Novel Mutations in the GTPBP3 Gene for Mitochondrial Disease and Characteristics of Related Phenotypic Spectrum: The First Three Cases From China

The rare reason for massive lactic aciduria and mitochondrial disorders: combined oxidative phosphorylation deficiency type 23 (COXPD23)

Mitochondrial respiratory chain dysfunction and impaired oxidative phosphorylation are rare but significant causes of mitochondrial diseases in children, presenting with diverse clinical features. Combined oxidative phosphorylation deficiency type 23 (COXPD23), an autosomal recessive disorder due to GTPBP3 gene mutations, typically manifests as lactic acidosis, hypertrophic cardiomyopathy, and encephalopathy. This case report describes a male infant born at 35 weeks gestation, who exhibited severe lactic aciduria and hypotonia but no cardiomyopathy, which is atypical for COXPD23. Genetic analysis revealed a novel homozygous missense variant in the GTPBP3 gene. Despite intensive metabolic and supportive treatments, the patient's condition worsened, leading to death on the 23rd day. This case emphasizes the need to consider mitochondrial cytopathies in neonates with persistent metabolic acidosis and hyperlactatemia and highlights the importance of early genetic screening for accurate diagnosis and management.

Echocardiographic manifestations of mitochondrial disease with GTPBP3 gene mutations: A case report

RATIONALE

Mitochondrial diseases are a group of disorders in which mutations in mitochondrial DNA or nuclear DNA lead to dysfunctional oxidative phosphorylation of cells, with mutations in mitochondrial DNA being the most common cause of mitochondrial disease, and mutations in nuclear genes being rarely reported. The echocardiographic findings of mitochondrial diseases with nuclear gene mutations in children's hearts are even rarer. Even more valuable is that we followed up the patient for 4 years and dynamically observed the cardiac echocardiographic manifestations of mitochondrial disease. Provide ideas for the clinical diagnosis and prognosis of mitochondrial diseases.

PATIENT CONCERNS

The patient was seen in the pediatric outpatient clinic for poor strength and mental retardation. echocardiography: mild left ventricular (LV) enlargement and LV wall thickening. Nuclear genetic testing: uanosine triphosphate binding protein 3 (GTPBP3) gene mutation. Diagnosis of mitochondrial disease.

DIAGNOSES

Mitochondrial disease with GTPBP3 gene mutations.

OUTCOMES

After receiving drug treatment, the patient exhibited a reduction in lactate levels, an enhanced physical condition compared to prior assessments, and demonstrated average intellectual development.

LESSONS SUBSECTIONS

For echocardiographic indications of LV wall thickening and LV enlargement, one needs to be alert to the possibility of hereditary cardiomyopathy, especially in children.

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

Background

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.

Methods

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.

Results

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.

Conclusions

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.

Biallelic variants in GTPBP3: New patients, phenotypic spectrum, and outcome

INTRODUCTION

COXPD23 is a rare mitochondrial disease caused by biallelic pathogenic variants in GTPBP3. We report on two siblings with a mild phenotype.

CASE REPORTS

The young boy presented with global developmental delay, ataxic gait and upper limbs tremor, and the older sister with absence seizures and hypertrophic cardiomyopathy. Respiratory chain impairment was confirmed in muscle.

DISCUSSION

Reviewed cases point toward clustering around two prevalent phenotypes: an early-onset presentation with severe fatal encephalopathy and a late milder presentation with global developmental delay/ID and cardiopathy, with the latter as, is the main feature. Our patients showed an intermediate phenotype with intrafamilial variability.

Modopathies Caused by Mutations in Genes Encoding for Mitochondrial RNA Modifying Enzymes: Molecular Mechanisms and Yeast Disease Models

In eukaryotes, mitochondrial RNAs (mt-tRNAs and mt-rRNAs) are subject to specific nucleotide modifications, which are critical for distinct functions linked to the synthesis of mitochondrial proteins encoded by mitochondrial genes, and thus for oxidative phosphorylation. In recent years, mutations in genes encoding for mt-RNAs modifying enzymes have been identified as being causative of primary mitochondrial diseases, which have been called modopathies. These latter pathologies can be caused by mutations in genes involved in the modification either of tRNAs or of rRNAs, resulting in the absence of/decrease in a specific nucleotide modification and thus on the impairment of the efficiency or the accuracy of the mitochondrial protein synthesis. Most of these mutations are sporadic or private, thus it is fundamental that their pathogenicity is confirmed through the use of a model system. This review will focus on the activity of genes that, when mutated, are associated with modopathies, on the molecular mechanisms through which the enzymes introduce the nucleotide modifications, on the pathological phenotypes associated with mutations in these genes and on the contribution of the yeast Saccharomyces cerevisiae to confirming the pathogenicity of novel mutations and, in some cases, for defining the molecular defects.