| Objective To explore the microsatellite instability of the 6 sites related with hMLH1 on chromosome 3, in order to find out the role MMR gene playing in malignant hematopathy's initiation and its progression.Method MSI and LOH in 70 cases of leukemia(including 44 cases of acute myeloblas-tic leukemia and 26 cases of acute lymphocytic leukemia and 7 cases of chronic leukemia and 6 cases of myelodysplastic syndrome (MDS) and 5 cases of multiple myeloma were detected by multiplex-PCR amplification at 6 microsatellites related with hMLHl on chromosome 3. gel electrophoresis and argentine dye.Result we detected MSI and LOH in 53 cases out of 70 acute leukemia, the frequencies of MSI on D3sl296,D3s1300 and D3sl304 which are all adjacent to the control sequence of hMLHl are 24.3%(17/70X32. 9%(23/70)and 18. 6%(13/70) respectively, a-mong those data, LOH are 7.1%(5/70X15. 8%(11/70) and 5. 7%(4/70). The MSI frequencies of D3sl298,D3sl561 and D3s1611 linked to hMLHl are 37.1%(26/70) ,25. 7% (18/70) and 10.0%(7/70) respectively; LOH are 8. 6%(6/70),8. 6%(6/70) and 7. 1% (5/70). More than 2 loci are abnormal in 36 cases. Only one case of accelerated CML shows MSI in 3 loci, 3 other CML at diagnostic stage are abnormal at one loci we detected. In addition, we've found MSI in 2 sites of two MDS(RAEB-T) patients, and also 1 MDS (RAEB-T) cases showed MSI in one loci. Among the 5 cases of MM, one case showed MSI in two loci, and another one showed MSI in one loci. One of the CLL cases showed MSI in one loci.Conclusion Since we get a high frequency of MSI and LOH on the loci related with hMLHl gene on chromosome 3, the mutation of the hMLHl plays a role in the initiation and the development of acute leukemia. Our findings of MSI in several sites at the same time mean that leukemia is an accumulate result from a multi-sites/steps mutation of MMR gene; and the developments of CML, MM and MDS might be related with the abnormal changes of microsatellite sites.
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