In silico Analysis of Two Novel Variants in the Pyruvate Carboxylase (PC) Gene Associated with the Severe Form of PC Deficiency

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.

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 PC gene of each neonate,  which both were confirmed by Sanger sequencing. Based on the ACMG guidelines, the p.G303Afs*40 was likely pathogenic, and the p.R156P was a 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 SNP 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 PCD. 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.