Alzheimer’s Disease Runs In The Family

A new study, out of the University of Washington, has suggested that there is a strong genetic component to Alzheimer’s disease. The study found that an individuals chances of developing Alzheimer’s disease are almost three times greater if both parents have been diagnosed with the disease.

The study, known as the Conjugal Alzheimer’s Disease Study, was funded by the National Institute on Aging and the U.S. Department of Veterans Affairs, and involved follow-up of the 111 families in which both parents had been diagnosed with the disease.

Of the 297 children born to the parents, 67 (23 percent) had been diagnosed with Alzheimer’s disease by the conclusion of the study. In the 98 children who had reached the age of 70 years, 41 of them (42 percent) had been diagnosed with Alzheimer’s disease. In the general population just 14 percent of those over the age of 70 are thought to be living with Alzheimer’s disease. Around 31 percent of the children older than 60 years and 36 percent of those over 65 years had developed Alzheimer’s disease compared to just 8 percent and 11 percent in the general population respectively.

Graph of Alzheimer's incidence when both parents have disease

The researchers also looked at whether a wider family history of Alzheimer’s disease (eg grandparents diagnosed with the illness) played a role in an individuals chances of developing AD. Although a history of the disease in the extended family wasn’t correlated with AD risk, it did appear to influence the age at disease onset. When there was no history of the disease on either side of the family (beyond the parents), the median age at onset was 72 years compared to just 57 years for individuals with a positive history of the disease on both sides of the family.

The genetic component to Alzheimer’s disease has yet to be understood fully. Currently only one gene, called ApoE, has been definitively linked to increased Alzheimer’s disease risk however it is likely that many more such genes exist. Those who have a particular form of the ApoE gene, called E4, are thought to be at increased risk of atherosclerosis, Alzheimer’s disease, and reduced growth of axons and dendrites in the brain (a lack of neuroplasticity). Studies have found that the presence of two E4 alleles results in around a 20-fold increased risk of developing Alzheimer’s disease by age 75 compared to individuals with no E4 alleles.

According to Dr. Thomas Bird, who is the director of the Genetics Core of the University of Washington Disease Research Center and senior author of the study, “I think it confirms that there’s a strong genetic component in the disease and that’s not a surprise.”

The study appears in the March edition of the journal, Archives of Neurolgy.