title: European external quality control study on the competence of laboratories to recognize rare sequence variants resulting in unusual genotyping results.
abstract: BACKGROUND
  Depending on the method used, rare sequence variants adjacent to the single nucleotide polymorphism (SNP) of interest may cause unusual or erroneous genotyping results. Because such rare variants are known for many genes commonly tested in diagnostic laboratories, we organized a proficiency study to assess their influence on the accuracy of reported laboratory results.
  
  
  METHODS
  Four external quality control materials were processed and sent to 283 laboratories through 3 EQA organizers for analysis of the prothrombin 20210G>A mutation. Two of these quality control materials contained sequence variants introduced by site-directed mutagenesis.
  
  
  RESULTS
  One hundred eighty-nine laboratories participated in the study. When samples gave a usual result with the method applied, the error rate was 5.1%. Detailed analysis showed that more than 70% of the failures were reported from only 9 laboratories. Allele-specific amplification-based PCR had a much higher error rate than other methods (18.3% vs 2.9%). The variants 20209C>T and [20175T>G; 20179_20180delAC] resulted in unusual genotyping results in 67 and 85 laboratories, respectively. Eighty-three (54.6%) of these unusual results were not recognized, 32 (21.1%) were attributed to technical issues, and only 37 (24.3%) were recognized as another sequence variant.
  
  
  CONCLUSIONS
  Our findings revealed that some of the participating laboratories were not able to recognize and correctly interpret unusual genotyping results caused by rare SNPs. Our study indicates that the majority of the failures could be avoided by improved training and careful selection and validation of the methods applied.
authors.affiliation: European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, Geel, Belgium.
authors.forename: János
authors.initials: J
authors.lastname: Márki-Zay
authors.forename: Christoph L
authors.initials: CL
authors.lastname: Klein
authors.forename: David
authors.initials: D
authors.lastname: Gancberg
authors.forename: Heinz G
authors.initials: HG
authors.lastname: Schimmel
authors.forename: László
authors.initials: L
authors.lastname: Dux
mesh_terms: D019411:Clinical Laboratory Techniques; D005060:Europe; D005838:Genotype; D006801:Humans; D007753:Laboratories / Q000706:statistics & numerical data*; D011786:Quality Control; D017422:Sequence Analysis, DNA / Q000379:methods*; D044366:Transition Temperature