NEW YORK (Reuters Health) - Environmental effects, rather than genetics, account for at least half of the variation in susceptibility to Alzheimer’s disease (AD) in old age, according to a report in the Annals of Neurology for February 2004, published online December 15.
Lead investigator Dr. Nancy L. Pedersen and colleagues suggest that “late-life interventions that help the individual to maintain cognitive status may help reduce the total population burden of Alzheimer morbidity before death.”
Most genetic linkages associated with AD were identified in early-onset AD cases based on disease prevalence, the authors note. But until now, the relative importance of genetic effects in very old age have not been quantified. Their strategy of evaluating incidence over a relatively short follow-up is likely to capture exposures relevant for new cases.
Therefore, Dr. Pedersen, at Karolinska Instututet in Stockholm and colleagues identified 662 pairs of twins age 50 and above documented in the Swedish Twin Registry. None was diagnose with AD at baseline. During an average follow-up of 5 years, AD was diagnosed in one or both members of 112 twin pairs.
AD developed in 26 of 265 monozygotic twin pairs, but in only five pairs were both members affected. Among the 397 dizygotic pairs, one member was affected in 42 pairs and both members in two. Thus, “heritability was discernibly lower” for those age 80 and above at baseline, the authors note. But they add that genetic factors for liability to AD are still considerable late in life.
They suggest that pertinent environmental factors may include “vitamin B12 deficits, drug-induced increments or decrements, recent head trauma, and other late-life exposures that are sufficient to reduce cognitive reserve past the threshold for clinical manifestation of the disease.”
“Our data cannot address whether any particular case is due to the environment or due to genes,” Dr. Pedersen told Reuters Health. “I suspect that both are important for most people.”
Even so, she believes that there are interventions that can slow or prevent the onset or severity. For instance, Dr. Pedersen added, “other work that we have done with the twins shows that those who have a more intellectually engaged lifestyle earlier in their lives are those who are at reduced risk of dementia later.”
“So not only should seniors be thinking about environmental changes, but also parents should be concerned about good health in their babies and young children,” she said. “Having a healthy brain as well as a healthy body requires attention to everything from nutrition to protection against toxins and trauma.”
Source: Ann Neurol 2004;55. [ Google search on this article ]
MeSH Headings:Biological Sciences: Biology: Genetics: Biological SciencesCopyright © 2002 Reuters Limited. All rights reserved. Republication or redistribution of Reuters content, including by framing or similar means, is expressly prohibited without the prior written consent of Reuters. Reuters shall not be liable for any errors or delays in the content, or for any actions taken in reliance thereon. Reuters and the Reuters sphere logo are registered trademarks and trademarks of the Reuters group of companies around the world.
