Interactions between apolipoprotein E and apolipoprotein(a) in patients with late-onset Alzheimer disease

Background: Apolipoprotein(a) [apo(a)], the distinctive, highly polymorphic glycoprotein of lipoprotein(a), shares a series of common features with apolipoprotein E (apoE), which is implicated in the development of Alzheimer disease. Objective: To determine whether apo(a) is associated with Alzheimer disease. Design: Case-control study. Setting: University hospitals in Europe. Participants: 285 patients with Alzheimer disease and 296 controls. Measurements: Plasma lipoprotein(a) levels, size of the apo(a) isoforms, and apoE and apo(a) genotyping. Results: Among carriers of the apoE epsilon 4 allele, lipoprotein(a) was associated with a progressive, age-dependent increased risk for late-onset Alzheimer disease (odds ratio for patients >80 years of age, 6.0 [95% CI, 1.2 to 30.8]; P < 0.01). Among noncarriers older than 80 years of age, lipoprotein(a) was associated with a reduced risk for Alzheimer disease (odds ratio, 0.4 [CI, 0.2 to 0.9]; P < 0.05). Conclusions: In this convenience sample, lipoprotein(a) was an additional risk factor for late-onset Alzheimer disease in carriers of the apoE epsilon 4 allele. However, lipoprotein(a) may protect against late-onset Alzheimer disease in noncarriers.