Type I diabetes
This is caused by islet beta cell destruction leading to absolute insulin deficiency. It is subclassified into type la (immune mediated) and type lb (idiopathic i.e. without known cause),
Type la diabetes or Immune mediated diabetes Our body has an ability to distinguish between its "own" cells and "foreign" cells. It rejects "foreign" cells by producing antibodies, the defence entities produced by lymphocytes, a type of white blood cells. These lymphocytes are part of an immune system which carries out a vital defence function. Sometimes, this immune system may go wrong and produce antibodies against the body's own cells (autoimmune mechanism; auto-self). When autoimmune mechanisms are directed against the insulin-producing beta cells of the pancreas, the latter are destroyed. The pancreas has a considerable reserve capacity. It has been estimated that until persons lose approximately 80 per cent of their beta cell mass, they do not present with overt diabetes. The process of beta cell destruction may start several years before diabetes actually manifests itself. The autoimmune destruction of the pancreas occurs in individuals who have an inherited susceptibility to such a process. The factors which actually trigger the autoimmune process in a susceptible individual are not exactly known. Certain viruses, chemical agents and drugs may be the triggering factors. It is suggested that breast milk may protect against this process.
This subtype of diabetes was previously encompassed by the terms insulin dependent diabetes mellitus (IDDM) or juvenile -onset diabetes.
The clinical features depend upon the rate of beta cell destruction. Some patients develop excessive urine, thirst, weight loss, weakness and may have apart from large amount of glucose, ketones (breakdown products of fats) in urine. Those with relatively slower rate of beta cell destruction, have a modest increase in blood glucose initially. However in the presence of a stress, like infection, the blood glucose may rise rapidly with an accumulation of ketones. If diagnosis is delayed, the patient may present with nausea, vomiting, dehydration, over breathing, pain in abdomen, drowsiness and large amount of ketones in blood and urine.
This subtype commonly occurs in childhood and adolescence, but can occur in any age. Its occurrence is rare in the first six months of life. The incidence begins to increase sharply at about nine months of age, reaches a peak at twelve to fourteen years of age and then declines. Both sexes can be affected. Some seasonal variations in its incidence have been reported.
This subtype occurs in most racial and ethnic groups, the risk being highest among the white population. Its incidence (frequency with which new patients are detected during a defined time period) is highest in Scandinavian countries and lowest in Japan. It occurs probably in less than 5 per cent of all diabetics in India. Its incidence is increasing in many countries.
Latent autoimmune diabetes in adults (I.ADA)
Some times, type 1 diabetes occurs after the age of 40 years. Though it resembles type 2 diabetes (diabetes occurring in middle age) their tests show autoimmunity. After some time, they become truly dependent on insulin.
Type lb diabetes
Some forms of type 1 diabetes have no known cause and hence are called idiopathic. This subtype is uncommon and occurs mostly in individuals of African or Asian origin.
This form of diabetes is strongly inherited. It lacks evidence for beta cell autoimmune destruction. Episodes of rise in blood glucose and accumulation of ketones may occur periodically. Varying degrees of insulin deficiency are seen between such episodes. These patients may require insulin treatment for survival from time to tune.