Le diagnostic prénatal dans les hémoglobinopathies humaines

Dubart, A; Goossens, Michel; Beuzard, Yves; Monplaisir, N; Dubuisson, JB; Henrion, R; Rosa, J

doi:10.1051/rnd:19800309

Cited by 1 publication

(1 citation statement)

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“…The hematologic data of simple heterozygotes for this mutation were typical of a 83-thalassemia trait and were inconsistent with the presence of a significant hemolytic process due to an unstable hemoglobin. Hemoglobin analysis was performed on fresh blood subsequently obtained from the patient and from another member of the family, who had inherited the same thalassemia allele along with the /3s-globin gene, in order to detect any hemoglobin mutant that might comigrate with either Hb A or acetylated Hb F. The pattern of the hemoglobins and ofthe globin chains was analyzed by isoelectric focusing (34) (Fig. 1) and electrophoresis in Triton/acid/urea (35) (data not shown), respectively.…”

Section: Resultsmentioning

confidence: 99%

A 5' splice-region G----C mutation in exon 1 of the human beta-globin gene inhibits pre-mRNA splicing: a mechanism for beta+-thalassemia.

Vidaud

Gattoni

Stévenin

et al. 1989

Proc. Natl. Acad. Sci. U.S.A.

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We have characterized a Mediterranean ,Bthalassemia allele containing a sequence change at codon 30 that alters both ,B-globin pre-mRNA splicing and the structure of the hemoglobin product. Presumably, this G -. C transversion at position -1 of intron 1 reduces severely the utilization of the normal 5' splice site since the level of the Arg -. Thr mutant hemoglobin (designated hemoglobin Kairouan) found in the erythrocytes of the patient is very low (2% of total hemoglobin). Since no natural mutations of the guanine located at position -1 of the CAG/GTAAGT consensus sequence had been isolated previously, we investigated the role of this nucleotide in the constitution of an active 5' splice site by studying the splicing of the pre-mRNA in cell-free extracts. We demonstrate that correct splicing of the mutant pre-mRNA is 98% inhibited. Our results provide further insights into the mechanisms ofpre-mRNA maturation by revealing that the last residue of the exon plays a role at least equivalent to that of the intron residue at position +5. and 3).The splicing of mRNA precursors requires at least two conserved sequences at the ends of introns: the 5' splice-site consensus sequence CAG/GTAAGT, which shows a striking complementarity to the 5'-terminal region ofU1 small nuclear RNA (snRNA), and the 3' splice-site consensus sequence Y"NCAG/ (4-6). Most of the naturally occurring mutations and in vitro-generated mutations that reduce the complementarity with U1 snRNA result in authentic 5' splice-site inactivation (for reviews, see refs. 7 and 8) and can activate cryptic sites (9-11). Biochemical data and complementation experiments also support the proposal that the 5' end of U1 snRNA interacts with the 5' splice site in mRNA precursors (12)(13)(14)(15). However, it is not possible to predict with confidence the effect of one mutation at a given 5' splice site. For instance, a number of point mutations in the 5' splice site of the large rabbit 3-globin intron do not severely inhibit splicing in transfected Hela cells or in vitro (10,16,17). These results could be interpreted by proposing that 5' splice sites whose sequences match best with the consensus can undergo point mutation without severe inactivation (18,19). Nevertheless, the strength of the 5' splice sites is probably not the only factor involved in the splice-site selection, which can be less dependent on match to the consensus than on the sequence context in which the 5' splice site resides (20). A possible explanation for these divergent observations could be that the individual contribution of exon or intron residues to the 5' splice site is not equivalent. However, the role of the nucleotides preceding the 5' splice site, which are moderately conserved, has not been extensively documented (8). It is striking that no natural mutations of the guanine at position -1 (present in 80% of cases for human genes) have been isolated.Here we describe the isolation and characterization of a G C mutation in the consensus sequence at the last nucleotide of exon 1...

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Section: Resultsmentioning

confidence: 99%