A novel mutation in GTPBP3 causes combined oxidative phosphorylation deficiency 23 by affecting pre-mRNA splicing

Combined Oxidative Phosphorylation Deficiency 23 (COXPD23) is a rare mitochondrial disease caused by mutations in the GTPBP3 gene. The rare incidence of the disease and the high clinical heterogeneity pose challenges in making a precise diagnosis. Investigations into the rare COXPD23 patients are of pathophysiological and etiological value. In this study, we investigated the genotype-phenotype relationship in a COXPD23 patient from a Manchu family, with GTPBP3 mutations.

Routine physical examinations, laboratory assays and imaging analyses were performed. The metabolic profiles of amino acids in blood, acylcarnitine in blood and organic acids in urine were used to determine the presence of inherited metabolic diseases. Genetic variations in the family were investigated using whole-exome sequencing and Sanger sequencing. Splicing disruption by a mutation was predicted and verified using a minigene assay.

The patient presented with severe lactic acidosis, neurological symptoms, multiple symmetrical lesions in the brain and serious mitochondrial energy metabolism disturbances. The c.689A > C (p.Q230P) and c.809-1_809delinsA compound heterozygous mutations were detected in GTPBP3. The novel c.809-1_809delinsA mutation was located at the splicing site of exon 7 and intron 6 and multiple tools predicted that it would disrupt the normal splicing. The minigene assay proved that the novel mutation resulted in two aberrant transcripts that created premature termination codons.

The clinical manifestations, brain imaging change, mitochondrial metabolism disturbances and the detection and validation of the GTPBP3 mutations expand the profile of COXPD23 and the pathogenic mutation spectrum. Our study improves the understanding of the pathophysiology and etiology of COXPD23.