Cognitive impairment is a key disabling symptom of psychotic disorders, predictive of worse functional and social outcomes. However, it is often overlooked compared to the positive features such as hallucinations. During my PhD I will use longitudinal data analysis methods to characterise developmental pathways to cognitive impairments in psychosis. I will focus on epigenetic markers, which capture how biological and environmental exposures — such as inflammation, stress, and ageing — influence gene expression, and investigate whether they are associated with cognitive outcomes in people with psychosis. I will utilise diverse population-based cohort studies from across the lifespan.