Diabetes mellitus (simplified model)

Diabetes mellitus is classified into two basic
types: type I (insulin-dependent diabetes mellitus,
IDDM) and type II (non-insulin-dependent,
NIDDM). The majority of diabetes type I
cases are caused by external factors, such as certain
viral infections, on a background of genetic
susceptibility. Diabetes type II is mainly due to
genetic factors, but also in part to overnourishment.
Apart from an autosomal dominant
hereditary form with onset in young adults, it is
not a monogenic disorder. Monozygotic twins
are concordant for type II in about 40–50% of
cases and for type I in about 25%, as opposed to
a risk of less than 10% for type I in first-degree
relatives (about 2–7% according to family relationship
and age at onset of disease). Diabetes
mellitus is a secondarymanifestation of a number
of genetically determined diseases, e.g., insulin
receptor defect (insulin resistance syndrome).