Prir to newborn screening and the availability of dietary treatment for phenylketonuria, most patients with classic phenylketonuria developed profound mental retardation and rarely reproduced. Newborn Screening for phenylketonuria has been routinely available throughout the United States for approximately 20 years. Many women who were identified as having elevated blood phenylalanine levels received dietary treatment, and in most cases they have attained normal intelligence. A significant number of these women have entered or are approaching their reproductive years, and are no longer receiving dietary treatment. After discontinuance of the diet, elevated blood phenylalanine levels and other biochemical changes of classic phenylketonuria again become evident.
Children born to mothers whose blood phenylalanine levels exceed about 1 mM have an extremely high incidence of microcephaly and mental subnormality due to the teratogenic effects of the maternal phenylalanine elevation. There is a suggestion that the incidence of other congenital anomalies, such as congenital heart defects, may be increased in the offspring of phenylketonuric mothers, but this is not definitely established. The vast majority of children born to phenylketonuric mothers do not have phenylketonuria and postnatal dietary therapy has not been helpful.
When maternal blood phenylalanine elevations are less than about 1 mM, the effect on offspring is not clear. The reproductive outcome of only a small number of patients in this category, as ascertained by an unbiased method, has been studied.
All women with persistent phenylalanine elevations should be counseled prior to pregnancy about the possible adverse effect of their condition on their offspring; in utero diagnosis of these adverse effects is not possible at the present time.
- Copyright © 1985 by the American Academy of Pediatrics