**2. Brief history of diabetes mellitus and the evolution of the classification**

In order to understand our point of view we must begin with a brief description of diabetes history and classification. The term diabetes (Greek: ) was coined by Aretaues of Cappadocia. It is derived from the Greek word , diabaínein that literally means "passing through" or "siphon", a reference to one of diabetes' major symptoms—excessive urine production. In 1675, Thomas Willis added the word mellitus, from the Latin meaning "honey", as a reference to the sweet taste of the urine. Matthew Dobson (1776) confirmed that the sweet taste was due to an excess of a kind of sugar in the urine and blood of people with diabetes. The ancient Indians tested for diabetes by observing whether ants were attracted to a person's urine, and called the ailment "sweet urine disease". The Korean, Chinese, and Japanese words for diabetes are based on the same ideographs (糖尿病), which mean "sugar urine disease".

As stated above, although diabetes has been recognized since antiquity, and treatments of different efficiencies have been known in several regions since the Middle Ages and for much longer in legends, the pathogenesis of diabetes has only been understood experimentally since about 1900 (Patlak, 2002a; 2002b). The endocrine role of the pancreas in metabolism, and indeed the existence of insulin, was not further clarified until 1922, when Banting and Best demonstrated that they could reverse induced diabetes in dogs by giving them a pancreatic islets of Langerhans extract of healthy dogs (Banting et al., 1922). However the precise molecular mechanism of the disease is just beginning to be unraveled. Fortunately, the increasing inventory of human genetic variation is easing our understanding of why susceptibility to the common disease varies between individuals and populations (Rotimi & Jorde, 2010), as we shall see.

In terms of classification, the first distinction between different presentations of the disease, as it is currently known, was clearly established by Sir H P Himsworth, and published in January 1936 (Himsworth, 1936). From its very beginning, the different classifications have undergone changes in the attempt to obtain a better adjustment of the organization of diabetes' nosology (Alberti & Zimmet, 1998): (1) Age, which was the main criterion of the first classification, was quickly abandoned because the different forms can appear at any age, although one is more frequently observed in childhood and youth and the other one in adults (at present, type 1 and 2 respectively); (2) Insulin dependence was the new clinical criterion taken into consideration, because it was easy to use in clinical practice and allowed to consider sub-groups with different pathogenic mechanisms; for several years insulin dependence was an indicator of the auto-immune process.

Currently, the classification of Diabetes mellitus (ADA, 2010; ALAD, 2010) contemplates four well-known major groups: (a) Type 1 Diabetes (T1DM), (b) Type 2 (T2DM), (c) Other specific types of diabetes, and (d) Gestational diabetes.

However, on the basis of clinical observations, genetics and molecular research studies carried out in some mixed populations such as those in Latin America (as we shall see below) would point out that this classification is not always adequate; phenotype does not always reflect genotype (Mimbacas et al., 2009).
