GPCPD1 and Huntington disease: Finally, in comparison to the HCs, pyridoxal kinase (PDXK) activity was decreased in the striatum and cortex [22], glycogen synthase kinase-3β (GSK-3β) activity increased in the hippocampus [23], glycerophosphocholine phosphodiesterase 1 (GPCPD1) expression was decreased in the cortex and striatum [24], and uric acid concentrations were decreased in the prefrontal cortex of HD patients [25].