The combination of PENK, IGHG1, and GNAL was able to accurately classify 88% of HD mutation carriers and 100% of control individuals, and improved discriminatory performance (Fig. 3A, AUC = 0.98) beyond what was observed for any individual protein (Fig. 2A, PENK AUC = 0.94) or the combination of all 26 CSF proteins by sPLS-DA (Fig. 2F, AUC = 0.90). This evidence concerns the gene IGHG1 and Huntington disease.