Motor Neurone Disease (MND) and schizophrenia have been shown to have a shared genetic origin by a Trinity College Dublin (TCD) led study that has wide implications for research into and treatment of the illnesses.
The research found many of the genes that are known to be associated with MND and schizophrenia are the same, implying a biological connection between what are currently considered very different conditions.
Although previous studies had identified likely genetic connections between schizophrenia and other neuropsychiatric illnesses like autism and bipolar affective disorder, this is first time a shared biological link has been identified with MND.
Earlier research in 2013 by a team led by Professor Orla Hardiman had noted that the families of those suffering from MND were also more likely to have had a family member die by suicide or have schizophrenia than those families where MND was not present.
This prompted the scientists to look in more detail for a biological link, in particular a genetic connection between MND and schizophrenia.
The researchers teamed up with other scientists at the University of Utrecht, Kings College London and the Project MinE and Psychiatric Genome Consortia.
Together they examined the genetic blueprints of 30,000 schizophrenia patients and 13,000 people with MND or ALS as it is also known.
The results, published in the journal Nature Communications, show an overlap of 14% in genetic susceptibility to the adult onset of MND and the development of schizophrenia.
The team says this does not mean that those with MND will develop schizophrenia, or vice versa - more that MND is not only a disorder of individual nerve cells, but a disorder of the way the nerve cells communicate either individually or over neural pathways and networks.
"So instead of thinking of ALS/MND as a degeneration of one cell at a time, and looking for a 'magic bullet' treatment that works, we should think about ALS/MND in the same way we think about schizophrenia," said Professor Orla Hardiman, Professor in Neurology at TCD and Consultant Neurologist at the National Neuroscience Centre at Beaumont Hospital.
"It is a problem of disruption in connectivity between different regions of the brain and we should look for drugs that help to stabilise the failing brain networks".
The team also says that the findings show that the divide between neurology and psychiatry is a false one.
"This study demonstrates the power of genetics in understanding the causes of diseases," said Dr Russell McLaughlin, Ussher Assistant Professor in Genome Analysis at TCD.
"While neurological and psychiatric conditions have very different characteristics and clinical presentations, our work has show that the biological pathways that lead to these diverse conditions have much in common."
The findings could have implications for future treatment of MND/ALS, suggesting drugs that focus exclusively on motor neurons may not be the right approach and that looking at drugs that impact the brain network might be better.
"We welcome these new findings and hoped this will be one step towards developing new drugs that will help to stabilise these brain networks and ultimately prevent the progression of MND in our families," said Aisling Farrell, CEO of the Irish Motor Neurone Disease Association.