Alpha-globin gene deletions associated with alpha A and alpha G Philadelphia in an Algerian family that includes two Hb G homozygotes

Hb St. Truiden [α68(E17)Asn→His] and Hb Westeinde [α125(H8)Leu→Gln]: two new abnormalities of the α2-globin gene

We report two new abnormal hemoglobins (Hbs) caused by mutations on the α2 gene. One resulted into an Asn→His substitution at position 68, the other in a Leu→Gln substitution at position 125. The first mutation was observed in a 61-year-old North European Belgian male during Hb A(1c) analysis and subsequently in other members of his family. The variant was expressed at a normal level and caused no hematological abnormalities in the carriers. The second was found in a 27-year-old Turkish male living in The Hague, The Netherlands, who presented with microcytic hypochromic parameters without iron deficiency and was also carrier of the common α2 IVS-I (-5 nt) deletion.

Hb G-Philadelphia, or [alpha 68(E17)Asn----Lys], in north Sardinia: detection by isoelectric focusing and identification by HPLC of tryptic peptides

11,129 individuals of the northern area of the island of Sardinia (7,717 newborns and 3,412 adults) were examined for the Hb G-Philadelphia variant [alpha 68(E17)Asn----Lys]. Hemolysates were analysed by isoelectric focusing, and the variant identified by reversed phase high performance liquid chromatography of tryptic peptides. A total of seven heterozygotes (1 in 1,589) were identified. This is probably the highest prevalence of this mutant so far described. Percentages of the variant (average 35.1 +/- 6.2%) were trimodally distributed with modes centering on 28, 36, and 42%, respectively. These values suggest that the G-Philadelphia allele occurs in Sardinians both on a single and on a double locus chromosome. The linkage with alpha-thalassemia may be the reason for the high frequency of the variant.

Asymptomatic association of hemoglobin Dunn (alpha 6[A4]Asp----Asn) and hemoglobin O-Arab (beta 121[GH4]Glu----Lys) in a Moroccan man

We report on the association of Hb Dunn (alpha 6[A4]Asp----Asn) and Hb O-Arab (beta 121 [GH4]Glu----Lys) in a healthy Moroccan man. Hb Dunn had the same electrophoretic properties as Hb G-Philadelphia, but its percentage was lower. Its identification was based on sequence determination of the alpha T1 peptide. Bgl II and Eco RI mapping showed the presence of four alpha-genes. Hb O-Arab was easily recognized through its electrophoretic properties and was confirmed by the suppression of the Eco RI site located in exon 3 of the beta-gene. The percentages of the various hemoglobins showed that the doubly mutated hemoglobin Dunn/O-Arab has a normal stability and suggested that the Dunn mutation is carried by the alpha 1-gene. In cord blood [propositus's son], the output of the alpha Dunn gene was found equivalent to that existing in the adult.

Genetic factors involved in human G gamma and A gamma globin gene expression

G gamma to A gamma globin ratios, haplotypes at the beta globin gene cluster and the C----T substitution at -158 5' to the G gamma globin gene were studied in three Algerian families that include SS or S-beta(0) thal patients. G gamma to A gamma ratios were found similar, within a family, in subjects displaying the same combination of chromosomes 11, the ratio observed for a given combination depending on the chromosome haplotypes. Our data can be explained by the existence of several alleles of a genetic factor closely linked to the beta globin gene cluster and involved in the determination of G gamma to A gamma globin ratio.

Alpha-thalassemia haplotypes in the Algerian population

DNA mapping was performed in seven unrelated Hb H patients and nine carriers for alpha-thalassemia trait originating from Algeria. This study has allowed us to identify four alpha-thalassemia haplotypes: the (-alpha 3.7) haplotype, which is the most frequent (18 of 23 alpha-thalassemic chromosomes), the (-(alpha)20.5) haplotype, a (--) haplotype, and an (alpha alpha)T haplotype. Our results also show that the (-alpha 3.7) haplotypes encountered in the Algerian population are heterogeneous and differ by the site of the unequal crossover responsible for the 3.7-kb deletion and the size of the interzeta fragment. In addition, during this survey we observed that normal chromosomes bearing a polymorphic BglII site are associated with different interzeta fragments.

Alpha-thalassemia due to the deletion of nucleotides -2 and -3 preceding the AUG initiation codon affects translation efficiency both in vitro and in vivo

We previously hypothesized that a 2 nucleotide deletion, causing a A-greater than C change at position -3 preceding the ATG initiation codon of alpha globin gene, reduced translation efficiency of alpha globin mRNA and was responsible for a form of alpha + thalassemia displayed by an Algerian patient. We presently show that this deletion leads to a 30-45% reduction in translation efficiency of synthetic alpha globin mRNA in rabbit reticulocyte lysate. In other experiments, we constructed alpha/G gamma hybrid globin genes in which the 3' end of normal or mutated alpha globin genes downstream to the ATG initiation codon was substituted by the 3' part of a G gamma globin gene. COS cells transfected with either of these 2 hybrid genes were shown to synthesize a similar amount of alpha/G gamma hybrid mRNAs but 50% less G gamma globin when transfected with the alpha/G gamma hybrid gene carrying the deletion. These results definitively establish that the 2 nucleotide deletion reduces translation efficiency by 30-50%. This contrasts with the 93% reduction induced by a similar A-greater than C change at position -3 in the different nucleotide context preceding the ATG codon of the rat preproinsulin gene.

The Hb F composition in a Moroccan family with beta zero-thalassaemia and Hb O-Arab

We report on a Moroccan family in which the proposita displays a picture of beta-thalassaemia intermedia, associated with heterozygous Hb O-Arab (beta 121 Glu----Lys) and a beta zero-thalassaemia trait. Hb O-Arab was ascertained by the disappearance of the Eco RI restriction site that normally overlaps the beta-globin gene codon 121. The proposita further presents high proportions of Hb F (12.1%) and of G gamma chains (68.6%). The transmission of the proband's haemoglobin markers was analyzed (the proband's husband displaying normal haemoglobin). The beta zero-thalassaemia and O-Arab genes underwent mutual exclusion. A high Hb F (9.28%) level was found in one child, in association with the beta zero-thalassaemia trait, while another child carrying the latter trait displayed normal levels of Hb F. This situation suggests that a heterocellular HPFH determinant is involved. However, there was no means to establish whether the high Hb F proportion in the mother results solely from the beta zero-thalassaemia -Hb O-Arab association or whether an additional HPFH determinant is present. No DNA deletion was detectably associated with the high proportion of Hb F. In this family, the G gamma percentage was high whenever the beta zero-thalassaemia gene was present, regardless of total Hb F percentage. This observation is consistent with the view that the control of the G gamma percentage in the adult is linked to the beta-locus.