LowproteinLIVING

National screening for PKU was started in the UK in 1969. This was the start of early diagnosis and successful treatment of PKU with diet. During the 1970s the PKU diet was routinely stopped at age 6 to 8 years old. It was thought that high levels of phenylalanine could not cause any further damage to the person’s brain or nervous system after this age. As research continued it became clear that children who were taken off diet were not doing as well as those who had stayed on diet.

This showed that the diet needed to continue for longer than was previously thought.  Newer research on people off diet suggest that high levels of phenylalanine may have an effect on brain function in adults.  This poses the question as to whether the low phenylalanine diet should be stopped at all.

Brain scans using Magnetic Resonance Imaging (MRI) show changes when there is a high level phenylalanine in the blood.  These changes can be reversed when the phenylalanine Levels are lowered. The long-term effect of this is unknown. Some patients who come off diet find that they do not feel as well as when they are on diet. Common symptoms include tiredness, poor concentration and a slight tremor in the hands. These symptoms are probably related to brain and nerve function.  A small number of PKU patients off diet have developed severe neurological problems such as leg stiffness and weakness.  In most of these cases the person has improved when they have returned to diet.

The main problem is that doctors do not yet know what long-term effect high phenylalanine levels have on the brain. Research continues but the answer to this question will not be known for several decades to come. In view of this and the current evidence the Report of Medical Research Council Working Party of PKU recommends that patients with PKU should remain on diet long-term if they are able to follow it safely and effectively.