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•TCR-triggered T-cell and Fc receptor–triggered NK-cell assays are most accurate for diagnosing defective cytotoxic lymphocyte exocytosis.•The standard K562 cell assay has high interindividual variability and is affected by expanded NK-cell subsets and transportation stress.

Several monogenic causes of familial myelodysplastic syndrome (MDS) have recently been identified. We studied 2 families with cytopenia, predisposition to MDS with chromosome 7 aberrations, immunodeficiency, and progressive cerebellar dysfunction. Genetic studies uncovered heterozygous missense mutations in SAMD9L, a tumor suppressor gene located on chromosome arm 7q. Consistent with a gain-of-function effect, ectopic expression of the 2 identified SAMD9L mutants decreased cell proliferation relative to wild-type protein. Of the 10 individuals identified who were heterozygous for either SAMD9Lmutation, 3 developed MDS upon loss of the mutated SAMD9Lallele following intracellular infections associated with myeloid, B-, and natural killer (NK)–cell deficiency. Five other individuals, 3 with spontaneously resolved cytopenic episodes in infancy, harbored hematopoietic revertant mosaicism by uniparental disomy of 7q, with loss of the mutated allele or additional in cisSAMD9Ltruncating mutations. Examination of 1 individual indicated that somatic reversions were postnatally selected. Somatic mutations were tracked to CD34+hematopoietic progenitor cell populations, being further enriched in B and NK cells. Stimulation of these cell types with interferon (IFN)-α or IFN-γ induced SAMD9L expression. Clinically, revertant mosaicism was associated with milder disease, yet neurological manifestations persisted in 3 individuals. Two carriers also harbored a rare, in transgerm line SAMD9Lmissense loss-of-function variant, potentially counteracting the SAMD9Lmutation. Our results demonstrate that gain-of-function mutations in the tumor suppressor SAMD9Lcause cytopenia, immunodeficiency, variable neurological presentation, and predisposition to MDS with −7/del(7q), whereas hematopoietic revertant mosaicism commonly ameliorated clinical manifestations. The findings suggest a role for SAMD9L in regulating IFN-driven, demand-adapted hematopoiesis.

Hemophagocytic lymphohistiocytosis (HLH) used to have a dismal prognosis. We report the final results of HLH-94, the largest prospective diagnostic/therapeutic HLH study so far. The treatment includes immunosuppressive and cytotoxic therapy aiming at clinical remission, followed by HSCT in patients with familial, persistent, or recurrent disease. Altogether, 249 patients fulfilled inclusion criteria and started HLH-94 therapy (July 1994-December 2003); 227 (91%) were followed-up for ≥ 5 years. At 6.2 years median follow-up, estimated 5-year probability of survival was 54% ± 6%. Seventy-two patients (29%) died before HSCT, 64 within 1 year, 97% of whom had active disease. In 124 patients who underwent HSCT, 5-year survival was 66 ± 8%; tendency to increased survival (P = .064) in patients with nonactive disease at HSCT. Patients with familial disease had a 5-year survival of 50% ± 13%; none survived without HSCT. Patients deceased during the first 2 months more often had jaundice, edema, and elevated creatinine. Forty-nine patients (20%) were alive without signs of HLH activity and off-therapy > 1-year without HSCT; they presented at older age (P < .001), were more often female (P = .011), and less often had CNS disease (P < .001) or hepatomegaly (P = .007). To conclude, HLH-94 chemoimmunotherapy has considerably improved outcome in HLH. Collaborative efforts are needed to further reduce early mortality, HSCT-related mortality, and neurologic late effects.

