The effects of metallothionein 2A polymorphism on placental cadmium accumulation: Is metallothionein a modifiying factor in transfer of micronutrients to the fetus?

Metallothionein affects the metabolism, transport and storage of micronutrients such as zinc, copper and iron, and the detoxification of heavy metals, especially cadmium. Cd is a common, highly toxic environmental pollutant that accumulates in human placenta, elevated concentrations of which are associated with impaired zinc transfer to the fetus. This prospective study investigated the effects of metallothionein 2A (MT2A) -5 A/G single nucleotide polymorphism on the accumulation of Cd in human placenta and micronutrient transfer to the fetus in 95 pregnant women and their newborns. Venous blood from the mother was collected to investigate Cd, Zn, Cu, Fe levels and MT2A polymorphism. Cord blood from the neonate and placenta was collected for metal levels. MT2A polymorphism was determined by the standard PCR-restriction fragment length polymorphism technique. Metal levels were analyzed by Atomic Absorption Spectrometry (AAS). Maternal blood Cd levels were statistically higher for mothers with a heterozygote genotype compared with a homozygote genotype (P<0.05). In contrast, placental Cd levels were significantly higher in mothers with a homozygote rather than a heterozygote genotype (P<0.05). No difference existed in cord blood Cd, Zn and Cu levels. However, cord blood Fe levels of newborns with heterozygote genotype mothers were higher than in others. Placental Cd levels of heterozygote genotype mothers were negatively associated with Zn in cord blood. Cd exposure at environmental levels may be associated with alteration of the umbilical cord micronutrient levels for newborns with mothers of a heterozygote genotype.