Development of a quantitative real-time PCR assay for detection of unknown alpha-globin gene deletions.

BACKGROUND: Alpha-Thalassemia is the most common inherited disorder of hemoglobin (Hb) synthesis in the world. Unlike beta-thalassemia, in which non-deletional mutations predominate, most of recognized alpha-thalassemia mutations include deletion of one or both alpha-globin genes. The importance of alpha-thalassemia detection is mainly due to its shared blood parameters with beta-thalassemia and its impact on discrimination between unknown alpha-thalassemia and normal HbA2 beta-thalassemia during thalassemia prevention program. MATERIALS AND METHODS: Cases with hematologic profile of low MCV, MCH, and normal HbA2 were enrolled in this study. Common alpha-globin deletional mutations including alpha(3.7)kb, alpha(4.2)kb, alpha(20.5)kb, and alpha(MED) and point mutation including 5 nt, Constant Spring (CS), and C19 were checked using either GAP-PCR or ARMS-PCR. Cases with unknown molecular defects were investigated further by direct gene sequencing. Finally, further study was done for probable unknown deletions by gene dosage analysis using real-time PCR. For this, five pairs of primers were used spanning from theta-globin gene up to the 3' upstream of alpha(2) gene. RESULTS: After validation of primers specificity and performing serial dilution analysis in order to calculate PCR efficiency, the assay was performed on normal samples and cases with known alpha-globin gene deletions as positive and negative controls, respectively. The assay was able to diagnose the control groups successfully. In 21 out of 29 unknown cases (72.4%), the assay showed various patterns of deletions in at 2 to 5 screened regions (theta gene up to the upstream of alpha2 gene). In 8 (27.6%) cases, deletions were seen in all regions. CONCLUSION: Gene dosage study by quantitative real-time PCR can be suggested as a rapid and reliable assay to screen probable carrier of alpha-thalassemia for unknown alpha-globin gene deletions.

Validation and comparison of two quantitative real-time PCR assays for direct detection of DMD/BMD carriers.

OBJECTIVES: To develop a robust and reliable assay for direct identification of female carriers of deletions in the dystrophin gene. DESIGN AND METHODS: We compared two quantitative real-time PCR approaches for the detection of the deletions of exons 4, 17, 47, and 50 in DMD/BMD carriers. One hundred and ten individuals from 26 unrelated families, including 8 large pedigrees characterized by having at least two DMD affected males, were studied. Carrier status of the subjects was also evaluated by MLPA. RESULTS: The results showed the gene dosage ratio of 0.99+/-0.14 and 1.09+/-0.19 for normal individuals and 0.48+/-0.06 and 0.50+/-0.10 for carriers in SYBR green and TaqMan probe assays, respectively. Carrier status was accurately attributed in 100% of cases and confirmed by MLPA. CONCLUSION: Quantitative real-time PCR can be used as a direct method for carrier detection in female relatives of DMD patients with known deletions. The results are comparable to the MLPA data.