Nondeletional type of hereditary persistence of fetal haemoglobin: molecular characterization of three unrelated Thai HPFH

Association of SNP in exon 1 of HBS1L with hemoglobin F level in beta0-thalassemia/hemoglobin E

Increase in fetal hemoglobin (Hb F) reduces globin chain imbalance in beta-thalassemia, consequently improving symptoms. QTL mapping together with previous genome-wide association study involving approximately 110,000 gene-based SNPs in mild and severe beta(0)-thalassemia/Hb E patients revealed SNPs in HBS1L significantly associated with severity and Hb F levels. Given its potential as binding site for transcription factor activator protein 4, HBS1L exon 1 C32T polymorphism was genotyped in 455 cases, providing for the first time evidence that C allele is associated with elevated Hb F level among beta(0)-thalassemia/Hb E patients with XmnI-(G)gamma-/-and XmnI-(G)gamma+/-polymorphisms.

Molecular analysis of beta-thalassemia in South Vietnam

In Vietnam, the carrier rate for beta-thalassemia varies from 1.5% to 25% depending on the ethnic groups of the population. The molecular basis of beta-thalassemia in South Vietnam was studied in 50 unrelated beta-thalassemia patients. Of these, 31 had beta-thalassemia/Hb E, 18 were homozygous for beta-thalassemia, and 1 carried the beta-thalassemia trait. The majority of the patients were Kinh, four were Chinese, and two were Kinh-Chinese. All had severe anemia and received blood transfusions regularly, every 1-3 months. Hepatosplenomegaly was found in all patients, and splenectomy had been done in six patients. Normal alpha-globin genotype (alpha alpha/alpha alpha) was found in all subjects. Reverse dot-blot hybridization using oligonucleotide probes specific for Southeast Asian mutations can detect beta-thalassemia in 60 chromosomes in addition to 31 chromosomes with beta(E) mutation. Excluding the beta(E) gene, six previously reported Thai and Chinese beta-thalassemia mutations were found, including codons 41/42 (-TCTT) 35.3%, codon 17 (A-->T) 25.0%, -28 (A-->G) 7.3%, codons 71/72 (+A) 7.3%, IVS-II nt 654 (C-->T) 7.3%, and IVS-I nt 1 (G-->T) 6.0%. The Vietnamese frameshift mutation at codon 95 (+A) was detected by ARMS in seven chromosomes (10.3%). DNA polymorphism of the beta-globin gene cluster carrying the codon 95 mutation was - + - - - - - + for (G)gamma/XmnI, epsilon/HincII, (G)gamma/HindIII, (A)gamma/HindIII, psi beta/HincII, 3' psi beta/HincII, beta/AvaII, and 3'beta/BamHI, respectively. The remaining mutation detected by the gap PCR was a large deletion known as the Chinese (G)gamma((A)gamma delta beta)(0)-thalassemia. The two most common mutations were the frameshift at codons 41/42 (-TCTT) and the nonsense mutation in codon 17 (A-->T). Thus beta-thalassemia mutations in South Vietnam is similar to the previous report from the North, although at different frequencies. This result will help to establish a center for prenatal diagnosis and for prevention and control of thalassemia in Vietnam.

Genetic factors affecting clinical severity in beta-thalassemia syndromes

PURPOSE

Heterogeneity in the clinical manifestation of beta-thalassemic diseases may occur from the nature of beta-globin gene mutations, alpha-thalassemia gene interaction, or differences in the amount of hemoglobin (Hb) F production. This study was conducted to determine whether these genetic determinant factors can predict phenotypic severity of patients with beta-thalassemia and to assess the relationship between the genotype and phenotype of the disease.

MATERIALS AND METHODS

A total of 144 patients with beta-thalassemia were divided into mild (46 patients), intermediate (55 patients), and severe groups (43 patients). DNA analysis based on polymerase chain reaction technique was performed to characterize types of beta-thalassemia mutation, interaction of alpha-thalassemia, and XmnI polymorphism 5' to Ggamma-globin gene.

RESULTS

Two alleles of mild beta-thalassemia mutation (beta+/beta+-thalassemia or beta+-thalassemia/Hb E) resulted in a mild clinical symptom whereas two alleles of severe beta-thalassemia mutation (betao/betao) produced a severe clinical phenotype. Compound heterozygosity for mild and severe alleles of beta-thalassemia (betao/ beta+-thalassemia or betao-thalassemia/Hb E) led to variable severity of anemia. Coinheritance of alpha-thalassemia alleviated the severity of beta-thalassemia disease in those patients with at least one allele of the mild beta-thalassemia genotype. DNA polymorphism at position-158 nt 5' to the Ggamma-globin gene was demonstrated by XmnI restriction enzyme. Homozygote of the XmnI site, +/+, was found to have a strong linkage with high Hb F levels and high hemoglobin production in two patients who had mild clinical symptoms. However, some patients who had XmnI site -/- also had mild clinical symptoms because the XmnI- was found to be associated with beta+-thalassemia mutation.

CONCLUSION

Types of beta-thalassemia mutation and coinheritance of alpha-thalassemia in the patient who has at least one allele of the mild beta-thalassemia genotype are predictive for the clinical severity of the disease. However, a mild clinical symptom in some patients with betao/beta+-thalassemia or betao-thalassemia/Hb E who do not have a detectable alpha-thalassemia haplotype and no linkage with XmnI++ suggests that there are other confounding factors responsible for the severity differences of the disease.

Localisation of cis regulatory elements at the beta-globin locus: analysis of hybrid haplotype chromosomes

Several cis elements at the beta-globin gene cluster and the upstream locus control region (LCR) have been implicated in modulation of fetal haemoglobin (Hb F) level in beta-globin disorders. To determine the role of elements at the LCR and the beta-globin gene cluster on HbF level among sickle cell anaemia (SCA) patients, hybrid haplotype betaS chromosomes exhibiting variation in the association of alleles of LCR hypersensitive site 2 (HS2) and the beta-globin gene cluster restriction fragment length polymorphosim (RFLP) haplotypes were identified in an unselected population of 100 patients. On 15 chromosomes the polymorphic HS2 short tandem repeat(TA)xN10-12(TA)y containing a Hox2 binding motif differed from that typically associated with the corresponding beta-globin gene cluster RFLP haplotype. Among patients homozygous for the Benin RFLP haplotype, in whom one chromosome carried the (TA)9N10(TA)10 allele, no effect on HbF level was observed. Polymorphism of the pre-Ggamma framework, an enhancer located 25 kb downstream of HS2 localised the breakpoint for each of these 'hybrid' haplotype chromosomes upstream of this element. Previously described hybrid haplotype chromosomes with the (TA)9N10(TA)10 HS2 allele associated with raised HbF by contrast arise by recombination 1 kb downstream of the pre-Ggamma framework. This study suggests that variability in HbF level associated with polymorphisn of the HS2 enhancer depend on downstream determinant (s) in tight linkage disequilibrium with HS2. The pre-Ggamma framework is the only known polymorphic cis-active determinant in this region.