CASP3 and Huntington disease: When relating the 2-methylbutyric acid to 181 CV-specific proteins one by one in HD patients controlling age and sex, the circulating 2-methylbutyric acid level was negatively associated with five proteins (kidney injury molecule 1, C-C motif chemokine 17, pulmonary surfactant-associated protein D, N-terminal prohormone brain natriuretic peptide, and bone morphogenetic protein 6 [BMP-6]) and positively associated with two proteins (serine/threonine-protein kinase 4 and caspase-3) (Figure 2A–C and Supplementary Table S2).