It can be primary, related to several molecular defects (mutations in perforin 1, UNC 13D, syntaxin 11, syntaxin-binding protein-2, SH2D1A, RAB27A, and XIAP or a defect on chromosome 9q21.3-22), or secondary to infections, autoimmune diseases, chronic inflammatory disorders, acquired immunodeficiencies, and various malignancies, mainly hematological malignancies [1, 2]. The gene discussed is RAB27A; the disease is acquired immunodeficiency.