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Different types of diabetes

• What are the different types of diabetes mellitus?
• What is Type 1.5 diabetes (latent autoimmune diabetes in adults)?
• How common is type 2 diabetes in childhood and adolescence?
• Gestational diabetes mellitus
• Other causes of diabetes mellitus

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What are the different types of diabetes mellitus?

There are two main types of diabetes: Type 1 diabetes (previously called insulin dependent diabetes) and Type 2 diabetes (previously known as non-insulin dependent diabetes). Over 90% of the diabetic patients have type 2 diabetes.

Type 1 diabetes develops when most or all of the beta cells in the pancreas that produce insulin have been destroyed causing severe lack of insulin in the body. The damage may be caused by a defect in the immune system, a viral infection or toxins. There is a significant genetic link to the development of Type 1 diabetes. For example, if an identical twin is affected, there is a 30-50% risk of development in the other twin.

Type 2 diabetes develops when the pancreas cannot produce enough insulin for the body’s needs or the body cannot used the insulin effectively, a condition called insulin resistance. (see metabolic syndrome)

The following table shows the main differences between type 1 and type 2 diabetes:

What is Type 1.5 diabetes (latent autoimmune diabetes in adults)?

Latent autoimmune diabetes (LADA) in adults is a form of type 1 diabetes, characterized by adult-onset diabetes, presence of circulating antibodies, commonly the anti-Glutamic Acid Decarboxylase antibody (GAD) and islet cell antibody (ICA), and does not need insulin treatment at the initial stage. Therefore it is also sometimes described as Type 1.5 diabetes.

According to the United Kingdom Prospective Diabetes study, approximately 10% of adults with diabetes actually have LADA. Patients may initially respond to oral agents, but rapidly require insulin treatment as it often progresses rapidly. It is believed to be caused by a marked loss of beta-cell (cells in the pancreas that produce insulin) function due to destruction by the antibodies, which eventually results in insulin deficiency.    

Acute symptoms of high blood glucose such as thirst, frequent urination, weight loss, etc are more frequent in patients with LADA than in patients with type 2 diabetes. Age of onset is usually <50 years and they do not have the associated conditions in type 2 diabetes e.g. hypertension, high serum triglycerides and low HDL-cholesterol.  Personal or family history of autoimmune disease is common. 

At the initial stage, oral agents such as sulphonylurea or metformin may be effective in controlling blood glucose. Insulin sensitizers such as rosiglitazone or pioglitazone may not be effective as the mechanism of LADA does not typically involve insulin resistance.

How common is type 2 diabetes in childhood and adolescence?

Prevalence of type 2 diabetes in children is increasing. It is likely that type 2 diabetes will be the predominant form in children within 10 years in many populations. Among children in Japan, type 2 diabetes accounts for 21% of childhood diabetes; 17% in Singapore. The majority are usually discovered incidentally e.g. on a routine medical examination. Many have obesity and sugar in the urine without any symptoms.

Risk factors are similar to those in adult type 2 diabetes such as obesity or overweight, sedentary lifestyle, family history of diabetes mellitus, unhealthy eating.

Gestational diabetes mellitus

Gestational diabetes mellitus occurs when elevated blood sugar is first recognised in pregnancy.(see gestational diabetes)

Other causes of diabetes mellitus

Other causes of diabetes are all very uncommon.

In maturity onset diabetes of the young (MODY), there is a genetic defect affecting insulin-secreting beta-cells in the pancreas. It usually occurs before age of 25 years. There is a family history of MODY and it is not associated with environmental factors.

Disorders of endocrine glands such as Cushing's syndrome, acromegaly (due to excessive growth hormone secretion), affect production and action of insulin resulting in diabetes mellitus.

Diseases of exocrine pancreas including pancreatitis (inflammation of the pancreas due to gallstones, alcoholism, etc) and cystic fibrosis can also lead to development of diabetes.

A number of drugs have been known to be associated with the development of glucose intolerance, insulin resistance or diabetes These drugs include corticosteroids, beta-blocker and thiazide diuretics.