To clarify the relationship between the expression of atherogenic small, dense lowdensity lipoprotein (SDLDL) and underlying lipid metabolic abnormalities, the prevalence of SDLDL in relation to the serum lipid phenotype was analyzed in 229 children. The LDL particle size was measured using gradient gel electrophoresis, and a particle size of less than 25.5 nm was considered to represent SDLDL. The overall prevalence of SDLDL in the sample population was 8.2% (19/229; 11/117 for boys and 8/112

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... or girls). Hyperlipidemia phenotype IIb (elevated concentrations of both triglyceride [ TG] and total cholesterol [ TC ]) was strongly associated with SDLDL in 83% (5/6) of the subjects. An elevated TG concentration (phenotype IV) was associated with SDLDL in 55% (10/18) of the subjects. The association between hyperlipidemia phenotype IIa (elevated TC but a normal TG concentration) and SDLDL was quite low (2%; 1/56), but SDLDL was detected in 5% (8/155) of the subjects who presented with normolipidemia. Therefore, these findings suggest that the expression of SDLDL is largely related to lipid abnormalities characterized by phenotype IIb or IV, the underlying metabolic abnormality of which is suspected to be insulin resistance; however, an additional mechanism for the formation of SDLDL that functions independently of plasma lipid abnormalities also seems to exist. J Atheroscler Thromb, 2004; 11: 220-223.