How is a positive result for phenylketonuria, (using the guthrie test) different from a negative result?
Phenylketonuria (PKU) is a genetic disorder that is characterized by an inability of the body to utilize the essential amino acid, phenylalanine. Amino acids are the building blocks for body proteins. ‘Essential’ amino acids can only be obtained from the food we eat as our body does not normally produce them. In ‘classic PKU’, the enzyme that breaks down phenylalanine phenylalanine hydroxylase, is completely or nearly completely deficient. This enzyme normally converts phenylalanine to another amino acid, tyrosine. Without this enzyme, phenylalanine and its’ breakdown chemicals from other enzyme routes, accumulate in the blood and body tissues. Although the term ‘hyperphenylalaninemia’ strictly means elevated blood phenylalanine, it is usually used to describe a group of disorders other than classic PKU. These other disorders may be caused by a partial deficiency of the phenylalanine breakdown enzyme or the lack of another enzyme important to the processing of this amino acid. A normal
