Serum remnant lipoprotein cholesterol/triglyceride ratio as an index for screening familial type III hyperlipidaemia.

Background: An elevated serum remnant lipoprotein cholesterol (RLP-C)/triglyceride (TG) ratio has not been evaluated as an index of familial type III hyperlipidaemia defined by the presence of beta-VLDL and apolipoprotein (Apo) E2/2 phenotype in the Japanese hyperlipidaemic population.
Methods: Serum lipids and lipoproteins from 514 individuals (200 men and 314 women, mean age 58 years) with total cholesterol >6.22 mmol/L and TG between 2.26 mmol/L and 9.04 mmol/L, selected from 25,080 subjects visiting the clinics for health checkup were analysed for a possible relationship with familial type III hyperlipoproteinaemia.
Results: Median RLP-C concentration and RLP-C/TG ratio were 0.30 and 0.11 mmol/L, respectively. When compared between subjects with (31 cases) and without (483 cases) a broad-beta band on electrophoresis, the RLP-C concentrations and RLP-C/TG ratio were 0.77 +/- 0.43 mmol/L versus 0.34 +/- 0.16 mmol/L (P<0.0001) and 0.15 +/- 0.023 versus 0.11 +/- 0.027 (P<0.0001), respectively. Three cases with broad-beta band positive (the presence of beta-VLDL) showed RLP-C/TG ratio greater than 0.23 and RLP-C greater than 0.78 mmol/L, suggestive of type III hyperlipoproteinaemia, despite a lack of characteristic Apo E2/2 homozygosity. Cases with Apo E/Apo CIII ratio greater than 1.0 were not detected in this study group.
Conclusion: Serum RLP-C concentration and RLP-C/TG ratio, together with Apo E/Apo CIII ratio appear to be useful for screening familial type III hyperlipidaemia in the Japanese hyperlipidaemic population.