ABSTRACT
We report the first identification of a point mutation located within the promoter region of the beta-globin gene at position -83 (G>A) and associated with the common heterozygous deletional alpha-thalassemia (alpha-thal) (-alpha(3.7)/alphaalpha). The patient was an adult male from Gabon belonging to the Obamba sub ethnic group, who was referred to our clinics for a mild microcytic anemia with a Hb A(2) level at the upper limit of the normal value (3.5%). This observation is a new example of alpha- and beta-thal co-inheritance with a normal Hb A(2) level, and illustrates a potential source of pitfall in screening for alpha- and beta-thal carriers.
Subject(s)
Point Mutation , Promoter Regions, Genetic/genetics , beta-Globins/genetics , Adult , Anemia/blood , Anemia/genetics , Base Sequence , DNA Mutational Analysis , Erythrocyte Indices , Humans , Male , Molecular Sequence Data , Polymerase Chain ReactionABSTRACT
Most adults affected with HFE hereditary hemochromatosis (HH type 1, MIMmusical sharp 235200) are homozygous for the p.Cys282Tyr mutation in HFE (NC_000006.10, region 26195427 to 26205038). The aim of this study was to investigate the molecular basis of iron overload in a patient presenting with severe clinical HH with one c.845G>A (p.Cys282Tyr) allele only. Molecular and pedigree studies demonstrated the presence of the c.845G>A (p.Cys282Tyr) mutation in one allele whereas the other carried the c.187C>G (p.His63Asp) mutation plus a new c.128G>A (p.Gly43Asp) substitution in cis. A molecular modeling study of the p.[Gly43Asp;His63Asp] and p.His63Asp variants versus the wild type was carried out using molecular dynamics (MD) simulation in presence of implicit solvent. We found that the c.187C>G (p.His63Asp) mutation does not introduce any major change in the 1- domains of HFE whereas the c.128G>A (p.Gly43Asp) substitution is responsible for a modification of the dynamics and the structure of the Gln40-Ser45 loop, a critical region for HFE-TfR1 interaction thus impairing HFE-TfR1 normal contact. We conclude that the occurrence of complex alleles may be an alternative explanation for the variability of the phenotype in individuals who are compound heterozygous for c.[187C>G]+[845G>A] (p.[His63Asp]+[Cys282Tyr]).
Subject(s)
Amino Acid Substitution , Antigens, CD/metabolism , Hemochromatosis/genetics , Heterozygote , Histocompatibility Antigens Class I/chemistry , Histocompatibility Antigens Class I/genetics , Membrane Proteins/chemistry , Membrane Proteins/genetics , Receptors, Transferrin/metabolism , Alleles , Amino Acids/genetics , Binding Sites , Hemochromatosis/metabolism , Hemochromatosis Protein , Histocompatibility Antigens Class I/metabolism , Humans , Male , Membrane Proteins/metabolism , Middle Aged , Models, Molecular , Mutation, Missense , Pedigree , Structure-Activity RelationshipABSTRACT
We have identified and characterized a novel beta-thalassemic mutation in a North African adult. The molecular defect consists of a two nucleotide (nt) deletion in the beta-globin gene at codon 76 [beta76 (-GC), c.229-230delGC]. This frameshift mutation generates a TGA stop codon at position 89. The carrier presented with mild microcytic anemia (Hb 12.8 g/dL, MCV 60 fL), no detectable Hb F, an elevated Hb A2 level (5.5%) with no other mutation in the beta-globin gene and none of the more common known deletions in the alpha-globin cluster. No abnormal hemoglobin (Hb) was present in routine electrophoresis or in high performance liquid chromatography (HPLC) analyses. Pathologic inclusions were absent in both mature red cells and in reticulocytes. This observation reinforces the hypothesis that nonsense and frameshift mutations that result in a premature stop codon in exon 1 or exon 2 inherited in the heterozygous state do not generate dominant beta-thalassemia (thal). This is the first example of a premature stop codon at position 89.
