KIR and HLA are the most polymorphic gene families in humans, and we have shown that particular maternal KIR in combination with fetal HLA-C variants are associated with preeclampsia and the other GOS.100, 101, 102 Women who have 2 KIR A haplotypes (KIR AA genotype) are at risk when there is a HLA-C allele belonging to the C2 group in the fetus. This evidence concerns the gene HLA-C and preeclampsia.