The function of LYST (lysosomal trafficking regulator) is incompletely understood, but its mutation is known to cause Chediak-Higashi syndrome and some forms of hemophagocytic lymphohistiocytosis, characterized by defective lymphocyte degranulation due to changes in the morphology and function of secretory lysosomes (59–62). The gene discussed is LYST; the disease is Chediak-Higashi syndrome.