Alzheimer Disease, Apolipoprotein E, and Apolipoprotein(a)

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The summary below is from the full report titled "Interactions between Apolipoprotein E and Apolipoprotein(a) in Patients with Late-Onset Alzheimer Disease.". It is in the 4 April 2000 issue of Annals of Internal Medicine (volume 132, pages 533-537). The authors are V. Mooser, N. Helbecque, J. Miklossy, S.M. Marcovina, P. Nicod, and P. Amouyel.

What is the problem and what is known about it so far?

Alzheimer disease is a medical condition in which abnormal substances build up in the brain, causing brain cells to gradually degenerate. As the brain tissue shrinks, patients experience a loss of mental abilities known as dementia. Apolipoproteins help transport fatty substances, or lipids, in the blood. Apolipoproteins and lipids form large particles called lipoproteins. There are several types of apolipoproteins. One particular apolipoprotein, apolipoprotein E (apoE) is thought to have something to do with Alzheimer disease. That is, people who carry a gene for a certain form of apoE (E4 isoform) may be more likely to develop Alzheimer disease. However, many people with apoE E4 never develop Alzheimer disease. Another apolipoprotein, apolipoprotein(a) [apo(a)], shares many common features with apoE, but its function in humans is unknown. However, because it resembles apoE so closely, experts believe it might also have some role in Alzheimer disease.

Why did the researchers do this particular study?

The researchers wanted to find out if apo(a) is associated with Alzheimer disease.

Who was studied?

From teaching hospitals in Europe, 285 people with Alzheimer disease (patients) and 296 nursing home residents older than 60 years of age who had normal mental abilities (controls or comparison group) were recruited into the study.

How was the study done?

The researchers collected blood samples from the patients and the controls. They measured apo(a) and apoE levels and performed special tests to determine which apolipoprotein genes each patient had.

What did the researchers find?

In people who carried the gene for apoE E4, increased levels of apo(a) in the blood were associated with Alzheimer disease. However, in people who did not carry the apoE E4 gene, increased apo(a) levels were actually associated with a reduced risk for Alzheimer disease.

What were the limitations of the study?

This was a relatively small study done in a relatively narrow geographic area of Europe. All of the patients were white. These findings might not apply to other populations. In addition, it is possible that factors other than the apolipoproteins really accounted for Alzheimer disease.

What are the implications of the study?

Apo(a) might be another factor contributing to the development of Alzheimer disease. Further research is needed to see whether the association is real and whether these findings might help us understand or treat Alzheimer disease.