RCT trial of diet treatment for adults with untreated PKU

Aim: Phenylketonuria (PKU) is a congenital metabolic disorder that, unless treated with a special low-phenylalanine (low-phe) diet from infancy, leads to severe intellectual disabilities. The aim of this study was to test the efficacy of the low-phe diet for adults with untreated PKU.Method: 36 adults with untreated PKU were recruited into a double-blind randomized controlled crossover trial. Measures included weekly blood phenylalanine levels, daily behavioural records, and, at the end of each phase, standardized measures of skills and behavioursand direct observations.Results: Blood phenylalanine levels were well controlled by the low-phe diet but there were no associated significant changes in challenging behaviours. However, people who had the low-phe diet first were significantly more likely to withdraw (chi-squared, p<0.01). Also carers made more positive comments at the end of the low-phe diet phase than at the end of other phases (chi-squared, p<0.001).Conclusions: Carers’ responses suggest detectable improvements in the behaviour of adults with PKU when treated with low-phe diet, but this is not supported by quantitative analysis