PKU is a relatively rare genetic metabolic disease. The body of PKU patients cannot break down phenylalanine, an amino acid contained in food protein, which causes phenylalanine to accumulate and increase in concentration in the body, and the elevated high phenylalanine can cause brain damage. If diet is not administered early enough in infancy, it can cause irreversible brain development disorders and mental retardation.
PKU is an autosomal recessive metabolic disorder. Classic PKU is caused by structural and functional defects in the phenylalanine hydroxylase gene located on the q22-24 region of chromosome 12. Phenylalanine hydroxylase breaks down phenylalanine to tyrosine in the liver. When its activity is reduced, phenylalanine cannot be broken down and accumulates in the blood and tissues and crosses the blood-brain barrier into the central nervous system, causing brain development disorders and mental retardation.
PKU can be classified into classic PKU and tetrahydrobiopterin deficiency (also known as BH4 deficiency) according to the pathogenesis. The main treatment for classic PKU is dietary control, i.e., restricting the intake of phenylalanine in food. Tetrahydrobiopterin deficiency is treated mainly with pharmacological control. There are different types of PKU and their treatment varies. The following further tests are needed for differential classification: (1) urinary pterin profile analysis (2) dihydropterine reductase activity assay (3) BH4 loading test. Parents should actively cooperate with the doctor to complete the above tests in order to clarify the classification and guide the treatment.