Interestingly, significantly lower mRNA expressions for eNOS and nNOS in the corpus cavernosum of Townes SCD mice was observed, which is consistent with a previous study showing that corpus cavernosum from eNOS- or both eNOS- and nNOS gene-deficient mice displays downregulation of PDE5 protein expression and activity [28]. Here, PDE5A is linked to Schnyder corneal dystrophy.