The higher incidence and delayed onset of late-onset neutropenia in our cohort might implicate 2 factors as follows: (i) high exposure to cytotoxic agents, including cyclophosphamide, which can induce neutropenia and (ii) persistent B cell depletion causing cytokine imbalances, such as B cell activating factor and stromal-derived factor 1, that might inhibit neutrophil production or egression. The gene discussed is TNFSF13B; the disease is neutropenia.