EWAS of motor progression in manifest HD cases exhibits significant (p < 10−7) associations with methylation levels at three loci: near PEX14 (p = 9.3 × 10−9), GRIK4 (p = 3.0 × 10−8), and COX4I2 (p = 6.5 × 10−8). This evidence concerns the gene GRIK4 and Huntington disease.