After newborn screening for suspected phenylketonuria you should: 1. Do PAH genetic testing on the child to confirm the diagnosis, if the child is found to have PAH genes with two disease-causing mutations and the mutations can be separated (i.e., one mutation in each parent), the diagnosis can be confirmed, if no genetic mutations are found, further investigation of the cause is needed. 2. Children diagnosed with phenylketonuria by genetic diagnosis need a special diet, i.e., recipes and diet plans under the guidance of a doctor, with the aim of controlling the child’s blood phenylalanine concentration at an appropriate level to avoid damage to the child’s nervous system as well as other tissues from high phenylalanine, which can lead to mental retardation and other disorders.