GPCPD1 and Huntington disease: Given that altered levels of choline metabolism metabolites have been demonstrated in the plasma of HD (Cheng et al., 2016), we examined the gene expression of enzymes involved in the choline metabolism pathway (Figure 7) including Gpcpd1, Chka, Chkb, Ppap2a, Pld1, and Chpt1, in the brains of R6/2 transgenic HD mice.