The myelodysplastic syndromes (MDS) constitute a heterogeneous group of clonal disorders arising from a multipotent haemopoietic progenitor which share a leukaemic propensity, 30% of cases culminating in acute myeloid leukaemia (AML). Their pathogenesis probably entails multiple steps, phenotypic progression being determined by either expansion or evolution of the abnormal clone. The clonal origin of certain cases of de novo AML is analogous to that of MDS and evidence that they share a common pathogenesis and distinct biological characteristics is beginning to emerge.

Chromosome Aberrations↗

PubMedDate not supplied

The consequence of nucleotide substitutions in the triosephosphate isomerase (TPI) gene promoter.

Mutations at -5A-->G, -8-->GA within the cap proximal element (CPE), and -24T-->G within the TATA box of the triosephosphate isomerase (TPI) gene promoter have been identified in populations with a wide geographical distribution. These mutations lie within, or in close proximity to, known cis-active elements in the TPI gene promoter. To determine the functional significance of mutation at these sites, which remains controversial, their effect on the expression of erythrocyte TPI enzyme activity was studied in 110 healthy unrelated subjects. The -5G mutation did not alter erythrocyte TPI level, whereas the -8A mutation was accompanied by a significant reduction in enzyme activity to around 90% and 76% of normal erythrocyte TPI activity in heterozygotes and homozygotes, respectively. The -8A -24G genotype was associated with 75% of normal TPI activity in a heterozygote studied, implying that substitution of G at position -24 within the canonical TATA motif causes an additive decrease in TPI gene transcription in erythroid cells. A DNA-protein complex of 125kDa which was competitively blocked by specific unlabelled oligomers was demonstrated at the CPE and TATA box by electrophoretic mobility shift analysis. These findings provide direct evidence that TPI promoter mutations are linked to a reduction of TPI enzyme activity in vivo.

Binding Sites↗

PubMedDate not supplied

Unique and recurrent WAS gene mutations in Wiskott-Aldrich syndrome and X-linked thrombocytopenia.

Wiskott-Aldrich syndrome (WAS) and X-linked thrombocytopenia (XLT) are allelic phenotypes caused by defects of the WAS gene. Fourteen distinct mutations including seven novel gene defects in 16 WAS and four XLT patients were identified by single strand conformation polymorphism analysis and DNA sequencing of the WAS gene. Eleven (79%) of these mutations are located within exons 1 to 4 with clustering in exon 2. Carrier detection in 33 at-risk females and prenatal diagnosis at 12 weeks gestation in one family with a novel WAS mutation was performed by direct mutation analysis. A remarkably high frequency (72%) of point mutations involved CpG dinucleotides. C-->T or G-->A transitions at CpG sites were identified in all isolated WAS cases (n = 7). Allele frequencies for the dinucleotide repeat at locus DXS6940 were determined in Northern European, African and Asian populations. Mutation screening alone or in combination with analysis of polymorphic loci DXS6940 and DXS255 delineated the germline origin of a unique insertion mutation and four recurrent CpG mutations, three of which arose spontaneously during maternal gametogenesis.

Asian People↗

PubMedDate not supplied

Rapid identification of hemoglobin variants by electrospray ionization mass spectrometry.

The precise identification of human hemoglobin variants, over 700 human hemoglobin variants are known, is essential for prediction of their clinical and genetic significance. A systematic approach to their rapid identification is described. Traditionally this requires protein or DNA characterization which entails lengthy analytical procedures. To overcome these obstacles a rapid approach to variant hemoglobin identification has been developed using conventional phenotypic methods combined with electrospray ionization-mass spectrometry (ESI-MS). The latter requires only a small amount of whole blood (10 microl) but in most cases 2 microl would have been sufficient and no preanalytical steps, such as separation of red cells or globin chains, are necessary. Aged, hemolyzed blood samples can also be analyzed. This approach has been used to positively identify 95% of the variants in over 250 samples. The remaining 5% in which a variant was detected by phenotypic techniques were not resolved by mass spectrometry. Ninety-nine different abnormalities comprising 36 alpha-chain variants, 59 beta-chain variants (including 2 extensions), and 4 hybrid hemoglobins were identified. These include 15 novel variants. The application of ESI-MS described requires approximately 1 h to prepare and analyze each sample and has minimal reagent costs. The turnaround time on a single sample can be as little as 2 h. This technique can now be considered a useful additional tool for reference laboratories.

Amino Acid Substitution↗

PubMedDate not supplied

Nucleotide variation regulates the level of enhancement by hypersensitive site 2 of the beta-globin locus control region.

The beta-globin locus control region hypersensitive site 2 (HS2) enhancer possesses a unique property for stimulating high-level globin gene expression. Although the deletion of cis-acting motifs influences the level of enhancement conferred by HS2, there is controversy on whether polymorphism of the same elements contributes to variation of the fetal hemoglobin (HbF) level among patients with sickle cell anemia. We analyzed reporter gene activity of constructs containing variant HS2 enhancers derived from beta(S) chromosomes to directly test the effect of polymorphism on enhancer activity. Constructs containing four enhancer variants linked to an identical gamma-globin promoter showed markedly different levels of reporter gene activity. Juxtaposition of HS2 derived from the Asian and Senegal chromosomes, which are associated with similarly high levels of HbF, to cognate sequence extending to -1500 of the (G)gamma globin gene showed significantly different levels of reporter gene activity. Our findings indicate that nucleotide variation regulates the level of enhancement conferred by HS2; however, the reporter activities showed no correlation with the level of Hb F associated with the common beta(S) chromosomes.

Binding Sites↗

PubMedDate not supplied

Fetal plasma tumor necrosis factor concentration in normal pregnancy.

The aim of the study was to investigate changes with gestation of fetal plasma tumor necrosis factor alpha (TNF-alpha) concentration. In a cross-sectional study, enzyme-linked immunoassay was used to measure plasma TNF-alpha concentration in 40 fetal blood samples obtained by cordocentesis (n = 25), cardiocentesis (n = 5) or at elective caesarean section (n = 10) at 12-38 weeks gestation. The fetal plasma concentration of TNF-alpha increased from a mean of 13.5 pg/ml at 12 weeks gestation to 37.5 pg/ml at 38 weeks (r = 0.59, p < 0.0001), and was significantly associated with the monocyte count (r = 0.56, p < 0.001). TNF-alpha is present in the fetal circulation from at least 12 weeks and the changes in plasma TNF-alpha concentration with gestation coincide with the development of the fetal monocyte-macrophage system.

Female↗