Association at the CPS1 locus. Top: The red line indicates the strength of association (-log10(P value)) of SNP rs2216405to the chemical shifts. The strongest association can be observed with the NMR signals at δ = 3.599 ppm (P <4.5 × 10-14). Middle: The blue line gives the squared Spearman correlation coefficient (rs2) for MS determined glycine and the NMR signals. The highest correlation (rs2 = 0.21) can be observed as a sharp peak at δ = 3.599 ppm. Bottom: The plot shows the NMR spectra of two samples, where one was spiked with glycine (green spectral line). The inset shows a magnification of the spectral region around δ = 3.6 ppm. This experiment confirms that the signal intensities at δ = 3.599 ppm are indeed driven by glycine.