title: APC promoter 1B deletion in familial polyposis--implications for mutation-negative families.
abstract: Over 1500 adenomatous polyposis coli (APC) gene mutations have already been identified as causative of familial adenomatous polyposis (FAP). However, routine genetic testing fails to detect mutations in about 10% of classic FAP cases. Recently, it has been shown that a proportion of mutation-negative FAP cases bear molecular changes in deep intronic and regulatory sequences. In this study, we used direct sequencing, followed by multiplex ligation-dependent probe amplification (MLPA) of genomic DNA from family members, affected by classic FAP. We first reported the family as mutation negative. With the launch of a new version of MLPA kit, we retested the family and a novel full deletion of promoter 1B was detected. The exact breakpoints of the deletion were determined by array comparative genomic hybridization (CGH) and long range polymerase chain reaction (PCR), followed by direct sequencing. The total APC expression levels were investigated by quantitative polymerase chain reaction (qPCR) assay and allele-specific expression (ASE) analysis. The APC gene expression was highly reduced, which indicates causative relationship. We suggest that there is a significant possibility that APC promoter 1B mutations could be found in mutation-negative FAP patients. In the light of our findings it seems reasonable to consider targeted genetic re-analysis of APC promoter 1B region in a larger cohort of unsolved cases.
authors.affiliation: Department of Medical Chemistry and Biochemitry, Sofia Medical University, Sofia, Bulgaria; Department of Medical Genetics, Genetic Medico-Diagnostic Laboratory Genica, Sofia, Bulgaria.
authors.forename: T K
authors.initials: TK
authors.lastname: Kadiyska
authors.forename: T P
authors.initials: TP
authors.lastname: Todorov
authors.forename: S N
authors.initials: SN
authors.lastname: Bichev
authors.forename: R V
authors.initials: RV
authors.lastname: Vazharova
authors.forename: A V
authors.initials: AV
authors.lastname: Nossikoff
authors.forename: A S
authors.initials: AS
authors.lastname: Savov
authors.forename: V I
authors.initials: VI
authors.lastname: Mitev
mesh_terms: D011125:Adenomatous Polyposis Coli / Q000209:etiology / Q000235:genetics* / Q000473:pathology*; D025601:Adenomatous Polyposis Coli Protein / Q000235:genetics*; D000328:Adult; D000368:Aged; D005091:Exons / Q000235:genetics; D005820:Genetic Testing; D018095:Germ-Line Mutation; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D008297:Male; D008875:Middle Aged; D011401:Promoter Regions, Genetic / Q000235:genetics*; D017384:Sequence Deletion
chemical_list: D025601:Adenomatous Polyposis Coli Protein
keywords: APC; FAP; colon cancer; promoter deletion