A Unique Case of Pyruvate Carboxylase Deficiency

The presence of pyruvate carboxylase in the human brain and its role in the survival of cultured human astrocytes

Pyruvate carboxylase (PC) is a mitochondrial, biotin-containing enzyme catalyzing the ATP-dependent synthesis of oxaloacetate from pyruvate and bicarbonate, with a critical anaplerotic role in sustaining the brain metabolism. Based on the studies performed on animal models, PC expression was assigned to be glia-specific. To study PC distribution among human neural cells, we probed the cultured human astrocytes and brain sections with antibodies against PC. Additionally, we tested the importance of PC for the viability of cultured human astrocytes by applying the PC inhibitor 3-chloropropane-1,2-diol (CPD). Our results establish the expression of PC in mitochondria of human astrocytes in culture and brain tissue and also into a subpopulation of the neurons in situ. CPD negatively affected the viability of astrocytes in culture, which could be partially reversed by supplementing media with malate, 2-oxoglutarate, citrate, or pyruvate. The provided data estimates PC expression in human astrocytes and neurons in human brain parenchyma. Furthermore, the enzymatic activity of PC is vital for sustaining the viability of cultured astrocytes.

Case Report: Prenatal neurological injury in a neonate with pyruvate carboxylase deficiency type B

Background

Pyruvate carboxylase (PC) is a key enzyme for gluconeogenesis. PC deficiency (PCD) is an extremely rare autosomal recessive metabolic disease and is divided into three types. Type B PCD is clinically featured by lactic acidosis, hyperammonemia, hypercitrullinemia, hypotonia, abnormal movement, and seizures.

Case presentation

Here, we report the first case of type B PCD in China, presenting with intractable lactic acidosis shortly after birth. A compound heterozygous mutation in the PC gene was identified by whole-exome sequencing, NM_001040716.2: c.1154_1155del and c.152G>A, which were inherited from her asymptomatic parents, respectively. Furthermore, prenatal neuroradiological presentations including widened posterior horns of lateral ventricles, huge subependymal cysts, and increased biparietal diameter and head circumference were concerned. Symptomatic treatment was taken and the infant died at 26 days.

Conclusion

To our knowledge, this is the minimum gestational age (22w5d) that's when the prenatal onset of the neuroradiologic phenotype of PCD was observed. PCD has a poor prognosis and lacks an effective treatment, so this paper is shared to highlight the importance of PCD prenatal diagnosis in the absence of family history.

PC Splice-Site Variant c.1825+5G>A Caused Intron Retention in a Patient With Pyruvate Carboxylase Deficiency: A Case Report

BACKGROUND

Pyruvate carboxylase deficiency (PCD; MIM#266150) is a rare autosomal recessive disorder characterized by a wide range of clinical features, including delayed neurodevelopment, elevated pyruvate levels, lactic acidosis, elevated ketone levels, and hyperammonemia. The pyruvate carboxylase (PC) gene was identified to be the disease-causing gene for PCD. A novel homozygous splice variant in the PC gene was identified in a Chinese boy, but the pathogenicity is still unclear. The objective of the present study was to determine the effect of this splice-site variant by reverse transcription analysis.

METHODS

We reported the clinical course of a 20-month-old Chinese pediatric patient who was diagnosed with PCD using whole-exome sequencing (WES). The effects of the variant on mRNA splicing were analyzed through the transcript analysis in vivo.

RESULTS

The results of metabolic blood and urine screening suggested PCD by employing tandem mass spectrometry. WES revealed a novel homozygous splice-site variant (c.1825+5G>A) in the PC gene. in vivo transcript analysis indicated that the splice-site variant caused the retention of 192 bp of the intron.

CONCLUSION

Thus, c.1825+5G>A was established as a pathogenic variant, thereby enriching the mutational spectrum of the PC gene and providing a basis for the genetic diagnosis of PCD.