**1. Introduction**

Diabetes mellitus is a metabolic disease that has a major impact on global public health, affecting more than 425 million people worldwide. The number of affected people tends to increase, mainly due to obesity, a risk factor closely related to type 2 diabetes mellitus (T2D), the most common form of diabetes. Hyperglycemia is the most striking feature of the disease, which is the increase of blood glucose levels above those presented by healthy individuals. This could be the main consequence of poor insulin secretion, lack of insulin sensitivity in target tissues or the combination of both [1, 2].

The genetic predisposition may be one of the determinants that favor the susceptibility to T2D development. Several variants of genes and even epigenetic modifications in histones and DNA methylation may influence the heritability of T2D [3, 4]. Due to the complexity of the interaction of different factors involved in this disease, genome-wide association studies (GWAS) have been performed in an attempt to identify genetic variants related to the increased risk of T2D.

In 2007, the first GWAS was performed in France in patients with T2D [5]; At present, at least 75 associated loci have been identified, including the *TCF7L2* transcription factor, which is the most common gene found, in addition to *PPARG, KCNJ11, FTO, CDKN2A/2B, CDKAL1, IGFBP2* among others [6]. Since then, similar studies showed that the loci presenting greater association with T2D vary as regards the relative risk between different ethnicities [7]. Besides, these variants explain only a low percentage of the disease heritability, most of which are found in intergenic or intronic regions [6]. Furthermore, DNA methylation patterns may contribute to genetic susceptibility to T2D. There is evidence of an increased risk of T2D development associated with distinct methylation patterns in some loci [8], but this approach is still a major challenge for researchers.

While obesity and overweight have been considered an important cause of T2D, a poor diet and lack of physical activity significantly contribute to an increased risk of insulin resistance and T2D [9].

One of the greatest concerns regarding the poor glycemic control in patients with T2D is related to the micro and macrovascular complications of diabetes. Since the onset of T2D did not present specific acute symptoms, 50% of adults with T2D do not know that they have the disease [9]. Chronic hyperglycemia induces a series of complications, such as retinopathy, neuropathy and nephropathy. In a long term, the high blood glucose levels may also induce endothelial dysfunction, which contributes to the increased risk for the development of cardiovascular diseases.
