With newborn screening being widely used for PKU, infants are diagnosed early and symptoms are prevented with early, life-long treatment. When PKU is untreated, however, blood phe levels can become elevated, a high level of blood phe is toxic to the brain, the following symptoms can occur when untreated or treated too late: mental retardation, seizures, and eczema / skin rash, behavioral or social problems, tremors or jerking movements in the arms and legs, hyperactivity, stunted growth, small head size (microcephaly), musty odor in the child's breath, skin or urine, caused by too much phenylalanine in the body, fair skin and blue eyes, because phenylalanine cannot transform into melanin - the pigment responsible for hair and skin color .