Normal lipoprotein(a) concentrations and apolipoprotein(a) isoforms in patients with insulin-dependent diabetes mellitus.

Lipoprotein(a) [Lp(a)] is an LDL particle in which apoliporotein B-100 is attached to a large plasminogen-like protein called apolipoprotein(a) [apo(a)]. Apo(a) has several genetically determined phenotypes differing in molecular weight, to which Lp(a) concentrations in plasma are inversely correlated, and plasma Lp(a) concentrations above 20-30 mg dl-1 are an independant risk factor for ischaemic heart disease (IHD). To investigate whether Lp(a) could be important for the high cardiovascular mortality rate in patients with insulin dependent diabetes mellitus (IDDM), we determined Lp(a) concentrations and phenotypes in a group of 108 men (median age 32 years) with IDDM without nephropathy. A group of 40-year-old men (n = 466) served as controls. The median Lp(a) concentration was 7.4 mg dl-1 [95% CI 4.9 to 11.7] in the diabetic patients and 6.3 mg dl-1 [95% CI 5.2 to 7.0] in controls. The Lp(a) concentration exceeded 30 mg dl-1 in 22% of IDDM patients and in 20% of controls (P = 0.13). Moreover, the distribution of apo(a) phenotypes did not differ between patients and control. Lp(a) levels and apo(a) phenotypes are thus apparently the same in IDDM patients without nephropathy and controls. These findings do not exclude the possibility that Lp(a) may be increased in patients with nephropathy in whom coronary artery disease frequently co-exist or that Lp(a) in a given concentration is more atherogenic in IDDM patients than in persons without IDDM.