Variability of reproductive casualty in maternal phenylalaninemia.

A biochemical survey of 4,000 parents of mentally retarded children did not identify any mothers with elevated phenylalanine blood levels. This finding and an analysis of nearly 100 reported cases of maternal phenylalaninemia suggest a low risk of reproductive casualty in phenylalaninemic mothers who somehow escaped the usual effects of phenylketonuria. Recent observation on cases of maternal phenylalaninemia who were detected through unselected screening indicate that the reproductive risk associated with the condition may have been overstimated in the past. This risk is concentrated in mothers who had been affected themselves. Mental level appears to be a stronger predictor of reproductive outcome in phenylalaninemic women than the degree of phenylalaninemia. Selective prenatal intervention based on maternal mental level is not possible, however, where the natural history of the condition has been altered. This is the case in phenylketonuric girls who has been treated during childhood. These girls are now reaching child-bearing age in fast growing numbers, as a result of screening for phenylketonuria. Prenatal intervention is appropriate for all of them until predictors are established that can identify those at risk of reproductive casualty.