Which ofthe following statements is true regarding type 1 diabetes mellitus -

Pathology Type 1 diabetes is a T cell-mediated autoimmune disease (p. 86) involving destruction of the insulin-secreting b cells in the pancreatic islets. Progressive loss of b cell function takes place over a prolonged period (months to years), but marked hyperglycaemia, accompanied by the classical symptoms of diabetes, occurs only when 80-90% of the functional capacity of b cells has been lost. Metabolic disturbances in type 1 diabetes Patients with type 1 diabetes present when progressive b-cell destruction has crossed a threshold at which adequate insulin secretion and normal blood glucose levels can no longer be sustained. Above a ceain level, high glucose levels may be toxic to the remaining b cells, so that profound insulin deficiency rapidly ensues, causing the metabolic sequ elae shown in Figure 21.5. Hyperglycaemia leads to glycosuria and dehydration, causing fatigue, polyuria, nocturia, thirst and polydipsia, susceptibility to urinary and genital tract infections, and later tachycardia and hypotension. Unrestrained lipolysis and proteolysis result in weight loss. Ketoacidosis occurs when generation of ketone bodies exceeds the capacity for their metabolism. Elevated blood H+ ions drive K+ out of the intracellular compament, while secondary hyperaldosteronism encourages urinary loss of K+. Thus patients usually present with a sho history (typically a few weeks) of hyperglycaemic symptoms (thirst, polyuria, nocturia and fatigue), infections and weight loss, and may have developed ketoacidosis . DAVIDSONS PRINCIPLES AND PRACTICE OF MEDICINE 22ND EDITION PAGE NO-803,804