Why Diet Is Important

It is well known that high Phe levels during early childhood can cause mental retardation. What is not as well understood is how high Phe levels affect adults who have managed PKU their whole lives. Recent research has shown that high Phe levels can affect adults, and that diet may not always be enough. Even adults who have managed their diet fairly well sometimes show mild symptoms, such as:

Psychiatric disorders^1,2,4

People with PKU are more likely to have psychiatric disorders like depression, phobias, anxiety, and hypochondria than people without PKU.

Case studies have shown that adults with high Phe can become dangerously hyperactive and, in extreme cases, even agoraphobic. Again, no one understands this relationship fully.

Attention deficit hyperactivity disorder (ADHD) symptoms^4,5

Studies on this issue suggest that elevated Phe levels are associated with ADHD symptoms. What’s more, the severity of these symptoms seems to depend on Phe levels. The higher the levels, the more severe the symptoms.

Cognitive problems⁹

A study comparing the performance of people with PKU and people with diabetes found that people with PKU scored lower on a special timed test. It wasn’t that the people with PKU got so many wrong answers, but instead it had to do with how many questions they were able to answer in the allotted time. In other words, they were simply slower at taking the test. The people with PKU kept their Phe levels within the targeted range, and their performance was more closely related to what their Phe level was when they took the test, instead of what it had been in the past.

Brain abnormalities^10,11

There are certain kinds of brain abnormalities that are noticeable in early-treated adults (adults who have been on the diet their whole lives). These abnormalities are more noticeable when the individual has unusually high Phe levels.

When some adults have unusually high Phe levels, despite the fact that they have maintained good control during childhood, their brains look different from those of people without PKU. The difference is in the amount of cerebral white matter in the brains of these people. Less white matter means slower communication between brain areas. A telephone modem versus a DSL.