Ansgar Schulz

Loss of the ClC-7 Chloride Channel Leads to Osteopetrosis in Mice and Man

Chloride channels play important roles in the plasma membrane and in intracellular organelles. Mice deficient for the ubiquitously expressed ClC-7 Cl(-) channel show severe osteopetrosis and retinal degeneration. Although osteoclasts are present in normal numbers, they fail to resorb bone because they cannot acidify the extracellular resorption lacuna. ClC-7 resides in late endosomal and lysosomal compartments. In osteoclasts, it is highly expressed in the ruffled membrane, formed by the fusion of H(+)-ATPase-containing vesicles, that secretes protons into the lacuna. We also identified CLCN7 mutations in a patient with human infantile malignant osteopetrosis. We conclude that ClC-7 provides the chloride conductance required for an efficient proton pumping by the H(+)-ATPase of the osteoclast ruffled membrane.

Long-term survival and transplantation of haemopoietic stem cells for immunodeficiencies: report of the European experience 1968–99

BACKGROUND Transplantation of allogeneic haemopoietic stem cells can cure several primary immunodeficiencies. This European report focuses on the long-term results of such procedures done between 1968 and December, 1999, for primary immunodeficiencies. METHODS The report includes data from 37 centres in 18 countries, which participated in a European registry for stem-cell transplantation in severe combined immuno deficiencies (SCID) and in other immunodeficiency disorders (non-SCID). 1082 transplants in 919 patients were studied (566 in 475 SCID patients, 512 in 444 non-SCID patients; four procedures excluded owing to insufficient data). Minimum follow-up of 6 months was required. FINDINGS In SCID, 3-year survival with sustained engraftment was significantly better after HLA-identical than after mismatched transplantation (77% vs 54%; p=0.002) and survival improved over time. In HLA-mismatched stem-cell transplantation, B(-) SCID had poorer prognosis than B(+) SCID. However, improvement with time occurred in both SCID phenotypes. In non-SCID, 3-year survival after genotypically HLA-matched, phenotypically HLA-matched, HLA-mismatched related, and unrelated-donor transplantation was 71%, 42%, 42%, and 59%, respectively (p=0.0006). Acute graft versus host disease predicted poor prognosis whatever the donor origin except in related HLA-identical transplantation in SCID. INTERPRETATION The improvement in survival over time indicates more effective prevention and treatment of disease-related and procedure-related complications--eg, infections and graft versus host disease. An important factor is better prevention of graft versus host disease in the HLA-non-identical setting by use of more efficient methods of T-cell depletion. For non-SCID, stem-cell transplantation can provide a cure, and grafts from unrelated donors are almost as beneficial as those from genetically HLA-identical relatives.

Osteopetrosis: genetics, treatment and new insights into osteoclast function.

Osteopetrosis is a genetic condition of increased bone mass, which is caused by defects in osteoclast formation and function. Both autosomal recessive and autosomal dominant forms exist, but this Review focuses on autosomal recessive osteopetrosis (ARO), also known as malignant infantile osteopetrosis. The genetic basis of this disease is now largely uncovered: mutations in TCIRG1, CLCN7, OSTM1, SNX10 and PLEKHM1 lead to osteoclast-rich ARO (in which osteoclasts are abundant but have severely impaired resorptive function), whereas mutations in TNFSF11 and TNFRSF11A lead to osteoclast-poor ARO. In osteoclast-rich ARO, impaired endosomal and lysosomal vesicle trafficking results in defective osteoclast ruffled-border formation and, hence, the inability to resorb bone and mineralized cartilage. ARO presents soon after birth and can be fatal if left untreated. However, the disease is heterogeneous in clinical presentation and often misdiagnosed. This article describes the genetics of ARO and discusses the diagnostic role of next-generation sequencing methods. The management of affected patients, including guidelines for the indication of haematopoietic stem cell transplantation (which can provide a cure for many types of ARO), are outlined. Finally, novel treatments, including preclinical data on in utero stem cell treatment, RANKL replacement therapy and denosumab therapy for hypercalcaemia are also discussed.

