Researchers have identified a genetic variation that increases a person’s risk for both Alzheimer’s and Parkinson’s. The finding implicates a family of proteins called “tau” as the likely contributor to both diseases.

Michael O’Donovan, Ph.D., a psychiatric geneticist at Cardiff University School of Medicine in the United Kingdom and recipient of the Foundation’s Lieber Prize for Schizophrenia Research in 2012, was a member of the large international team* of scientists that carried out the analysis. The work was published February 17th in the journal Molecular Psychiatry.

Alzheimer’s disease and Parkinson’s disease are distinct neurodegenerative disorders, but there is evidence that their biological causes may overlap. To uncover factors that contribute to the development of both diseases, Dr. O’Donovan and his collaborators conducted a detailed analysis of data from previous genetic studies.

These studies examined the genomes of nearly 90,000 individuals, searching for genetic variations that were linked with either Alzheimer’s or Parkinson’s. Eight genetic variations were more common among people with Parkinson’s disease than they were among people who don’t have the disease. The team found that one of these eight genetic variations was also more common among people with Alzheimer’s disease than it was in unaffected individuals.

The genetic variation the team identified affects a single letter in the genetic code, in a region spanning a gene called microtubule-associated protein tau (MAPT). The MAPT gene encodes the set of proteins called tau. Healthy neurons need tau to function properly, but these proteins have also been found in toxic tangles of nerve cells that have been seen in patients with Alzheimer’s disease. The nerve cell tangles are considered a hallmark of the disease, but it has not been clear whether they cause neurodegeneration or are merely associated with it. Abnormal accumulation of tau proteins is also linked with other forms of dementia, and genetic data have suggested that misregulation of tau proteins may contribute to the development of Parkinson’s disease.

According to the scientists, the MAPT gene’s association with both Alzheimer’s and Parkinson’s diseases suggest similarities in how the two disorders develop and indicate that tau’s role in Alzheimer’s disease should be studied more closely.

* Other former NARSAD grantees involved in this research:

Yanyan Wang, Ph.D.: 1994, 1998 Young Investigator (YI)

Julie A. Williams, Ph.D.: 2007 YI

Michael J. Owens, M.D., Ph.D.: 1990 YI, 2000 Independent Investigator

Alicia K. Smith, Ph.D.: 2012 YI

Read the abstract.