Long-term treatment for hyperphenylalaninemia and phenylketonuria: a risk for nutritional vitamin B12 deficiency?

PURPOSE: The objective of the study was to determine the incidence of vitamin B12 deficiency in patients under long-term treatment for phenylketonuria (PKU) and hyperphenylalaninemia (HPA), as well as its associations with B12 vitamin parameters (holotranscobalamin - active vitamin B12, serum folate, total plasma homocysteine, and plasma methylmalonic acid concentration).

PATIENTS AND METHODS: The group consisted of 51 PKU (n=29) and HPA (n=22) patients aged 3-48 years (28 children, 23 adults).

RESULTS: A significant difference in serum folate levels was discovered between adult HPA patients and PKU patients (p=0.004, Mann-Whitney U-test). A significant difference in plasma homocysteine concentrations within the normal levels (p=0.032, χ2-test) was detected between adult HPA and PKU patients. In the group of adults, we also found significant differences in serum holotranscobalamin concentrations regarding both concentration levels and the proportion of patients with concentrations within the normal levels (p=0.031, Mann-Whitney U-test; p=0.006, χ2-test).

CONCLUSION: We have proven that adult patients with PKU and HPA are at risk of vitamin B12 nutritional deficiency. The most effective parameter for these adults is the monitoring of holotranscobalamin in the serum.