Fig. 2 ANXA5 a) locus and variants b) haplotyping results. Blue = wild-type, green = M2
The human ANXA5 gene, situated on chromosome 4, encodes a calcium-dependent phospholipid binding protein, which acts as a placental anticoagulant. A variant haplotype of ANXA5 contains 4 nucleotide substitutions which lie within the space of 57 nucleotides in the promoter (Fig. 2a). These substitutions reduce the activity of the promoter substantially, and if the embryo inherits the M2 haplotype from either parent, the risk of miscarriage increases substantially. Rather than testing the parents, by amplifying across the region in blastocyst DNA, followed by sequencing, we are able to identify embryonic ANXA5 haplotypes (Fig. 2b).