I. What is phenylketonuria? Phenylketonuria (PKU) is a metabolic disease caused by a genetic mutation that leads to an increase in phenylalanine concentration in blood and urine. II. What damage does PKU do to the human body? The accumulation of phenylalanine in brain tissue causes damage to brain cells, resulting in mental retardation and abnormal behavior: excitement, hyperactivity, isolation, etc.; phenylalanine cannot be converted to complexine, resulting in insufficient synthesis of melanin, resulting in yellow hair and fair skin; more phenylacetic acid is excreted in urine, which has a special odor similar to that of rat urine. Third, what causes PKU? The mutation of PAH gene leads to the deficiency of phenylalanine hydroxylase, which makes phenylalanine unable to be metabolized. Is PKU hereditary? PKU is a typical autosomal recessive disease, that is, each person has two PAH genes, one of which is broken and the other is normal and does not develop, called a carrier, but if both genes are broken, it develops. If both parents are carriers and both parents pass the bad PAH gene to their child, the child will have both bad PAH genes and will develop the disease. V. How to detect PKU? PKU is suspected if the child is found to have abnormally high phenylalanine during newborn screening. VI. How to confirm the diagnosis of PKU? The child will be tested for the PAH gene and if the child is found to have If the PAH gene is found to have two disease-causing mutations and the mutations can be separated (i.e., one mutation in each parent), the diagnosis can be confirmed. How to treat PKU? Children diagnosed with phenylketonuria by genetic testing need to be put on a special diet, i.e., recipes and diet programs are developed 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 and other tissues caused by high phenylalanine, which can lead to mental retardation and other conditions. How to prevent PKU? If both parents are carriers of the disease-causing gene, amniotic fluid should be taken between 16-20 weeks of pregnancy for PAH gene testing of the fetus. If the fetus inherits two mutations, it will have the disease in the future and it is recommended to terminate the pregnancy, if only one mutation is inherited or no mutation is transmitted, it will not have the disease after birth.