Furthermore, a research study conducted an integrative analysis of genome-wide association study (GWAS) and brain region-related enhancer maps showed that insomnia associated genes (MADD, CASP9, PPP2R3C and, PLEKHM2) were significantly enriched in neural stem cells, highlighting a set of potential points which suggests that neural stem cells may contribute to insomnia via regulating the generation of sleep-waking switch-related neurons. Here, CASP9 is linked to insomnia.