title: High-resolution melting (HRM) re-analysis of a polyposis patients cohort reveals previously undetected heterozygous and mosaic APC gene mutations.
abstract: Familial adenomatous polyposis is most frequently caused by pathogenic variants in either the APC gene or the MUTYH gene. The detection rate of pathogenic variants depends on the severity of the phenotype and sensitivity of the screening method, including sensitivity for mosaic variants. For 171 patients with multiple colorectal polyps without previously detectable pathogenic variant, APC was reanalyzed in leukocyte DNA by one uniform technique: high-resolution melting (HRM) analysis. Serial dilution of heterozygous DNA resulted in a lowest detectable allelic fraction of 6% for the majority of variants. HRM analysis and subsequent sequencing detected pathogenic fully heterozygous APC variants in 10 (6%) of the patients and pathogenic mosaic variants in 2 (1%). All these variants were previously missed by various conventional scanning methods. In parallel, HRM APC scanning was applied to DNA isolated from polyp tissue of two additional patients with apparently sporadic polyposis and without detectable pathogenic APC variant in leukocyte DNA. In both patients a pathogenic mosaic APC variant was present in multiple polyps. The detection of pathogenic APC variants in 7% of the patients, including mosaics, illustrates the usefulness of a complete APC gene reanalysis of previously tested patients, by a supplementary scanning method. HRM is a sensitive and fast pre-screening method for reliable detection of heterozygous and mosaic variants, which can be applied to leukocyte and polyp derived DNA.
authors.affiliation: Department of Clinical Genetics, Leiden University Medical Center, P.O. Box 9600, 2300 RC, Leiden, The Netherlands.
authors.forename: Astrid A
authors.initials: AA
authors.lastname: Out
authors.forename: Ivonne J H M
authors.initials: IJ
authors.lastname: van Minderhout
authors.forename: Nienke
authors.initials: N
authors.lastname: van der Stoep
authors.forename: Lysette S R
authors.initials: LS
authors.lastname: van Bommel
authors.forename: Irma
authors.initials: I
authors.lastname: Kluijt
authors.forename: Cora
authors.initials: C
authors.lastname: Aalfs
authors.forename: Marsha
authors.initials: M
authors.lastname: Voorendt
authors.forename: Rolf H A M
authors.initials: RH
authors.lastname: Vossen
authors.forename: Maartje
authors.initials: M
authors.lastname: Nielsen
authors.forename: Hans F A
authors.initials: HF
authors.lastname: Vasen
authors.forename: Hans
authors.initials: H
authors.lastname: Morreau
authors.forename: Peter
authors.initials: P
authors.lastname: Devilee
authors.forename: Carli M J
authors.initials: CM
authors.lastname: Tops
authors.forename: Frederik J
authors.initials: FJ
authors.lastname: Hes
mesh_terms: D011125:Adenomatous Polyposis Coli / Q000235:genetics*; D000293:Adolescent; D000328:Adult; D000368:Aged; D015331:Cohort Studies; D005260:Female; D017491:Genes, APC; D006801:Humans; D008297:Male; D008875:Middle Aged; D009030:Mosaicism; D009154:Mutation; D016133:Polymerase Chain Reaction; D020641:Polymorphism, Single Nucleotide