ACO2 and Huntington disease: Aco2 activity of PBMC was significantly reduced in both HD patients (p < 0.001, 6.3 ± 0.3 mU/mg protein) and PreHD carriers (p < 0.05, 7.2 ± 0.2 mU/mg protein) compared with the controls (9.8 ± 0.4 mU/mg protein) (Figure 5B).