Non-HDL-cholesterol/apolipoprotein B ratio: A useful distinguishing feature in the screening for type III hyperlipoproteinemia

Background

Dysbetalipoproteinemia, also known as type III hyperlipoproteinemia (type III HL), is characterized by the accumulation of β-very low density lipoprotein (β-VLDL). However, demonstration of the presence of β-VLDL is not easy because it requires preparative ultracentrifugation of lipoproteins. The primary genetic defect in type III HL is the presence of apolipoprotein (apo) E2, a mutant form of apoE. However, another metabolic defect, such as overproduction of VLDL, is also required for the full phenotype. Patients with only E2 homozygosity usually do not have HL. Because apoE genotyping is expensive, the selection of patients for this analysis by effective use of common clinical measures would be very helpful.

Objective

We examined the non-HDL-C/apoB ratio as an index for type III HL screening.

Methods

We studied nine patients with type III HL. Most patients with type III HL show mixed hyperlipidemia. We compared the plasma of patients with combined hyperlipidemia and the dyslipidemia of hypothyroidism with those with type III HL. The serum levels of total cholesterol, triglyceride, and high-density lipoprotein cholesterol (HDL-C), as well as the serum apoB and apoE levels, were measured by routine laboratory methods.

Results

Individual values of serum lipids and apolipoproteins did not distinguish type III HL from the two other types of HL. The non-HDL-C/apoB ratio in type III HL was significantly greater than that in the two comparison groups, with no overlap.

Conclusion

The non-HDL-C/apoB ratio is a novel index that appears to be reliable for screening of patients for type III HL, and the index can be determined at regular clinical laboratories without the need for any complicated lipoprotein analysis. Thus, we propose the clinical usefulness of this index.

Keywords: Apolipoprotein B, Combined hyperlipoproteinemia, Dysbetalipoproteinemia, Dyslipidemia in hypothyroidism, Non-HDL cholesterol, Type III hyperlipoproteinemia