Maternal 25-hydroxyvitamin D concentration and offspring birth size: effect modification by infant VDR genotype.

Background/objectives: We tested the hypothesis that the relationship between maternal 25-hydroxyvitamin D (25-(OH)D) and offspring birth size differs according to offspring vitamin D receptor (VDR) genotype (Apa1, Bsm1, Fok1 or Taq1).
Subjects/methods: Mothers of 354 singleton babies had serum 25-(OH)D concentration measured at 28-30 weeks of gestation and consented to measurement of their babies soon after birth. DNA was extracted from the babies' Guthrie cards.
Results: There was evidence of effect modification by infant FokI genotype. Babies of deficient mothers had lower birth weight with FF or Ff, but not ff genotype (P-value for interaction after adjustment for potential confounding factors=0.02), but thicker subscapular and suprailiac skinfolds with ff, but not FF or Ff genotype (P=0.008 and 0.02, respectively). Sample size was insufficient to investigate effect modification by the other VDR polymorphisms.
Conclusions: These preliminary findings suggest that studies of maternal vitamin D status and birth size may need to take VDR genotype into account.