Phenylketonuria

There are several types that are distinguished. Phenylketonuria I – the classic form, occurs when there is a complete lack of phenylalanine hydroxylase (EC 1.14.16.1). Without treatment, there is complete mental retardation. Death occurs between 20-30 years. Such patients make up about 1% of all psychiatric clinic patients. This is the most common inherited genetic defect: affects 1 in 14,000 newborns (USA). In Japan – 1 in 200,000, in Western Europe – 1 in 5,000 (Dublin), and among Caucasians – 1 in 10,000 newborns. Phenylalanine cannot convert to tyrosine, so it accumulates in the blood, in all body fluids, and tissues. Normally, there is 30-120 µM (0.5-2.0 mg/dL) of phenylalanine in the blood. Under these conditions, phenylalanine is transaminated into phenylpyruvate. Large amounts of it are excreted in the urine (about 2 g per day). Phenylalanine forms other products – phenyllactate, phenylacetate, and the glutamine α-amino group forms an amide bond with the phenylacetate carboxyl group, forming a conjugate – phenylacetylglutamine. In phenylketonuria, higher amounts of phenylacetylglutamine are excreted in the urine (2-3 g per day). Under normal conditions, these reactions occur weakly. In case of dihydropteridine reductase (EC 1.5.1.34) deficiency, types II and III PKU occur. Symptoms are similar to classic PKU symptoms. All types of PKU are not completely curable yet, but pathological processes can be stopped by removing phenylalanine from the baby’s diet. Casein has little phenylalanine. Phenylalanine can be removed from it after hydrolysis.

Source | Glossary of Most Commonly Used Biomedical Terms and Concepts | Lithuanian University of Health Sciences | Academician Professor Antanas Praškevičius, Professor Laima Ivanovienė