WHIM‐associated mutations of CXCR4 result in the production of a C‐terminal truncated receptor that displays impaired internalisation and enhanced signalling, resulting in abnormal neutrophil retention in the bone marrow (myelokathexis) and a consequent chronic blood neutropenia (Figure 1).15, 16 Therefore, despite having normal numbers of mature neutrophils in the bone marrow, some WHIM patients exhibit a blood neutropenia. The gene discussed is CXCR4; the disease is neutropenia.