Plasma phenylalanine is associated with decreased serum ubiquinone-10 concentrations in phenylketonuria

Decreased serum ubiquinone-10 concentrations is a common condition in patie nts with phenylketonuria (PKU) under dietary treatment. Our aim was to inve stigate the implication of the metabolic abnormalities of PKU (low concentr ations of tyrosine and high concentrations of phenylalanine) and the effect of treatment with phenylalanine-restricted diets in decreased ubiquinone-1 0 concentrations in PKU patients. We studied 30 PKU patients (age range 5 m onths to 35 years; median age 7 years) under dietary treatment. Correlation between plasma tyrosine or phenylalanine and serum ubiquinone-10 concentra tions was investigated. Daily cholesterol intake was calculated from the da ta obtained through a dietary questionnaire. The index of dietary control ( IDC) was calculated as the average of the medians of plasma phenylalanine c oncentrations obtained every 6 months in the metabolic control of patients. Negative correlations were observed between serum ubiquinone and the IDC ( r=-0.46; p <0.01) in PKU patients. No correlation was observed between tyro sine or daily cholesterol intake and serum ubiquinone concentrations. After adjustment for daily cholesterol intake by multiple linear regression anal ysis, for each 113 units of increase in IDC values serum ubiquinone decreas ed 0.1 mu mol/L. According to our results, the main factor associated with the decreased serum ubiquinone concentrations was high plasma phenylalanine values. Although daily cholesterol intake seems to be associated with ubiq uinone concentrations, it may not be relevant if we take into account the l ow intake of cholesterol in treated PKU patients.