I’ve recently published a paper with my Cambridge collaborators in the journal Genes, Brain and Behavior. There is a lot of research currently looking into the genetics of psychological disorders. But we now know that most result from a very complex interplay of multiple genetic and environmental factors, which makes traditional genetic approaches less useful than we might hope. One promising approach is to investigate the genetics of psychological endophenotypes—these are traits linked to a disorder, but which are likely to have a relatively simple relationship with genetic mechanisms. Basic visual functions seem to be ideal candidates for this sort of study, because in many cases we know a lot about the underlying physiology.
Other researchers have found that some people with schizophrenia have abnormal sensitivity to a whole host of visual stimuli. One class that keeps coming up is stimuli that vary slowly in luminance across space (‘low spatial frequency’) and are rapidly flickered or briefly flashed (‘high temporal frequency’). Some children with autism spectrum disorder also have abnormal sensitivity to these stimuli. In our study, we asked whether genetic differences among people with no history of psychological disorder could account for individual differences in visual sensitivity to low spatial frequency, high temporal frequency stimuli.
We found that they could. Most interestingly, the genomic region that best predicted visual sensitivity was one that has been associated previously with both schizophrenia and autism. The mutation with the strongest association was in a gene known as PDZK1, a binding protein that interacts with receptors known to regulate critical functions in the subcortical visual system. This starts to help us understand what might be happening when we find abnormal sensitivity in people with the disorders: Some of the same mutations that appear to convey risk for autism and schizophrenia also affect visual development. This may be through entirely different biological pathways—the PDZK1 protein has many different functions in many different parts of the body. So perhaps the association between visual abnormalities and psychological disorders boils down, at least partly, to shared genetic causes.