Novel syntaxin 11 gene (STX11) mutation in three Argentinean patients with hemophagocytic lymphohistiocytosis

Familial hemophagocytic lymphohistiocytosis in a girl with a novel homozygous mutation of STX11: A case report

RATIONALE

Familial hemophagocytic lymphohistiocytosis (FHL) is a rare fatal autosomal recessively inherited disease and can be divided into five types. The mortality of untreated patients is up to 95% and it can be healed only after immunochemotherapy for disease control and hematopoietic stem cell transplantation. Clinical data of a girl with late-onset and recurrent hemophagocytic lymphohistiocytosis (HLH) was retrospectively analyzed to determine the etiology and potential pathogenic gene.

PATIENT CONCERNS AND CLINICAL FINDINGS

The proband was a female child patient from a consanguineous marriage family who was 11 years old, and clinically manifested delayed (onset at the age of 4 years and 6 months) and recrudescent HLH. Both of her elder brothers died at the ages of 4 and 5 years, respectively. The patient had a degranulation function defect of CD107a in natural killer (NK) cells, and the degranulation function of cytotoxic T lymphocytes (CTL) obviously declined (ΔMFI: 1.4%, normal ≧2.8%); the degranulation function of NK cells and CTL of her father was also obviously reduced. To identify possible underlying genetic causes, gene mutation analysis was undertaken. A novel homozygous nonsense mutation in STX11 (c.49C>T, p.Q17X) was documented, arising from both her parents.

DIAGNOSIS

According to the clinical manifestations and detection results of STX11, the diagnosis of FHL-type 4 was confirmed and her parents were heterozygotic carriers.

INTERVENTIONS AND OUTCOMES

Good responses to HLH-2004 chemotherapy had been achieved for each onset, and the maximum remission duration (without taking any drug) was 23 months. The patient has been alive for 82 months since the onset, and has stopped taking dexamethasone and etoposide, but is still on oral cyclosporine to maintain the treatment. She has performed HLA matching and now is actively looking for a donor to prepare hematopoietic stem cell transplantation.

CONCLUSIONS

Relevant gene detections should be implemented at the earliest for young patients from consanguineous marriages and with a family history of HLH so as to provide a basis for etiological diagnosis and radical treatment by hematopoietic stem cell transplantation and provide accurate genetic counseling for family members.

A Novel Syntaxin 11 Gene (STX11) Mutation c.650T>C, p.Leu217Pro, in a Korean Child With Familial Hemophagocytic Lymphohistiocytosis

We report the first Far Eastern case of a Korean child with familial hemophagocytic lymphohistiocytosis (HLH) caused by a novel syntaxin 11 (STX11) mutation. A 33-month-old boy born to non-consanguineous Korean parents was admitted for intermittent fever lasting one week, pancytopenia, hepatosplenomegaly, and HLH in the bone marrow. Under the impression of HLH, genetic study revealed a novel homozygous missense mutation of STX11: c.650T>C, p.Leu217Pro. Although no large deletion or allele drop was identified, genotype analysis demonstrated that the homozygous c.650T>C may have resulted from the duplication of a maternal (unimaternal) chromosomal region and concurrent loss of the other paternal allele, likely caused by meiotic errors such as two crossover events. A cumulative study of such novel mutations and their effects on specific protein interactions may deepen the understanding of how abnormal STX1 expression results in deficient cytotoxic function.

Hemophagocytic lymphohistiocytosis: review of etiologies and management

Hemophagocytic lymphohistiocytosis (HLH) covers a wide array of related life-threatening conditions featuring ineffective immunity characterized by an uncontrolled hyperinflammatory response. HLH is often triggered by infection. Familial forms result from genetic defects in natural killer cells and cytotoxic T-cells, typically affecting perforin and intracellular vesicles. HLH is likely under-recognized, which contributes to its high morbidity and mortality. Early recognition is crucial for any reasonable attempt at curative therapy to be made. Current treatment regimens include immunosuppression, immune modulation, chemotherapy, and biological response modification, followed by hematopoietic stem-cell transplant (bone marrow transplant). A number of recent studies have contributed to the understanding of HLH pathophysiology, leading to alternate treatment options; however, much work remains to raise awareness and improve the high morbidity and mortality of these complex conditions.

Analysis of familial hemophagocytic lymphohistiocytosis type 4 (FHL-4) mutant proteins reveals that S-acylation is required for the function of syntaxin 11 in natural killer cells

Natural killer (NK) cell secretory lysosome exocytosis and cytotoxicity are impaired in familial hemophagocytic lymphohistiocytosis type 4 (FHL-4), a disorder caused by mutations in the gene encoding the SNARE protein syntaxin 11. We show that syntaxin 11 binds to SNAP23 in NK cells and that this interaction is reduced by FHL-4 truncation and frameshift mutation proteins that delete all or part of the SNARE domain of syntaxin 11. In contrast the FHL-4 mutant proteins bound to the Sec-1/Munc18-like (SM) protein Munc18-2. We demonstrate that the C-terminal cysteine rich region of syntaxin 11, which is deleted in the FHL-4 mutants, is S-acylated. This posttranslational modification is required for the membrane association of syntaxin 11 and for its polarization to the immunological synapse in NK cells conjugated to target cells. Moreover, we show that Munc18-2 is recruited by syntaxin 11 to intracellular membranes in resting NK cells and to the immunological synapse in activated NK cells. This recruitment of Munc18-2 is abolished by deletion of the C-terminal cysteine rich region of syntaxin 11. These results suggest a pivotal role for S-acylation in the function of syntaxin 11 in NK cells.

Analyses of the PRF1 gene in individuals with hemophagocytic lymphohystiocytosis reveal the common haplotype R54C/A91V in Colombian unrelated families associated with late onset disease

Familial hemophagocytic lymphohistiocytosis (FHL), is a rare autosomal recessive disorder characterized by an impairment of cytotoxic cells and uncontrolled activation of macrophages. This study presents the first description of four patients with FHL type 2 in Latin America. Patient 1 fulfilled the disease diagnostic criteria since 2 months of age, whereas patients 2, 3 and 4 exhibited the typical manifestations of the disease only later in their childhood. The PRF1 genetic analysis in these patients revealed two previously reported mutations: L17fsx50 and R54C. Interestingly, seven out of the 8 alleles evaluated here in patients carried the haplotype R54C/A91V, suggesting that this is a highly frequent FHL type 2 allele in Colombia. This haplotype confers residual cytotoxic function leading to late onset disease. Therefore, this report highlights the remarkable complexity of FHL diagnostic, emphasizing the importance of the genetic characterization of the disease.

Unusual functional manifestations of a novel STX11 frameshift mutation in two infants with familial hemophagocytic lymphohistiocytosis type 4 (FHL4)

Familial hemophagocytic lymphohistiocytosis (FHL) is typically an autosomal recessive, early-onset, life-threatening immune disorder. Loss-of-function mutations in STX11 have been found to impair NK cell degranulation and cytotoxicity. Here, we describe two unrelated infants of Punjabi descent presenting with FHL and carrying a novel, homozygous STX11 frameshift mutation [c.867dupG]. Western blot analysis indicated absence of syntaxin-11. Unexpectedly, degranulation by NK cells from one of the patients was not impaired, although patient NK cells showed mildly and significantly decreased cytotoxicity, respectively. Importantly, these observations imply that STX11 should be sequenced in HLH patients even when impaired NK cell degranulation is not found.