We report an STXBP2 homozygous missense mutation c.1139A>G, p.(Gln380Arg) consistent with a genetic diagnosis of familial hemophagocytic lymphohistiocytosis type 5 associated with chronic diarrhea in a seven-year-old girl.
The second and third patients with homozygous splice site mutation (c.430-1G>A) in STXBP2 were siblings who presented at birth with fevers, elevated aspartate aminotransferase, alanine aminotransferase, and hyperferritinemia but did not fulfill FHL criteria.
FHL mutation analysis of the patient and her parents revealed that she presented compound heterozygosity for STXBP2: a novel missense mutation c.663G > C (p.Glu221Asp) and the known pathogenic splice-site mutation c.1247-1G > C (p.Val417LeufsX126).
Novel Patient with Late-Onset Familial Hemophagocytic Lymphohistiocytosis with STXBP2 Mutations Presenting with Autoimmune Hepatitis, Neurological Manifestations and Infections Associated with Hypogammaglobulinemia.
The Sec/Munc protein, Munc18-2, and its binding partner Syntaxin 11 (STX11) are both required for granule secretion, with mutations in either leading to the primary immunodeficiency, Familial Haemophagocytic Lymphohistiocytosis (FHL4 and 5).
In the majority of cases, these disorders are caused by biallelic inactivating germline mutations in genes such as RAB27A (GS) and PRF1, UNC13D, STX11, and STXBP2 (F-HLH).
Intrinsic defects in erythroid cells from familial hemophagocytic lymphohistiocytosis type 5 patients identify a role for STXBP2/Munc18-2 in erythropoiesis and phospholipid scrambling.
Recent analysis of patients with familial hemophagocytic lymphohistiocytosis type 5 has identified the E132A mutation in the hydrophobic pocket of Munc18-2, prompting us to examine the role of this region in the context of immune cell secretion.
Familial hemophagocytic lymphohistiocytosis (FHL) is a rare primary immune disorder defined by mutations in the syntaxin binding protein 2 (STXBP2) alias MUNC18-2.
Mutations in either syntaxin 11 (Stx11) or Munc18-2 abolish cytotoxic T lymphocytes (CTL) and natural killer cell (NK) cytotoxicity, and give rise to familial hemophagocytic lymphohistiocytosis (FHL4 or FHL5, respectively).
Distinct mutations in STXBP2 are associated with variable clinical presentations in patients with familial hemophagocytic lymphohistiocytosis type 5 (FHL5).
We analyzed disease manifestations, NK-cell and T-cell cytotoxicity and degranulation, markers of T-cell activation and B-cell differentiation as well as Natural Killer T cells in 8 patients with atypical familial hemophagocytic lymphohistiocytosis due to mutations in UNC13D and STXBP2.
Here, we show that the gene encoding syntaxin-binding protein 2 (Munc18-2; official gene symbol STXBP2) is mutated in another subset of patients with FHL (designated by us as "FHL5").