HDAC9 and Schnyder corneal dystrophy: HDAC mRNA expression (including Class I and Class IIa HDACs and known targets for VPA such as HDAC2, 4 and 7) was increased in the mucosa overlying SCD compared to NSCD intestinal segments [n = 6].9,17 In addition, collagen gene expression was significantly increased in SCD compared to NSCD mucosa [Table 1].