Gabriele Strauss

Compound inheritance of a low-frequency regulatory SNP and a rare null mutation in exon-junction complex subunit RBM8A causes TAR syndrome

The exon-junction complex (EJC) performs essential RNA processing tasks. Here, we describe the first human disorder, thrombocytopenia with absent radii (TAR), caused by deficiency in one of the four EJC subunits. Compound inheritance of a rare null allele and one of two low-frequency SNPs in the regulatory regions of RBM8A, encoding the Y14 subunit of EJC, causes TAR. We found that this inheritance mechanism explained 53 of 55 cases (P < 5 × 10−228) of the rare congenital malformation syndrome. Of the 53 cases with this inheritance pattern, 51 carried a submicroscopic deletion of 1q21.1 that has previously been associated with TAR, and two carried a truncation or frameshift null mutation in RBM8A. We show that the two regulatory SNPs result in diminished RBM8A transcription in vitro and that Y14 expression is reduced in platelets from individuals with TAR. Our data implicate Y14 insufficiency and, presumably, an EJC defect as the cause of TAR syndrome.

X-linked thrombocytopenia (XLT) due to WAS mutations: clinical characteristics, long-term outcome, and treatment options

A large proportion of patients with mutations in the Wiskott-Aldrich syndrome (WAS) protein gene exhibit the milder phenotype termed X-linked thrombocytopenia (XLT). Whereas stem cell transplantation at an early age is the treatment of choice for patients with WAS, therapeutic options for patients with XLT are controversial. In a retrospective multicenter study we defined the clinical phenotype of XLT and determined the probability of severe disease-related complications in patients older than 2 years with documented WAS gene mutations and mild-to-moderate eczema or mild, infrequent infections. Enrolled were 173 patients (median age, 11.5 years) from 12 countries spanning 2830 patient-years. Serious bleeding episodes occurred in 13.9%, life-threatening infections in 6.9%, autoimmunity in 12.1%, and malignancy in 5.2% of patients. Overall and event-free survival probabilities were not significantly influenced by the type of mutation or intravenous immunoglobulin or antibiotic prophylaxis. Splenectomy resulted in increased risk of severe infections. This analysis of the clinical outcome and molecular basis of patients with XLT shows excellent long-term survival but also a high probability of severe disease-related complications. These observations will allow better decision making when considering treatment options for individual patients with XLT.

Use of recombinant factor VIIa (NovoSeven®) in patients with Glanzmann thrombasthenia

Recombinant factor VIIa (rFVIIa; NovoSeven, Novo Nordisk, Bagsvaerd, Denmark) appears effective and relatively safe for the treatment of bleeding and for surgical prophylaxis in patients with Glanzmann thrombasthenia as reported to the International Registry on rFVIIa and Congenital Platelet Disorders. One of the shortcomings of the Registry data is the heterogeneity of treatment protocol, including dosage, number of doses used, duration of treatment before declaration of failure, and mode of rFVIIa administration (bolus v continuous infusion). The data are not yet sufficient to define optimal regimens for various indications such as the type of bleeding or the type of procedures. The place of this drug compared to platelet transfusion in the overall management of patients with Glanzmann thrombasthenia will need to be determined in relationship to a number of challenges and unresolved issues in the clinical care of these patients. These issues include: how to improve local measures for patients with mucosal bleeds, optimal management of young women during menarche, optimal platelet transfusion regimens for various indications, the relationship between antiplatelet antibodies detected by monoclonal antibody-specific immobilization of platelet antigens (MAIPA) and effectiveness of platelet transfusion, whether there are other biological tests that may correlate with effectiveness of platelet transfusion, and management of pregnancy and delivery regarding antiplatelet immunization.

Congenital amegakaryocytic thrombocytopenia: a retrospective clinical analysis of 20 patients.

