The type-1 diabetes is also called IDDM or insulin-dependent diabetes mellitus, as the patient must be treated (supplemented) with exogenous insulin, due to destruction of beta cells of pancreas which secrete insulin. As the insulin secreting beta cells are destroyed the pancreas (beta cells of pancreas) can not produce insulin and must be supplied from outside.

Autoimmune cause of type 1 diabetes:

The main cause of type diabetes is autoimmune (“immune-mediated form” of type I diabetes mellitus). Due to autoantibodies directed against the insulin secreting beta cells of pancreas, in the patient’s blood the beta cells are destroyed by the autoantibodies. The numbers of beta cells of pancreas are normal at the time of birth, but months or years after birth due to development of autoantibodies the destruction of beta cells of pancreas starts. The time taken for destruction of beta cells of pancreas may vary from patient to patient.

More than 95% of patient with type-1 diabetes develop the disease before 25 years of age. The onset of type 1 diabetes is usually acute (developing over a period of a few days to weeks). The acuteness of type 1 diabetes is destruction of more than 80% of beta cells of pancreas. The pancreas can maintain supply of insulin if beta cell mass of at least 20% is functioning and if the functional beta cell mass falls below 20% the clinical symptoms of diabetes develop.

In rare instances, especially among individuals of African or Asian origin, there may not be any autoantibodies directed against the insulin secreting beta cells of pancreas in the blood. But the clinical symptoms are similar to “immune-mediated form”, called “idiopathic form” of type I diabetes mellitus.

Genetic cause of type 1 diabetes:

There is some genetic factor in causation of type 1 diabetes, but the association is less strong than that of type-2 diabetes. The concordance of type 1 diabetes in identical twins ranges between 30% and 70%, which indicate there is an association of genetic factor (s), but environmental and other factors play a major role. The major susceptibility gene for type 1 diabetes is located in the HLA (human leukocyte antigen) region on chromosome-6. Individuals with type 1 diabetes have HLA DR3 and/or DR4 haplotype. In USA it was seen that 40 % of type 1 diabetes have the HLA loci with haplotypes DQA1*0301, DQB1*0302, and DQB1*0201 in compare to only 2% among normal population.

The risk of developing type1 diabetes is 10 fold if you have a first degree relative with type 1 diabetes. If a parent has type-1 diabetes the risk of developing type-1 diabetes among siblings is 5-15%.

Environmental causative factors for type 1 diabetes:

Several environmental factors have been proposed as the cause of type-1 diabetes, by triggering the autoimmune process in genetically susceptible individuals, but none have been proved conclusively. The reason in difficulty in identification of environmental trigger may be, because the event may precede the onset of DM by several years. Some probable environmental triggers include viruses (such as coxsackie virus and rubella virus), bovine (not human) milk proteins, and nitrosourea compounds.