[Clinical analysis of preimplantation genetic diagnosis with HLA matching for beta-thalassemia]

OBJECTIVE

To investigate the efficacy and feasibility of preimplantation genetic diagnosis(PGD)with human leukocyte antigen(HLA)matching for beta-thalassemia.

METHODS

A total of 43 referred beta-thalassemia couples, with at least on child in need of hematopoietic stem cell transplantation(HSCT), underwent PGD for HLA matching at the First Affiliated Hospital of Sun Yat-sen University from 2010 to 2015. PGD cycles of these couples were retrospectively analyzed, and 15 infants born from PGD-HLA were followed up.

RESULTS

A total of 84 oocyte retrieval cycles were performed, providing 14±7 oocytes per cycle. Fifty nine embryos biopsied cycles were done, including 24 cleavage stage and 35 blastocyst stage biopsy cycles. In cleavage stage, 259 embryos were biopsied, 93.4%(242/259)of them with conclusive molecular diagnosis, and the percentage of unaffected embryos(normo-homozygote and heterozygote)was 71.4%(185/259). The percentage of HLA matched unaffected embryos was 9.3%(24/259). In blastocyst stage, 306 embryos were biopsied, while 93.8%(287/306)of them were conclusive, and the percentage of unaffected embryos was 70.6%(216/306). The percentage of HLA matched unaffected embryos in blastocyst stage biopsy was 14.4%(44/306), which was higher than in cleavage stage biopsy(P< 0.05). Forty three female carriers underwent 48 embryo transfer cycles including 3 fresh and 45 frozen-thawed embryo transfer cycles. Three fresh embryo transfer cycles were done after cleavage stage biopsy, resulted in a birth of healthy twins born at 36 weeks' gestation. All the embryos were frozen after blastocyst biopsied. Totally, 54 frozen-thawed embryos that were transferred in 45 frozen-thawed embryo transfer cycles included 25 embryo from cleavage stage biopsy and 29 embryo from blastocyst stage biopsy, and 42 of them were HLA matched. Clinical pregnancy rate and implantation rate per cycle in frozen-thawed embryo transfer were 38%(17/45)and 37%(20/54)respectively. A total of 15 infants were born, 2 were from a fresh embryo transfer cycle, and 13 were from frozen-thawed embryo transfer cycles. RESULTS of prenatal diagnosis from delivered cases were matched to that of PGD. Four sick children have been cured by HSCT from these HLA matched born siblings.

CONCLUSION

PGD with HLA matching is an established method for conceiving a child who may donate hematopoietic stem cells to save an ill sibling.

Roles of the polypyrimidine tract and 3' noncoding region of hepatitis C virus RNA in the internal ribosome entry site-mediated translation

Hepatitis C virus (HCV) genome contains a 3'noncoding region (3'NCR) consisting of a variable region, a polypyrimidine tract (polyU/UC) and the X region. To examine the roles of 3'NCR and polyU/UC tract in the internal ribosome entry site (IRES)-mediated translation process, a variety of 3'NCRs containing different lengths of polyU/UC tract were obtained from HCV infected patients and cloned respectively to the downstream of the firefly luciferase coding gene linked to HCV 5'NCR and 30 nucleotides of core gene (containing IRES element). The results of in vitro translation in rabbit reticulocyte lysate (RRL) and cell transfection assay in mammalian cells showed that the IRES-mediated translation efficiency could be enhanced by the full-length of 3'NCR of HCV RNA. However, contradictory results were observed when the role of polyU/UC tract in the IRES-mediated translation was studied. While the IRES-mediated translation efficiency was inhibited by the presence of polyU/UC tract in in vitro translation experiments, transfection of these expression cassettes into hepatic cell line showed that polyU/UC tract enhanced IRES-mediated translation efficiency in vivo. Cellular-fraction complement experiments showed that cellular factors were required for the enhancement by the polyU/UC tract. Further antibody blocking assay and UV cross-linking assay suggested the correlation of IRES-mediated translation with host factors, including the La protein. The data above also indicated that the modulations of the IRES-mediated translation by the HCV 3'NCR and the polyU/UC tract were in a length-independent manner.

Mechanisms underlying the antiarrhythmic and arrhythmogenic actions of quinidine in a Purkinje fiber-ischemic gap preparation of reflected reentry

The effects of therapeutic levels of quinidine were studied in an ischemic gap preparation of reflected reentry. The preparation consisted of a Purkinje fiber mounted in a three-compartment chamber. A narrow central compartment was perfused with a solution prepared to mimic the extracellular milieu at a site of ischemia. Quinidine in concentrations that exert little effect on normal Purkinje tissue, 1 to 2 micrograms/ml, greatly impaired conduction and markedly prolonged refractoriness across the ischemic gap. The drug effected these changes by (1) extending the inexcitable zone within the depressed region, (2) decreasing the amplitude of the input signal entering this zone, and (3) decreasing the excitability of the tissue beyond the depressed zone (evaluated by current clamp techniques). These actions of the drug produced both antiarrhythmic and proarrhythmic effects. When the initial level of conduction impairment was high, quinidine totally suppressed reflected reentry at all frequencies by precipitating complete anterograde conduction block. At intermediate levels of block, the drug generally caused a prominent shift of the frequency dependence of reentrant activity to lower stimulation rates. Finally, when conduction was relatively less impaired, quinidine created the conditions for reflected reentry to occur. Our results suggest that the heart rate dependence of reentrant arrhythmias might be of prognostic value in the administration of antiarrhythmic drugs.