Since, about 28 miRNAs can target the CYP2C19 gene, we believe that during the disease status in children with epilepsy, or during treatment with phenobarbital, one or multiple miRNA may be involved, along with the regulation of the CYP2C19 gene, which in turn up-regulates or down regulates the genes and also changes the genetic variations of the gene. The gene discussed is CYP2C19; the disease is epilepsy.