Quantitative Requirements of Docosahexaenoic Acid for Neural Function in Children With Phenylketonuria

Patients with phenylketonuria (PKU) have an inborn error in the metabolism of the amino acid phenylalanine (Phe) and thus must follow a strictly controlled protein-restricted diet from early infancy. This protein-restricted diet is devoid of natural dietary sources of n-3 long chain polyunsaturated fatty acids (LC-PUFA), such as eggs, meat, milk or fish. Therefore, blood concentrations of n-3 LC-PUFA, especially of docosahexaenoic acid (DHA) are reduced in PKU children compared to healthy controls. DHA availability is considered important for optimal neurological function. Previous studies have shown that neural function of PKU children is improved by high dose supplementation of fish oil providing DHA, as shown by significant improvements of both visual evoked potential latencies and of fine motor skills and coordination, but no dose response relationship has been established so far.

This multicentric double-blind randomized trial aims at determining quantitative DHA requirements for optimal neural function in PKU children. Patients with classical PKU from several major treatment centers in Europe will be randomized to receive between 0 and 8 mg of DHA per kg body weight daily for a duration of 6 months. Biochemical (fatty acid composition of plasma phospholipids, lipoprotein metabolism and metabolic profiles), and functional testing (visual evoked potentials, fine motor skills, cognitive function and markers of immune function) will be performed at baseline and after 6 months. Intake per kg body weight will be related to outcome parameters and thus a possible dose response relationship will be defined. The results from this study are expected to contribute to the improvement of the diet of PKU patients, but they also have the potential to help defining quantitative DHA needs of healthy children.

The primary hypothesis is that supplementation with DHA improves visual function in children with PKU.