KDR and isolated hemihyperplasia: Despite the inferred role of VEGF-A in IH, it was not until work by Jinnin et al. (48) that the demonstration of the VEGFR-2 isoform, coupled with the reduced decoy receptor VEGFR-1, led to the proposed predominant action of the VEGF-A ligand in promoting enhanced signaling via VEGFR-2 phosphorylation (48, 49) possibly with the aid of the molecular chaperone, COSMC (50).