ABSTRACT
This chapter discusses the original 4 inborn errors which resulted in cystinuria, alkaptonuria, pentosuria, and albinism. Phenylketonuria, or PKU, derives its name from the presence of phenylketones in urine. It has become the inborn error of metabolism to receive the greatest amount of attention. PKU occurs as a result of the absence of the enzyme phenylalanine hydroxylase. Normally, phenylalanine is metabolized by oxidation to tyrosine, and this reaction is catalyzed by the enzyme phenylalanine hydroxylase. The advantages of screening in specific instances of high risk groups, such as the Amish communities with recorded intramarriages, outweigh the relatively low incidence of PKU even in these high risk groups. The urine test must be performed on a fresh urine specimen. Alkaline specimens, which are obtained when bacterial decomposition occurs on standing, react with the ferric ions to produce ferric hydroxide, giving an interfering orange color.
