Decreased serum ubiquinone-10 concentrations in phenylketonuria

Background: Ubiquinone-10 is a lipid with important metabolic functions that may be decreased in phenylketonuria (PKU) because patients with PKU consume diets restricted in natural proteins. Objective: We studied serum ubiquinone-10 concentrations in PKU patients. Design: This was a retrospective, transversal study in which we compared serum ubiquinone-10, plasma cholesterol, plasma tyrosine, and plasma phenylalanine concentrations in 43 PKU patients with concentrations in a reference population (n = 102). Serum ubiquinone, 10 concentrations were analyzed by HPLC with ultraviolet detection. Plasma tyrosine and phenylalanine were measured by ion-exchange chromatography. Results: Serum ubiquinone-10 concentrations in PKU patients were significantly lower than in the reference population (P < 0.01 for patients aged 1 mo to < 8 y and P < 0.00005 for patients aged 8-33 y). Moreover, 5 of 18 PKU patients (28%) in the younger age group and 10 of 23 (43%) in the older age group had serum ubiquinone-10 concentrations below the reference interval. Conclusions: Serum ubiquinone-10 deficiency appears to be related to the restricted diet of PKU patients. Because serum ubiquinone-10 plays a major antioxidant role in the protection of circulating lipoproteins, the correction of ubiquinone-10 concentrations should be considered in PKU patients. Further investigation seems advisable to elucidate whether the deficiency in serum ubiquinone-10 status is clinically significant.