Rapid intracellular transport and secretion of cytotoxic granules through the immunological synapse requires a balanced interaction of several proteins. Disturbance of this highly regulated process underlies familial hemophagocytic lymphohistiocytosis (FHL), a genetically heterogeneous autosomal-recessive disorder characterized by a severe hyperinflammatory phenotype. Here, we have assigned FHL-5 to a 1 Mb region on chromosome 19p by using high-resolution SNP genotyping in eight unrelated FHL patients from consanguineous families. Subsequently, we found nine different mutations, either truncating or missense, in STXBP2 in twelve patients from Turkey, Saudi Arabia, and Central Europe. STXBP2 encodes syntaxin binding protein 2 (Munc18-2), involved in the regulation of vesicle transport to the plasma membrane. We have identified syntaxin 11, a SNARE protein mutated in FHL-4, as an interaction partner of STXBP2. This interaction is eliminated by the missense mutations found in our FHL-5 patients, which leads to a decreased stability of both proteins, as shown in patient lymphocytes. Activity of natural killer and cytotoxic T cells was markedly reduced or absent, as determined by CD107 degranulation. Our findings thus identify a key role for STXBP2 in lytic granule exocytosis.

Familial hemophagocytic lymphohistiocytosis (FHL) is a rare autosomal recessive disorder characterized by hyperactive phagocytes and defects in natural killer cell function. It has been shown previously that mutations in the perforin 1 gene (PRF1) and in UNC13D are associated with FHL2 and FHL3, respectively, indicating genetic heterogeneity. We performed genome-wide homozygosity mapping in a large consanguineous Kurdish kindred with five children affected with FHL. Linkage to a 10 cM region on chromosome 6q24 between D6S1569 and D6S960 defined a novel FHL locus. By screening positional candidate genes, we identified a homozygous deletion of 5 bp in the syntaxin 11 gene (STX11) in this family. We could demonstrate that syntaxin 11 protein was absent in the mononuclear cell fraction of patients with the homozygous 5 bp deletion. In addition to this family, we found homozygous mutations in STX11 in five consanguineous Turkish/Kurdish FHL kindreds including two families with the 5 bp deletion, one family with a large 19.2 kb genomic deletion spanning the entire coding region of STX11 (exon 2) and two families with a nonsense mutation that leads to a premature stop codon in the C-terminal end of the protein. As both STX11 and UNC13D are involved in vesicle trafficking and membrane fusion, we conclude that, besides mutations in perforin 1, defects in the endocytotic or the exocytotic pathway may be a common mechanism in FHL.

Familial hemophagocytic lymphohistiocytosis (FHL) is a life-threatening disorder

Communicated by Jurgen HorstFamilial hemophagocytic lymphohistiocytosis (FHL) is an autosomal-recessive disease that affects young children. It presents as a severe hyperinflammatory syndrome with activated macrophages and T lymphocytes. Mutations in the perforin 1 gene (PRF1) were found in FHL-2 in 15-50% of all cases. Defective granule exocytosis caused by mutations in the hMunc13-4 gene (UNC13D) has been described in FHL-3. FHL-4 patients have mutations in STX11, a t-SNARE involved in intracellular trafficking. We analyzed a large group of 63 unrelated patients with FHL of different geographic origins (Turkey:32; Germany:23; others:8) for mutations in STX11, PRF1, and UNC13D. We identified mutations in 38 samples (20 in PRF1, 12 in UNC13D, and six in STX11). Of 32 patients from Turkey, 14 had mutations in PRF1, six had mutations in UNC13D, and six had mutations in STX11. The mutation Trp374X in PRF1 was found in 12 patients from Turkey and was associated with a very early onset of the disease below the age of 3 months in all cases. In contrast, three of 23 and four of 23 patients from Germany, and three of eight and two of eight from other origins showed mutations in PRF1 and UNC13D, respectively, but none in STX11. Thus, FHL-2, FHL-3, and FHL-4 account for 80% of the HLH cases of Turkish origin, and for 30% of German patients. Furthermore, we identified mutations in RAB27A in three patients with FHL-related Griscelli syndrome type 2. In functional studies using a mammalian two-hybrid system we found that missense mutations Ala87Pro in Rab27a and Leu403Pro in hMunc13-4 each prevented the formation of a stable hMunc13-4/Rab27a complex in vitro. Our findings demonstrate extensive genetic and allelic heterogeneity in FHL and delineate an approach for functionally characterizing missense mutations in RAB27A and UNC13D. Hum Mutat 27(1), [62][63][64][65][66][67][68] 2006.

Familial hemophagocytic lymphohistiocytosis (FHL) is a genetically determined

SummaryHaemophagocytic lymphohistiocytosis (HLH) in the context of malignancy is mainly considered a challenge of adult haematology. While this association is also observed in children, little is known regarding inciting factors, appropriate treatment and prognosis. We retrospectively analysed 29 paediatric and adolescent patients for presenting features, type of neoplasm or preceding chemotherapy, treatment and outcome. Haemophagocytic lymphohistiocytosis was considered triggered by the malignancy (M-HLH) in 21 patients, most of whom had T-(n = 12) or B-cell neoplasms (n = 7), with Epstein-Barr virus as a co-trigger in five patients. In eight patients, HLH occurred during chemotherapy (Ch-HLH) for malignancy, mainly acute leukaemias (n = 7); an infectious trigger was found in seven. In Mand Ch-HLH, median overall survival was 1Á2 and 0Á9 years, and the 6 month survival rates were 67% and 63%, respectively. Seven of 11 deceased M-HLH patients exhibited active malignancy and HLH at the time of death, while only two out of five deceased Ch-HLH patients had evidence of active HLH. To overcome HLH, malignancy-and HLH-directed treatments were administered in the M-HLH cohort; however, it was not possible to determine superiority of one approach over the other. For Ch-HLH, treatment ranged from postponement of chemotherapy to the use of etoposide-containing regimens.

PRF1 mutations are spread over the functional domains. Specific mutations are strongly associated with Turkish, African American and Japanese ethnic groups. Later onset and residual cytotoxic function are observed in patients with at least one missense mutation.

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