Intake of major nutrients by women in the Maternal Phenylketonuria (MPKU) Study and effects on plasma phenylalanine concentrations.

BACKGROUND

Women with untreated phenylketonuria (PKU) often have poor reproductive outcomes.

OBJECTIVE

We assessed the effects of intakes of major nutrients on plasma phenylalanine concentrations and we measured phenylalanine hydroxylase activity and phenylalanine intakes in pregnant women with PKU.

DESIGN

Dietary intakes and plasma phenylalanine concentrations were compared in 4 subject groups defined on the basis of plasma phenylalanine concentrations: group 1 (n = 23), <360 micromol/L by 10 wk gestation and 120-360 micromol/L throughout the remainder of pregnancy; group 2 (n = 46), <600 micromol/L but not <360 micromol/L by 10 wk gestation and 120-600 micromol/L throughout the remainder of pregnancy; group 3 (n = 24), <600 micromol/L by 10 wk gestation but >600 micromol/L at least once thereafter; group 4 (n = 147), never <600 micromol/L.

RESULTS

Except in the first trimester, mean intakes of phenylalanine, energy, and fat tended to be greater in group 1 than in the other groups. The mean protein intake of group 1 tended to be greater than that of the other groups. Intakes of protein (P < 0.0001), fat (P < 0.0001), and energy (P < 0.007) were negatively correlated with maternal plasma phenylalanine concentrations. It appeared that genotype did not affect phenylalanine tolerance.

CONCLUSIONS

Maternal genotype appeared to have little influence on phenylalanine requirements during the first trimester. Early decline and maintenance of maternal plasma phenylalanine concentrations at <360 micromol/L and mean protein intake greater than the recommended dietary allowance (RDA) with mean energy intake near the RDA resulted in the best reproductive outcomes. Inadequate intakes of protein, fat, and energy may result in elevated plasma phenylalanine concentrations and may contribute to poor reproductive outcomes.