Hb Buffalo [α89(FG1)His→Gln (α1)], Observed Solely and in the Presence of an Hb S [β6(A3)Glu→Val] Heterozygosity

The hemoglobin (Hb) pattern of a 32-year-old Somali male living in The Netherlands, during routine diabetes mellitus monitoring, showed two more peaks in addition to the characteristic heterozygous Hb A/S pattern. A major peak of 15% faster than Hb A, and a minor one of 10.8%, overlapping Hb A2 and the glycated Hb S1c fraction were present. The patient was not anemic or microcytic but had a low haptoglobin level, possibly indicating a slightly elevated red blood cell (RBC) turnover. Hb S was confirmed by a sickle test and at the DNA level. The DNA sequence of the alpha1 gene revealed a C-->G transversion at position 89, changing the local positively charged histidine to a neutral glutamine. This mutant has been previously described in a Yemenite woman and two apparently unrelated Somali males. Our case is the first showing Hb Buffalo in combination with Hb S and a G6PD deficiency, and is again observed in a Somali. No functional abnormalities associated with mutations at this amino acid residue are reported in the literature. Also, in this case no sign of any hematological abnormalities that could not be explained by the Hb S heterozygosity G6PD deficiency was found. The abnormal alpha chain is expressed at the expected rate and without thalassemic effect or instability. The mutated alpha chain seems to associate with a slight preference to the beta(A) (15%) rather than with the beta(S) counterpart. The sum of both Hb A(Buffalo) and Hb S(Buffalo) results in about 19-20% of total Hb. This figure is in agreement with a stable mutant of the alpha1 gene.

Hb Suan‐Dok [α109(G16)Leu→Arg; CTG→CGG (α2)] Described in a Patient of African Ancestry

A 58-year-old Black female from Curaçao (West Indies) was recently referred to our Laboratory for a persistent microcytic hypochromic anemia. An analysis 13 years earlier had shown no abnormal hemoglobin (Hb) fractions and a balanced beta/alpha synthetic ratio. The hematological indices were again compatible with thalassemia and no abnormal fractions were observed on electrophoresis or high-performance liquid chromatography (HPLC). None of the seven common alpha-thalassemia (thal) deletion defects were present. Direct sequencing of the alpha2 gene revealed a CTG-->CGG single base substitution at codon 109. This mutation was previously described in a Thai patient (Hb Suan-Dok), inducing Hb H disease in association with a - -(SEA) allele. In contrast with earlier reports we were unable to identify any native Hb fraction. The balanced beta/alpha ratio indicated that alpha2-Suan-Dok is formed but does not form tetramer formation unless alpha-thal is present.

Hb Oegstgeest [alpha104(G11)Cys-->Ser (alpha1)]. A new hemoglobin variant associated with a mild alpha-thalassemia phenotype

A microcytic hypochromic anemic state was observed in an 8-year old Black female of Surinam origin during pre-operative Hb S [beta6(A3)Glu-->Val] screening. Her high zinc protoporphyrin (ZPP) level suggested a chronic iron depletion but, in contrast, the high red blood cell (RBC) count (5.85 x 10(12)/L) was indicative of a possible coexisting thalassemia. No abnormal hemoglobin (Hb) bands were present on high performance liquid chromatography (HPLC) or alkaline electrophoresis and the Hb A2 level was normal. Break point polymerase chain reaction (PCR) failed to reveal any of the common alpha-thalassemia (thal) mutations but selective DNA sequencing of both alpha-globin genes disclosed a TGC-->AGC transversion at codon 104 of the alpha1 gene. Cystine at codon 104 is involved in alpha/beta globin contact and has been described to be a critical amino acid of the alpha2 chain when substituted by a tyrosine (Hb Sallanches), inducing Hb H (beta4) disease in the homozygous state. Our heterozygous patient had a moderate anemia of 12.2 g/dL and a borderline haptoglobin suggesting some degree of hemolysis.

A new polyadenylation site mutation associated with a mild beta-thalassemia phenotype

At least 180,000 autochthonous and allochthonous people are carriers of a large spectrum of hemoglobinopathies in The Netherlands. We describe two cases, the first, a 33-year old Surinamese Creole woman, studied because of an intermediate hemolytic anemia; the second, a couple requesting analysis because of a previously diagnosed carrier state in the male partner, while the carrier state in the pregnant female was uncertain.

