Do Ancient Viruses Trigger Motor Neuron Disease?
Late last month (September 2015) researchers from the National Institute of Health, USA, announced a potentially remarkable discovery. Preliminary research suggests that dormant genes from fossil viruses buried in our DNA might be partially to blame for motor neuron disease. If true this is a finding with the potential to revolutionise our understanding and treatment of this terrible condition.
It’s estimated that an average of 8% of the human genome comes from viruses. The theory is that over evolutionary time some viruses have infiltrated our genetic code, becoming harmless hitchhikers that merely add to our own surplus ‘junk’ DNA. These dormant passengers are called Human Endogenous Retroviruses (HERVs) and recently there has been a surge in research interest implicating them in everything from diabetes to schizophrenia. Its a controversial subject and so far no known human disease has been definitively linked to a HERV, but that might be about to change.
The new research focused on patients suffering from amyotrophic lateral sclerosis (ALS), a degenerative neurological condition that causes difficulty walking, swallowing and breathing. The team took brain samples from ALS patients as well as from healthy brains and from sufferers of Alzheimer’s for comparison. What they discovered was elevated levels of mRNA coded for by a specific HERV called HERV-K, as well as high levels of an associated protein called Env in the brain of ALS patients. Both findings were absent from the other two sample groups. This suggested to the researchers that HERV-K was actually active and producing proteins in the ALS sufferers.
Given the potential importance of this discovery the team decided to follow it up in the lab. By genetically engineering mice to active the HERV-K gene the researchers were able to artificially elevate the amount of Env being produced by the mice. What they found was that these mice died far earlier then normal and developed ALS-like symptoms as they aged. Autopsies later revealed damage to the motor neurons similar to that observed in ALS patients. While not conclusive proof this did further suggest a potential link between HERV-K and ALS.
Any conclusions drawn from this research are merely tentative and we should be cautious about assigning too much significance to the findings. Until another team replicates the results and further tests can be carried out these apparent correlations could be nothing more then coincidental. However, if HERV-K really is responsible, at least in part, for the development of ALS then it suggests that this disease might be treatable using anti-viral therapies similar to those used for AIDS patients. This would offer a much needed medical solution for a previously incurable disease.
Reference: Li, W., et al. 2015. Human endogenous retrovirus-K contributes to motor neuron disease. Science Translational Medicine. 7(307). DOI: 10.1126/scitranslmed.aac8201
Featured Image: Courtesy of Nath lab, NINDS, NIH, Bethesda, MD