hyperphenylalaninemia

Hyperphenylalaninemia is a medical disorder characterized by abnormally high levels of the amino acid phenylalanine in the blood, cerebrospinal fluid, and urine. This condition arises from an inherited inability of the body to properly metabolize phenylalanine, typically by the enzyme phenylalanine hydroxylase. When this enzyme is inactive, phenylalanine cannot be converted to tyrosine, leading to its accumulation.1

This buildup interferes with neurotransmitter production in the central nervous system, potentially causing cognitive dysfunction, seizures, and developmental abnormalities. It can also affect melanin production, leading to lighter skin, hair, and eye color. Hyperphenylalaninemia can be caused by phenylketonuria (PKU) or by deficiencies in tetrahydrobiopterin (BH4), a cofactor necessary for phenylalanine hydroxylase activity. Treatment usually involves a diet low in phenylalanine.1