Viruses lying dormant inside the human genome may “reawaken” to cause motor neuron disease, according to new research published in the journal Science Translational Medicine.
The study also raises the possibility that antiretroviral therapy might be useful in some form of treatment.
The study found that the genome of the Human endogenous retrovirus called HERV-K, was abnormally activated in the brains of deceased Lou Gehrig’s disease patients.
The work follows on from a 2011 study when, Avindra Nath and his colleagues found that proteins synthesized by HERV-K were concentrated in the brains of patients with the disease.
But there are still questions to be answered.
“Perhaps most fundamental is the proverbial chicken and egg challenge: Is the activation of HERV-K a cause or a consequence of motor neuron degeneration? In this context, the most compelling aspect of their transgenic mouse work is the finding that elevated expression of the HERV-K env protein is directly pathogenic to motor neurons,” an accompanying analysis in the journal said.
Humans have for generations been passing on genetic remnants of HERV infections that may have happened millions of years ago. Although nearly 8% of the normal human genome is made up of these genes, very little is known about their role in health and disease.
“People call the genes for these viruses junk DNA. Our results suggest they may become activated during ALS,” said Nath, clinical director at the NIH’s National Institute of Neurological Disorders and Stroke and a senior author of the study.
“Ultimately we hope the results will lead to effective treatments for a heartbreaking disorder.”
Lou Gehrig’s disease, or amyotrophic lateral sclerosis (ALS), is a progressive and fatal neurodegenerative disease which destroys the motor neurons that control speech, movement, swallowing and breathing.
On rare occasions, HIV-infected, AIDS patients develop ALS-like symptoms. In many of these patients, the symptoms can be reversed by treatment with antiretroviral drugs.
Previous studies found reverse transcriptase, a protein encoded by retroviral genes, in the blood of some ALS patients but its role in the disorder is unknown.
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