Analyses of serum lipoprotein(a) and the relation to phenotypes and genotypes of apolipoprotein(a) in type 2 diabetic patients with retinopathy.

Abstract

To elucidate the association of lipoprotein(a) (Lp(a)) with diabetic retinopathy (DR), we studied the serum Lp(a) concentrations (n = 412), apolipoprotein(a) (apo(a)) phenotypes expressed by the number of kringle 4 (K4) repeats (n = 150), apo(a) gene genotypes (n = 161) of type 2 diabetes with or without DR. The 5'-untranslated region of apo(a) gene was classified into seven haplotypes (A to G) and 18 genotypes by PCR-RFLP at three distinct sites. The serum Lp(a) concentrations were significantly higher in diabetic patients than in normal controls. Furthermore, the patients with DR, especially proliferative retinopathy showed higher serum Lp(a) concentrations than those without DR. Although a negative correlation was found between the serum Lp(a) concentrations and the number of K4 repeats in total diabetic patients, no difference was seen in the distribution of the number of K4 repeats between those with and without DR. In the same apo(a) phenotypes, the patients with DR had higher Lp(a) concentrations than those without DR. Among the genotypes, type CC showed significantly higher serum Lp(a) concentrations than the other genotypes. However, there was no difference in the ratios of the type CC between the patients with and without DR. In conclusion, other factors than phenotypes and genotypes in the 5'-untranslated region of apo(a) may be responsible for the elevation of serum Lp(a) in diabetic patients with retinopathy.