Complete Mitochondrial Genome of a French Bulldog with Carcinoma planoepitheliale keratodes G1: A Descriptive Case Report

French Bulldogs, like other brachycephalic breeds, are predisposed to a variety of genetic and tumour-related disorders. While mitochondrial DNA (mtDNA) mutations have been documented in canine tumours, no prior study has examined the entire mitochondrial genome in this breed. In this study, we analysed mtDNA obtained from blood and tumour tissue of a 10-year-old male French Bulldog diagnosed with carcinoma planoepitheliale keratodes (G1). Complete sequencing and comparative bioinformatic analysis revealed 22 sequence variants, including nine in protein-coding genes, two in RNA-coding genes, two in the control region, and nine within the variable number tandem repeat (VNTR) region. Identical variants were present in both blood and tumour tissue, indicating that no detectable tumour-specific mtDNA mutations were observed. Notably, the m.1397A>T transversion in the 16S rRNA gene and an insertion (m.2679_2680insG) in the tRNA-Leu(UUR) gene were identified, both mapping to conserved loci in the human mitochondrial genome. Among the coding variants, four nonsynonymous variants (including p.Cys55Tyr and p.Ser471Asn) were detected, two of which affected highly conserved amino acid positions. Most nonsynonymous changes were localised in random coil regions and internal mitochondrial compartments, whereas synonymous changes appeared mainly within transmembrane helices. The control region displayed the highest degree of polymorphism, including eight positions with A/G heteroplasmy and one length variant due to polyT extension. These findings represent the first documentation of full mitochondrial genome sequence variants in a French Bulldog with cancer providing descriptive data for future breed population and oncological research. Further studies are warranted to determine whether these alterations are breed- or tumour-specific.