We also examined how many of the enhancers in the reference brain are active (i.e., have enriched H3K27ac) in each of the individuals in our cohort. As expected, not every reference enhancer was active in each individual. On average, only ~70% ± 15% (~54,000) of the enhancers in the reference brain were active in an individual in the cohort, and a similar fraction of the reference enhancers was active in more than half the cohort (68%) (Fig. 3B). To estimate the total number of enhancers in the PFC, we calculated the cumulative number of active regions across the cohort (fig. S25). This increased for the first 20 individuals sampled but saturated at the 30th. Thus, we hypothesize that pooling PFC enhancers from ~30 individuals is sufficient to cover nearly all possible PFC enhancer regions, estimated at ~120,000.
