Sir.—Levy and Waisbren1,2 have shown that maternal hyperphenylalaninemia during pregnancy causes characteristic embryopathy including mental retardation, microcephaly, low birth weight, congenital heart disease, and typical dysmorphic facies. Although it is believed that phenylalanine embryopathy may be prevented by a low-phenylalanine diet, preferably beginning before conception,3,4 the "safe" maternal serum phenylalanine level has not been established. We observed a woman of normal health and intelligence with previously undiagnosed hyperphenylalaninemia who gave birth to two infants with severe phenylalanine embryopathy, causing mental retardation and microcephaly. Before her third pregnancy, she started a low-phenylalanine diet that resulted in excellent control of serum phenylalanine levels, but the third child has dysmorphic facies and delayed development.
Patient Report.—A 30-year-old woman was seen in May 1987 for prenatal counseling. Hyperphenylalaninemia had been diagnosed in 1985 when, after the birth of her second abnormal infant, she was discovered to have serum phenylalanine levels
BACHMAN RP, SCHOEN EJ, BACKSTROM MV, LEE RF, WILLIAMS SR, JURECKI ER. Phenylalanine Embryopathy in Three Siblings: Implications of Maternal Diet Therapy. Am J Dis Child. 1993;147(1):22-23. doi:10.1001/archpedi.1993.02160250024009