A newly released research paper by Valentina Moskvina, Ph.D., and associates from the Cardiff University School of Medicine in Wales, U.K. looked at both Alzheimer’s and Parkinson’s and did not find a common genetic link between them. This was a statistical meta analysis of a prodigious number of studies that examined the genetics and pathology of patients with Parkinson’s or Alzheimer’s. Data was analyzed three different ways and all three ways showed no genetic commonality.
Both diseases can appear to have some similarities, both being progressive neurodegenerative diseases with onset later in life and the development of dementia in later stages of the disease. The causes of these diseases are distinct, with Parkinson’s resulting from a lack of dopamine production in the substantia nigra causing a movement disorder. In Alzheimer’s, it is the hippocampus and the entorhinal cortex that are affected with the depletion of acetylcholine resulting in learning and memory difficulties. As the diseases progress, neurodegeneration progresses leading to dementia. However many people with Parkinson’s never experience dementia or memory problems whereas Alzheimer’s is the cause of most dementia and memory problems.
Some genetic studies have suggested there might be genetic connections between the two diseases and there have been reports of Alzheimer’s pathology in Parkinson’s patients and Parkinson’s in Alzheimer’s patients. Having one disease does not exclude the possibility of having the other, but does not mean that the two are connected. One of genome wide studies is finding new genes that are linked to either disease, and Dr. Moskvina has herself found new genes related to Alzheimer’s. This study has helped by showing that there is not a single gene that can give rise to either disease but there are some genetic regions that increase the risk for developing both diseases.
One important note about this study is that they did not include people with Lewy-Body Dementia, which shares some similarities with Alzheimer’s. The researchers also noted there is always a possibility that more refined methods for research on genetics might become available in the future that could still find a common basis for these diseases.
Valentina Moskvina et al. Analysis of Genome-Wide Association Studies of Alzheimer Disease and of Parkinson Disease to Determine If These 2 Diseases Share a Common Genetic Risk. JAMA Neurol., 2013 DOI:10.1001/jamaneurol.2013.448