During the extraction of data, 13 articles were excluded, because they did not provide allele frequencies needed for OR calculation, the contents were lack of control, their contents mainly associated with cancer therapy, or they studied fewer CASP9 SPNs (eg. rs1052571, 2308941, 4645980), leaving 15 eligible articles [6]–[8], [10]–[21] including 17 data sets based on the search criteria (Fig. 1). Here, CASP9 is linked to cancer.