Delta-thalassemia due to a mutation in an erythroid-specific binding protein sequence 3' to the delta-globin gene.
We have previously described a family of Northern Sardinian descent in which the propositus was affected by thalassemia major resulting from compound heterozygosity for codon 39 nonsense mutation and the beta +IVS II nt 745 mutation and in which all heterozygotes for the beta +IVS II nt 745 mutation had normal hemoglobin (Hb) A2 levels. To define the reasons for normal HbA2 levels in otherwise typical beta-thalassemia heterozygotes, we cloned and sequenced the delta-thalassemia gene in cis to the beta +IVS II nt 745 mutation. The sequence analysis showed a single nucleotide substitution (G----A) at position 69 nts (delta +69) downstream to the polyA addition site. Dot blot analysis with an oligonucleotide probe complementary to the delta +69 mutation detected this mutation in several heterozygotes for the beta +IVS II nt 745 mutation from the proband's family, but failed to show it either in a group of normal individuals of the same origin or in nonrelated heterozygotes for the beta +IVS II nt 745 mutation of the same or different descent from the proband. The delta +69 (G----A) mutation may be responsible for the low delta-globin output from the beta +IVS II nt 745 chromosome or could be a silent polymorphism not affecting the function of the delta-globin gene. The normal G at position 69 is part of a sequence very similar to the core DNA (A/T)GATA(A/G) motif (GATA box) that is a binding site for the GATA-1 protein. Gel-retardation assay has shown that a DNA fragment containing the GATA motif with the G----A at position +69 has increased binding affinity for erythroid-specific DNA binding protein(s) as compared with the wild-type sequence. These findings may suggest that the delta +69 mutation is responsible for the deficient function of the in cis delta-globin gene.
Moi
P
P
Ospedale Regionale per le Microcitemie, USL 21, Cagliari, Italy.
Loudianos
G
G
Lavinha
J
J
Murru
S
S
Cossu
P
P
Casu
R
R
Oggiano
L
L
Longinotti
M
M
Cao
A
A
Pirastu
M
M
D001483:Base Sequence; D001665:Binding Sites; D004247:DNA / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004262:DNA Restriction Enzymes; D004268:DNA-Binding Proteins / Q000378:metabolism*; D050981:Erythroid-Specific DNA-Binding Factors; D050982:GATA1 Transcription Factor; D005914:Globins / Q000235:genetics*; D006801:Humans; D007558:Italy; D008969:Molecular Sequence Data; D009154:Mutation; D010375:Pedigree; D013789:Thalassemia / Q000235:genetics*; D014157:Transcription Factors / Q000378:metabolism*
D004268:DNA-Binding Proteins; D050981:Erythroid-Specific DNA-Binding Factors; D050982:GATA1 Transcription Factor; C494688:GATA1 protein, human; D014157:Transcription Factors; D005914:Globins; D004247:DNA; D004262:DNA Restriction Enzymes