Pyruvate carboxylase, a mitochondrial enzyme, catalyses the conversion of glycolytic end-product pyruvate to tricarboxylic acid cycle intermediate, oxaloacetate. Rare pyruvate carboxylase deficiency manifests in three clinical and biochemical phenotypes: neonatal onset type A, infantile onset type B and a benign C type. The objective of this case series is to expand the knowledge of overlapping clinical and biochemical phenotypes of pyruvate carboxylase deficiency. We report three Sri Lankan neonates including two siblings, of two unrelated families with pyruvate carboxylase deficiency. All three developed respiratory distress within the first few hours of birth. Two siblings displayed typical biochemical findings reported in type B. The other proband with normal citrulline, lysine, moderate lactate, paraventricular cystic lesions, bony deformities, and a novel missense, homozygous variant c.2746G>C [p.(Asp916His)] in the PC gene, biochemically favoured type A. Our findings indicate the necessity of prompt laboratory investigations in a tachypneic neonate with coexisting metabolic acidosis, as early recognition is essential for patient management and family counselling. Further case studies are required to identify overlapping symptoms and biochemical findings in different types of pyruvate carboxylase deficiency phenotypes. Pyruvate carboxylase (PC) deficiency is characterized in most affected individuals by failure to gain weight and/or linear growth failure, developmental delay, epilepsy, and metabolic acidosis. Three clinical phenotypes are recognized. Type A (infantile form) is characterized by infantile onset of metabolic and lactic acidosis, delayed motor development, intellectual disability, poor linear growth and/or weight gain, and neurologic findings (apathy, hypotonia, pyramidal and extrapyramidal signs, ataxia, and seizures). Brain anomalies can be noted. Most affected children die in infancy or early childhood. Type B (severe neonatal form) is characterized by neonatal or infantile onset of hypothermia, respiratory distress/failure, vomiting, severe lactic acidosis, hyperammonemia, and often hypoglycemia. Neurologic findings include brain abnormalities, lethargy, hypotonia, and pyramidal and extrapyramidal signs. Death typically occurs by age eight months. Type C (intermittent/attenuated form) is characterized by relatively normal or mildly delayed neurologic development, motor and/or gait abnormalities, (rarely) seizures, episodic movement disorders, and metabolic acidosis. Life span is unknown but survival into adulthood has been reported. The diagnosis of PC deficiency is established in a proband whose newborn screening or biochemical findings suggest PC deficiency based on identification of either (1) biallelic pathogenic variants in PC on molecular genetic testing or (2) PC deficiency in whole blood. Treatment of manifestations: Intravenous glucose-containing fluids, hydration, and correction of metabolic acidosis; pharmacologic therapies (amino acid supplements, cofactors, and vitamins) may improve some findings but not neurologic manifestations; orthotopic liver transplantation may be indicated in some affected individuals; anaplerotic therapies, such as triheptanoin, have had variable success (primarily for individuals with PC deficiency type C) but need further evaluation. Surveillance: A team of multidisciplinary specialists is often required to monitor existing manifestations, the individual's response to treatment, and the emergence of new manifestations. Agents/circumstances to avoid: A ketogenic diet is contraindicated, and it is critical to avoid fasting. Evaluation of relatives at risk: It is appropriate to clarify the genetic and/or biochemical status of apparently asymptomatic older and younger at-risk sibs of an affected individual with PC deficiency type C in order to identify as early as possible those who would benefit from prompt initiation of treatment and preventive measures. PC deficiency is inherited in an autosomal recessive manner. If both parents are known to be heterozygous for a PC pathogenic variant, each sib of an affected individual has at conception a 25% chance of inheriting biallelic pathogenic variants and being affected, a 50% chance of inheriting one pathogenic variant and being heterozygous, and a 25% chance of inheriting neither of the familial PC pathogenic variants. Once the PC pathogenic variants have been identified in an affected family member, molecular genetic carrier testing for at-risk relatives, prenatal testing, and preimplantation genetic testing are possible.