Congenital amegakaryocytic thrombocytopenia (CAMT) is a rare bone marrow failure syndrome characterised by isolated thrombocytopenia because of ineffective megakaryocytopoiesis at birth. In the last 10 years, we collected data from 20 patients diagnosed with CAMT based on a severe thrombocytopenia since birth and absent or markedly decreased numbers of megakaryocytes in the bone marrow. Fanconis anaemia and thrombocytopenia absent radii syndrome were ruled out for all patients. We retrospectively compared the clinical courses, laboratory findings and treatment outcome. Development of pancytopenia was observed in 14 of the patients, only one patient presented with an isolated thrombocytopenia over a period of over 14 years. One boy died from bleeding complications. We defined two groups of patients according to the course of platelet counts during the first year of life, which also differed in the course of development of pancytopenia. Physical anomalies in addition to haematopoiesis were found in a number of patients: two children presented with cardiac defects, six with growth abnormalities, and four with retardation of psychomotor development. Fifteen patients were treated with haematopoietic stem cell transplantation, four of whom died of transplantation‐related events.

SNX10 mutations define a subgroup of human autosomal recessive osteopetrosis with variable clinical severity.

Human Autosomal Recessive Osteopetrosis (ARO) is a genetically heterogeneous disorder caused by reduced bone resorption by osteoclasts. In 2000, we found that mutations in the TCIRG1 gene encoding for a subunit of the proton pump (V‐ATPase) are responsible for more than one‐half of ARO cases. Since then, five additional genes have been demonstrated to be involved in the pathogenesis of the disease, leaving approximately 25% of cases that could not be associated with a genotype. Very recently, a mutation in the sorting nexin 10 (SNX10) gene, whose product is suggested to interact with the proton pump, has been found in 3 consanguineous families of Palestinian origin, thus adding a new candidate gene in patients not previously classified. Here we report the identification of 9 novel mutations in this gene in 14 ARO patients from 12 unrelated families of different geographic origin. Interestingly, we define the molecular defect in three cases of “Västerbottenian osteopetrosis,” named for the Swedish Province where a higher incidence of the disease has been reported. In our cohort of more than 310 patients from all over the world, SNX10‐dependent ARO constitutes 4% of the cases, with a frequency comparable to the receptor activator of NF‐κB ligand (RANKL), receptor activator of NF‐κB (RANK) and osteopetrosis‐associated transmembrane protein 1 (OSTM1)‐dependent subsets. Although the clinical presentation is relatively variable in severity, bone seems to be the only affected tissue and the defect can be almost completely rescued by hematopoietic stem cell transplantation (HSCT). These results confirm the involvement of the SNX10 gene in human ARO and identify a new subset with a relatively favorable prognosis as compared to TCIRG1‐dependent cases. Further analyses will help to better understand the role of SNX10 in osteoclast physiology and verify whether this protein might be considered a new target for selective antiresorptive therapies.

Two patterns of thrombopoietin signaling suggest no coupling between platelet production and thrombopoietin reactivity in thrombocytopenia-absent radii syndrome

Background Thrombocytopenia with absent radii syndrome is defined by bilateral radius aplasia and thrombocytopenia. Due to impaired thrombopoietin signaling there are only few bone marrow megakaryocytes and these are immature; the resulting platelet production defect improves somewhat over time. A microdeletion on chromosome 1q21 is present in all patients but is not sufficient to form thrombocytopenia with absent radii syndrome. We aimed to refine the signaling defect in this syndrome. Design and Methods We report an extended study of 23 pediatric and adult patients suffering from thrombocytopenia with absent radii syndrome in order to scrutinize thrombopoietin signal transduction by immunoblotting and gel electrophoretic shift assays. In addition, platelet immunotyping and reactivity were analyzed by flow cytometry. Results were correlated with clinical data including age and platelet counts. Results Two distinct signaling patterns were identified. Juvenile patients showed abrogated thrombopoietin signaling (pattern #1), which is restored in adults (pattern #2). Phosphorylated Jak2 was indicative of activation of STAT1, 3 and 5, Tyk2, ERK, and Akt, showing its pivotal role in distinct thrombopoietin-dependent pathways. Jak2 cDNA was not mutated and the thrombopoietin receptor was present on platelets. All platelets of patients expressed normal levels of CD41/61, CD49b, and CD49f receptors, while CD42a/b and CD29 were slightly reduced and the fibronectin receptor CD49e markedly reduced. Lysosomal granule release in response to thrombin receptor activating peptide was diminished. Conclusions We show a combined defect of platelet production and function in thrombocytopenia with absent radii syndrome. The rise in platelets that most patients have during the first years of life preceded the restored thrombopoietin signaling detected at a much later age, implying that these events are uncoupled and that an unknown factor mediates the improvement of platelet production.

