title: Mapping the deletion endpoints in individuals with 22q11.2 deletion syndrome by droplet digital PCR.
abstract: BACKGROUND
  Chromosome 22q11.2 deletion syndrome (22q11DS) is the most common human microdeletion syndrome and is associated with many cognitive, neurological and psychiatric disorders. The majority of individuals have a 3 Mb deletion while others have a nested 1.5 Mb deletion, but rare atypical deletions have also been described. To date, a study using droplet digital PCR (ddPCR) has not been conducted to systematically map the chromosomal breakpoints in individuals with 22q11DS, which would provide important genotypic insight into the various phenotypes observed in this syndrome.
  
  
  METHODS
  This study uses ddPCR to assess copy number (CN) changes within the chromosome 22q11 deletion region and allows the mapping of the deletion endpoints. We used eight TaqMan assays interspersed throughout the deleted region of 22q11.2 to characterize the deleted region of chromosome 22 in 80 individuals known to have 22q11DS by FISH. Ten EvaGreen assays were used for finer mapping of the six identified individuals with 22q11DS atypical deletions and covering different regions of chromosome 22.
  
  
  RESULTS
  ddPCR provided non-ambiguous CN measurements across the region, confirmed the presence of the deletion in the individuals screened, and led to the identification of five differently sized and located deletions. The majority of the participants (n = 74) had the large 3 Mb deletions, whereas three had the smaller 1.5 Mb deletions, and the remaining three had an interstitial deletion of different size.
  
  
  CONCLUSIONS
  The lower cost, rapid execution and high reliability and specificity provided by ddPCR for CN measurements in the 22q11 region constitutes a significant improvement over the variable CN values generated by other technologies. The ability of the ddPCR approach, to provide a high resolution mapping of deletion endpoints may result in the identification of genes that are haplo-insufficient and play a role in the pathogenesis of 22q11DS. Finally, this methodology can be applied to the characterization of other microdeletions throughout the genome.
authors.forename: Vicki J
authors.initials: VJ
authors.lastname: Hwang
authors.forename: Dianna
authors.initials: D
authors.lastname: Maar
authors.forename: John
authors.initials: J
authors.lastname: Regan
authors.forename: Kathleen
authors.initials: K
authors.lastname: Angkustsiri
authors.forename: Tony J
authors.initials: TJ
authors.lastname: Simon
authors.affiliation: Department of Biochemistry and Molecular Medicine, UC Davis, 2700 Stockton Blvd, Suite 2102, Sacramento 95817, CA, USA. ftassone@ucdavis.edu.
authors.forename: Flora
authors.initials: F
authors.lastname: Tassone
mesh_terms: D000293:Adolescent; D002648:Child; D002874:Chromosome Mapping; D002892:Chromosomes, Human, Pair 22; D056915:DNA Copy Number Variations; D004062:DiGeorge Syndrome / Q000175:diagnosis / Q000235:genetics*; D005260:Female; D017353:Gene Deletion; D056726:Genetic Association Studies; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D008297:Male; D016133:Polymerase Chain Reaction / Q000191:economics / Q000379:methods*