Hb zoeterwoude [beta23(B5)Val-->Ala)]: a new beta-globin variant found in association with erythrocytosis

We describe the characterization of a new hemoglobin (Hb) variant found in a 77-year-old Dutch woman, suspected of hypoxia-mediated erythrocytosis. The typical blood parameters (Hb 17.3 g/dL; PCV 0.525 L/L; RBC 5.82 x 10(12)/L) could not be explained by any of the pathological or physiological conditions causing erythrocytosis. The patient was preventively phlebotomized because of intermittent claudication and erythrocytosis. At the hematological and biochemical levels, no anemia or hemolysis were present and no abnormal Hb fractions were detectable on alkaline electrophoresis or high performance liquid chromatography (HPLC). Molecular analysis revealed intact alpha-globin genes and a heterozygosity for a GTT-->GCT transition at codon 23 of the beta-globin gene, causing a Val-->Ala amino acid substitution. The P50 measured in full blood indicated that this mutant has an elevated oxygen affinity. This is the fourth single nucleotide substitution at codon 23 of the beta gene and the second associated with erythrocytosis. Because the family was not available for investigation no information was obtained as to whether the mutation represents a de novo event or was inherited, and might be a more common cause of erythrocytosis in Dutch patients. Considering the relatively high frequency of beta-thalassemia (thal) in the large allochthonous population in The Netherlands, combinations of Hb Zoeterwoude and beta-thal traits may lead to hemizygosity, with severe hypoxia and erythrocytosis from a few months after birth.

A new Hb evanston allele [alpha14(A12)Trp --> Arg] found solely, and in the presence of common alpha-thalassemia deletions, in three independent Asian cases

Hb Evanston [alpha14(A12)Trp --> Arg] is considered to be a rare alpha chain mutant, and was originally observed in two Black families in 1982, inducing a mild Hb H disease phenotype in a homozygous state for the -alpha3.7 deletion ( -alpha(Evanston)/ -alpha). The mutant, evidently linked with one of the two -alpha3.7 thalassemia (thal) alleles, was considered to be unstable and rapidly proteolyzed. We describe Hb Evanston in three new independent Asian cases, all induced by a TGG --> CGG transition. In all cases the mutation is linked to the alpha1-globin gene, either on a wild type allele or in linkage with the common -alpha3.7 and -alpha4.2 deletion alleles. The beta/alpha ratio was balanced in the presence of the mutation only, and accordingly unbalanced in co-inheritance with the deletion defects. Although a second independent mutation event on a -alpha3.7 or a -alpha4.2 deletion allele could not be excluded, we conclude that at least one independent Hb Evanston mutation has occurred on a wild type allele in the Asian populations. Unstable Hb tetramers tend to degrade and disappear during purification. Both Hb Evanston tetramers, formed in combination with normal beta and delta chains, remain perfectly stable after extensive purification and concentration steps, suggesting an early posttranslational thalassemic effect, probably at the dimer/tetramer affinity level.

Molecular spectrum of alpha-thalassemia in Tunisia: epidemiology and detection at birth

We present the characterization of the molecular spectrum and frequency data of alpha-thal (thal) defects in Tunisia, and an evaluation of the efficacy and limitations of Hb Bart's (gamma4) measurement for the screening of alpha-thal at birth. Cord blood samples were collected from two different areas: the northeast of the country, an area where Hb H (beta4) disease frequently occurs, and Tunis, the capital city, representative of the average Tunisian population. From the first group, 110 samples with Hb Bart's and/or microcytosis at birth were selected from 1270 randomly collected samples. Two additional population samples, one from the same northeastern region (n = 90), the other from Tunis (n = 104) were collected randomly. Nine common deletional alpha-thal defects and nondeletional mutations were screened. In the northeastern samples, selected for the presence of Hb Bart's and microcytosis, the -alpha3.7 deletion was the most common defect (4.5% allele frequency) followed by a polyadenylation (poly A) signal mutation (1.8%), the five nucleotide (nt) deletion and the -alpha4.2 deletion (both 0.9%). The African polymorphism (G-->TCGGCCC at position 7238 and T-->G at 7174) was found with an allele frequency of 11% in the selected northeastern samples. In the random population samples, the overall alpha-thal allele frequency was 4% in the northeast region, against 2% in the average Tunisian population. The +14 (G-->C) polymorphism in the 5'UTR (untranslated region) of the alpha2 gene and the African polymorphism in the second intron of the same gene, were found in 3.5% of the alleles. No alpha0-thal alleles were found among the 304 blood samples studied at the DNA level during this survey.