The presence of excess phenylalanine in the blood (as in phenylketonuria)
At phenylalanine levels near 20 mg/dl (1200 mmol/l), phenylketonuria (pku)-like symptoms may emerge, including more pronounced developmental abnormalities,eczema, and vomiting. Preliminary evidence indicates milder attention and organizational problems may arise when levels exceed 6 mg/dl.
People with untreated classic pku have levels of phenylalanine high enough to cause severe brain damage and other serious health problems. Mutations in the pah gene that allow the enzyme to retain some activity result in milder versions of this condition, such as variant pku or non-pkuhyperphenylalaninemia.