Type 1 diabetes mellitus (T1D) is an inherited polygenic chronic autoimmune disease caused by immune destruction of pancreatic beta cells, resulting in insulin deficiency [1,2,3]. Most genes associated with T1D susceptibility are related to the immune response [4]. Genetic variation in the region known as the human leukocyte antigen complex (HLA), especially in class II HLA antigens, is associated with genetic risk in T1D patients [4,5,6]. Generally, the risk conferred by HLA system genes that is more prevalent in White, Caucasian, and European-American individuals [2, 3, 5].

Another molecular marker that could be included in ancestry studies in patients with T1D is mitochondrial DNA (mtDNA). Mitochondria are membranous organelles, formed by a double membrane, present in almost all eukaryotic cells [7,8,9]. They are fundamental for a variety of biological functions, being responsible for regulating a wide range of cellular processes such as ATP production through oxidative phosphorylation (OXPHOS), apoptosis, β-oxidation of fatty acids, calcium homeostasis regulation, production of reactive oxygen species (ROS), and iron-sulfur cluster biogenesis [7,8,9].

Mitochondria have their own DNA, mtDNA, which in mammals is present in thousands of copies per cell and is inherited in a non-Mendelian maternal manner. mtDNA is a circular double-stranded DNA molecule, consisting of a heavy strand (H) and a light strand (L), without histones and organized into nucleoprotein complexes called nucleoids. It has a size of 16.5 kb, containing 37 genes responsible for encoding 13 protein subunits of the OXPHOS system, as well as two rRNAs and a set of 22 tRNAs for mitochondrial translation [7, 8]. In addition to the coding region, mtDNA contains a non-coding control region, a short displacement loop, a hypervariable segment (HVS) known as the D-loop, which houses almost all mtDNA replication and transcription [9, 10].

Thus, mtDNA has many effects, including adaptive mechanisms to deal with environmental changes and mechanisms related to cellular physiology, growth characteristics and inflammatory systems. All the abovementioned actions have a great impact on a broad range of metabolic and degenerative diseases, such as cancer, diabetes, and aging, which are related to polymorphisms and mutations in these genes [11,12,13,14].

According to Cardena, mtDNA through hypervariable regions (HVS) could be a good marker for inferring probable maternal geographic origin [15]. Brazil has important genetic diversity due to its colonization of different migratory flows and miscegenation between Native American, European, and African individuals [16, 17]. Therefore, to date, no evaluation of mtDNA in patients with T1D has been carried out in Brazil. Thus, this pilot study aimed to analyze the maternal genetic origin of patients with T1D in a highly admixed population.