Increased expression of GUCY1A2 found in FXS NPCs may reduce cAMP signaling via the NO/cGMP-PDE2-pathway (Polito et al., 2013), which coincides with increased activity of Pde2a in Fmr1 KO mouse brain as well as with the observation that targeting Pde2a rescues adult Fmr1 KO mouse phenotype (Maurin et al., 2019). Here, FMR1 is linked to fragile X syndrome.