s, clinical presentation, and principles of management of diabetes.
DM is broadly classified into three types by etiology and clinical presentation, type 1 diabetes, type 2 diabetes, and gestational diabetes (GDM). Some other less common types of diabetes include monogenic diabetes and secondary diabetes.
Type 1 Diabetes Mellitus (T1DM)
Type 1 diabetes mellitus (T1DM) accounts for 5% to 10% of DM and is characterized by autoimmune destruction of insulin-producing beta cells in the islets of the pancreas. As a result, there is an absolute deficiency of insulin. A combination of genetic susceptivity and environmental factors such as viral infection, toxins, or some dietary factors have been implicated as triggers for autoimmunity. T1DM is most commonly seen in children and adolescents though it can develop at any age.
Type 2 Diabetes Mellitus
Type 2 diabetes mellitus (T2DM) accounts for around 90% of all cases of diabetes. In T2DM, the response to insulin is diminished, and this is defined as insulin resistance. During this state, insulin is ineffective and is initially countered by an increase in insulin production to maintain glucose homeostasis, but over time, insulin production decreases, resulting in T2DM. T2DM is most commonly seen in persons older than 45 years. Still, it is increasingly seen in children, adolescents, and younger adults due to rising levels of obesity, physical inactivity, and energy-dense diets.
Gestational Diabetes Mellitus
Hyperglycaemia, which is first detected during pregnancy, is classified as gestational diabetes mellitus (GDM), also known as hyperglycemia in pregnancy. Although it can occur anytime during pregnancy, GDM generally affects pregnant women during the second and third trimesters. According to the American Diabetes Association (ADA), GDM complicates 7% of all pregnancies. Women with GDM and their offspring have an increased risk of developing type 2 diabetes mellitus in the future.
GDM can be complicated by hypertension, preeclampsia, and hydramnios and may also lead to increased operative interventions. The fetus can have increased weight and size (macrosomia) or congenital anomalies. Even after birth, such infants may have respiratory distress syndrome and subsequent childhood and adolescent obesity. Older age, obesity, excessive gestational weight gain, history of congenital anomalies in previous children, or stillbirth, or a family history of diabetes are risk factors for GDM.
A single genetic mutation in an autosomal dominant gene causes this type of diabetes. Examples of monogenic diabetes include conditions like neonatal diabetes mellitus and maturity-onset diabetes of the young (MODY). Around 1 to 5% of all diabetes cases are due to monogenic diabetes. MODY is a familial disorder and usually presents under the age of 25 years.
Secondary diabetes is caused due to the complication of other diseases affecting the pancreas (for example, pancreatitis), hormone disturbances (for example, Cushing disease), or drugs (for example, corticosteroids).
Diabetes is a worldwide epidemic. With changing lifestyles and increasing obesity, the prevalence of DM has increased worldwide. The global prevalence of DM was 425 million in 2017. According to the International Diabetes Federation (IDF), in 2015, about 10% of the American population had diabetes. Of these, 7 million were undiagnosed. With an increase in age, the prevalence of DM also increases. About 25% of the population above 65 years of age has diabetes.
In T1DM, there is cellular-mediated, autoimmune destruction of pancreatic beta cells. T1DM has a strong genetic predisposition. The major histocompatibility complex (MHC), also known as human leukocyte antigens (HLA), is reported to account for approximately 40 to 50% of the familial aggregation of T1DM. The significant determinants are polymorphisms of class II HLA genes encoding DQ and DR4-DQ8, with DR3-DQ2, found in 90% of T1DM patients.
Another form of T1DM is latent autoimmune diabetes of adults (LADA). It occurs in adulthood, often with a slower course of onset.
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