WAS and Wiskott-Aldrich syndrome: Wiskott–Aldrich syndrome protein (WASP) is an actin nucleation factor.287 Mutations in WASP cause Wiskott–Aldrich syndrome (WAS), which is an X chromosome-linked disease characterized by thrombocytopenia, eczema, and immune deficiency.288 WASP controls the transcription of splicing factors via phase separation.