GUCY2C and Parkinson disease: Overexpression of Gucy2c mRNA in PD patients and mice treated with MPTP mirrors our findings in SNpc isolated from Gucy2c−/− mice (Fig. 4g), which were generated by inserting a neomycin cassette into exon 1 of the Gucy2c gene, allowing expression of Gucy2c mRNA, but not GUCY2C protein42.