Although both groups cannot be strictly compared to each other, because adults were healthy and fasting [28] and children had intellectual disability, one might hypothesize that age-related changes in the activity of the extracellular ALPL enzyme (OMIM *171760), which hydrolyzes PLP into PL, might underlie this observation, since it is known that plasma ALPL activities are higher in children than in adults [29,30]. This evidence concerns the gene ALPL and Intellectual disability.