Effect of MKL1 mutation on F-actin. (A) F-actin (Alexa Fluor 647 phalloidin) content in lymphoid and myeloid cells was analyzed by flow cytometry. Patient cells were stained with carboxyfluorescein diacetate succinimidyl ester (CFSE) and mixed with unstained control cells before fixation and staining. Representative data from 2 experiments. (B) Confocal images of patient cells (CFSE, green), F-actin (Alexa Fluor 647 phalloidin, red), and mixed with control cells (unstained). Scale bar = 5 μm. Data were analyzed from 1 experiment. (C) Quantification of the phalloidin MFI observed in (B). (D) Sequence analysis of control and patient samples leading to the identification of the MKL1 mutation. (E) MKL1 expression visualized by western blot in control and patient peripheral blood mononuclear cells (PBMCs). ***P < .001. GAPDH, glyceraldehyde-3-phosphate dehydrogenase.