TPP1 and Bone marrow hypocellularity: Human patients with two mutations in the TPP1 gene (single amino acid deletion + missense mutation) require regular platelet and red blood cell transfusions for bone marrow failure 66; however homozygous mouse mutants of Tpp1 were embryonic lethal 67, suggesting that the “blunt” loss of function created by targeted gene knock‐out in mice enables creation of much more severe phenotypes compares to human, but also result in loss of viability preventing further disease modeling.