WAS and X-linked severe congenital neutropenia: X-linked neutropenia (XLN) is a more recently described WASp-associated disease caused by point mutations (WASpL270P, WASpS272P, WASpI276S, and WASpI294T) in the WASp GTPase-binding domain that renders WASp constitutively active by destroying the autoinhibited folding of WASp [33–37].