Prior to newborn screening and the availability of dietary treatment for phenylketonuria, most patients with classic phenylketonuria developed profound mental retardation and rarely reproduced.1,2 Newborn screening for phenylketonuria has been routinely available throughout the United States for approximately 25 years. Many infants who were identified as having elevated blood phenylalanine concentrations received dietary treatment. In most cases they have attained normal intelligence. A significant number of women who are no longer being treated have entered or are approaching their reproductive years.

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