Reticular dysgenesis (aleukocytosis) is caused by mutations in the gene encoding mitochondrial adenylate kinase 2

Human severe combined immunodeficiencies (SCID) are phenotypically and genotypically heterogeneous diseases. Reticular dysgenesis is the most severe form of inborn SCID. It is characterized by absence of granulocytes and almost complete deficiency of lymphocytes in peripheral blood, hypoplasia of the thymus and secondary lymphoid organs, and lack of innate and adaptive humoral and cellular immune functions, leading to fatal septicemia within days after birth. In bone marrow of individuals with reticular dysgenesis, myeloid differentiation is blocked at the promyelocytic stage, whereas erythro- and megakaryocytic maturation is generally normal. These features exclude a defect in hematopoietic stem cells but point to a unique aberration of the myelo-lymphoid lineages. The dramatic clinical course of reticular dysgenesis and its unique hematological phenotype have spurred interest in the unknown genetic basis of this syndrome. Here we show that the gene encoding the mitochondrial energy metabolism enzyme adenylate kinase 2 (AK2) is mutated in individuals with reticular dysgenesis. Knockdown of zebrafish ak2 also leads to aberrant leukocyte development, stressing the evolutionarily conserved role of AK2. Our results provide in vivo evidence for AK2 selectivity in leukocyte differentiation. These observations suggest that reticular dysgenesis is the first example of a human immunodeficiency syndrome that is causally linked to energy metabolism and that can therefore be classified as a mitochondriopathy.

Defibrotide in the treatment of children with veno-occlusive disease (VOD): a retrospective multicentre study demonstrates therapeutic efficacy upon early intervention

Summary:Veno-occlusive disease (VOD) of the liver is a complication observed particularly in patients undergoing hematopoietic stem cell transplantation (HSCT). Defibrotide (DF) is a polydeoxyribonucleotide with aptameric activity on endothelium. We evaluated in a retrospective analysis the efficacy of DF in pediatric patients developing hepatic VOD after HSCT.A total of 45 patients between 0.2 and 20 years (median age: 8.2 years) with hepatic VOD were treated with DF: 22 patients (49%) met risk criteria for severe or progressive disease and 23 (51%) for moderately severe and mild disease. The median duration of DF treatment was 17 days. In all, 34 patients (76%) achieved complete response (CR) with a survival rate of 64% at day 100. CR rate in patients with severe disease was 50% with long-term survival of 36%. The average DF dose in the CR group was 45 mg/kg/day and in the no responder (NR) group 27 mg/kg/day. The use of additional drugs besides DF to treat VOD made no difference in the outcome compared to DF alone. The average interval from diagnosis to start of DF was 1 day in the CR and 5.5 days in NR group. In multivariate analysis, early intervention remained the only significant factor for a CR.

An Immunodeficiency Disease with RAG Mutations and Granulomas

We describe three unrelated girls who had an immunodeficiency disease with granulomas in the skin, mucous membranes, and internal organs. All three girls had severe complications after viral infections, including B-cell lymphoma associated with Epstein-Barr virus (EBV). Other findings were hypogammaglobulinemia, a diminished number of T and B cells, and sparse thymic tissue on ultrasonography. Molecular analysis revealed that the patients were compound heterozygotes for mutations in recombination activating gene 1 or 2 (RAG1 or RAG2). In each case, both parents were heterozygous carriers of a RAG mutation. The mutations were associated with reduced function of RAG in vitro (3 to 30% of normal activity). The parents and one sibling in the three families were healthy.

Impaired gastric acidification negatively affects calcium homeostasis and bone mass.

Activation of osteoclasts and their acidification-dependent resorption of bone is thought to maintain proper serum calcium levels. Here we show that osteoclast dysfunction alone does not generally affect calcium homeostasis. Indeed, mice deficient in Src, encoding a tyrosine kinase critical for osteoclast activity, show signs of osteopetrosis, but without hypocalcemia or defects in bone mineralization. Mice deficient in Cckbr, encoding a gastrin receptor that affects acid secretion by parietal cells, have the expected defects in gastric acidification but also secondary hyperparathyroidism and osteoporosis and modest hypocalcemia. These results suggest that alterations in calcium homeostasis can be driven by defects in gastric acidification, especially given that calcium gluconate supplementation fully rescues the phenotype of the Cckbr-mutant mice. Finally, mice deficient in Tcirg1, encoding a subunit of the vacuolar proton pump specifically expressed in both osteoclasts and parietal cells, show hypocalcemia and osteopetrorickets. Although neither Src- nor Cckbr-deficient mice have this latter phenotype, the combined deficiency of both genes results in osteopetrorickets. Thus, we find that osteopetrosis and osteopetrorickets are distinct phenotypes, depending on the site or sites of defective acidification (pages 610–612).

