More and more evidence suggests a link between mental and physical conditions such as ADHD and obesity (Cortese et al., 2016), eating disorder and inflammatory bowel disease (Larsen et al., 2018). Similar to the g-factor and p-factor (Caspi et al., 2015), Our team at University of Southampton has hypothesised one general disease factor (d-factor; Cortese et a., 2021) that summarises individual’s propensity to both mental and physical disorders, and accounts for the comorbidity between mental and physical conditions. We have been testing this hypothesis using two longitudinal datasets: the millennium cohort study and the 1970 British Cohort Study. We found that from adolescence to adulthood, association between mental and physical conditions strengthen gradually, and that there is indeed a general d-factor that explains individual propensity to develop comorbid mental and physical conditions. We would like to (1) test the hypothesis of d factor longitudinally from childhood to early adulthood, (2) examine the genetic and epi-genetic foundation of the general disease factor, and (3) investigate environmental risk factors related to higher d-factor scores.