DNA methylation is one of the risk factors that impact the mRNA level of genes, we analyzed the association between DNA methylation and mRNA expression for MMPs, and found that the DNA methylation level of MMP2, MMP7, MMP9, MMP14, MMP15, MMP19, MMP21, MMP23B, MMP24, MMP25 and MMP28 could impact its mRNA level in PCa (all, P<0.05) (Figure 1B). The gene discussed is MMP21; the disease is posterior cortical atrophy.