Other Forms of Diabetes Mellitus

Genetic Defects Affecting Pancreatic Beta Cells,
e.g. Maturity Onset Diabetes of the Young (MODY)
This is an unusual form of diabetes, which has been the subject of considerable research in recent years. Although it superficially resembles Type 2 diabetes, there are a number of important differences. MODY appears in childhood or young adulthood, before the age of 25 years, and in most cases at least one or even two other members of the immediate family are affected. It has an entirely genetic origin and the defects (or mutations) in the genes involved have been identified. Environmental factors do not contribute to MODY and those affected are of normal weight and rarely obese. Five sub-groups of MODY have been identified (MODY 1, 2, 3, 4, 5 - depending upon the precise mutations in the genes involved) which produce diabetes of varying degrees of severity. Hence treatment also varies accordingly, with one form usually managed by diet alone while others require drug or insulin therapy. The risk of complications likewise varies between the different forms of MODY. In one in five families affected by this syndrome, the genetic defect involved is not one that has been previously identified. Hence it is likely that further sub-groups of MODY will emerge in the future when further mutations are identified. The pattern of inheritance involved in MODY is called 'autosomal dominance' and there is a 50 per cent risk of diabetes in the child of an affected parent. It has been suggested that genetic screening of the offspring of a MODY parent might be helpful but there is also concern that this might raise more problems than it solves. Although 'at risk' children with the genetic defect for MODY can be identified, it is far from certain that any preventive treatment that may be attempted will be effective.

Genetic Defects in Insulin Action,
e.g. 'Leprechaunism' and Rabson-Mendenhall Syndrome
There are a number of rare, genetic abnormalities affecting the insulin receptors, resulting in severe disruption of their structure and function. Severe insulin resistance and diabetes are characteristic of these syndromes, along with various other metabolic features.

Diseases of the Exocrine Pancreas,
e.g. Pancreatitis, Cystic Fibrosis, Haemochromatosis
The pancreas is vulnerable to a number of conditions and disorders which, if severe, may cause secondary diabetes. Pancreatitis (inflammation of the pancreas) may be acute (and usually transient), or chronic and long-lasting (often caused by alcoholism). People with the chronic condition are at risk of diabetes, as are those with cancer of the pancreas and patients who have undergone surgical removal (pancreatectomy) of the whole or part of the gland as a method of treatment. Cystic fibrosis is a condition that affects all the glands of the body, including the pancreas. Improved treatment for sufferers and increased survival times mean that diabetes is a common complication, usually appearing in the teenage years or young adulthood and eventually requiring insulin therapy. Haemochromatosis is a rare metabolic, genetic disorder which is characterized by iron being deposited in various organs, including the liver and pancreas. Diabetes requiring insulin treatment develops in about half of those affected. It is sometimes called 'bronzed diabetes' due to an unusual pigmentation of the skin which is a feature of haemochromatosis. The disorder causes a number of serious complications, of which diabetes is only one and sufferers require intensive treatment.

Diabetes that Develops as a Feature of Endocrinopathies
Endocrinopathies (diseases due to disorders of the endocrine glands) and in particular autoimmune conditions, such as Graves' disease, acromegaly, and Cushings syndrome, primarily affect hormone-secreting glands, causing hormone imbalances which affect the production and action of insulin. It has also been found that people with Type 1 diabetes run an increased risk of developing other autoimmune disorders. People suffering from these conditions are likewise at greater risk of developing diabetes which may require insulin treatment or insulin resistance or impaired glucose tolerance.

Some other autoimmune disorders, e.g. Addison's disease, primary hypothyroidism and so-called Stiff Man syndrome, are associated with an increased sensitivity to insulin and hence hypoglycaemia. People with Type 1 diabetes run an increased risk of developing these types of disorders.

Coeliac disease or gluten enteropathy is another autoimmune condition with some similarities to diabetes. It is a wasting disease in which the intestines are unable to absorb fat. There may be hypoglycaemia caused by malabsorption and the symptoms are caused by an intolerance to the protein, gluten, found in wheat and rye flour, which damages the lining of the intestines. It is treated by a strict and lifelong adherence to a gluten-free diet but some people also have an additional need for insulin therapy.

Diabetes Caused by Drugs or Chemicals,
e.g. Coticosteroids, Thiazide Diuretics and Beta-blockers
Quite a number of drug treatments are associated with the development of glucose intolerance, insulin resistance or diabetes. Also, when these drugs are taken by people with existing diabetes, they may lead to a lowering of gly-caemic control so that someone with Type 2 syndrome that had been managed with tablets may then require insulin. It may be that some patients are in a higher risk group for glucose intolerance, insulin resistance or diabetes, or are undiagnosed for these conditions at the start of drug treatment. Many of the drugs are used to treat serious conditions with a known link to diabetes such as hormonal disorders, hypertension and heart and circulatory disease.

Diabetes Caused by Infections,
e.g. Congenital German Measles (Rubella)
Various viral infections have been implicated in the development of Type 1 diabetes. Infection of a developing foetus with rubella leads to a 20 to 40 per cent risk of autoimmune diabetes in the child.

Uncommon Forms of Immune-mediated Diabetes
This is a group of rare disorders, such as Stiff Man syndrome, which are associated with the development of diabetes.

Other Genetic Syndromes which may confer a Greater Risk of Diabetes.
A number of inherited, chromosomal abnormalities carry an increased risk of diabetes. Their number include Down's syndrome, Turner's syndrome, Klinefelter's syndrome, Friedreich's ataxia, neonatal diabetes, and mitochondrial syndromes passed through the maternal line.

Gestational Diabetes Mellitus: Diabetes First Diagnosed in Pregnancy
This is regarded as a special category which includes impaired glucose tolerance and transient diabetes, both precipitated and diagnosed in pregnancy but resolving after the birth, and diabetes that has been pre-existing but first comes to light during pregnancy. While transient diabetes and IGT usually disappear after delivery, affected women have a greater risk of eventually developing Type 2 diabetes. Women with pre-existing but formerly unsuspected diabetes are usually older mothers who are overweight or obese, and in almost all cases they are affected by Type 2 syndrome. These women continue to need treatment for their diabetes following delivery. A small number of, usually young, women diagnosed with gestational diabetes are discovered to have Type 1 syndrome. It is thought that the metabolic changes that occur during pregnancy (which for all women are pro-diabetic) may exacerbate or at least reveal the existence of diabetes that had previously not reached a stage of producing symptoms.

The incidence of gestational diabetes varies between different populations and racial groups. Southern Asian women are affected at twice the rate (4 to 5 per cent) of white Europeans (1 to 2 per cent). Women belonging to some racial groups (e.g. Latin Americans) who develop gestational diabetes that initially resolves, nevertheless are at greater risk of a fairly rapid development of Type 2 diabetes.

The more unusual categories of (secondary) diabetes described above have been included as a matter of interest and information. Treatment of these conditions may require a multi-targeted approach of which diabetes control may be only one aspect.

Information about diffrent diabetes types.