Diabetes mellitus is a heterogenous
disorder defined by the presence of hyperglycemia.
Hyperglycemia in all cases is due to a functional
deficiency of insulin action which can be due to a
decrease in insulin secretion by the beta cells of
pancreas or a decrease of responses to insulin by
target tissues. Chronic hyperglycemia can lead to
damage of organs including the eyes and kidneys,
or damage of blood vessels and nerves.