Patients with insulin-dependent diabetes mellitus (IDDM) have an excess mortality, predominantly attributable to cardiovascular disease. To determine the effect of IDDM on potential risk factors for cardiovascular mortality, we studied subjects from the British Diabetic Twin Study Group. Forty-five identical twin pairs discordant for IDDM were recruited in addition to 45 matched nondiabetic singleton control subjects. All were selected to be normotensive and to have normal albumin excretion rates. Four variables differed significantly between the diabetic twins and their nondiabetic identical co-twins: diabetic twins had higher systolic blood pressure (sBP) ([mean ± SD] 127 ± 17 vs. 123 ± 18 mmHg, P < 0.05), high-density lipoprotein (HDL) cholesterol (1.36 ± 0.31 vs. 1.25 ± 0.29 mM, P < 0.05) and fibrinogen (3.23 ± 0.81 vs. 2.98 ± 0.71 mg/ml, P < 0.05) but lower factor VII (114 ± 34 vs. 122 ± 31%, P < 0.05). All four of these risk factors were significantly correlated (P < 0.001) within the identical twin pairs, as were the other risk factors. These significant correlations within twins for the risk factors studied reflects the impact of shared genetic and environmental influences. IDDM affects sBP, HDL cholesterol, fibrinogen, and factor VII, but only sBP and fibrinogen are affected adversely.

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