Patients with R307C/H GATA1 mutations display elevated ADA levels and impaired erythropoiesis. (A) Images of May-Grünwald-Giemsa–stained peripheral blood smears and bone marrow (BM) aspirates of indicated cases. (B) Pedigrees of 3 families with cases of congenital hemolytic anemia and elevated erythrocyte ADA (eADA) levels. Measured eADA levels are indicated. In all cases, GATA1 point mutations affecting Arg307 (R307) were identified. (C) Distribution of eADA levels in healthy controls (n = 21), suspected carriers (n = 2), and cases (n = 3). (D) Depiction of reported mutations in GATA1. Previously reported pathogenic variants are indicated with arrows and corresponding amino acid (aa) changes. R307 is in the middle of a 20-aa (black bar) region near the C-terminus. Circles represent projection of variants and their allele count as identified in ostensibly healthy individuals (n = 141 456; gnomAD). DNA binding zinc finger domains and the region around R307 are depleted for variants, indicating coding constraint. (E) aa conservation near R307 for indicated selected species. (F) Schematic of primary cell experiment. BM mononuclear cells (MNCs) from healthy donors and R307C mutant cells were in vitro differentiated into erythroblasts and sorted (gate as indicated), and differentiation and proliferation kinetics were monitored. (G) X-fold expansion of sorted healthy donor and R307C primary cells over the indicated time frame. (H) Flow cytometric plots of CD71 and CD235a surface marker–stained populations of healthy donor and R307C primary cells examined at indicated time points of culture. (I) Images of May-Grünwald-Giemsa–stained cytospin preparations of healthy donor and R307C primary cells at indicated time points of culture (×63 original magnification). Hb, hemoglobin.