Lp(a) better predicts CHD than apo(a) isoform size in men
MedWire News: Elevated levels of lipoprotein (Lp)(a) are significantly and independently associated with coronary heart disease (CHD) risk in men, say US researchers.
However, apolipoprotein (apo)(a) isoform size - which has previously been shown to be inversely correlated with levels of Lp(a) - does not contribute to this association, and the cholesterol content in Lp(a) does not add significant information about CHD risk, reports the team.
Stefania Lamon-Fava, from Tufts University in Boston, Massachusetts, and colleagues measured plasma Lp(a), Lp(a) cholesterol levels, and apo(a) isoform size in 1328 men and 1562 women from the 5th examination cycle of the Framingham Offspring Study (1991-1995).
Two different immunoassays were used to measure Lp(a) levels: the Northwest Lipid Metabolism and Diabetes Research Laboratories (NWRL) assay and an assay from Wako Chemicals USA (Wako).
Over a mean follow-up period of 13.3 years, the team observed nearly 150 CHD events; 98 in men and 47 in women.
In men, median plasma Lp(a) levels were approximately two-fold higher in CHD cases than in control patients, at 36.3 nmol/l (NWRL) and 20.6 mg/dl (Wako) versus 18.1 nmol/l and 10.8 mg/dl, respectively.
Furthermore, when male participants were divided according to tertiles of plasma Lp(a) levels, the risk for incident CHD was nearly 2.5-fold greater for men in the upper tertile of Lp(a) levels (39.4-469.4 nmol/l [NWRL] or 20.7-145.8 mg/dl [Wako]) compared with those in the lower tertile (0.6-8.1 nmol/l [NWRL] or 0.2-8.1 nmol/l [Wako]), and this remained significant when apo(a) isoform size was added to the model.
Men in the lowest tertile of apo(a) isoform size had a 1.6-fold greater risk for incident CHD than those in the highest tertile. However, Lamon-Fava et al report that the strength of this association was lower than that observed for Lp(a) levels, and the significance was abolished after adjustment for plasma Lp(a) levels.
This indicates that plasma Lp(a) levels are more informative than apo(a) isoform size in risk prediction, writes the team in the Journal of Lipid Research.
No significant associations were observed between the cholesterol content in Lp(a) and CHD risk in men.
In women, none of the variables assessed showed a significant association with CHD risk, but the researchers say this may be because of the low event rate in the Framingham Offspring Study.
The authors conclude that while their study confirms a causative link between elevated Lp(a) and CHD in men, the mechanism responsible for the atherogenicity of Lp(a) remains unclear.
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By Nikki Withers