Double Heterozygosity for Hb Durham-N.C. (HBB: c.344T>C) [β114(G16)Leu→Pro] and the IVS-I-110 (HBB: c.93-21G>A) Causing a Severe β-Thalassemia Phenotype

Abstract

The evaluation of a 10-month-old girl of Sicilian origin with a clinical phenotype of severe thalassemia led to the identification of two β-globin gene defects, a β-thalassemia (β-thal), mutation at IVS-I-110 (HBB: c.93-21G>A) and a variant hemoglobin (Hb) mutation at codon 114 (HBB: c.344T>C) on the other allele, reported as Hb Durham-N.C. (also known as Hb Brescia) [β114(G16)Leu→Pro] in the HbVar database. A very low Hb level (Hb 3.5?g/dL), microcytosis [mean corpuscular volume (MCV) 63.2 fL] and hypocromia [mean corpuscular Hb (MCH) 19.6?pg], increased red blood cell (RBC) distribution width (RDW) (36.0%), higher reticulocytes (6.2%), anisocytosis, poikilocytosis, hypocromia, basophilic stippling and inclusion body formation, were present in the affected subject. Analysis of other family components showed the presence of HBB: c.93-21G>A defect in the mother and in her brother, while Hb Durham-N.C. was absent in all other relatives, thus, this mutation has arisen as a de novo defect. This is the first case described as a severe thalassemic phenotype in a compound heterozygote carrier of this unstable Hb and a common β-thalassemic allele. The important information gained from this case is that a rare dominant or recessive mutation may arise in every individual, even if this is a very rare event.     

Further Identification of The Hyperunstable α-Globin Chain Variant Hb Heraklion [codons 36/37 (–CCC); Pro→0 (α1)] in Greek Cases With Co-Inherited α+-Thalassemia Mutations

We report four Greek cases (from three unrelated families), who all had a similar atypical thalassemia intermedia phenotype, characterized by chronic moderate anemia, mild hemolysis and splenomegaly in the absence of abnormal hemoglobin (Hb) fractions. In all four cases (two unrelated children and two siblings), DNA analysis identified common α⁺-thalassemia (α⁺-thal) mutations in trans to the in frame 3 bp deletion (?CCC) on the α1-globin gene between codons 36 and 37, which has previously been reported as Hb Heraklion in a single Greek case. Clinical, hematological and biochemical findings in all cases, including a follow-up evaluation of the original case, are described. All the cases originated from the Greek island of Crete.     

Methemoglobin Forming Effect of Dimethyl Trisulfide in Mice

Abstract

Dimethyl trisulfide (DMTS) is a natural organic trisulfide that has been patented as a promising antidotal candidate against cyanide (CN). The primary mode of action of DMTS is as a sulfur donor that enables the conversion of CN to thiocyanate. Recently, it was discovered that DMTS is capable of oxidizing hemoglobin (Hb) to methemoglobin (MetHb) in vitro. The goal of these experiments was to measure the extent of DMTS-induced MetHb formation in vivo. In these experiments, intramuscular (IM) injections of formulated DMTS were administered to mice. Following the IM injection, blood was drawn and analyzed for MetHb using a rapid spectrophotometric method. Methemoglobin levels peaked in a dose-dependent manner between 20 and 30?min., and then began dropping. The highest MetHb levels measured for the 50, 100, 200 and 250?mg/kg doses of DMTS were respectively 3.28, 6.12, 9.69, and 10.76% MetHb. These experiments provide the first experimental evidence that IM administered DMTS generates MetHb in vivo and provide additional evidence for the presence of a secondary therapeutic pathway for DMTS - CN scavenging by DMTS-generated MetHb.     

