Three new, separate research studies suggest that a gene or genes on chromosome 10 may be risk factors for late onset Alzheimer’s disease (AD). The findings, reported in the December 22, 2000, issue of Science, are important new evidence that more than one gene may play a role in development of AD later in life.

For the past several years, a particular gene on chromosome 19 has been the only widely recognized genetic risk factor in late onset Alzheimer’s disease. Scientists have long suspected that more than one gene may be involved in increasing an individual’s risk of developing late onset AD. Some reports have shown evidence of a risk factor gene on a region of chromosome 12, and investigators worldwide have searched intensively for other genes, on other chromosomes, that might also play a role.

There are two types of AD -- early onset and late onset. In early onset AD, symptoms first appear before age 60. Some early onset disease runs in families and involves inherited mutations that are believed to be the actual cause of the disease. So far, three early onset genes with AD-causing mutations have been identified. Early onset AD is rare, about 5-10 percent of cases.

The findings reported December 22 concern late onset AD, the most common form of the disease, which develops in people 60 and older and is thought to be less likely to occur in families. Late onset AD may run in some families, but a gene may not be the absolute determinant of whether an individual will develop AD. Rather, the role of genes involved in late onset may be to modify the risk of developing AD by affecting factors involved in the formation of plaques and tangles or other AD-related pathologies in the brain.

Scientists hope that by identifying and understanding the function of risk factor genes, as well as possible non-genetic factors like severe head injury, estrogen use, or education that may influence the development of AD, treatments can be developed and the progression of the disease can be slowed or stopped. It is estimated that up to 4 million Americans currently suffer from AD.