What is Diabetes?
Causes of Diabetes
Types of Diabetes

Types of Diabetes

Most common types of diabetes, classified by causes and characteristics of the disease, are listed in Table 1 below ( and in Table 1 of “Diagnosis and classification of diabetes mellitus,” 2009). The hallmark for all forms of diabetes is high blood glucose levels. Assigning the type of diabetes mellitus is only important in understanding the pathogenesis in order to treat it effectively.

Table 1. Classification and observations of the different forms of diabetes mellitus

Type Causes/Characteristics Clinical Profile/Comments
Type 1 Diabetes Autoimmune; also knows as juvenile or insulin-dependent diabetes Insulin is either not produced or produced in insufficient amounts due to β-cell destruction; requires supplemental insulin
Type 2 Diabetes Polygenic; influenced by environment and lifestyle; also known as adult-onset or insulin-independent diabetes Decreased responsiveness to insulin; increased incidence in individuals with obesity and family history of diabetes due to dual defects - insulin resistance and impaired insulin secretion capacity
Gestational Diabetes Subset of Type 2 Diabetes; diagnosed as glucose intolerance during pregnancy Insulin resistance; condition may persist after pregnancy
Prediabetes May be genetic or environmental May have arisen due to obesity and family history; usually can be mitigated by lifestyle changes
Maturity-onset diabetes of the young (MODY) Monogenic; inherited in an autosomal dominant pattern; early age onset of hyperglycemia (generally before age of 25) Impaired insulin secretion with minimal or no defects in insulin action
Secondary Diabetes Induced by side effects of medications, infections, pancreas dysfunction (e.g. due to use of steroids, alcoholism, pancreatitis, etc.), or rare autoimmune disorders Loss of pancreatic function, insulin resistance or impaired insulin secretion, depending on the specific cause(s)

Type 1 diabetes

Type 1 diabetes is commonly referred to as juvenile or insulin-dependent diabetes. It is a condition that typically occurs in children and adolescents, arising from immune (T-cell-mediated) destruction of insulin-producing pancreatic β-cells. Adults may also be diagnosed with Type 1 diabetes, also called Latent Autoimmune Diabetes in Adults (LADA). Type 1 diabetes must be treated with exogenous insulin.

Type 2 diabetes

Type 2 diabetes, also known as adult-onset or non-insulin dependent diabetes, is more frequently seen in older individuals and caused by lifestyle and environmental-linked risk factors. The interplay of mild or severe insulin resistance, reduced or insufficient insulin secretion, and elevated glucose production creates a metabolic environment that leads to diabetes, requiring a lifetime of lifestyle management and/or specific treatment.

Gestational diabetes

Gestational diabetes may develop in some pregnant women. In general, pregnancy confers a state of insulin resistance and hyperglycemia, to allow the fetus to access glucose from the umbilical blood supplies. Occasionally the mother's pancreatic function is unable to compensate for the diabetogenic environment of pregnancy (Glitmartin et al., 2008), and it may be considered a form of type 2 diabetes. During pregnancy, the high blood glucose levels may have to be treated, either by lifestyle changes and/or medication, to ensure the health of both mother and baby. Often, women who develop gestational diabetes are predisposed to develop diabetes in the years following the pregnancy.


Prediabetes is a condition that precedes type 2 diabetes and is characterized by blood glucose level that is higher than normal but not yet high enough to be diagnosed and treated as diabetes. These individuals may also have an increased risk for heart disease. Individuals with prediabetes typically develop type 2 diabetes within 10 years of initial diagnosis. However the diabetes diagnosis can be delayed or avoided with lifestyle changes, such as moderate physical activity, modest weight loss, and careful management of quality and quantity of food eaten.

Maturity-onset diabetes of the young (MODY)

Maturity-onset diabetes of the young (MODY) is a collection of rare monogenic disorders characterized by (an autosomal dominant mode of) genetic inheritance and early onset age (typically less than 25 years). These non-insulin dependent diabetic conditions affect 1-2% of diabetes patients and are characterized by impaired glucose-stimulated insulin secretion (Gupta et al., 2005). In the autosomal dominant pattern of inheritance, one abnormal copy of the gene is sufficient for an individual to be affected, so there is a 50/50 chance of the mutant gene being passed onto future generations. Often masquerading as Type 1 diabetes or Type 2 diabetes, MODY manifests itself in many forms.

Secondary diabetes

Secondary diabetes refers to a condition where high blood glucose and diabetes like symptoms arise as a consequence of another disease state such as pancreatic cancer, pancreatitis, cystic fibrosis, etc. (diabetes.co.uk/secondary-diabetes.html). Some specific drugs such as corticosteroids, antipsychotics, and statins can also induce diabetes. While the primary cause of this condition cannot be removed, this type of diabetes may have to be managed by a combination of lifestyle changes, medication, and insulin.


Diagnosis and classification of diabetes Mellitus (2009). Diabetes Care, 33(Supplement_1), S62–S69. https://doi.org/10.2337/dc10-s062

Gilmartin, A. B., Ural, S. H., Repke, J. T. (2008). Gestational diabetes mellitus. Reviews in Obstetrics & Gynecology 1,129-34. PMID: 19015764

Canadian Diabetes Association (2016) "History of Diabetes". www.diabetes.ca/about-diabetes/history-of-diabetes

Gupta, R. K., Vatamaniuk, M. Z., Lee, C. S., Flaschen, R. C., Fulmer, J. T., Matschinsky, F. M., Duncan, S. A., Kaestner, K. H. (2005). The MODY1 gene HNF-4α regulates selected genes involved in insulin secretion. Journal of Clinical Investigation, 115(4), 1006–1015. https://doi.org/10.1172/jci200522365

Diabetes Types: www.diabetes.co.uk/diabetes-types.html

April 2017, Jennifer Jiang, Dr. Shuchismita Dutta; Reviewed by Drs. Stephen Schneider and Stephen K. Burley