Fig. 1.

Uptake values of 10 amino acids competing for a common transporter (LAT1) at the blood–brain barrier were calculated from plasma amino acid profiles of a Mennonite boy drinking a standard infant MSUD formula. Samples were collected during the 22 months before the trial period. Uptake values are expressed as z-scores, where z = [(patient value − control mean)/control standard deviation]. Normal values, taken from 52 control subjects, lie between +2 and −2 (gray area). Averaged over long periods, brain uptake of most LAT1 substrates is low (right panel). Uptake values for BCAAs (left panel) are highly variable, reflecting the unstable BCAA homeostasis characteristic of classical MSUD.