In this study, we used cloning and sequence analysis to define the molecular defect in two .delta.-thalassemia genes, one associated with reduced output of .delta.-globin chains (.delta.+thal) from a Sardinian and the other with a complete suppression of .delta.-chain production from the affected locus (.delta.othal) from a Southern Italian. Sequence analysis of the .delta.+thal gene showed a G .fwdarw. T substitution at the first nucleotide of codon 27 (.delta.+27) which produces an amino acid change (Ala .fwdarw. Ser) and presumably activates a cryptic splice site located at this position. Therefore, only a fraction of the transcript is processed from this site, as indicated by the clinical phenotype of .delta.+thal. DNA sequencing of the .delta.othal gene revealed a T .fwdarw. C substitution at position 1 of IVS-1, which abolishes the splicing at this site and thus leads to complete deficiency of normal mRNA explaining the clinical phenotype of .delta.othal. Oligonucleotide analysis was used to confirm the coinheritance of the .delta.+27 mutation in a group of Sardinians with thalassemia like phenotype and normal HbA2 level who, on the basis of genetic criteria, were supposed to be double heterozygous for .delta.-thalassemia and .beta.-thalassemia. The definition of .delta.-thalassemia defects in each high-risk area facilitates identification of double heterozygotes for .delta.- and .beta.-thalassemia by DNA analysis and may thus improve genetic counseling.
DELINEATION OF THE MOLECULAR BASIS OF DELTA AND NORMAL HBA-2 BETA-THALASSEMIA
TAGARELLI A;
1988
Abstract
In this study, we used cloning and sequence analysis to define the molecular defect in two .delta.-thalassemia genes, one associated with reduced output of .delta.-globin chains (.delta.+thal) from a Sardinian and the other with a complete suppression of .delta.-chain production from the affected locus (.delta.othal) from a Southern Italian. Sequence analysis of the .delta.+thal gene showed a G .fwdarw. T substitution at the first nucleotide of codon 27 (.delta.+27) which produces an amino acid change (Ala .fwdarw. Ser) and presumably activates a cryptic splice site located at this position. Therefore, only a fraction of the transcript is processed from this site, as indicated by the clinical phenotype of .delta.+thal. DNA sequencing of the .delta.othal gene revealed a T .fwdarw. C substitution at position 1 of IVS-1, which abolishes the splicing at this site and thus leads to complete deficiency of normal mRNA explaining the clinical phenotype of .delta.othal. Oligonucleotide analysis was used to confirm the coinheritance of the .delta.+27 mutation in a group of Sardinians with thalassemia like phenotype and normal HbA2 level who, on the basis of genetic criteria, were supposed to be double heterozygous for .delta.-thalassemia and .beta.-thalassemia. The definition of .delta.-thalassemia defects in each high-risk area facilitates identification of double heterozygotes for .delta.- and .beta.-thalassemia by DNA analysis and may thus improve genetic counseling.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
