Serum vitamin B12 concentrations within reference values do not exclude functional vitamin B12 deficiency in PKU patients of various ages.

Unlabelled: Homocysteine (Hcy) and in particular methylmalonic acid (MMA) are considered reliable parameters for vitamin B(12) status in healthy individuals. Phenylketonuria (PKU) patients are at risk for functional vitamin B(12) deficiency based on their diet.

Objective: The aim of this study was to investigate the prevalence of functional vitamin B(12) deficiency in continuously treated PKU patients and the association of parameters of vitamin B(12) and metabolic control.