Apolipoprotein (a) phenotypes and lipoprotein (a) concentrations in patients with type III hyperlipoproteinaemia

Genetic and Mechanistic Insights into the Modulation of Circulating Lipoprotein (a) Concentration by Apolipoprotein E Isoforms

PURPOSE OF REVIEW

Lipoprotein (a) [Lp(a)] is a highly atherogenic lipoprotein species. A unique feature of Lp(a) is the strong genetic determination of its concentration. The LPA gene is responsible for up to 90% of the variance in Lp(a), but other genes also have an impact.

RECENT FINDINGS

Genome-wide associations studies indicate that the APOE gene, encoding apolipoprotein E (apoE), is the second most important locus modulating Lp(a) concentrations. Population studies clearly show that carriers of the apoE2 variant (ε2) display reduced Lp(a) levels, the lowest concentrations being observed in ε2/ε2 homozygotes. This genotype can lead predisposed adults to develop dysbetalipoproteinemia, a lipid disorder characterized by sharp elevations in cholesterol and triglycerides. However, dysbetalipoproteinemia does not significantly modulate circulating Lp(a). Mechanistically, apoE appears to impair the production but not the catabolism of Lp(a). These observations underline the complexity of Lp(a) metabolism and provide key insights into the pathways governing Lp(a) synthesis and secretion.

Prevalence and association of atherosclerosis at three different arterial sites in patients with type III hyperlipoproteinemia

We have examined the prevalence of clinically significant atherosclerosis in 78 patients with type III hyperlipoproteinemia (HLP) and homozygosity for apolipoprotein (apo) E2. Forty-six of these individuals (59%) had no atherosclerosis, 32 patients (41%) had atherosclerosis, i.e., atherosclerosis of the extracranial carotid arteries (CAA), coronary arteries (CAD) or/and peripheral arteries of the legs (PVD), either singly or in combination. No association could be shown with respect to the co-prevalence of atherosclerotic lesions at these different arterial sites, except for the high predictive value (pv = 0.88, P = 0.006) of CAA for the presence of PVD. Hence, documentation of atherosclerosis under clinical aspects at one of these exposed arterial territories does not allow a reliable prediction of generalised atherosclerosis or local atherosclerosis at other sites of the arterial tree in individuals with this familial lipoprotein disorder. Therefore, assessment of the extent of clinically significant atherosclerosis in type III HLP patients should include careful and thorough examination of the extracranial carotid arteries, the coronary arteries, and the peripheral arteries of the legs.