Prior to the analyses NMR was transformed using rank transformation to obtain a normal distribution. The transformation was employed with the rntransform() function available in the R statistical software package GenABEL [42], which replaces the median NMR value with the value zero and transforms the rest of the values so that they are N(0,1)-normally distributed around this value. NMR distributions before and after the transformation are shown in S1 Fig.
