Type 2 Diabetes Mellitus: Etiology, Pathogenesis and Clinical Manifestations

Abstract

Type 2 diabetes mellitus affects about 3% of the population or 100 million people worldwide. The prevalence is higher in Europe and the USA, affecting 5–7% of the population and is increasing. Many cases (30% or more) are undiagnosed. Although common, its pathogenesis remains unclear. There are many reasons for this. Perhaps the most important is the heterogeneity of type 2 diabetes due in part to a variable interplay between genetic and environmental factors. Although the diagnosis rests on documentation of hyperglycemia it is important to appreciate that other metabolic abnormalities, for example disturbances of lipid metabolism, are also present and may precede the emergence of hyperglycemia (see Chapter VI.11). As depicted in Figure 1, overt hyperglycemia and the syndrome of type 2 diabetes is due to a variable combination of insulin resistance affecting the liver and peripheral insulin target tissues and of impaired insulin secretion. Since insulin resistance and abnormalities of insulin secretion may be associated with other pathologies, for example liver disease, renal disease, glucocorticoid, growth hormone or thyroid hormone excess, diabetes may be secondary to these conditions (see Chapter V.5).