New Genetic Connections of Alzheimer's Disease Identified

Highlights

• In neurodegenerative conditions like Alzheimer's disease, there is the accumulation of neurofibrillary tangles (NFT) inside the neuron.
• The NFTs consist of abnormal Tau proteins which leads to cognitive decline in neurodegenerative conditions.
• A genetic variant within the protein tyrosine phosphatase receptor-type delta (PTPRD) gene that may contribute to the accumulation of NFT has been identified.

A new gene that is associated with susceptibility to a common form of brain pathology called Tau, has been discovered. Tau pathology is associated with cognitive decline in various neurodegenerative conditions.

Abnormal tau proteins accumulates in several different conditions, including Alzheimer's disease, certain forms of dementia and Parkinsonian syndromes as well as chronic traumatic encephalopathy that occurs with repeated head injuries.

While symptomatic treatments exist, there are currently no preventive therapies for cognitive decline.

Investigators at Rush University Medical Center and the Brigham and Women's Hospital in Boston have identified a genetic variant within the protein tyrosine phosphatase receptor-type delta (PTPRD) gene that leads the accumulation of neurofibrillary tangles.

In Alzhiemer's disease, the neurofibrillary tangles, which are insoluble twisted fibers, accumulate inside the neurons.

These tangles consist of abnormal tau proteins. The abnormal tau proteins leads to the collapse of a structure called a microtubule that otherwise helps transport nutrients and other important substances from one part of the nerve cell to another.

"Aging leads to the accumulation of many different pathologies in the brain," said co-principal investigator Dr. David Bennett who directs the Alzheimer Disease Center at Rush.

"One of the most common forms of pathology is the neurofibrillary tangle (NFT) that was at the center of our study," he said. "The NFT is thought to be more closely related to memory decline than other forms of aging-related pathologies, but there are still very few genes that have been implicated in the accumulation of this key feature of Alzheimer's disease and other brain diseases." Bennett added.

The investigators analyzed autopsies from 909 individuals participating in studies of aging based at Rush University, and assessed the human genome for evidence of a genetic variant that could affect NFT.

Lead author Dr. Lori Chibnik of Brigham and Women's Hospital said that "The variant that we discovered is common: most people have one or two copies of the version of the gene that is linked to accumulating more pathology as you get older. Interestingly, tangles can accumulate through several different mechanisms, and the variant that we discovered appears to affect more than one of these mechanisms."

Tau pathology is more closely connected to loss of brain function with advancing age and may be more impactful as a target. The advent of new techniques to measure Tau in the brains of living individuals with positron emission tomography offers a biomarker for therapies targeting Tau.

Dr. De Jager, co-principal investigator at Brigham and Women's Hospital notes, "This study is an important first step. However, the result needs further validation, and the mechanism by which the PTPRD gene and the variant that we have discovered contribute to the accumulation of NFT remains elusive. Other studies in mice and flies implicate PTPRD in memory dysfunction and worsening of Tau pathology, suggesting that altering the level of PTPRD activity could be helpful in reducing an individual's burden of Tau pathology."

Further evaluation of PTPRD is required as the field of neurodegeneration searches for robust novel targets for drug development.

The study is published in Molecular Psychiatry.

References

1. Amyloid Plaques and Neurofibrillary Tangles - (http://www.brightfocus.org/alzheimers/infographic/amyloid-plaques-and-neurofibrillary-tangles)
2. Lori Chibnik et al. PTPRD locus and limited pleiotropy with other neuropathologies. Molecular Psychiatry; (year) DOI: 10.1038/mp.2017.20

Source: Medindia