A person lives an average of four to eight years after being diagnosed with Alzheimer’s, though it can be longer, depending on other factors. One may assume that if a sibling is diagnosed with the disease, they’d be more apt to die first, due to their condition. However, a new study finds that among twins, this may not be the case.
Research recently published in Alzheimer’s & Dementia: The Journal of the Alzheimer’s Association used data from the Swedish Twin Registry to compare the lifespans of a twin who is diagnosed with dementia, with their twin who is not. The findings showed that, especially for identical twins, their lifespans are about the same. Researchers say this suggests that genetics and environment – not just dementia – may contribute to earlier mortality.
The study’s first author Jung Yun Jang, who conducted the research as part of her doctoral studies in clinical science at the University of Southern California, says, “We expected a different result. We expected that, in twins where one developed dementia and the other did not, the difference in lifespan would be just like we see in unrelated people.
“We assumed the reason a person who has developed dementia has a shortened life expectancy is because the dementia leads to other medical conditions that affect mortality. What we’re seeing instead is the increased risk of mortality is not due to just the dementia itself, but also a whole package of other influences that the person brings to their disease.”
The study involved 90 pairs of identical twins, who share 100% of their genotype, and 288 pairs of fraternal twins, who share 50%. In each pair, one twin had dementia and the other didn’t. The research showed that among the identical twins, both experienced a similar shortening of their life expectancy. Among fraternal twins, this wasn’t quite as strong, but there was still a slightly shortened lifespan compared with people who didn’t have a sibling with the disease.
The researchers say their findings provide another hypothesis for mortality within dementia patients, that it may not be due to just the development of the disease. For example, genetics and a shared environment could give both twins serious health conditions, like cardiovascular disease, that increase dementia risk.
Margaret Gatz, study co-author who has done extensive aging and cognition research within the Swedish Twin Registry, explains, “What happens early in the life course is really important. You may not be able to change that for yourself, but it does seem like the message to parents is, make sure your kid eats healthy, make sure your kid gets exercise, make sure your kid gets an education. You’re actually contributing to giving that kid a lower chance of developing dementia 75 years later.”
You can read the whole study here.