TMD blast cells express only the shorter variant of GATA-1. Whole-cell extracts were prepared using triple-detergent lysis buffer. Proteins were transferred onto polyvinylidene difluoride membranes and processed for reaction with the anti–GATA-1 polyclonal antibody, M-20, which recognizes the C-terminus of GATA-1. (A) CMK, MGS, and blast cells from 3 patients with TMD expressed only the shorter variant of GATA-1. In each lane, 15 μg protein was loaded. (B) An identical sized GATA-1 protein is expressed in MGS and blast cells from a patient with TMD (TMD 21). The predicted protein encoded by the open reading frame of the mutant GATA-1 gene in TMD 21 is 378 amino acids, whereas that of MGS is 330 amino acids. In contrast, blast cells from a patient with AMKL, but not from Down syndrome, expressed full-length GATA-1.