Defibrotide for prophylaxis of hepatic veno-occlusive disease in paediatric haemopoietic stem-cell transplantation: an open-label, phase 3, randomised controlled trial

BACKGROUND Hepatic veno-occlusive disease is a leading cause of morbidity and mortality after haemopoietic stem-cell transplantation (HSCT). We aimed to assess whether defibrotide can reduce the incidence of veno-occlusive disease in this setting. METHODS In our phase 3 open-label, randomised controlled trial, we enrolled patients at 28 European university hospitals or academic medical centres. Eligible patients were younger than 18 years, had undergone myeloablative conditioning before allogeneic or autologous HSCT, and had one or more risk factor for veno-occlusive disease based on modified Seattle criteria. We centrally assigned eligible participants on the basis of a computer-generated randomisation sequence (1:1), stratified by centre and presence of osteopetrosis, to receive intravenous defibrotide prophylaxis (treatment group) or not (control group). The primary endpoint was incidence of veno-occlusive disease by 30 days after HSCT, adjudicated by a masked, independent review committee, in eligible patients who consented to randomisation (intention-to-treat population), and was assessed with a competing risk approach. Patients in either group who developed veno-occlusive disease received defibrotide for treatment. We assessed adverse events to 180 days after HSCT in all patients who received allocated prophylaxis. This trial is registered with ClinicalTrials.gov, number NCT00272948. FINDINGS Between Jan 25, 2006, and Jan 29, 2009, we enrolled 356 eligible patients to the intention-to-treat population. 22 (12%) of 180 patients randomly allocated to the defibrotide group had veno-occlusive disease by 30 days after HSCT compared with 35 (20%) of 176 controls (risk difference -7·7%, 95% CI -15·3 to -0·1; Z test for competing risk analysis p=0·0488; log-rank test p=0·0507). 154 (87%) of 177 patients in the defibrotide group had adverse events by day 180 compared with 155 (88%) of 176 controls. INTERPRETATION Defibrotide prophylaxis seems to reduce incidence of veno-occlusive disease and is well tolerated. Thus, such prophylaxis could present a useful clinical option for this serious complication of HSCT. FUNDING Gentium SpA, European Group for Blood and Marrow Transplantation.

Long-term outcome and lineage-specific chimerism in 194 patients with Wiskott-Aldrich syndrome treated by hematopoietic cell transplantation in the period 1980-2009: an international collaborative study.

In this retrospective collaborative study, we have analyzed long-term outcome and donor cell engraftment in 194 patients with Wiskott-Aldrich syndrome (WAS) who have been treated by hematopoietic cell transplantation (HCT) in the period 1980- 2009. Overall survival was 84.0% and was even higher (89.1% 5-year survival) for those who received HCT since the year 2000, reflecting recent improvement of outcome after transplantation from mismatched family donors and for patients who received HCT from an unrelated donor at older than 5 years. Patients who went to transplantation in better clinical conditions had a lower rate of post-HCT complications. Retrospective analysis of lineage-specific donor cell engraftment showed that stable full donor chimerism was attained by 72.3% of the patients who survived for at least 1 year after HCT. Mixed chimerism was associated with an increased risk of incomplete reconstitution of lymphocyte count and post-HCT autoimmunity, and myeloid donor cell chimerism < 50% was associated with persistent thrombocytopenia. These observations indicate continuous improvement of outcome after HCT for WAS and may have important implications for the development of novel protocols aiming to obtain full correction of the disease and reduce post-HCT complications.

Transplantation in patients with SCID: mismatched related stem cells or unrelated cord blood?

Pediatric patients with SCID constitute medical emergencies. In the absence of an HLA-identical hematopoietic stem cell (HSC) donor, mismatched related-donor transplantation (MMRDT) or unrelated-donor umbilical cord blood transplantation (UCBT) are valuable treatment options. To help transplantation centers choose the best treatment option, we retrospectively compared outcomes after 175 MMRDTs and 74 UCBTs in patients with SCID or Omenn syndrome. Median follow-up time was 83 months and 58 months for UCBT and MMRDT, respectively. Most UCB recipients received a myeloablative conditioning regimen; most MMRDT recipients did not. UCB recipients presented a higher frequency of complete donor chimerism (P = .04) and faster total lymphocyte count recovery (P = .04) without any statistically significance with the preparative regimen they received. The MMRDT and UCBT groups did not differ in terms of T-cell engraftment, CD4(+) and CD3(+) cell recoveries, while Ig replacement therapy was discontinued sooner after UCBT (adjusted P = .02). There was a trend toward a greater incidence of grades II-IV acute GVHD (P = .06) and more chronic GVHD (P = .03) after UCBT. The estimated 5-year overall survival rates were 62% ± 4% after MMRDT and 57% ± 6% after UCBT. For children with SCID and no HLA-identical sibling donor, both UCBT and MMRDT represent available HSC sources for transplantation with quite similar outcomes.