title: A mosaic PTEN mutation causing Cowden syndrome identified by deep sequencing.
abstract: OBJECTIVE
  Mosaic PTEN mutations are not well described in Cowden syndrome. We report a 40-year-old woman with a clinical diagnosis of Cowden syndrome including Lhermitte-Duclos disease, who had a mosaic PTEN mutation detected by next-generation deep sequencing.
  
  
  METHODS
  Complete PTEN gene sequencing by the Sanger method and deletion/duplication analysis performed on DNA extracted from blood leukocytes at a commercial clinical laboratory did not identify a mutation. Because of high suspicion of a PTEN mutation, we repeated testing by next-generation sequencing using the ColoSeq assay, which sequences the entire PTEN locus at >320-fold average coverage.
  
  
  RESULTS
  ColoSeq identified a frameshift PTEN mutation (c.767_768delAG) in 1.7% of sequencing reads from peripheral blood leukocytes (21/1,184 reads), which is below the limit of detection of most Sanger sequencing methods. The mutation was detected at full heterozygous levels in skin fibroblasts and a cerebellar tumor, and at approximately the 25% level in colonic and endocervical mucosa, confirming somatic mosaicism.
  
  
  CONCLUSIONS
  Our report highlights the power of deep next-generation sequencing to identify mosaic mutations that can be missed by traditional less sensitive approaches. We speculate that mosaic PTEN mutations are more common in Cowden syndrome than previously described.
authors.affiliation: Department of Laboratory Medicine, University of Washington, Seattle, Washington, USA.
authors.forename: Colin C
authors.initials: CC
authors.lastname: Pritchard
authors.forename: Christina
authors.initials: C
authors.lastname: Smith
authors.forename: Tatyana
authors.initials: T
authors.lastname: Marushchak
authors.forename: Karen
authors.initials: K
authors.lastname: Koehler
authors.forename: Heidi
authors.initials: H
authors.lastname: Holmes
authors.forename: Wendy
authors.initials: W
authors.lastname: Raskind
authors.forename: Tom
authors.initials: T
authors.lastname: Walsh
authors.forename: Robin L
authors.initials: RL
authors.lastname: Bennett
mesh_terms: D000328:Adult; D002478:Cells, Cultured; D002528:Cerebellar Neoplasms / Q000235:genetics*; D005260:Female; D016368:Frameshift Mutation; D006223:Hamartoma Syndrome, Multiple / Q000235:genetics*; D006579:Heterozygote; D059014:High-Throughput Nucleotide Sequencing; D006801:Humans; D009030:Mosaicism; D051059:PTEN Phosphohydrolase / Q000235:genetics*
chemical_list: D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human