Tyrosine supplementation during pregnancy in a woman with classical phenylketonuria. A case report.

: A woman with classical phenylketonuria (PKU) adhered poorly to a phenylalanine-restricted diet but did receive tyrosine supplementation from the 14th week of gestation until delivery. At birth the infant demonstrated a head circumference more than two standard deviations below the mean but at 2 years of age had a development quotient (DQ) of 94. This case illustrates the fact that while single case reports may be of value in disproving a theory, they are not sufficient to prove an association because biologic variation may explain one's results. Thus, while tyrosine supplementation may explain the relatively normal DQ, the results are also compatible with the moderate degree of phenylalanine restriction obtained. Current evidence favors the elevated maternal phenylalanine level as the cause of defects in offspring of women with PKU, but tyrosine supplementation should be considered if the level is subnormal.