OA patients and controls. In patients with IVA, no abnormalities were detected. Impaired BCAA catabolism in PA, but not in MMA or IVA, was associated with a previously unrecognised, metabolic syndrome-like phenotype with abdominal adiposity potentially resulting from ectopic lipid storage. These findings suggest the need for early cardiometabolic risk factor screening in PA.

Recent advances in understanding beta-ketothiolase (mitochondrial acetoacetyl-CoA thiolase, T2) deficiency

Beta-ketothiolase (mitochondrial acetoacetyl-CoA thiolase, T2) deficiency (OMIM #203750, *607809) is an inborn error of metabolism that affects isoleucine catabolism and ketone body metabolism. This disorder is clinically characterized by intermittent ketoacidotic crises under ketogenic stresses. In addition to a previous 26-case series, four series of T2-deficient patients were recently reported from different regions. In these series, most T2-deficient patients developed their first ketoacidotic crises between the ages of 6 months and 3 years. Most patients experienced less than three metabolic crises. Newborn screening (NBS) for T2 deficiency is performed in some countries but some T2-deficient patients have been missed by NBS. Therefore, T2 deficiency should be considered in patients with severe metabolic acidosis, even in regions where NBS for T2 deficiency is performed. Neurological manifestations, especially extrapyramidal manifestations, can occur as sequelae to severe metabolic acidosis; however, this can also occur in patients without any apparent metabolic crisis or before the onset of metabolic crisis.

Inborn errors of metabolism associated with hyperglycaemic ketoacidosis and diabetes mellitus: narrative review

Inborn errors of metabolism (IEM) are heterogeneous group of disorders that might present in the clinics or emergency departments in different phenotypes, and one of these is a diabetes scenario. Diabetes is the most common endocrine disorder among children. The mechanism of how IEM could lead to diabetes is unclear; however, the postulated pathogenesis consists of three mechanisms: 1) accumulation of toxic substance in the gland, ruining structure and normal functionality, 2) disturbing energy availability required for hormone synthesis and 3) defect of complex molecules. The differential diagnosis of IEM associated with hyperglycaemic ketoacidosis and diabetes include: organic acidemias specifically propionic acidemia, methylmalonic acidemia, isovaleric acidemia, hereditary hemochromatosis, aceruloplasminemia, holocarboxylase synthetase deficiency, β-ketothiolase deficiency and finally, cystinosis, Rogers syndrome (thiamine-responsive megaloblastic anaemia) and congenital disorders of glycosylation type Ia. Clinical approach will help in ready diagnosis and treatment for IEM disorders in early detection of diabetes. In this review, we will discuss the differential diagnosis, clinical features and diagnostic approaches of IEM presenting as hyperglycaemic ketoacidosis and diabetes.

Comparison of Methods of Initial Ascertainment in 58 Cases of Propionic Acidemia Enrolled in the Inborn Errors of Metabolism Information System Reveals Significant Differences in Time to Evaluation and Symptoms at Presentation

OBJECTIVES

To compare time to evaluation and symptoms at diagnosis of propionic acidemia (PA) by method of ascertainment, and to explore correlations between genotype and biochemical variables.

STUDY DESIGN

Clinical symptoms, genotype, and biochemical findings were analyzed retrospectively in 58 individuals with PA enrolled in the Inborn Errors of Metabolism Information System (IBEM-IS) based on the type of initial ascertainment: abnormal newborn screening (NBS), clinical presentation (symptomatic), or family history.

RESULTS

The average age at initial evaluation and treatment was significantly younger in patients ascertained via abnormal NBS compared with those referred for clinical symptoms. Furthermore, the majority of individuals ascertained because of abnormal NBS were asymptomatic at diagnosis, compared with a minority of clinical presentations. A notable difference in the frequency of metabolic acidosis at initial presentation was observed between those with abnormal NBS (12.5%; 2 of 16) and those with an abnormal clinical presentation (79%; 19 of 24). The frequency of hyperammonemia was similar in the 2 groups.

CONCLUSION

Our data support the continued value of NBS to identify individuals with PA, who are diagnosed and treated earlier than for other modes of ascertainment. There were no statistically significant correlations between genotype and NBS for C3 acylcarnitines. Although expanded use of NBS has allowed for early diagnosis and treatment, long-term outcomes of individuals with PA, especially with respect to mode of ascertainment, remain unclear and would benefit from a longitudinal study.

The metabolome profiling and pathway analysis in metabolic healthy and abnormal obesity

OBJECTIVES

Mechanisms of the development of abnormal metabolic phenotypes among obese population are not yet clear. In this study, we aimed to screen metabolomes of both healthy and subjects with abnormal obesity to identify potential metabolic pathways that may regulate the different metabolic characteristics of obesity.

METHODS

We recruited subjects with body mass index (BMI) over 25 from the weight-loss clinic of a central hospital in Taiwan. Metabolic healthy obesity (MHO) is defined as without having any form of hyperglycemia, hypertension and dyslipidemia, while metabolic abnormal obesity (MAO) is defined as having one or more abnormal metabolic indexes. Serum-based metabolomic profiling using both liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry of 34 MHO and MAO individuals with matching age, sex and BMI was performed. Conditional logistic regression and partial least squares discriminant analysis were applied to identify significant metabolites between the two groups. Pathway enrichment and topology analyses were conducted to evaluate the regulated pathways.

RESULTS

A differential metabolite panel was identified to be significantly differed in MHO and MAO groups, including L-kynurenine, glycerophosphocholine (GPC), glycerol 1-phosphate, glycolic acid, tagatose, methyl palmitate and uric acid. Moreover, several metabolic pathways were relevant in distinguishing MHO from MAO groups, including fatty acid biosynthesis, phenylalanine metabolism, propanoate metabolism, and valine, leucine and isoleucine degradation.

CONCLUSION

Different metabolomic profiles and metabolic pathways are important for distinguishing between MHO and MAO groups. We have identified and discussed the key metabolites and pathways that may prove important in the regulation of metabolic traits among the obese, which could provide useful clues to study the underlying mechanisms of the development of abnormal metabolic phenotypes.

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.

Defect of cobalamin intracellular metabolism presenting as diabetic ketoacidosis: a rare manifestation

Hypoglycemia is the usual feature of commonly occurring organic acidemias. Organic acidemias manifesting as hyperglycemia or diabetic ketoacidosis are rare and only a few cases have been reported. We report a 13-month-old boy who presented with vomiting, dehydration, coma, hyperglycemia, high anion gap metabolic acidosis and ketosis, mimicking diabetic ketoacidosis (DKA). Treatment with parenteral fluid, electrolytes, and insulin infusion resulted in an improvement in hyperglycemia, but persistence of metabolic acidosis and lack of improvement of neurologic status led us to suspect an organic acidemia. Urinary organic acid analysis revealed increased methylmalonic acid levels. In addition, hyperhomocysteinemia and homocystinuria were also noted in presence of normal vitamin B12 levels. This confirmed the diagnosis of cobalamin metabolism defect leading to combined methylmalonic aciduria and homocystinuria. There was some improvement in neurologic status and metabolic parameters after treatment with low-protein diet, vitamin B12, folic acid, and L-carnitine, but he ultimately succumbed to polymicrobial nosocomial sepsis. The entire MMACHC gene of the patient was sequenced and no mutations were identified. This is probably the first case report of cobalamin intracellular metabolism defect (CblC/CblD/CblF/CblJ or ABCD4) presenting as diabetic ketoacidosis.