STXBP2 and hemophagocytic syndrome: <i>STXBP2-R190C</i> Variant in a Patient With Neonatal Hemophagocytic Lymphohistiocytosis (HLH) and <i>G6PD</i> Deficiency Reveals a Critical Role of STXBP2 Domain 2 on Granule Exocytosis.