Inherited inborn errors of metabolism (IEMs) are a relatively rare group of disorders whose identified number has grown steadily to approximately 1,000 individual disorders. This represents an aggregate incidence of 1:600 to 1:1,000 newborn infants. In the United States there are approximately 4 million births annually, translating to the potential detection of 6,000 affected newborns each year. Most affected infants are healthy appearing and asymptomatic at birth. Onset of illness ranges from hours after birth to weeks or even months of age. Early recognition and timely treatment can avert early death and long-term morbidity, emphasizing the importance of newborn screening (NBS).

In 1963, Dr Robert Guthrie developed the first NBS blood test that detected the autosomal recessively inherited disorder phenylketonuria (PKU). Guthrie’s bacterial inhibition assay required a spot of blood placed on a filter paper disc transferred to an agar plate containing a substance that inhibited the growth of bacteria....

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