Six studies [7, 13, 15, 18, 20, 22] compared the serum level of PTH (Table 3) and the combined SMD was 0.18 (95% CI: − 0.20 to 0.43; z = 0.94, P = 0.36), showing that valproic acid did not affect the level of serum PTH in children with epilepsy (Fig. 3b). This evidence concerns the gene PTH and epilepsy.