Coinheritance of Hb A2-Melbourne (HBD: c.130G>A) and Hb E (HBB: c.79G>A) in Laos and Simultaneous High Resolution Melt Detection of Hb A2-Melbourne and Hb A2-Lampang (HBD: c.142G>A) in a Single Tube

Abstract

We report the molecular and hematological identifications of a Hb A₂ variant [coinheritance of Hb A₂-Melbourne (HBD: c.130G>A) and Hb E (HBB: c.79G>A)] found for the first time in the Lao People’s Democratic Republic (PDR). The subject was a 29-year-old pregnant Laotian woman who was a foreign worker in Thailand and was diagnosed with thalassemia and hemoglobinopathies. Capillary electrophoresis (CE) demonstrated 1.6% of Hb A₂, with a minor unknown peak at the initial Z1 zone (1.7%). Identification of abnormal hemoglobin (Hb) using direct DNA sequencing showed a genetic defect causing a δ-globin gene missense mutation at codon 43 (GAG>AAG) causing a glutamic acid to lysine substitution corresponding to Hb A₂-Melbourne. The origin of Hb A₂-Melbourne in Lao PDR may be similar to a case found in Thailand with the [+ –?– –?– + +] haplotype. We developed a method that could clearly detect Hb A₂-Melbourne and Hb A₂-Lampang (HBD: c.142G>A) mutations in a single tube using high resolution melt (HRM) analysis. The HRM analysis is a more effective method for rapid detection than conventional polymerase chain reaction (PCR), as there is no need for a post-PCR step, and no exposure to ethidium bromide. This new method would be a useful addition for the first investigation of a suspected Hb A₂ variant in the routine molecular setting.     

Nondeletional Hb Queens Park [α32(B13)Met→Lys]/Hb H (β4) Disease

A rare nondeletional α-thalassemia-2 (α-thal-2) allele was identified in a Thai boy with Hb H (β4) disease. The proband has α-thal-1 (– –^SEA type) together with a non productive Hb Queens Park (HBA1:c.98T>A) [α32(B13)Met→Lys] α1-globin variant. No abnormal hemoglobin (Hb) fraction was detected by high performance liquid chromatography (HPLC). The clinical effect of this mutation in the proband was comparable to that of deletional α-thal-2 present in Hb H disease.     

Developmental Effect of the XmnI Site on Gγ-Globin Gene Expression Among Newborn Hb F-Malta-I [Gγ117(G19)His→Arg,CAT→CGT] Heterozygotes and Adult β+-Thalassemia Homozygotes

Hb F-Malta-I [^Gγ117(19)His→Arg, CAT→CGT] is a stable and benign variant of Hb F found in 1.8% of Maltese newborn. We studied 120 Hb F-Malta-I heterozygotes and four Hb F‐Malta-I homozygotes. The mean proportion of ^Gγ-F-Malta-I in Hb F was 0.26 ± 0.03 for the Hb F-Malta-I heterozygotes and 0.58 ± 0.06 for the Hb F-Malta-I homozygotes. The Hb F-Malta-I allele was shown to occur on a background of the common Mediterranean haplotype Va [+ + ? ? ? ? ? + + ?]. Furthermore, the common Mediterranean haplotypes Va, IIIb [? + + + ? + + + + ?], I [+ + ? ? ? ? ? + + +] and II [? + ? + + ? + + + +] accounted for most (66.2%) of the wild-type alleles among the tested Hb F-Malta-I heterozygotes.

Different genotypes at the 5′ ? HincII, ^Gγ and ^Aγ HindIII, and 3′ψβ HincII sites (but not at the 5′ ^Gγ XmnI site) were found to be linked to significant variations in the proportion of ^Gγ-F-Malta-I and ^Gγ-globins in the Hb F of newborn Hb F-Malta-I heterozygotes. Moreover, the 5′ ^Gγ XmnI site was found to be associated with variations in Hb F and ^Gγ-globin levels in a population of adult Maltese β-thalassemia (thal) homozygotes. This implies that a determinant linked to the XmnI site which effects ^Gγ-globin gene expression is active in anemic adults but not in normal infants.     

