Question
What are the causes of phenylketonuria?
Answer
Phenylketonuria is a common amino acid metabolism disorder primarily caused by a defect in phenylalanine and related enzymes, leading to the inability to convert phenylalanine into tyrosine. This results in the accumulation of phenylalanine in the body, which is then excreted through urine. This disease belongs to the more common types of genetic amino acid metabolism defects and is inherited in an autosomal recessive manner. Phenylalanine is one of the essential amino acids needed by the body; newborns require approximately 0.5 grams daily, while children and adults need more, around 4 grams. The conversion of phenylalanine into tyrosine requires not only the enzyme phenylalanine hydroxylase (PAH) but also tetrahydrobiopterin (BH4) as a cofactor.