MT-ATP6 and hyperinsulinemic hypoglycemia, familial, 4: The pathogenic variant NC_012920.1(MT-ATP6):m.8993T>G in which a thymine to guanine transversion occurs at nucleotide position 8993, located at the ATP6 locus on the mitochondrial DNA (mtDNA), was one of the first described mtDNA variants and is the most prevalent variant in patients with ATP6 deficiencies [5,6].