Inadequate iron availability as a possible cause of low serum carnitine concentrations in patients with phenylketonuria

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Abstract
A previous observation of decreased serum carnitine concentrations in phenylketonuria (PKU) was investigated in 169 patients either on a strict diet (n=107; median: 8.1 years) or off diet (n=62; median: 15.0 years). Fifty-seven metabolically healthy children (median: 8.5 years) served as controls. PKU patients on a strict diet and older than 2 years had significantly lower serum carnitine concentrations (19.4±5.4 μmol/l) than those off diet (29.6±6.7 μmol/l). PKU patients on diet also had significantly lower concentrations of haemoglobin and serum ferritin than those off diet. A linear correlation existed between total serum carnitine and ferritin concentrations up to 40 μg/l (r=0.52;P<0.01). As iron is an essential cofactor of carnitine synthesis we conclude that reduced endogenous carnitine synthesis due to an inadequate availability of iron may be a major cause of low serum carnitine concentrations. The low carnitine content of the strict and highly protein-reduced diet additionally contributes to a decrease in the serum carnitine concentration. Our results show that a further optimization of the PKU diet increasing either iron availability or carnitine intake should be considered.