Additional genetic diseases in which HLH is a typical and common manifestation (primary HLH) include congenital immunodeficiency syndromes, such as Griscelli syndrome type 2 (GS2), caused by mutations of RAB27A, Chédiak–Higashi syndrome, X-linked lymphoproliferative disease, X-linked immunodeficiency with magnesium defect, interleukin-2-inducible T-cell kinase deficiency, and Hermansky–Pudlak syndrome. The gene discussed is ITK; the disease is hemophagocytic syndrome.