THE EFFECTS OF THE APOLIPOPROTEIN-B SIGNAL PEPTIDE (INS DEL) AND XBAIPOLYMORPHISMS ON PLASMA-LIPID RESPONSES TO DIETARY CHANGE/

There is interindividual variation in plasma lipid response to dietary changes. The polymorphisms which are associated with plasma lipid lev els could possibly explain part of this variation. Therefore, the apol ipoprotein B (apo B) signal peptide insertion/deletion (ins/del) and X baI restriction fragment length polymorphisms are possible regulators of plasma lipid responses. We examined their role in the regulation of plasma lipid responses in 87 North Karelians (43 men, 44 women). The dietary study consisted of a 2-week baseline period (34-35% of energy from fat), followed by an 8-week low-fat (24 En%), low-cholesterol (27 9 mg/d) diet period and an 8-week switchback period. In this study pop ulation the apo B ins/del and XbaI polymorphisms exhibited mainly simi lar and partly significant effects on the responses of plasma very low -density lipoprotein (VLDL) and high density lipoprotein(2) (HDL(2)) c holesterol to dietary changes. After consumption of the low saturated fat, low-cholesterol diet, ins/ins and X-/X- homozygotes showed the gr eatest increase in VLDL cholesterol (p < 0.05 for differences between ins/del genotypes) and the greatest fall in HDL(2) cholesterol (p = 0. 01 for ins/del and p = 0.05 for XbaI), while only minimal alterations were seen in the del/del and X+/X+ groups. After returning to the orig inal diet, the changes of these lipids were reversed, ins/ins and X-/X - homozygotes having the greatest reductions in VLDL cholesterol (p < 0.05 for XbaI) and the greatest increases in HLDL(2) cholesterol (p < 0.001 for XbaI). The findings suggest that plasma VLDL and HDL(2) chol esterol responsiveness to diet may be partly explained by variation at the apo B gene.