* Clinical data in Column 1 are % changes in blood levels of metabolites averaged over 42 Down patients compared to 38 control patients . Columns 2 and 3 show % changes in model values. In columns 2 and 3, bCys and bGSH indicate model blood concentrations, and the other metabolites are intracellular. Column 2 shows the effect of increasing the dosage of CBS by a factor of 1.5. Column 3 shows the effect of increased CBS combined with moderate oxidative stress. For discussion, see the text.