Progress in our understanding of the pathophysiology of diabetes melli
tus has been made possible because of the availability of animal analo
gs of the various human diseases. Diabetes mellitus can be mild, moder
ate or severe depending on the genetic error that is responsible for t
he disease. Present estimates of errors that result in diabetes range
from 20 to 100. Because similar errors have been found in spontaneousl
y diabetic animals scientists have been able to identify the sequence
of metabolic events and subsequent tissue change in many of these phen
otypes. Studies of the efficacy of various drugs, diets and lifestyle
choices on disease development and management thus were made possible.