>> Type 2 diabetes mellitus (T2DM), so-called maturity-onset diabetes or diabetes with visceral fat, is a metabolic disease underpinned by pancreatic beta-cell insulin secretion defects and varying degrees of insulin resistance in key metabolically active organs (mainly in liver, adipose tissue and skeletal muscle). Either one of these two defects may dominate to a variable extent to cause chronic hyperglycemia (high blood glucose levels). T2DM is the most frequent form of diabetes, accounting for more than 92% of all treated diabetic cases, and is usually diagnosed in middle-age people; but it can also develop more rarely in young individuals (sometimes from teen years) due to the increasing obesity prevalence in dolescents.
>> Type 1 diabetes (T1DM) is far less frequent (about 6% of all treated diabetic cases) and is caused by an autoimmune destruction of insulin-secreting pancreatic beta-cells leading to an almost complete inability to secrete insulin in affected people. Therefore, those people need lifelong regular insulin injections. T1DM is mainly diagnosed in childhood and in young adults with the positivity of specific autoantibodies (glutamic acid decarboxylase [GAD], protein tyrosine phosphatase IA-2, or zinc transporter 8 [ZnT8]) in up to 90-95% of newly diagnosed type 1 diabetes patients
>> Gestational diabetes (GDM) is defined as an abnormal glucose tolerance diagnosed for the first time in pregnancy resulting in hyperglycemia of variable severity during pregnancy. In a physiological situation, insulin sensitivity declines with advancing gestation and a compensatory increase in insulin secretion maintains a normal glucose homeostasis. GDM occurs if pancreatic β-cells are unable to face the increased insulin demand during pregnancy. GDM is most often a forerunner of T2DM, and women presenting with GDM are at very high risk of developing diabetes in later life; or even diabetes may persist after delivery. Pathophysiological mechanisms underlying genes for monogenic diabetes and T2DM appear to also apply to GDM, with the common thread being pancreatic β-cell dysfunction and decreased insulin secretion. The most common complication of GDM is delivery of infants large for gestational age (LGA) in terms of body weight, which is linearly related to maternal plasma glucose levels.
>> MODY (Maturity-Onset Diabetes of the Young) is a rare monogenic form of early-onset non autoimmune diabetes that is characterized by functional defects of insulin-producing pancreatic b cells and hyperglycemia early in life. It is estimated to be the underlying cause of diabetes in 1-2% of patients diagnosed with diabetes. The recognition of MODY is based on a chronic hyperglycemia diagnosed before the age of 25–30 years and a strong family history of dominantly-inherited diabetes within families. MODY is clinically and genetically heterogeneous with at least 15 genetic subtypes identified so far. As marked differences in drug therapy response exist according to the genetic subtype, an early etiological genetic diagnosis will guide the most appropriate clinical management (e.g. inexpensive oral sulfonylureas are the optimal treatment in patients with a mutation in HNF1A or HNF4A genes).