BACKGROUND: WHIM (Warts, Hypogammaglobulinemia, Infections and Myelokathexis) syndrome is an ultrarare inborn error of immunity caused by heterozygous, hyperfunctional CXCR4 mutations that impede leukocyte egress from bone marrow, resulting in panleukopenia. The gene discussed is CXCR4; the disease is infection.