Platelet-producing normal and WAS MKs have the same morphological aspect. CD34⁺ cells of WAS patients (A) or normal controls (B) were purified from blood or bone marrow and were grown in the presence of PEG-rHuMGDF and SCF. Analysis of cultured cells under light microscopy by day 8 allowed the identification of platelet-producing MK characterized by the extension of very long and thin pseudopods. They give rise to proplatelets by breaking irregularly at several constriction sites. The frequency and appearance of these platelet shedding MKs were similar in WAS patients (A) and in normal controls (B).