An inherited disorder of the amino acid metabolism, it is the most common inherited metabolic disease affecting brain development. It affects nearly one in 10,000 newborns in the United States and Europe. It is more frequent among certain groups of northern European populations and their descendants, and rare among Asians.
In Phenylketonuria, the metabolic disorder is the inability to convert a substance called phenylalanine to tyrosine due to absence or deficiency of an enzyme called phenylalanine hydroxylase. The defect in phenylketonuria can be represented as follows:
Phenylalanine hydroxylase enzyme (Absent or deficient)
No conversion due to enzyme deficiency
Excessive accumulation of phenylalanine in blood and body fluids