Phenylalanine hydroxylase deficiency (PHD) is a treatable metabolic disorder in which the body cannot properly break down the amino acid phenylalanine, a building block of protein.
Accumulation of phenylalanine can cause varying degrees of intellectual disability, developmental delay, seizures, and behavioral problems. Symptoms can arise shortly after birth.
PHD is caused by pathogenic (disease-causing) variants in the PAH gene and exhibits autosomal recessive inheritance. This means that both parents must be carriers to have a 25% chance to have a child with the condition. The risk of being a carrier is based on a person’s ancestry or ethnic background. Individuals of Ashkenazi Jewish descent have a 1 in 225 chance to be a carrier of PHD.
Carriers of this condition typically do not experience any symptoms.
Another name for this condition is phenylketonuria (PKU).