The β-GLobin Gene Haplotypes Associated With Hb D-Los Angeles [β121(GH4)Glu→Gln] in Western Iran

Hb D-Los Angeles is characterized by the substitution of glutamine for glutamic acid at position 121 of the β-globin chain. The present investigation is the first study on the β-globin gene haplotypes associated with β-D-Los Angeles in Western Iran. Thirty two individuals from 11 unrelated families from Western Iran were studied. The Hb D-Los Angeles status of all cases was confirmed using polymerase chain reaction (PCR) followed by digestion with EcoRI. The haplotype of the β‐globin gene cluster was determined by a PCR-RFLP (restriction fragment length polymorphism) procedure. The haplotype background of the β^A chromosomes was also determined in 35 normal subjects from the same geographic region. The β-globin gene haplotype analysis demonstrated that all β-D-Los Angeles genes (23 genes) were in linkage disequilibrium with haplotype I [+????++]. Among the 70 β^A chromosomes, 30 chromosomes (42.9%) were associated with haplotype I. The present study indicates the unicentric origin of the β-D-Los Angeles gene in Western Iran. It seems that this mutation may have occurred at the same chromosomal background common in the local population.     

Hb Bleuland [α108(G15)Thr→Asn,ACC→AAC (α2)]: A New Abnormal Hemoglobin Associated with a Mild α-Thalassemia Phenotype

We report a new structural defect of the α2-globin chain, not detectable on high performance liquid chromatography (HPLC) or electrophoresis, characterized in a 12-year-old boy of Surinamese-Hindustani origin. The child was suspected to be a carrier of α-thalassemia (thal) because of microcytic hypochromic parameters in the absence of iron depletion. Gap-polymerase chain reaction (gap-PCR) revealed only normal fragments in the proband, and the pattern of a ?α^4.2 (leftward) deletion in his father and sister. Direct sequencing of the α-globin genes revealed an ACC→AAC transversion at codon 108 of the α2-globin gene in the proband, in his mother and in a younger sister. The new mutation predicts a Thr →Asn amino acid substitution at the corresponding residue. Threonine, a covalent binder with an R-active OH group, situated in the G helix of the α-globin chain, is involved in α1β1 contacts. Asparagine, being an equally covalent binder but with a different R-active H₂N-C=O group, could make the mutated chain less suitable for tetramer cooperation. Alternatively, an absent or reduced interaction with the α hemoglobin (Hb) stabilizing protein (AHSP) could lead to loss of α chains. Hb Bleuland is the first mutation described at codon 108 and is therefore interesting in regard to the possible effects and genetic risk. The nearest variant, Hb Suan-Dok [α109(G16)Leu →Arg, CTG→CGG (α2)] was originally observed in a Thai patient affected with Hb H, in combination with an α⁰-thal allele. The same Hb Suan-Dok mutation, recently described in our laboratory in a carrier of African ancestry, was also not detectable as a protein and presented with an α-thal phenotype similar to Hb Bleuland.     

HB Fannin-Lubbock-I with A Single GGC>GAC Mutation at β119(GH2)Gly→Asp in a Homozygous Mexican Patient

We studied a fast-moving, abnormal hemoglobin (Hb) identified as Fannin–Lubbock-I [β119(GH2)Gly→Asp] in a homozygous Mexican girl. To date, homozygosity for the Hb Fannin-Lubbock-I variant has not been reported. Her parents and five other relatives were heterozygotes. The 5′ β-globin haplotype analysis showed that the mutation was associated with haplotype 2 [? + + ? +]for the ε, ^Gγ, ^Aγ, 5′ and 3?′ψβ-globin sites, and also segregated with the TGTTC haplotype, which was constructed with five polymorphic sites of the β-globin gene [exon 1-nucleotide (nt) 6 (C>T) and IVS-II-16 (C>G), IVS-II-46 (T>C), IVS-II-74 (G>T), and IVS-II-81 (C>T). In 1994, a variant with an additional mutation at codon 111 [β111(G13)Val→Leu] was described in five Spanish families. This variant was termed Hb Fannin-Lubbock-II, and the question of the existence of Hb Fannin-Lubbock-I arose. However, based on our findings, we were able to confirm the existence of Hb Fannin-Lubbock-I and propose that this mutation has a different origin from the one identified in Spanish families.