Development and applications of external quality control materials for MTHFR 677C/T genotypes

Abstract

Objective To evaluate the performance of MTHFR 677 genotyping external quality assessment (EQA) program using plasmid DNA constructed in vitro as quality control samples and discuss the problems in clinical laboratories enrolled in the program. Methods Recombinant plasmid carrying MTHFR 677C locus sequence was constructed as wild type sample and plasmid with MTHFR 677T mutation was generated with site-directed mutagenesis as mutant type sample. Heterozygous mutant samples were obtained after equal proportion of the two plasmids. EQA scheme were held twice a year in 2016 and 2017, and sample panels contained 5 different samples using recombinant plasmid DNA containing all types of MTHFR 677 locus genotypes. Participating laboratories were asked to test samples using their routine methods and report the results before deadlines. 26, 28, 52 and 56 effective reports were received respectively in the four EQA schemes. The scores of each lab were calculated based on their results and the overall compliance of different samples as well as the sensitivity and specificity of different methods were calculated using Microsoft Excel. Results MTHFR 677 locus genotypes of the constructed plasmid were verified by Sanger sequencing and there was no failure of sample detection in the four EQA schemes, which suggest that the plasmid has good clinical applicability. About 96.15%(25/26), 100%(28/28), 96.15%(50/52)and 98.21%(55/56)of the laboratories submitted correct results for all samples in the four EQA schemes. The overall compliance rate were 99.23% (129/130), 100%(140/140), 96.92% (252/260) and 98.93% (277/280) respectively. All laboratories using digital FISH and microarrays got full marks in four EQA schemes. The compliance rates for fluorescent PCR were 97.5% (39/40), 100% (45/45), 94.29% (66/70) and 100% (95/95) respectively, while the rates were 100% (20/20), 100% (15/15), 90% (36/40) and 92.5% (37/40) for Sanger sequencing. Conclusions The recombinant plasmid DNA constructed in this study can effectively detect the performance of reagents with good clinical applicability. The results of EQA programs suggested that the overall accuracy rate of laboratories enrolled was high enough, while some laboratories′ performance still needs to be improved. Quality controls in clinical laboratories were essential to assure the accuracy of results.(Chin J Lab Med, 2018, 41: 749-754) Key words: Methylenetetrahy drofolate reductase(NADPH); Plasmids; Genetic testing; Quality control