Potential Risks to Stable Long-term Outcome of Allogeneic Hematopoietic Stem Cell Transplantation for Children With Cerebral X-linked Adrenoleukodystrophy

Key Points Question What are the risks to stable neurocognitive outcome after allogeneic hematopoietic stem cell transplantation for childhood cerebral X-linked adrenoleukodystrophy? Findings This single-center case series involving 36 boys with cerebral X-linked adrenoleukodystrophy found that all patients with favorable neuroimaging and matched bone marrow transplant had stable neurocognitive survival. In contrast, the disease progressed for all patients without these factors, and many developed major functional disabilities. Meaning Patients without matched bone marrow transplant or with unfavorable neuroimaging findings may need therapeutic options other than hematopoietic stem cell transplantation.

Mini photopheresis for refractory chronic graft-versus-host disease in children and adolescents: MINI PHOTOPHERESIS FOR CHRONIC GVHD

Extracorporeal photopheresis (ECP) has been established to treat graft‐versus‐host disease. Our mini ECP technique (mini‐ECP) allows for treatment of patients with GVHD and contraindications for classical ECP or low body weight. The safety and efficacy of applying ECP for the long‐term treatment of chronic GVHD (cGVHD) have not been described.

Unexpected pregnancy after allogeneic stem cell transplantation.

Premature ovarian failure is a considerable problem following treatment of childhood cancer that depends on clinical risk factors and treatment. This year, we reported in your journal that an imminent infertility can be early identified by repeated, considerably reduced anti-Müllerian hormone values. This information can improve the patients’ chances of having children of their own through either suitably timed family planning or the use of reproductive medical methods. To emphasize the need and adequate use of reliable prognostic fertility markers after cancer therapy, we want to report a recent and unexpected pregnancy after allogeneic hematopoietic stem cell transplantation (HSCT). The future mother received an allogeneic HSCT with a conditioning regimen of busulfan with 4 ¥ 4 mg/kg bodyweight (BW) and cyclophosphamide with 2 ¥ 60 mg/kg BW at the age of 11 years due to the diagnosis of paroxysmal nocturnal hemoglobinuria. The patient developed an arterial hypertension 3 years after transplantation. The menarche occurred at the age of 13 years. Since then, she has had no further menstrual period in the following years. Four years after HSCT, the patient was diagnosed with a hypergonadotropic hypogonadism due to lower estradiol, higher luteinizing hormone and follicle-stimulating hormone values. Furthermore, a stagnation of the pubertal development occurred, which was treated subsequently with an estradiol-replacement-therapy. At the age of 18 years, she had a complete pubertal development with Tanner stages B5 and P5. Based on this development, the patient was told that she was infertile. Recently, this woman gave birth to an extremely low BW preterm infant at 25 weeks of gestation. She learned about her pregnancy at 22 weeks of gestation, most likely related to her notion of permanent infertility and her obesity concealing the gain in weight and abdominal girth. After 24 weeks 5/7 of gestation, progressive hypertension (175/105 mmHg), low platelet counts (91/nL) and tripled liver enzymes to the standard value prompted a cesarean section. A baby girl was born with a BW of 720 g and Apgar values of 7, 8 and 9 after 1, 5 and 10 min who eventually required prolonged mechanical ventilation and abdominal surgery for ileal volvulus. In conclusion, the need and adequate use of reliable prognostic fertility markers after cancer therapy needs to be emphasized. With the resulting information, the patient should be counseled regarding the possibility of timed family planning or the use of reproductive medical methods. Still, this counseling has to include the small chance of an unexpected pregnancy.