title: Repeat long QT syndrome genetic testing of phenotype-positive cases: prevalence and etiology of detection misses.
abstract: BACKGROUND
  Approximately 75% of long QT syndrome (LQTS) has been explained genetically through research-based and, more recently, commercial genetic testing. While novel LQTS-susceptibility genes or mutations in unexplored regions of known genes underlie the genetic mechanism for some of the 25% "genotype-negative" remnant, it is likely that some cases represent false-negative test results owing to mutation detection failures.
  
  
  OBJECTIVE
  To determine the prevalence and etiology of false negatives that occurred with research-based mutational analysis involving denaturing high-performance liquid chromatography (DHPLC) followed by DNA sequencing (DHPLC-SEQ) in our previously published cohort of unrelated patients referred for LQTS genetic testing.
  
  
  METHODS
  Forty-four LQTS cases (29 men, average age 23 ± 15 years, average corrected QT interval 516 ± 56 ms) deemed genotype negative following DHPLC-SEQ were selected for repeat genetic testing using direct DNA sequencing.
  
  
  RESULTS
  LQTS-causing mutations were identified in 7 of 44 (16%) phenotype-positive/previously genotype-negative subjects, including 4 mutations in KCNQ1 (S225L, G568R, R591H, and R594Q), 2 in KCNH2 (H70R and G925R), and 1 in SCN5A (V411M). None of these variants were seen in more than 2600 reference alleles. Analysis of the misses revealed (1) normal DHPLC detection profile in 2, (2) allelic dropout in 2, (3) failure to correctly optimize DHPLC conditions in 1, and (4) failure to detect abnormal DHPLC signal in 2.
  
  
  CONCLUSIONS
  Repeat genetic testing using direct DNA sequencing may be warranted for LQTS phenotype-positive individuals who were pronounced genotype negative during the decade of research-based mutational analysis that involved intermediate mutation detection methods such as DHPLC.
authors.affiliation: Mayo Medical School, Rochester, Minnesota 55905, USA.
authors.forename: Morgan M
authors.initials: MM
authors.lastname: Medlock
authors.forename: David J
authors.initials: DJ
authors.lastname: Tester
authors.forename: Melissa L
authors.initials: ML
authors.lastname: Will
authors.forename: J Martijn
authors.initials: JM
authors.lastname: Bos
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Ackerman
mesh_terms: D000483:Alleles; D002851:Chromatography, High Pressure Liquid; D004247:DNA / Q000235:genetics*; D004252:DNA Mutational Analysis; D005188:False Negative Reactions; D005260:Female; D020022:Genetic Predisposition to Disease; D005820:Genetic Testing / Q000379:methods*; D005838:Genotype; D006801:Humans; D008133:Long QT Syndrome / Q000175:diagnosis* / Q000453:epidemiology / Q000235:genetics; D008297:Male; D008910:Minnesota / Q000453:epidemiology; D009154:Mutation; D015995:Prevalence; D015203:Reproducibility of Results; D055815:Young Adult
chemical_list: D004247:DNA