Diabetes is a complex metabolic disorder with multiple etiological factors. According to present (latest or new) classification system, diabetes is classified into four different types.

-Type I diabetes.

-Type II diabetes.

-Other specific types of diabetes.

-Gestational diabetes.

The present classification system of diabetes mellitus was developed due to problem in the previous classification system of diabetes mellitus, definition and nomenclature, was developed by The National Diabetes Data Group of USA, in 1979 that was later accepted by WHO. According to older classification, diabetes was classified into 2 (two) major types namely:

Type I diabetes mellitus was formerly called Insulin-Dependent Diabetes Mellitus (IDDM) or juvenile diabetes, as most (more than 95%) of the patients with type I diabetes develop the disease before the age of 25 years. Type I diabetes is an autoimmune disease and autoimmune reaction/process leads to destruction of ? (beta) cells of pancreas, which secrete insulin and lead to absolute insulin deficiency.

The incidence of type 1 diabetes is same in both sexes (males and females). Type 1 diabetes is more common among white race (Caucasoid population). In type I diabetes, a family history of type 1 diabetes mellitus, gluten enteropathy or celiac disease or other endocrine diseases can commonly be present.

Type 2 diabetes mellitus was called Non Insulin-Dependent Diabetes Mellitus (NIDDM) or adult onset diabetes. The characteristics of type 2 diabetes are “insulin resistance” in peripheral tissues and secretary defects of beta cells of pancreas which secrete insulin. Among all types of diabetes the type 2 diabetes is the commonest form. Type 2 diabetes is more common among women, especially women with a history of gestational diabetes and in blacks, Hispanics and Native Americans.

Type 2 diabetes has a strong genetic predisposition, evident from twin studies. The concordance of type 2 diabetes is 70%-90% among identical twins and if both parents have type II diabetes the risk of developing type 2 diabetes is approximately 40% among siblings. The other predisposing factors (including environmental factors) of development of type 2 diabetes include obesity, over nutrition, sedentary lifestyle (lack of physical activity) etc.

The “other specific types of diabetes” include the types of diabetes caused by several etiological factors; other than the three types namely type 1 diabetes, type 2 diabetes and GDM (gestational diabetes mellitus). This other specific types of diabetes was formerly called maturity-onset diabetes of the young (MODY) or diabetes with defects of insulin action.

The “other specific types of diabetes” includes several categories. The categories are given below:

Genetic defects of beta cell function due to mutations in:

• Hepatocyte nuclear transcription factor (HNF) 4-alpha (MODY-1).
• Glucokinase enzyme (MODY-2).

Gestational diabetes mellitus (GDM) can be defined as “development of any degree of glucose intolerance, which is recognized for the first time during present pregnancy” and occurs is approximately 4% of all pregnancies. Most women who develop diabetes generally revert to normal after delivery and a few continues to have glucose intolerance, even after delivery and continues to have diabetes. Even those who revert to normal from gestational diabetes after delivery have high risk of developing diabetes in later life and 30%-60% of women with gestational diabetes eventually develop diabetes in later life.

The prevalence of gestational diabetes varies in different race and ethnic groups. The variation in the prevalence of gestational diabetes in different races and ethnic groups may be due genetic predisposition as well as different criteria and screening regimens used for detection of gestational diabetes.