G6PC1 and Glycogen storage disease due to glycogenin deficiency: For a subset of 9 of the 19 SNPs that affect AAs conserved in mouse and human G6PC1, mutation of these AAs in human G6PC1 has been shown to cause glycogen storage disease type 1a (GSD1a) (26), directly demonstrating that they are functionally important (Fig. 2; Table 1).