Rapid detection of Chinese G gamma+(A gamma delta beta)zero-thalassemia by polymerase chain reaction

Detection of three common α-thalassemia in non-deletion types and six common thalassemia in deletion types by QF-PCR

OBJECTIVE

Thalassemia is one of the most common monogenic hereditary diseases in tropical and subtropical regions. An effective way to avoid the birth of severe thalassemia patients is to strengthen the thalassemia screening of couples before wives are pregnant. Thalassemia gene carriers can be diagnosed by molecular biology in order to conduct effective guidance for fertility.

DESIGNS AND METHODS

For --(SEA) and --(THAI) of α-thalassemia and HPFH-SEA and DBT of β-thalassemia, we design the fGap-PCR primer; for α(CS)α, α(QS)α and α(WS)α, we design the fAS-PCR primer; for -α(3.7)and -α(4.2), we design the QF-PCR primer; and lastly, we use universal primers and multiple-tailed primers to make a single-tube QF-PCR system.

RESULTS

When the QF-PCR system is used to diagnose 123 screening samples of thalassemia genotyping, the typing result is consistent with conventional diagnosis of Gap-PCR and PCR-RDB.

CONCLUSIONS

Compared with conventional Gap-PCR and PCR-RDB, this QF-PCR system is easy to operate, has high precision, and can diagnose genotypes in a large scale. Its automatic operation is more suitable for the large-scale screening of the thalassemia gene.

Molecular characterization and PCR diagnosis of Thailand deletion of alpha-globin gene cluster

Thailand deletion of alpha-Thalassemia (thal) 1 involves the zeta2-, phi zeta1-, alpha2-, alpha1-, and theta1-globin genes. In Southeast Asians and Taiwanese, this mutation is the second most common long-segment deletion of two alpha-globin genes, after the Southeast Asian deletion. To define the Thailand deletion breakpoints, we used polymerase chain reaction (PCR) to amplify the normal-sequence DNA fragments across the breakpoints. The amplified products were sequenced directly or after cloning into pGem-3Z or pCR2.1 vectors. Comparison of the normal and mutant sequences revealed that the 5' breakpoint lies between nucleotides 1,269 and 1,290 upstream of the initiator codon adenine of the zeta2-globin gene, and the 3' breakpoint lies between nucleotides 29,387 and 29,408 downstream of it. A total of 30,677 nucleotides were deleted. Both breakpoints mentioned above lie within the Alu repetitive sequences and an extensive sequence homology is present around the two breakpoints. These findings suggest that homologous recombination is the mechanism by which the deletion occurs. Based on our data, we used three oligonucleotide primers to amplify the regions across the deletion and its corresponding normal sequence. The feasibility of PCR diagnosis was confirmed in 20 carriers with this deletion.

Molecular characterization of beta-thalassemia in Taiwan and the identification of two new mutations

Polymerase chain reaction-based techniques were used to study the molecular defects of 480 unrelated beta-thalassemia heterozygotes in Taiwan. Analysis of artificially created restriction sites and gap-polymerase chain reaction were performed to detect four common mutations, i.e. IVS-II-654 (C-->T), codons 41/42 (-TCTT), codon 17 (A-->T), -28 (A-->G), and a deletional form of delta beta-thalassemia in the Chinese population. In cases with negative or ambiguous results with the aforementioned methods, direct DNA cycle sequencing using either S35-dATP or a fluorescent dye terminator, was carried out to determine the defects. A total of 14 different mutations have been found in this series. The IVS-II-654 mutation was the most common (39.6%), followed by the codons 41/42 mutation (37.9%). The four common genotypes accounted for 92.3% of defects. Two new mutations were detected: codon 31 (-C) and codons 40/41 (+T). Both defects resulted in a frameshift and a premature terminator, the former at codon 60, the latter at codon 43. Although we have studied our cases extensively, the molecular defects in seven alleles are still unknown.