Genetic control of myeloproliferation in BXH-2 mice

While studying the unique Nramp1 (Slc11a1)-independent susceptibility to Mycobacterium bovis (BCG) infection of BXH-2 mice, we noted that these mice develop important splenomegaly and enlargement of lymph nodes. Segregation analyses in several F2 crosses showed that splenomegaly segregates as a single recessive trait caused by a novel mutation in BXH-2, independent of the infection. Histologic and fluorescence-activated cell sorter (FACS) analyses indicated that splenomegaly is associated with a large increase in Mac1+/GR1+ (macrophage antigen-1+/granulocyte differentiation antigen 1+) granulocyte precursors in spleen, lymph nodes, and bone marrow, resembling a myeloproliferative syndrome. This is concomitant to extramedullary erythropoiesis in the spleen, as measured by proportion of Ter119+ erythroid cells. The locus controlling this myeloproliferative syndrome and splenomegaly was designated Myls and maps to an 18 centimorgan (cM) region of chromosome 8, which also contains an integrated copy of an N-ecotropic murine leukemia virus (MuLV) provirus (Emv2). The relationship between Myls, expansion of Mac1+/GR1+ cells, and Emv2 was investigated. Homozygosity at Myls is necessary but not sufficient for B-ecotropic virus replication in splenocytes, the extent of which appears to be under separate genetic control. Our results suggest a model in which Myls-dependent myeloproliferation in BXH-2 acts as a predisposing factor for the subsequent development of virally induced myeloid leukemia characteristic of this strain.     

Insights from CREDENCE trial indicate an acute drop in estimated glomerular filtration rate during treatment with canagliflozin with implications for clinical practice

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Elevated circulating endothelial membrane microparticles in paroxysmal nocturnal haemoglobinuria

We analysed endothelial cell membrane microparticles (ECMP) in the peripheral blood of patients with paroxysmal nocturnal haemoglobinuria (PNH) (n = 9), aplastic anaemia (AA) (n = 10), sickle cell disease (SCD) (n = 8), and healthy donors (HD) (n = 11). There was no clinically manifested thrombosis in the PNH or AA group, except one cured thrombophlebitis (PNH), while all SCD patients had a history of vaso-occlusive crises. We used three-colour flow cytometry with blood cell-specific antibodies and antibodies to endothelial antigens CD105 and CD144. Phosphatidylserine-positive microparticles were detected using the annexin V-binding (AVB) assay. The population of CD105+AVB+ ECMP was significantly (P < 0.05) higher in SCD (median: 0.568 x 10(9)/l; 25-75th percentile range: 0.351-0.976 x 10(9)/l) and PNH (0.401 x 10(9)/l; 0.19-0.441 x 10(9)/l) patients when compared with AA (0.122 x 10(9)/l; 0.061-0.172 x 10(9)/l) or HD (0.180 x 10(9)/l; 0.137-0.217 x 10(9)/l) group. Even more pronounced differences were observed in ECMP exhibiting a marker of inflammatory stimulation CD54 (CD105+CD54+). Similarly, ECMP that exhibited endothelial specific and proteolysis-sensitive antigen CD144 were increased in SCD and PNH, but not in AA. Elevated CD54+ ECMP may reflect the inflammatory status of endothelial cells in SCD and PNH, while CD144+ ECMP could indicate continuous endothelial stimulation and/or injury. Analysis of circulating ECMP appears promising to provide useful information on the status of the vascular endothelium in PNH and SCD.     

Four new cases of congenital secondary hypothyroidism due to a splice site mutation in the thyrotropin-beta gene: phenotypic variability and founder effect

Isolated TSH deficiency is a rare cause of congenital hypothyroidism. We here report four children from two consanguineous Turkish families with isolated TSH deficiency. Affected children who were screened at newborn age had an unremarkable TSH result and a low serum TSH level at diagnosis. Age at diagnosis and clinical phenotype were variable. All affected children carried an identical homozygous splice site mutation (IVS2 + 5 G--> A) in the TSHbeta gene. This mutation leads to skipping of exon 2 and a loss of the translational start codon without ability to produce a TSH-like protein. However, using specific monoclonal antibodies, we detected a very low concentration of authentic, heterodimeric TSH in serum, indicating the production of a small amount of correctly spliced TSH mRNA. By genotyping all family members with polymorphic markers at the TSHbeta locus, we show that the mutation arose on a common ancestral haplotype in three unrelated Turkish families indicating a founder mutation in the Turkish population. These results suggest that this TSHbeta mutation is among the more common TSHbeta gene mutations and stress the need for a biochemical and molecular genetic workup in children with symptoms suggestive of congenital hypothyroidism, even when the neonatal TSH screening is normal.     

Endotoxin-induced suppression of erythropoiesis: the role of erythropoietin and a heme synthesis stimulating factor

The regulation of erythropoiesis is primarily controlled by erythropoietin (Ep). Recently, however, other factors that both stimulate and inhibit erythropoiesis have been reported. Using an in vitro liquid culture of bone marrow cells, a factor in normal mouse serum was demonstrated that markedly stimulated heme synthesis by marrow erythroid cells. In this study, the role of this heme synthesis stimulating factor (HSF) and Ep in the erythropoietic suppression caused by endotoxin administration to mice was examined. Although HSF levels did not alter appreciably after endotoxin injection, marrow erythroid cells from these animals became unresponsive to the factor. This could be reversed if Ep was added to the culture in vitro or if the hormone was injected into the mice 18 hr prior to harvesting the marrow. This marrow erythroid cell response is identical to that seen in animals in whom Ep levels are markedly reduced, such as that found in exhypoxic polycythemia, and suggest a decrease in the hormone following endotoxin administration. Additional studies demonstrated that when Ep was injected into mice 6 hr after endotoxin administration, an increase in femoral erythroid colony-forming units (CFU-E), proerythroblast number, and 59 Fe incorporation into femoral marrow cells could be demonstrated. These findings, together with the marrow erythroid cell response to the hormone, suggest that the mechanism for suppression of erythropoiesis after endotoxin injection is a reduction in the level of circulating Ep.