Phenylketonuria is a disorder that increases phenylalanine levels in the blood. If left untreated from birth, it can cause permanent intellectual disabilities in children as well as risks of intellectual disabilities for babies born to pregnant women with PKU. Symptoms of PKU include low birth weight, behavioral problems, mood issues, seizures, and increased risk of pregnancy loss if the condition is uncontrolled. Early treatment with a low-phenylalanine diet can prevent these issues.