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Type 1 Diabetes

Type 1 diabetes (formerly Insulin-Dependent Diabetes Mellitus or IDDM) is the less common of the two main forms of diabetes and, in some ways, is easier to understand. This is because in the vast majority of cases, the diabetes arises because of a gradual and progressive autoimmune destruction of the beta islet cells of the pancreas which produce insulin. An autoimmune response can be thought of as a form of self-destruction. For some reason, the body's immune system fails to recognize some component or substance that belongs to itself and produces antibodies to attack and destroy that element, as though it were foreign or invading. In the case of Type 1 diabetes, it is the all-important insulin-producing cells that are attacked, but it takes some time for the situation to become critical. In fact, it is only after most (about 90 per cent) of the beta cells have been destroyed that the person begins to show classical symptoms of diabetes. These may include any of those described under defining and diagnosing diabeteS above, but in particular, marked osmotic symptoms, weight loss and tiredness. When tests are carried out, they reveal ketonuria and significant hyperglycaemia. Usually, the symptoms are sufficiently noticeable to prompt the person to seek medical help, but this is not always the case. Unfortunately, about 5 to 10 per cent of people with Type 1 diabetes are not diagnosed until they are admitted to hospital in the emergency stage of diabetic ketoacidosis (DKA). The key feature of Type 1 disease is that those affected need insulin replacement therapy for life in order to ensure survival.

There is a long, asymptomatic period in Type 1 diabetes (called the prodromal period) during which the beta cells are progressively being destroyed. The peak age for symptoms to appear and for diagnosis to be made is 11 to 13 years. However, this is not always the case, and mature and even elderly people are occasionally diagnosed. Initiation of insulin treatment in Type 1 diabetes quite often restores some beta cell function for a short period of time. This is known as the 'honeymoon period' and it usually lasts between six and twelve months. While it lasts, only small doses of insulin are needed and it is thought that this may extend the length of the honeymoon period itself. Unfortunately, it usually ends suddenly during a time of illness or other period of stress.

People with Type 1 diabetes have high levels of antibodies to islet cells circulating in their blood and these can be detected by laboratory analysis. Occasionally, high levels of antibodies are found in the blood of older people who were initially thought to have Type 2 diabetes, indicating that autoimmune destruction of beta cells has been taking place. These people may be designated as having Autoimmune Diabetes in Adults (LADA) to distinguish this more unusual form of Type 1 syndrome. Almost all cases of Type 1 syndrome involve autoimmune destruction of beta cells and consequent loss of insulin, as described above. However, as is so often the case in medicine, exceptions have been recorded, and in the ADA classification, this highly unusual form is designated Idiopathic Type 1 diabetes, indicating that it is of unknown origin. Affected people (who are most likely to be of African or East Asian origin) appear to have the symptoms of Type 1 syndrome and may present with ketosis, requiring emergency treatment. However, blood testing does not detect the antibodies normally associated with the disorder and the treatment needed by this unusual group may change over time. There may even be periods when their diabetes can be controlled by the oral antidiabetic drugs more appropriate to Type 2 disease. There is a significant genetic link in the development of Type 1 diabetes and the genes involved have been identified. They are known as Class 2 major histocompatibility complex (MHC) and they are located on the short arm of chromosome 6. They are responsible for the production of Human Leukocyte Antigens (HLA), and people with genetically determined Type 1 diabetes produce certain antigens which are implicated in the autoimmune response. Many studies have been carried out to quantify the risk to an individual of developing Type 1 diabetes if he or she has a close relative already affected. Some of the most interesting studies have involved identical and non-identical twins and the approximate risks are as follows:

mother affected: 2 to 3 per cent risk of Type 1 diabetes developing in children
father affected: 5 to 10 per cent risk of Type 1 diabetes developing in children
both parents affected: 30 per cent risk of development in children
brother or sister affected: 10 per cent risk of development in siblings
identical twin affected: 30 to 50 per cent risk of development in other twin
non-identical twin affected: 20 per cent risk of development in other twin.

From these figures it can be seen that genetic factors at present identified do not account for all the incidence of Type 1 diabetes. It is believed that environmental factors are important, and suggested culprits include viruses (e.g. Coxsackie B4, rubella [Germanmeasles], cytomegalovirus), in utero exposure to serum albumin in cows' milk and ingestion of nitrosamines in smoked foods during infancy. It has, however, proved difficult to pinpoint environmental causes with any certainty. Their significance would seem to be confirmed by the fact that the incidence of Type 1 diabetes is rising in many countries, including the UK, where the number of children under 16 years diagnosed with the disorder doubled during the last quarter of the twentieth century.

People with Type 1 diabetes are at some risk of sudden death from severe metabolic episodes such as DKA, but in general only if specific circumstances apply or if the condition is not being managed and controlled. In the long term, there is an increased risk of diabetic complications and death from coronary heart disease or kidney failure. However, on an individual basis, there is a great deal that can be done to lower the chances of these conditions arising and to lessen the threat that they pose.

Information about diffrent diabetes types.