Clinical and genetic heterogeneity in black patients with homozygous beta-thalassemia from the southeastern United States.
The presence of various substitutions and deletions resulting in beta-thalassemia was studied in 19 black patients with homozygous beta-thalassemia and in numerous relatives; all patients were from Georgia, South Carolina, and Alabama. Methodology included gene mapping, amplification of genomic DNA with Taq polymerase, identification of known nucleotide substitutions or a single nucleotide deletion through hybridization with synthetic oligonucleotides, cloning and sequencing of a beta-globin gene, and sequencing of amplified genomic DNA. Of the 38 chromosomes tested, 21 (55%) had the A----G substitution at nt -29, eight (21%) had the C----T substitution at nt -88, three (8%) had the substitution at codon 24, while one each of the following abnormalities were also detected: frameshift at codon 6, a C----A mutation at nt 848 of the beta IVS-II (new), an A----T mutation at codon 61 (new), a deletion of 1.35 kilobases including the 5' end of beta, a Ggamma(Agamma delta beta)(0)-thalassemia, and one thalassemia determinant that remained unidentified. The C----A mutation at nt 848 of IVS-II occurred at a position 3 nucleotides 5' to the third exon, adjacent to the invariant AG dinucleotide of the acceptor sequence. The A----T mutation in codon 61 (AAG----TAG) resulted in the creation of a stop codon and thus in beta(0)-thalassemia. The various mutations occurred on chromosomes with different haplotypes; however, chromosomes with a specific mutation but with different haplotypes belonged to one specific framework, which suggested that crossovers were responsible for these different types. Hemoglobin (Hb) F levels were generally high (55% to 75% with 98.5% in one patient with beta(0)/beta(0)); a few patients with specific haplotypes and an alpha-thalassemia-2 heterozygosity had a lower Hb F level. The Ggamma in the Hb F was consistently high when the C----T mutation occurred at nt -158 to the Cap site of the Ggamma-globin gene; seven patients with +/+ at this site had an average Ggamma of 73.8%, eight patients with +/- had 64.8%, and one patient with -/- had 34.2%. Variations in hematologic values and in Hb F, Ggamma, and Hb A2 levels of relatives with a beta-thalassemia heterozygosity depended to some extent on the types of mutations or deletions and on the haplotypes of the chromosomes with the beta-thalassemia determinant.
Gonzalez-Redondo
J M
JM
Department of Cell and Molecular Biology, Medical College of Georgia, Augusta 30912-2100.
Stoming
T A
TA
Lanclos
K D
KD
Gu
Y C
YC
Kutlar
A
A
Kutlar
F
F
Nakatsuji
T
T
Deng
B
B
Han
I S
IS
McKie
V C
VC
D000293:Adolescent; D000328:Adult; D000368:Aged; D001483:Base Sequence; D044383:Black People; D002648:Child; D002675:Child, Preschool; D003062:Codon / Q000302:isolation & purification; D004252:DNA Mutational Analysis; D005260:Female; D005319:Fetal Hemoglobin / Q000235:genetics; D006239:Haplotypes; D006579:Heterozygote; D006720:Homozygote; D006801:Humans; D007223:Infant; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D010375:Pedigree; D013789:Thalassemia / Q000097:blood / Q000235:genetics*; D014481:United States; D001741:Black or African American
D003062:Codon; D005319:Fetal Hemoglobin