The study is designed to give five groups of eight individuals each different doses of omega-3 adjusted to body surface area. The first group starts out on a dose of omega-3 fatty acids that is similar to the generally recommended daily intake for adults (200-400 mg). A dose escalation is then done performed group wise. The highest possible dose in this study (2 x 3000mg/day at dose level 3000 mg/m2 to a child at 1.55 m2, 3871 mg/m2) is still lower than what has previously been given as maximum to children in other studies. The investigators will keep escalating the dose level within the study only as long as no unacceptable side effects are reported.