Final answer:
Phenylketonuria (PKU) is identified by elevated blood phenylalanine levels and is caused by a lack of the enzyme phenylalanine hydroxylase. Symptoms include intellectual disability and neurological problems, which can be managed through a strict low-phenylalanine diet.
Step-by-step explanation:
The condition characterized by blood phenylalanine levels greater than 20 mg/dL is Phenylketonuria (PKU). PKU is a genetic disorder resulting from a deficiency in the enzyme phenylalanine hydroxylase, which is needed to metabolize the amino acid phenylalanine into tyrosine. Without this enzyme, phenylalanine levels in the body become toxic, particularly harming the central nervous system and brain. Common symptoms of PKU include intellectual disability, behavioral or neurological issues, seizures, and musty body odor. It is vital for individuals with PKU to adhere to a diet low in phenylalanine to prevent these symptoms and manage their condition effectively.