Pyruvate carboxylase is a mitochondrial enzyme essential for the tricarboxylic acid cycle (TCA), gluconeogenesis and fatty-acid synthesis. Pyruvate carboxylase deficiency (PCD) mostly presents with life-limiting encephalopathy (types A/B). A milder type C presentation is rare, with a comparatively favourable prognosis. Therapies remain essentially supportive. Triheptanoin is an odd-chain triglyceride, with the potential to replenish TCA intermediates (anaplerosis), and its metabolites cross the blood-brain-barrier. Outcomes of triheptanoin treatment in PCD types A/B have been disappointing, but have not been reported in type C. Here, we present two new patients with PCD type C, and report the response to treatment with triheptanoin in one. Patient 1 (P1) presented with neonatal-onset lactic acidosis and recurrent symptomatic lactic acidosis following exercise and during illnesses, with frequent hospitalisations. Speech development was delayed. MRI-brain showed delayed cerebral myelination. Patient 2 (P2) presented with episodic ketoacidosis, hyperlactataemia and hypoglycaemia at 2 years of age, with gross motor delay and mild global volume loss on MRI brain. Treatment with triheptanoin was commenced in P1 at 3 years of age with up-titration to 35 mL/day (25% of daily energy intake) over 6 months, due to transient diarrhoea. Dietary long-chain triglycerides were restricted, with fat-soluble vitamin supplementation. Subsequently, hospitalisations during intercurrent illnesses decreased, post-exertional hyperlactataemia resolved and exercise tolerance improved. Continued developmental progress was observed, and repeat MRI 18 months after initiation showed improved myelination. Triheptanoin was well-tolerated and appeared efficacious during 2 years' follow-up, and has potential to restore energy homeostasis and myelin synthesis in PCD type C.

The consumption of rice contaminated with arsenic on a long-term basis has emerged as a pressing public health issue of global significance. Arsenic-induced urinary injury, particularly kidney damage, has received widespread attention. In this study, mice model under long-term arsenic exposure was established, mouse were exposed to rice arsenic (30 mg/kg) for 14 months. Changes of related metabolites were observed based on kidney metabolomics and lipidomics, and major biomarkers were screened by urine metabolomics. The results showed that phosphatidylethanolamine (PE) was significantly increased and phosphatidycholine (PC) and phosphatidylglycerol (PG) were significantly reduced after arsenic exposure, leading to related downstream lipid metabolism disorders. The metabolic pathways for amino acid and energy were observed to be impacted. In addition, metabolic disorders due to arsenic exposure may be associated with inherited neurometabolic disorders, such as D-2-hydroxyglutaric aciduria (D-2-HGA), and pyruvate carboxylase deficiency (PCD), which is predicted based on significant difference biomarkers (2-oxoglutarate, malic acid, and succinic acid) screened for urine. This study elucidates the mechanism of toxicity in the urinary system induced by arsenic exposure at nearly half life cycle, which furnishes crucial scientific evidence pertaining to the toxicity and risk evaluation associated with chronic exposure to the arsenic.

Pyruvate carboxylase (PC) deficiency (PCD), due to biallelic PC variants, is a rare inherited metabolic disease, which is characterized by seizures, global developmental delay, as well as lactic acidosis, and elevated plasma pyruvate and alanine levels in affected individuals. In the present study, a new induced pluripotent stem cell line (SHCDNi007-A) was generated from the peripheral blood mononuclear cells of a 2-month-old male infant with biallelic PC mutations c.(182 T > C;2581G > A), i.e. p.(Ile61Thr;Val861Met). This cell line is expected to facilitate the in vitro modeling of the disease pathophysiology and the development of future therapeutics for PCD.

Inborne errors of metabolism are a common cause of neonatal death. This study evaluated the acute early-onset metabolic derangement and death in two unrelated neonates. Whole-exome sequencing (WES), Sanger sequencing, homology modeling, and in silico bioinformatics analysis were employed to assess the effects of variants on protein structure and function. WES revealed a novel homozygous variant, p.G303Afs*40 and p.R156P, in the pyruvate carboxylase (PC) gene of each neonate, which both were confirmed by Sanger sequencing. Based on the American College of Medical Genetics and Genomics guidelines, the p.G303Afs*40 was likely pathogenic, and the p.R156P was a variant of uncertain significance (VUS). Nevertheless, a known variant at position 156, the p.R156Q, was also a VUS. Protein secondary structure prediction showed changes in p.R156P and p.R156Q variants compared to the wild-type protein. However, p.G303Afs*40 depicted significant changes at C-terminal. Furthermore, comparing the interaction of wild-type and variant proteins with the ATP ligand during simulations, revealed a decreased affinity to the ATP in all the variants. Moreover, analysis of Single nucleotide polymorphism impacts on PC protein using Polyphen-2, SNAP2, FATHMM, and SNPs&GO servers predicted both R156P and R156Q as damaging variants. Likewise, free energy calculations demonstrated the destabilizing effect of both variants on PC. This study confirmed the pathogenicity of both variants and suggested them as a cause of type B Pyruvate carboxylase deficiency. The results of this study would provide the family with prenatal diagnosis and expand the variant spectrum in the PC gene,which is beneficial for geneticists and endocrinologists.