Study Finds Half of Susceptibility to Alzheimer's Due to Environmental Factors

A study of twins in Sweden has found that at least half of people's susceptibility to Alzheimer's disease can be attributed to factors other than genes.

As reported in the December 15 on-line edition of Annals of Neurology, researcher Nancy Pedersen, of the Karolinska Institute in Stockholm, and her colleagues studied 662 pairs of twins between the ages of 52 and 98 years. Over five years, 5.8 percent of the study participants were diagnosed with Alzheimer's.

Of the identical twins where one of the siblings developed Alzheimer's, the other twin also developed the disease in 32.2 percent of the cases. Among the nonidentical twins, this figure was only 8.7 percent.

The researchers calculated that half or more of the susceptibility to Alzheimer's disease in later life is attributable to environmental causes.

Several earlier twin studies suggested that even among late-onset cases of Alzheimer's, the contribution of genes was higher than that of the environment, perhaps as high as 75 percent. But these studies were not set up to specifically look at very old people.

Other sources: Annals of Neurology