Newborn metabolic screening: a search for "nature's experiments".

The rationale for metabolic screening includes discovery of new diseases, development of treatment methods, determination of the true incidence of disease in order to provide genetic counseling, and relief to the taxpayer when retardation is preventable. The number of diseases for which we can now screen is large and growing and must be periodically reviewed. Physical, cultural, and religious factors affect gene pool mixing, making it impossible to predict a priori what the incidence of a given disorder will be within the population screened. This paper reviews the rationale for establishing neonatal metabolic screening programs and the significance of the information gained.