In theory, dietary control can be relaxed after basic brain maturation, but the problem is not so simple. The age of termination of dietary therapy is internationally inconclusive, but all agree that it should be maintained until at least 12 years of age. The PKU research class in the United States treated up to 6 years of age as one group, and the other group continued treatment. After more than ten years of follow-up, it was found that there was a significant difference in academic performance between the two groups, with the former group being the laggards. High blood Phe concentrations also predispose to mental and behavioral problems such as spasticity and emotional instability. Therefore, Japanese scholars advocate that treatment should be extended for as long as possible and that strict dietary control is necessary at least until adulthood. Whether lifelong treatment is necessary remains controversial.