To confirm the results of microarray analysis, four CpG sites located in the promoter regions (two CpGs from CST11 gene, one from PI3 gene and one from SLC43A3 gene) with differential methylation between patients with endometriosis and healthy women were selected for validation analysis by conventional bisulphite Sanger sequencing in an extended group of patients and controls from LS (n = 15) and MS phase (n = 14). Here, PI3 is linked to endometriosis.