TABLE 2.

Factor loadings from exploratory factor analysis

mRNA expression of placental Fe transport proteins	Correlation with factor 1	Correlation with factor 2	Correlation with factor 3
FLVCR2	0.88	0.08	−0.05
DMT1	0.86	−0.10	0.19
TfR1	0.62	−0.03	0.00
LRP1	0.57	0.10	−0.15
HRG1	0.54	0.25	0.06
FPN	0.19	0.79	−0.13
Zyklopen	0.07	0.69	−0.08
FLVCR1	−0.03	0.35	0.17
Hepcidin	0.06	0.02	0.73

Exploratory factor analysis with quartimin rotation was applied to measures of mRNA expression for placental Fe transporters, as these measures were shown to be highly interrelated. Three factors adequately described 70% of the variation among these variables. How much a variable correlated with a derived factor is represented by the factor loading score shown above (33). Factor loading scores >0.5 are italicized. Proteins known to facilitate nonheme Fe import loaded highly on factor 1 along with proteins thought to participate in cellular heme import. Ferroportin and zyklopen, the 2 proteins critical for nonheme Fe export, loaded predominantly on factor 2 with FLVCR1, which may be an intracellular or cellular heme exporter in placenta. Hepcidin loaded independently on factor 3. This analysis included a subset of adolescents that had mRNA expression data for all proteins evaluated (n = 48). This subset did not statistically differ from the larger study population for the characteristics listed in Table 1. FPN, ferroportin.