Heightened penile erection and increased relaxation of the corpus cavernosum smooth muscle are linked to decreased PDE5 protein expression in penile tissue from SCD mice (Champion et al., 2005; Bivalacqua et al., 2013; Silva et al., 2016a; Silva et al., 2016b; Musicki et al., 2018; Musicki et al., 2021; Pinheiro et al., 2022). The gene discussed is PDE5A; the disease is Schnyder corneal dystrophy.