Analysis of intron 22 inversions of the factor VIII gene in severe hemophilia A: implications for genetic counseling

Intrachromosomal recombinations involving F8A, in intron 22 of the factor VIII gene, and one of two homologous regions 500 kb 5' of the factor VIII gene result in large inversions of DNA at the tip of the X chromosome. The gene is disrupted, causing severe hemophilia A. Two inversions are possible, distal and proximal, depending on which homologous region is involved in the recombination event. A simple Southern blotting technique was used to identify patients and carriers of these inversions. In a group of 85 severe hemophilia A patients, 47% had an inversion, of which 80% were of the distal type. There was no association with restriction fragment length polymorphism (RFLP) haplotypes. The technique has identified a definitive genetic marker in families previously uninformative on RFLP analysis and provided valuable information for genetic counselling information may now be provided for carriers without the need to study intervening family members and the diagnosis of severe hemophilia A made in families with only a nonspecific history of bleeding. Analysis of intron 22 inversion should now be the first-line test for carrier diagnosis and genetic counselling for severe hemophilia A and may be particularly useful when there is no affected male family member or when intervening family members are unavailable for testing.     

Human granulocyte-macrophage colony-stimulating factor receptor signal transduction requires the proximal cytoplasmic domains of the alpha and beta subunits

Human granulocyte-macrophage colony-stimulating factor (GM-CSF) controls the production, maturation, and function of cells in multiple hematopoietic lineages. These effects are mediated by a cell-surface receptor (GM-R) composed of alpha and beta subunits, each containing 378 and 881 amino acids, respectively. Whereas the alpha subunit exists as several isoforms that bind GM-CSF with low affinity, the beta common subunit (beta c) does not bind GM-CSF itself, but acts as a high- affinity converter for GM-CSF, interleukin-3 (IL-3), and IL-5 receptor alpha subunits. The cytoplasmic region of GM-R alpha consists of a membrane-proximal conserved region shared by the alpha 1 and alpha 2 isoforms and a C-terminal variable region that is divergent between alpha 1 and alpha 2. The cytoplasmic region of beta c contains membrane proximal serine and acidic domains. To investigate the amino acid sequences that influence signal transduction by this receptor complex, we constructed a series of cytoplasmic truncation mutants of the alpha 2 and beta subunits. To study these truncations, we stably transfected the IL-3-dependent murine cell line Ba/F3 with wild-type or mutant cDNAs. We found that the wild-type and mutant alpha subunits conferred similar low-affinity binding sites for human GM-CSF to Ba/F3, and the wild-type or mutant beta subunit converted some of these sites to high- affinity; the cytoplasmic domain of beta was unnecessary for this high- affinity conversion. Proliferation assays showed that the membrane- proximal conserved region of GM-R alpha and the serine-acidic domain of beta c are required for both cell proliferation and ligand-dependent phosphorylation of a 93-kD cytoplasmic protein. We suggest that these regions may represent an important signal transduction motif present in several cytokine receptors.     

Increased adhesion of erythrocytes to components of the extracellular matrix: isolation and characterization of a red blood cell lipid that binds thrombospondin and laminin

Red blood cell (RBC) adhesion to the vascular endothelium is increased in several pathologic conditions, including sickle cell disease and malaria. However, RBC interactions with components of the subendothelial matrix are not well-characterized. Under in vitro flow conditions of 1 dyne/cm2, washed RBCs bound to the purified adhesive molecules thrombospondin (TSP) and laminin. Sickle RBCs had the greatest adhesion of all tested RBCs. The adhesion of sickle RBCs to immobilized TSP was inhibited by the anionic polysaccharides high molecular weight (MW) dextran sulfate and chondroitin sulfate A, but not other anionic polysaccharides of similar structure and/or charge density. These data were consistent with the RBC adhesive molecule being a sulfated glycolipid. Therefore, TSP-binding lipids from normal and sickle RBCs were isolated and characterized. The TSP-binding lipid was purified by alkaline methanolysis, anion exchange chromatography and preparative thin layer chromatography (TLC). A homogeneous band on TLC was identified using a specific overlay TSP-binding assay. TSP binding to the purified lipid was stable to bass and neuraminidase treatment, labile to acid treatment, and was inhibited by high MW dextran sulfate, similar to that seen with intact RBCs binding to immobilized TSP under conditions of flow. In addition, soluble laminin bound to the purified RBC lipid. This acidic TSP- and laminin-binding lipid(s) isolated from both sickle and normal RBC membranes may contribute to erythrocyte interactions with the subendothelial matrix, hereby participating in the pathogenesis of vaso-occlusive diseases.     

Residual amounts of glycoprotein Ib concomitant with near-absence of glycoprotein IX in platelets of Bernard-Soulier patients

A study of the Bernard-Soulier syndrome in two unrelated families using different polyclonal antibodies in a sensitive immunoblot assay showed residual amounts of platelet membrane glycoprotein (GP) lb in the eight homozygotes, as well as the near-absence of GPlb beta and GPIX. The eight heterozygotes studied showed a double band pattern for GPlb and about half the normal level of GPlb beta and GPIX. Therefore, we conclude that the Bernard-Soulier syndrome is heterogeneous and is probably not due to gene deletions.     

