Adults whose parents both developed Alzheimer's disease are more likely than the rest of the population to develop it too, say U.S. researchers.
The findings are the result of a study of 111 families in which both parents had been clinically diagnosed with Alzheimer's disease, the leading cause of dementia in the elderly.
Of the 297 children of these families who reached adulthood, 22.6 per cent developed Alzheimer's. That compares with an estimated six to 13 per cent of the general population who are expected to develop the disease.
Even the numbers the researchers saw may not be the whole story. That's because the risk of Alzheimer's increases with age and almost 80 per cent of the 240 unaffected individuals had not yet reached the age 70.
"Following these families as the offspring continue to age will provide increasingly informative data," said the researchers, who were led by Dr. Suman Jayadev, of the University of Washington, Seattle.
Of those among the 297 who had reached 70, 41.8 per cent had developed Alzheimer's.
The authors of the study, which is published in the Archives of Neurology, say their findings confirm that there's a strong genetic component to the disease -- something that's been suspected for a while.
"Because Alzheimer's disease is so common in the general population, it is not uncommon for both spouses to develop the disease. Offspring of two such affected individuals would presumably carry a higher burden of these Alzheimer's disease-associated genes."
Children with no history of the disease beyond their parents had an older age at onset (72 years) compared with those who had one parent with family history of the disease (60 years) or both parents with family history of the illness (57 years).
"The role of family history and the specific genes involved in this phenomenon require a better definition," the authors conclude.
