The studies of hemoglobinopathies and thalassemia in China - the experiences in Shanghai Institute of Medical Genetics

Background: In the past two decades, a large-scale survey of hemoglobinopat hies and thalassemia was carried out in mainland China, involving nearly on e million people in 28 provinces. The incidences of hemoglobin (Hb) variant s, alpha -thalassemia and beta -thalassemia were 0.33%, 2.64% and 0.66%, re spectively. The chemical structural analysis identified 67 Hb variants. Amo ng them, 20 are new variants. The analysis of the alpha -globin gene organi zation in III HbH patients showed 76 cases (68.5%) were of the deletion typ e, 8 had Hb Constant Spring and the other cases were of non-deletion type. The results of the molecular characterization of snore than 200 P-thalassem ia alleles showed that the most common types of beta -thalassemia mutations in China are CD 41/42 (-4 bp), IVS-II-nt.654 C --> T, CD 17 A --> T, CD 71 /72 (+A) and -28 A --> G. Methods: To explore the simple method for molecul ar diagnosis of beta -thalassemia, multiplex allele-specific amplification (MAS-PCR) was used that could simultaneously detect the above five common t ypes of beta -thalassemia mutations. Results: Based on the molecular analys is of P-thalassemia intermedia, P-thalassemia homozygotes or compound heter ozygotes combined with a-thalassemia, as well as the conjunctive abnormalit ies of P-thalassemia heterozygote with triplicated haplotype of a-globin ge nes, were the most common cause of thalassemia intermedia in China. We also used the RT-PCR quantitation method to show that the most common P-thalass emia allele, IVS-II-nt.654 C --> T, still produced a small amount (about 15 %) of normally spliced beta -globin mRNA, therefore, causing beta (+)-thala ssemia. In clinical trials of hydroxyurea (HU) treatment for beta -thalasse mia patients, we found that HU may enhance the expression of the beta -glob in gene in some patients, leading to an alleviation of clinical symptoms. I n the studies of the reversal of aberrant splicing of IVS-II-nt.654 C --> T allele by the antisense approach, we constructed a mammalian expression ve ctor that can produce an antisense RNA targeting against the aberrant splic e sites of IVS-II-nt.654 C T pre-mRNA. Conclusions: The results indicated t hat the antisense RNA produced from the vector could efficiently suppress t he aberrant splicing pattern and restore the correct splicing pathway in vi tro and in vivo, leading to the improvement of globin chain biosynthesis in thalassemia cells. (C) 2001 Published by Elsevier Science B.V.