Kostmann syndrome, or severe congenital neutropenia (SCN), is an autosomal recessive disorder of neutrophil production. To investigate the potential role of apoptosis in SCN, bone marrow aspirates and biopsies were obtained from 4 patients belonging to the kindred originally described by Kostmann and 1 patient with SCN of unknown inheritance. An elevated degree of apoptosis was observed in the bone marrow of these patients, and a selective decrease in B-cell lymphoma-2 (Bcl-2) expression was seen in myeloid progenitor cells. Furthermore, in vitro apoptosis of bone marrow-derived Kostmann progenitor cells was increased, and mitochondrial release of cytochrome cwas detected in CD34+and CD33+progenitors from patients, but not in controls. Administration of granulocyte colony-stimulating factor (G-CSF) restored Bcl-2 expression and improved survival of myeloid progenitor cells. In addition, cytochrome crelease was partially reversed upon incubation of progenitor cells with G-CSF. In sum, these studies establish a role for mitochondria-dependent apoptosis in the pathogenesis of Kostmann syndrome and yield a tentative explanation for the beneficial effect of growth factor administration in these patients. (Blood. 2004;103:3355-3361)

Hemophagocytic lymphohistiocytosis (HLH) comprises familial (primary) hemophagocytic lymphohistiocytosis (FHL) and secondary HLH (SHLH), both clinically characterized by fever, hepatosplenomegaly, and cytopenia. FHL, an autosomal recessive disease invariably fatal when untreated, is associated with defective triggering of apoptosis and reduced cytotoxic activity, resulting in a widespread accumulation of T lymphocytes and activated macrophages. In 1994 the Histiocyte Society initiated a prospective international collaborative therapeutic study (HLH-94), aiming at improved survival. It combined chemotherapy and immunotherapy (etoposide, corticosteroids, cyclosporin A, and, in selected patients, intrathecal methotrexate), followed by bone marrow transplantation (BMT) in persistent, recurring, and/or familial disease. Between July 1, 1994, and June 30, 1998, 113 eligible patients aged no more than 15 years from 21 countries started HLH-94. All had either an affected sibling (n = 25) and/or fulfilled the Histiocyte Society diagnostic criteria. At a median follow-up of 3.1 years, the estimated 3-year probability of survival overall was 55% (95% confidence interval ± 9%), and in the familial cases, 51% (± 20%). Twenty enrolled children were alive and off therapy for more than 12 months without BMT. For patients who received transplants (n = 65), died prior to BMT (n = 25), or were still on therapy (n = 3), the 3-year survival was 45% (± 10%). The 3-year probability of survival after BMT was 62% (± 12%). HLH-94 is very effective, allowing BMT in most patients. Survival of children with HLH has been greatly improved.

Familial hemophagocytic lymphohistiocytosis (FHL) is a frequently missed and almost uniformly fatal childhood disorder. It is characterized by fever, hepatosplenomegaly, cytopenia, coagulopathy, and hypertriglyceridemia. The pathogenesis of FHL is not known but the above clinical and laboratory findings are compatible with reported in vitro and in vivo effects of several inflammatory cytokines. We measured circulating interferon-γ (IFN-γ), tumor necrosis factor/cachectin (TNF), and interleukin-6 (IL-6) in nine children with FHL. During active disease, elevated IFN-γ was detected in seven of seven children, TNF in six of six, and IL-6 in two of six children studied. Thus, important inflammatory cytokines are augmented in active FHL and may contribute to the pathogenesis of the disease. Soluble CD8 was also increased in seven of seven children, which suggests a pathophysiologic importance of cytotoxic T lymphocytes. Because FHL appears to be associated with a systemic hypercytokinemia, our results also indicate that studies of FHL may contribute to the understanding of cytokine effects in vivo. Moreover, FHL is a hereditary disorder, suggesting that the hypercytokinemia is caused by a genetic defect in cytokine regulation.

Myelodysplastic syndrome (MDS) is a heterogeneous group of clonal hematopoietic diseases characterized by impaired hematopoiesis and progression to acute myeloid leukemia (AML). Although rare, several monogenic causes of familial MDS/AML have recently been molecularly defined. We studied two families with variable manifestation of cytopenia, MDS with cytogenetic aberrations involving chromosome 7, immunodeficiency, and neurologic disease consistent with ataxia-pancytopenia syndrome.