MMP9 and Dravet syndrome: DS patients had an increased gene expression of MMP9, which might be relative with the lower level of average methylation in exon 4, near the promoter region of the MMP9. Notably, DNA methylation of individual CpG sites showed negative correlations with clinical symptoms such as the social amotivation factor of SANS and negative syndromes of BPRS in DS patients, but not in NDS patients.