Abnormal proplatelet formation in B₃ D723H megakaryocytes. (A) Light phase-contrast microscopy of propositus and control MKs derived from peripheral blood CD34⁺ stem cells cultured in serum-free medium for 10 days. Arrowheads point to the proplatelet swellings and the bulbous tips. Scale bar equals 10 μm. (B) Quantification of the average diameter of the proplatelet swellings from propositus (n = 15) and control (n = 30). Bars represent the mean plus or minus SD.