Complement component 3 (C3) genetics and diabetes mellitus.

Complement component 3 (C3) phenotype and allele frequencies were defined in 312 patients with type-1 diabetes (insulin-dependent diabetes mellitus), 256 patients with type-2 diabetes (non-insulin-dependent diabetes mellitus), 114 apparently non-diabetic first-degree relatives of type-1 diabetics, in 10 families (29 members) with a familial history of type-1 or type-2 diabetes, in 181 patients with coronary heart disease and 255 subjects with arterial hypertension. 512 blood donors served as controls. All persons investigated were Europeans. There is no evidence that genes linked to C3 influence susceptibility to type-1 and type-2 diabetes and to their late complications as well as to atherosclerosis and essential hypertension. The distribution of apolipoprotein E phenotypes in patients and controls was likewise not significantly different. The combined evaluation of data from linked genes (C3 and apo E) could not improve the results. Deductions of C3 as a genetic disease marker have to be interpreted with caution.