Phenylketonuria
This is a defect in Amino Acid Metabolism and another component tested in the Newborn Screening test.
Phenylketonuria (PKU) is an autosomal recessive inborn error of metabolism. In this disorder, there is an absence of phenylalanine hydoxylase thus resulting to accumulation of phenylalanine in the blood.
Clinically, the babies with this defect will have mental retardation and seizures. Musty odor is the classical picture and this is because of the excess of phenyacetic acid in the urine.
The reasons individuals with PKU will have mental retardation are:
1. Accumulation of a toxic metabolite phenylethylamine in the presence of high concentrations of phenylalanine. This metabolite is neurotoxic and can cause damage to the brain
2. Deficiency of Serotonin
3. Increased phenylalanine concentration serving as a deterrent in the transport of other amino acids into the different cells thus resulting to protein synthesis deficiency
Because of the availability of the newborn screening tests, affected babies are easily identified and treated. Treatment consists of elimination of most of the phenylalanine in the diet. PKU should be treated as early as possible. Studies showed that when treatment is started within the first three weeks of life, the IQ’s of phenylketonurics compare favorably with those of their normal siblings. When treatment is started after 8 months of age, the IQ does not differ from that of untreated individuals