title: MLH1 methylation screening is effective in identifying epimutation carriers.
abstract: Recently, constitutional MLH1 epimutations have been identified in a subset of Lynch syndrome (LS) cases. The aim of this study was the identification of patients harboring constitutional MLH1 epimutations in a set of 34 patients with a clinical suspicion of LS, MLH1-methylated tumors and non-detected germline mutations in mismatch repair (MMR) genes. MLH1 promoter methylation was analyzed in lymphocyte DNA samples by MS-MLPA (Methylation-specific multiplex ligation-dependent probe amplification). Confirmation of MLH1 constitutional methylation was performed by MS-MCA (Methylation-specific melting curve analysis), bisulfite sequencing and pyrosequencing in different biological samples. Allelic expression was determined using heterozygous polymorphisms. Vertical transmission was evaluated by MS-MLPA and haplotype analyses. MS-MLPA analysis detected constitutional MLH1 methylation in 2 of the 34 individuals whose colorectal cancers showed MLH1 methylation (5.9%). These results were confirmed by bisulfite-based methods. Both epimutation carriers had developed metachronous early-onset LS tumors, with no family history of LS-associated cancers in their first-degree relatives. In one of the cases, the identified MLH1 constitutional methylation was monoallelic and results in MLH1 and EPM2AIP1 allele-specific transcriptional silencing. It was present in normal somatic tissues and absent in spermatozoa. The methylated MLH1 allele was maternally transmitted and methylation was reversed in a daughter who inherited the same allele. MLH1 methylation screening in lymphocyte DNA from patients with early-onset MLH1-methylated LS-associated tumors allows the identification of epimutation carriers. The present study adds further evidence to the emerging entity of soma-wide MLH1 epimutation and its heritability.
authors: Hereditary Cancer Program, Catalan Institute of Oncology, ICO-IDIBELL, L'Hospitalet de Llobregat, Barcelona, Spain.
authors: Marta
authors: M
authors: Pineda
authors: Pilar
authors: P
authors: Mur
authors: María Dolores
authors: MD
authors: Iniesta
authors: Ester
authors: E
authors: Borràs
authors: Olga
authors: O
authors: Campos
authors: Gardenia
authors: G
authors: Vargas
authors: Sílvia
authors: S
authors: Iglesias
authors: Anna
authors: A
authors: Fernández
authors: Stephen B
authors: SB
authors: Gruber
authors: Conxi
authors: C
authors: Lázaro
authors: Joan
authors: J
authors: Brunet
authors: Matilde
authors: M
authors: Navarro
authors: Ignacio
authors: I
authors: Blanco
authors: Gabriel
authors: G
authors: Capellá
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000483:Alleles; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D003123:Colorectal Neoplasms, Hereditary Nonpolyposis / Q000175:diagnosis / Q000235:genetics*; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D005260:Female; D020868:Gene Silencing; D006580:Genetic Carrier Screening; D018095:Germ-Line Mutation; D006239:Haplotypes; D006579:Heterozygote; D006801:Humans; D008297:Male; D008875:Middle Aged; D000070957:MutL Protein Homolog 1; D009687:Nuclear Proteins / Q000235:genetics*; D009928:Organ Specificity; D010375:Pedigree; D011110:Polymorphism, Genetic; D017422:Sequence Analysis, DNA; D014158:Transcription, Genetic
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; C483189:EPM2AIP1 protein, human; C501486:MLH1 protein, human; D009687:Nuclear Proteins; D000070957:MutL Protein Homolog 1