A group of chromosomal regions that could be linked to the onset of Alzheimer's and Parkinson's diseases have been discovered by researchers at Duke University Medical Center.

Until now, geneticists have been trying to identify individual genes that control the risk of developing the diseases. However, the age at which a person who is genetically predisposed to the diseases develops symptoms is just as important, according to Margaret Pericak-Vance, PhD, director of the Center for Human Genetics at Duke and principal investigator of the study.

"Risk is only one mode of genetic expression. Age at onset of disease can also be genetically influenced," said Pericak-Vance. "Understanding the regulation of onset will open new avenues of research that could one day make it possible to delay onset beyond an individual's normal lifespan."

Researchers conducted the first genomic screen to study age at onset in 449 families with multiple family members who had Alzheimer's disease and 174 families with multiple family members who had Parkinson's disease.

Age at onset of Alzheimer's disease is when the patient begins to suffer short-term memory loss or disorientation that interferes with activities of daily living. The average age at onset for patients in the study with Alzheimer's disease was 72.8 years and 60.1 years old for Parkinson's disease.

A significant number of patients with Alzheimer's disease developed signs of Parkinson's disease, including rigidity and gait abnormalities.

Researchers reported in the American Journal of Human Genetics they found that chromosome 10, believed to contain a risk gene for Alzheimer's disease, might contain an age at onset gene that affects both Alzheimer's and Parkinson's diseases. They also found strong evidence for an age at onset gene for Parkinson's disease on chromosome 1.

"We tested the hypothesis that in some cases the same gene controls onset in two distinct neurodegenerative disorders that share some common features: Alzheimer's disease and Parkinson's disease. We found evidence supporting this hypothesis on chromosome 10," said Pericak-Vance.

Other sources: Duke University Medical Center