I could be wrong, and someone correct me if I am, but I think this power point is focusing more on the issues that people with non compliantPKU have.
The sixth slide even shows the shocking percent of people with PKU in different age groups that are on diet, but still have higher than ideal phe levels. On the twelfth slide it does say that people with PKU have slightly lower IQ's than their siblings and peers, BUT take a look at the thirteenth slide. Of the children involved in this study from 0-12 years of age some of them had average phe levels up to 750 ummol/L or 12.5 mg/dl. The recommended phe level for PKU patients is 120-360 ummol/L or 2-6 mg/dl. The average phe level of someone who does not have PKU is less than 60 ummol/L or 1.0 mg/dl, so it makes sense that with high phe levels that are over ten times greater than the general population that more problems would be seen.
You kind of have to take this power point with a grain of salt. It definitely has plenty of great information and kudos to whoever put it together, but sometimes power points, graphs, studies, etc can be misinterpreted without a presenter to talk us through it. For all I know I could even be misreading this power point LOL ;). Regardless of whether or not I’m reading this power point wrong though I do know that most of these issues do not apply to me.