ABSTRACT
Most products needed for normal development that are reduced by a metabolic error e.g. tyrosine in infants with phenylketonuria (PKU) are provided through the placenta by the mother. Because newborn screening for PKU nationwide has been in place for the longest, the best understanding of screening is for this disorder. In 1954, Horst Bickel and coworkers demonstrated that a phenylalanine-restricted diet could prevent mental retardation in children with PKU. The addition of hypothyroidism to newborn screening using the same filter paper blood spot used for PKU began in the 1970s. Discussions of the needs of a newborn screening program were extensively held in the early years of screening programs. The original Guthrie method for phenylalanine, a bacterial inhibition assay, continues to be used in most state screening programs. In this assay, a phenylalanine analog, which inhibits bacterial growth, is added to the culture plate.