Herpesvirus type 6 in patients undergoing bone marrow transplantation: serologic features and detection by polymerase chain reaction

To evaluate the potential role of human herpesvirus type 6 (HHV-6) infection in patients after bone marrow transplantation (BMT) we sequentially analyzed buffy coat leukocytes, oral lavage fluid, and urine from 57 patients for the presence of HHV-6 DNA by polymerase chain reaction (PCR) before and after 60 BMTs. Twenty-four patients undergoing autologous BMT and 36 with allogeneic BMT were studied. Thirty-six patients (60%) were PCR positive in one or more tests. The majority of PCR-positive patients had positive results only sporadically, in 1 (n = 23) or 2 weeks (n = 5). Six patients were positive in 3 to 5 weeks. In 2 patients, we found a high frequency of positive tests, in 7 of 7 and 10 of 10 weeks analyzed. Twenty-four patients (40%) remained PCR negative throughout the post-BMT period. There was a significant correlation between the results of HHV-6 PCR and the occurrence of acute graft-versus-host disease (aGVHD). In grade II-IV, 6 of 8 (75%) patients had 2 or more positive PCR tests, compared with 5 of 25 (20%) patients without or with grade I aGVHD (P = .01). There was no difference in the outcome of PCR tests with respect to the type of BMT or pre-BMT HHV-6 enzyme-linked immunosorbent assay titers. Restriction enzyme analysis of PCR amplificates from 18 patients showed HHV-6 variant B in 16 (88.9%) and variant A in 2 cases (11.1%). We conclude that HHV-6 DNA can be detected in 60% of the patients after BMT. HHV-6 DNA can be detected more frequently in patients with moderate and severe aGVHD than in patients without aGVHD or with mild aGVHD.     

Production of interleukin-1 alpha, interleukin-1 beta and tumor necrosis factor by human mononuclear cells stimulated with granulocyte- macrophage colony-stimulating factor [see comments]

Recent studies have examined the synergistic effects of granulocyte- macrophage colony-stimulating factor (GM-CSF) and hematopoietin-1 (now identified as Interleukin-1, IL-1) on bone marrow colony formation. In the present report, human peripheral blood mononuclear cells (MNCs) were stimulated in vitro with recombinant human GM-CSF (rGM-CSF) and production of IL-1 alpha, IL-1 beta, and tumor necrosis factor (TNF) was measured by specific radioimmunoassays. In the MNCs of 20 individuals, rGM-CSF's ability to induce the three cytokines was variable. Nearly all donors responded to low-dose rGM-CSF (0.02 to 2 ng/mL) with production of TNF, whereas some individuals did not produce IL-1 alpha or IL-1 beta. The MNCs from some subjects stimulated with high-dose rGM-CSF (10 to 80 ng/mL) produced as much cytokine as in response to 10 ng/mL endotoxin. Localization (ie, extracellular or cell- associated cytokine) was specific for the cytokine rather than the stimulus. Indomethacin increased the amount of cytokine produced in response to rGM-CSF for IL-1 beta and TNF but not for IL-1 alpha. In addition, interferon-gamma (INF-gamma) upregulated the amount of TNF induced by rGM-CSF in all donors examined, with variable effect on IL-1 alpha and IL-1 beta. Suboptimal levels of endotoxin incubated with rGM- CSF did not alter the amount of IL-1 produced as compared with cells stimulated with rGM-CSF alone, whereas TNF production showed either no change or a slight decrease in production. These data suggest that GM- CSF may play an important role in the host defense response by stimulating production of these cytokines.     

The acute chest syndrome in sickle cell disease: incidence and risk factors. The Cooperative Study of Sickle Cell Disease

The acute chest syndrome (ACS), a pneumonia-like illness in sickle cell patients, is one of the most frequent causes of their morbidity and hospitalizations. Repeated ACS events may predict the development of chronic lung disease. ACS is reported as a frequent cause of death in these patients. We examine here the incidence and risk factors of ACS in 3,751 patients with sickle cell disease who were observed prospectively for at least 2 years (19,867 patient-years [pt-yrs]) as part of a multicenter national study group. The ACS, defined by a new pulmonary infiltrate on x-ray, occurred at least once in 1,085 patients (2,100 events). ACS incidence was higher in patients with homozygous sickle cell disease (SS; 12.8/100 pt-yrs) and in patients with sickle cell-beta(0) -thalassemic (9.4/100 pt-yrs), and lower in patients with hemoglobin (Hb) SC disease (5.2/100 pt-yrs) and patients with sickle cell-beta(+) thalassemia (3.9/100 pt-yrs). alpha-Thalassemia did not affect the rate of ACS incidence in SS patients. Within each Hb type the incidence was strongly but inversely related to age, being highest in children 2 to 4 years of age (25.3/100 pt-yrs in SS) and decreasing gradually to its lowest value in adults (8.8/100 pt-yrs in SS). In SS children (< 10 years of age), we documented an age-related within- person reduction in ACS attack rates. Adults with a higher ACS rate had a higher rate of mortality (from all causes) than those with low ACS rates. This increased rate of mortality might also have contributed to the decline in ACS rate with age. In multivariate analysis, other factors affecting incidence in SS patients were degree of anemia (lower ACS rates in patients with lower steady-state Hb levels) and fetal Hb (lower rates in patients with high fetal Hb). There was also a positive association between ACS rate and steady-state leukocyte count. The relationship of ACS rate to higher steady-state Hb levels in SS patients is unexplained but might be caused by increased blood viscosity.