Controlled diet in phenylketonuria may cause serum carnitine deficiency.

Serum carnitine levels may be reduced in patients with phenylketonuria (PKU) owing to low carnitine intake, deficient carnitine synthesis and acylcarnitine production from phenylalanine metabolites. In order to investigate the possible carnitine deficiency we determined serum carnitine in its different forms and the precursors and cofactors involved in its synthesis in a group of patients with PKU or hyperphenylalaninaemia. Free, total and acylcarnitine values were significatively reduced only in PKU patients with Phe-restricted diet which had not been supplemented with carnitine. Acylcarnitine/free carnitine ratio and all the other parameters studied were normal in all patients. We conclude that the low serum carnitine levels in PKU patients with a strict diet are a consequence of the low carnitine intake.