Background:Elevated serum lipoprotein(a) [Lp(a)] concentrations have been demonstrated to be associated with cardiovascular diseases due to premature atherosclerosis. However, the association of Lp(a) phenotypes with the development of these diseases remains largely unexplored.Methods:We analyzed the population-based frequencies of serum Lp(a) phenotypes in 269 Japanese children aged 8-13 years in one community. According to the different apolipoprotein(a) [apo(a)] electrophoretic mobilities, Lp(a) was classified into seven single-band and respective double-band phenotypes. Each individual expressed a single (homozygotic) or a double band (heterozygotic).Results:The serum Lp(a) concentration frequency distribution was skewed toward lower levels with a mean ± SD of 15.5 ± 18.0 mg/dl and a median of 11.0 mg/dl. The Lp(a) phenotype frequencies revealed that the frequency of double-band phenotype expression (55%) was higher than that of single bands (44%) and that the frequency of phenotypes representative of low molecular weight apo(a) was very low (2%). The mean serum Lp(a) concentration of the double-band-expressing subjects was higher than that of subjects with the single-band phenotype (20.1 ± 19.9 vs. 10.5 ± 15.9 mg/dl, p < 0.01).Conclusions:These findings of Lp(a) phenotypes in children seemed to differ from those in Japanese adults in another study; contrary to expectation, the predominant Lp(a) phenotypes found in children were those frequently associated with cardiovascular diseases in adults. Thus, it is speculated that children whose Lp(a) phenotypes remain unchanged during the transition to adulthood may show an increased susceptibility to cardiovascular disease, although the nutritional effects on the Lp(a) phenotypes cannot be neglected.