Study finds mental illness may have an unusual evolutionary basis
New Delhi, Oct 28: A new study has found that the common syndromes of severe mental illness, such as schizophrenia, bipolar disorder, dementia, obsessive-compulsive disorder, and addiction, may have an unusual evolutionary basis. The constant prevalence of mental illness across the history of the human species suggests a Darwinian paradox. Despite causing significant disease, there seems little impact on selection for fitness. Genetic variation that predisposes to psychiatric disease is seen across all populations and is quite common. Previous selection, over evolution, may produce a bias towards certain kinds of variation that may cause disease later in life. These mechanisms may protect against inflammation or infection when young, only to predispose towards disease when one is older. In the new study, researchers at the National Institute of Mental Health and Neurological Sciences (NIMHANS), Bengaluru, and Institute of Genomics at the University of Tartu, Estonia, explored these aspects through the genetic analysis of individuals from families who have multiple affected members, considering that the increased prevalence of illness in a particular family should point to even more extreme evidence of the risky alleles. The study compared the genetic sequences of exomes (the regions that are translated into proteins) from individuals in 80 such families and compared them against African and South Asian populations. They also looked for evidence of Neanderthal genes in the sample, as the persistence of these ancient genomes in modern humans seems to correspond to some traits as well as the risk of disease. “We observed evidence of selection in 74 genes, which were mainly involved in immunological and defence responses, including activation and regulation of interferon-gamma, cytokine and immune system, and different signalling pathways”, said Dr Ajai K. Pathak, one of the lead authors of the study. The study inferred that almost one-fourth, 20 out of the 74 putatively selected genes were implicated in the risks of illnesses such as schizophrenia, dementia, and Parkinson’s disease and general attributes such as intelligence and cognitive abilities. “There was also evidence of Neanderthal genes, but their variation and distribution were much the same in the south Indian population and did…
