GP1BA and hemorrhagic disease: Similarly, a missense mutation leading to a rare bleeding disorder, BSS, was mapped to an evolutionary conserved and hydrophobic residue at the core of the LRR region in the GPIb-IX-V complex.39 In contrast, Thr145 responsible for HPA-2, located at the same repeat region (Fig. 1D), is exposed to the solvent and is evolutionary variable.