PDE5A and snowflake vitreoretinal degeneration: PDE5 mRNA and protein are expressed in brain tissue of humans and experimentalanimals.30, , –33 Western blot detects PDE5 inboth meningeal and larger cerebral arteries of experimental rodents and humanparticipants34,35 and immunohistochemical labelling shows that PDE5 is present insmooth muscle cells of small arterial vessels.36 PDE5 activity in SVD has not been reported.