Explanation:

Phenylketonuria (PKU) is a rare but potentially serious inherited disorder. The body breaks down protein in foods like meat and fish into amino acids, which are the "building blocks" of protein. These amino acids are then used to make its own proteins. Any amino acids that aren't needed are broken down further and removed from the body. People with PKU can't break down the amino acid phenylalanine, which then builds up in the blood and brain. This can lead to brain damage. Without treatment, PKU can damage the brain and nervous system, which can lead to learning disabilities.