Alpha thalassemia

A newly-characterized alpha-thalassaemia-1 deletion removes the entire alpha-like globin gene cluster in an Italian family

We describe a new deletional form of alpha thalassaemia which encompasses the entire alpha-like globin gene cluster in a 15-year-old boy of Southern Italian descent. The deletion removes approximately 31 kb, the 5'-end point is located approximately 4 kb upstream of the xi gene, while the 3'-end point maps between the alpha 1- and theta 1-globin genes. The interaction of this deletion with the common-alpha 3.7 form gives origin to a classical form of haemoglobin (Hb) H disease in the propositus of this study. Deletional forms of xi alpha-thalassaemia are uncommon in the Mediterranean basin; as for other unusual xi alpha-thalassaemia forms, heterozygotes for this mutation may escape detection in population surveys based on zeta and alpha probes.

Human alpha-globin genes demonstrate autonomous developmental regulation in transgenic mice

Recent studies have demonstrated that transcriptional activation of the human adult beta-globin transgene in mice by coinsertion of the beta-globin cluster locus control region (beta-LCR) results in loss of its adult restricted pattern of expression. Normal developmental control is reestablished by coinsertion of the fetal gamma-globin transgene in cis to the adult beta-globin gene. To test the generality of this interdependence of two globin genes for their proper developmental control, we generated transgenic mice in which the human adult alpha-globin genes are transcriptionally activated by the beta-LCR either alone or in cis to their corresponding embryonic zeta-globin gene. In both cases, the human globin transgenes were expressed at the appropriate developmental period. In contrast to the beta-globin gene, developmental control of the human adult alpha-globin transgenes appears to be autonomous and maintained even when activated by an adjacent locus control region.

Human alpha-globin genes demonstrate autonomous developmental regulation in transgenic mice

Recent studies have demonstrated that transcriptional activation of the human adult beta-globin transgene in mice by coinsertion of the beta-globin cluster locus control region (beta-LCR) results in loss of its adult restricted pattern of expression. Normal developmental control is reestablished by coinsertion of the fetal gamma-globin transgene in cis to the adult beta-globin gene. To test the generality of this interdependence of two globin genes for their proper developmental control, we generated transgenic mice in which the human adult alpha-globin genes are transcriptionally activated by the beta-LCR either alone or in cis to their corresponding embryonic zeta-globin gene. In both cases, the human globin transgenes were expressed at the appropriate developmental period. In contrast to the beta-globin gene, developmental control of the human adult alpha-globin transgenes appears to be autonomous and maintained even when activated by an adjacent locus control region.

Thalassemia: genotypes and phenotypes

The large degree of phenotypic heterogeneity of thalassemia can now be related to the underlying genomic defects. This information has accumulated rapidly over the last years through the recent advances in molecular technology. The list of main types of thalassemia (alpha or beta) that can be differentiated includes several gene deletions (complete or partial) and point mutations (or very short deletions). These occur within the genes or across the flanking DNA sequences and apparently interfere with the expression of these genes. From a quantitative point of view, the severity of the condition is directly related to the amount of functional globin chain mRNA which is made available to the ribosomes; this may vary from zero (gene deletions, frameshift, non-sense mutations or mutations at the splice-junction nucleotides) to very little (mostly hnRNA processing mutants) or to slightly subnormal (transcriptional mutants, mutations resulting in cryptic site activation or in defective cleavage of the poly-A tail). A few hyper-unstable globin chains also produce a thalassemic phenotype. This pattern is straightforward in the alpha-thalassemias. In the beta-thalassemias, the decreased beta-chain synthesis reflects the available mRNA, but the phenotypic expression depends also on the ability of the patient to reactivate gamma-chain synthesis and complement the red cell content with hemoglobin F.

Detection of the Hb Quong Sze mutation in a Chinese family by selective amplification of the alpha 2-globin gene and restriction map analysis with Msp I

The polymerase chain reaction technique combined with restriction map analysis with Msp I and hybridization with synthetic oligonucleotide probes has been used to identify Hb Quong Sze [alpha 125(H8)Leu----Pro] in a Chinese family in Guangxi (Quong Sze), P. R. China. Our data and those described in an earlier publication (1) indicate that the Hb Quong Sze carriers originate from the same province of the People's Republic of China, namely Guangxi.

Inactivation of human alpha-globin gene expression by a de novo deletion located upstream of the alpha-globin gene cluster

Synthesis of normal human hemoglobin A, alpha 2 beta 2, is based upon balanced expression of genes in the alpha-globin gene cluster on chromosome 16 and the beta-globin gene cluster on chromosome 11. Full levels of erythroid-specific activation of the beta-globin cluster depend on sequences located at a considerable distance 5' to the beta-globin gene, referred to as the locus-activating or dominant control region. The existence of an analogous element(s) upstream of the alpha-globin cluster has been suggested from observations on naturally occurring deletions and experimental studies. We have identified an individual with alpha-thalassemia in whom structurally normal alpha-globin genes have been inactivated in cis by a discrete de novo 35-kilobase deletion located approximately 30 kilobases 5' from the alpha-globin gene cluster. We conclude that this deletion inactivates expression of the alpha-globin genes by removing one or more of the previously identified upstream regulatory sequences that are critical to expression of the alpha-globin genes.

Hb Hekinan observed in three Chinese from Macau; identification of the GAG----GAT mutation in the alpha 1-globin gene

Hb Hekinan, an alpha chain variant that is characterized by a Glu----Asp mutation at position alpha 27, was observed in three Chinese females attending a prenatal clinic in Macau. The relative quantities of the stable hemoglobin were 13-14% (average 13.3%); its identification was greatly aided by the separation and purification of the peptides by reversed phase high performance liquid chromatography. Dot-blot analysis of amplified DNA with 32P-labeled probes located the mutation in codon 27 of the minor alpha 1-globin gene; the change involved a GAG (coding for glutamic acid) to GAT (coding for aspartic acid) mutation.