[Exploration of methodology for assay of single nucleotide polymorphism in thiopurine methyltransferase gene]

The aim of the present study was to gain an insight into the thiopurine methytransferase (TPMT) genotyping assay, which was based on polymerase chain reaction (PCR), allele-specific PCR, restriction digestion of PCR products, denaturing high-performance liquid chromatography (DHPLC) and SNaPshot sequencing and in combination with direct DNA sequencing. Among the f our methods to test TPMT genetic SNPs based on PCR, allele specific PCR was not able to differentiate wild type from varied type. BsiYI, MwoI and AccI to digest PCR products were used so that SNP in TPMT exon 5, 7 and 10 tested. It showed that there were no differences between the results of digestion of PCR products and those of DNA sequence analysis. Therefore, this method was reliable. But some other methods were still needed to look for a compensation, because no restriction map changing resulted from the 2 SNPs in TPMT promotor was found. As to the results of DHPLC, those for the screening of TPMT exon-5 and -10 for SNPs were the same as restriction analysis of PCR products and direct DNA sequencing. But the variation of the heterozygotes in exon-7 was high, which was different from the results of direct DNA sequencing. After changing the Tm of DNA step by step, It was found that all the samples showed single peak when the temperature was 54 degrees C. But this result was unbelievable because a heterozygote in exon 7 as positive control could not be found. Therefore, it was necessary to test the sensitivity and accuracy of DHPLC, though DHPLC could be used as an effective method of SNPs screening. The results of the SNaPshot sequencing were also same as those of restriction analysis of PCR products and direct DNA sequencing. And the results showed that the bases of TPMT promoter -91 and -168 were G, instead of A and T. The results of the four methods to detect TPMT genetic SNPs based on PCR showed that SNPs analysis technique should be a combination of the techniques above-mentioned. One technique alone could not satisfy the need in clinics and research. The compensation of each other was very important.