In addition to CRMP2, Drp1, a large GTPase involved in mitochondrial fission [27], was hyperphosphorylated at Ser 616 in neurons from HD patients (Figure 2G,J) and this was most likely due to phosphorylation by Cdk-5 and GSK-3β [63,64,65]. Here, CRMP1 is linked to Huntington disease.