Retrotransposons are movable genetic elements that are found throughout the genome. Insertion of new retrotransposon copies in or near genes could be involved in disease pathogenesis. Now, Miki Bundo and colleagues have identified a high copy number of the retrotransposon L1 specifically in neurons within the postmortem prefrontal cortex from individuals with schizophrenia compared to normal controls and other psychiatric diseases (Neuron doi:10.1016/j.neuron.2013.10.053, 2 January 2014). Using whole-genome sequencing of brain DNA from the patients with schizophrenia versus control subjects, the authors found that L1 insertions sites in individuals with schizophrenia often occur in or near genes linked to neuronal and synaptic function.

Mechanistically, maternal immune activation in pregnant mice with the immunostimulant poly-I:C led to increased L1 copy number in the offspring. The findings suggest how early environmental risk factors, which have been previously linked to increased disease risk, could drive genetic changes that contribute to the pathogenesis of schizophrenia or other illnesses.