ABSTRACT
OBJECTIVE: Alpha-thalassemia is frequently encountered in eastern Saudi Arabia. We wanted to find out laboratory based incidence and laboratory features of Hemoglobin H disease in the Dammam region. METHODS: We retrospectively analyzed the results of Hemoglobin electrophoresis carried out during the last 5 years in our laboratory. Hemoglobin electrophoresis was performed on cellulose acetate, pH 8.6 using Helena or Biomidi kits. Hemoglobin S was confirmed by sickle solubility test. Variant hemoglobin if present, was confirmed by citrate agar (pH 6.0) electrophoresis. Helena rapid electrophoresis system was used for plate densitometry. The diagnosis of Hemoglobin H disease was made on the basis of the presence of Hemoglobin H on electrophoresis supplemented by demonstration of Hemoglobin H inclusions in red blood cells. RESULTS: Fifteen thousand, four hundred and ninety two blood samples were analyzed by Hemoglobin electrophoresis. We found 100 cases of Hemoglobin H disease, only one case was non-Saudi. The age ranged between 45 days to 85 years. There were 51 females and 49 males. Children (less than 12 years) were 35 and of adults there were 65. There were 35 adult females and 30 adult males. The mean +/- standard deviation of Hemoglobin H in children was 13.54 +/- 7, in adult females the mean +/- standard deviation of Hemoglobin H was 12 +/- 5.4, and in adult males it was 11.99 +/- 6.4. The Hemoglobin H inclusions seen in red blood cells ranged from 2.6-80 in children and 10-80 in adults. The sickle cell trait was co-existent in 7 cases. Hemoglobin Bart's along with Hemoglobin H was seen in 32 cases. Hemoglobin F was present, beyond first year of life in 34 cases. The Hemoglobin A2 as measured by densitometry was significantly low in all of the 3 age groups as compared to corresponding controls. The complete blood count results were available for analysis in only 26 cases of Hb H disease. The mean +/- SD values of Hb (g/dl), Hct (ratio), MCV (fl), MCH (pg) MCHC (g/dl), RDW-SD (fl) and RDW-CV (%) in these patients (all age groups together) were 8.15 +/- 1,.278 +/-.04, 59.4 +/- 5.8, 17.65 +/- 2.1, 29.4 +/- 1.7, 37.8 +/- 8.7 and 25.1 +/- 4.6. The mean Hb, Hct, MCV, MCH and MCHC were significantly reduced in all 3 age groups as compared to corresponding controls. RBC counts and RDW-CV were elevated in Hb H disease compared to corresponding controls. The blood film showed typical red cell morphology. CONCLUSION: Hb H disease is not infrequently encountered in the Dammam region. This condition should be kept in mind while evaluating patients for anemia. The genetic studies to determine the exact alpha-thalassemia determinants producing Hb H disease in eastern Saudi Arabia are needed.
Subject(s)
alpha-Thalassemia/epidemiology , Adolescent , Adult , Aged , Aged, 80 and over , Child , Child, Preschool , Electrophoresis , Female , Humans , Incidence , Infant , Male , Middle Aged , Retrospective Studies , Saudi Arabia/epidemiology , alpha-Thalassemia/diagnosisABSTRACT
A region of DNA sequence of the bacterial transposon Tn7, which is required for transposition, has been determined. This DNA sequence completes an 8351 base pair (bp) region containing five long open reading frames (ORF's) that correspond to the genetically defined genes, tnsA, B, C, D and E, required for Tn7 transposition. All of the ORF's are oriented in the same direction, ie. inward from the element's right end. The genes are in a very compact arrangement with the presumed initiation codons never more than two bases beyond the preceding termination codon. Domains with similarity to the helix-turn-helix genre of Cro-like, sequence specific DNA binding sites occur within the deduced amino acid (a.a.) sequence of the TnsA, TnsB, TnsD and TnsE proteins. Translation of the tnsC ORF reveals strong homology to a consensus sequence for nucleotide binding sites as well as a region of similarity to a transcriptional activator (MalT). No striking a.a. sequence similarity to other DNA recombinases is observed. The possible roles of these proteins in Tn7 transposition is discussed in light of the analysis presented.
Subject(s)
DNA Transposable Elements , Escherichia coli/genetics , Genes, Bacterial , Amino Acid Sequence , Base Sequence , Codon/genetics , Molecular Sequence Data , Restriction Mapping , Sequence Homology, Nucleic AcidABSTRACT
The large (14 kb; kb = 10(3) bases) bacterial transposon, Tn7 (encoding resistance to trimethoprim and streptomycin/spectinomycin), has unusual properties. Like other elements, Tn7 transposes with low efficiency and low target-site specificity, but Tn7 also transposes, with high frequency in a unique orientation, to a preferred "attachment" site, called attTn7, in the Escherichia coli chromosome and similarly into plasmids containing attTn7. We developed a novel bacteriophage M13-based assay system to measure the transposition frequency of Tn7 to M13mp phage vectors containing attTn7 on a cloned 1 kb fragment of chromosomal DNA. Phage harvested from a Tn7 donor strain were used to infect recipient bacteria with selection for trimethoprim resistance. Transposition frequency, expressed as the number of trimethoprim-resistant colonies per plaque-forming unit, was found to be approximately 10(-4) to M13mp::attTn7, in contrast to 10(-10) to M13mp recombinants with approximately 1 kb insertions of other, "generic brand", DNA. By deletion analysis of M13mp::attTn7, we show that attTn7 is contained within a 64 base-pair region; sequences adjacent to the actual insertion site and encoding the carboxy terminus of the glmS gene are required. This assay also provided evidence for transposition immunity conferred by the right end of Tn7.
