Highly sensitive MLH1 methylation analysis in blood identifies a cancer patient with low-level mosaic MLH1 epimutation

Estela Dámaso, Júlia Canet-Hermida, Gardenia Vargas-Parra, Àngela Velasco, Fátima Marín, Esther Darder, Jesús Del Valle, Anna Fernández, Àngel Izquierdo, Gemma Mateu, Glòria Oliveras, Carmen Escribano, Virgínia Piñol, Hugo Ikuo Uchima, José Luis Soto, Megan Hitchins, Ramon Farrés, Conxi Lázaro, Bernat Queralt, Joan BrunetGabriel Capellá, Marta Pineda

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Constitutional MLH1 methylation (epimutation) is a rare cause of Lynch syndrome. Low-level methylation (≤ 10%) has occasionally been described. This study aimed to identify low-level constitutional MLH1 epimutations and determine its causal role in patients with MLH1-hypermethylated colorectal cancer. Eighteen patients with MLH1-hypermethylated colorectal tumors in whom MLH1 methylation was previously undetected in blood by methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) were screened for MLH1 methylation using highly sensitive MS-melting curve analysis (MS-MCA). Constitutional methylation was characterized by different approaches. MS-MCA identified one patient (5.6%) with low-level MLH1 methylation (∼ 1%) in blood and other normal tissues, which was confirmed by clonal bisulfite sequencing in blood. The patient had developed three clonally related gastrointestinal MLH1-methylated tumor lesions at 22, 24, and 25 years of age. The methylated region in normal tissues overlapped with that reported for other carriers of constitutional MLH1 epimutations. Low-level MLH1 methylation and reduced allelic expression were linked to the same genetic haplotype, whereas the opposite allele was lost in patient's tumors. Mutation screening of MLH1 and other hereditary cancer genes was negative. Herein, a highly sensitive MS-MCA-based approach has demonstrated its utility for the identification of low-level constitutional MLH1 epigenetic mosaicism. The eventual identification and characterization of additional cases will be critical to ascertain the cancer risks associated with constitutional MLH1 epigenetic mosaicism.

Idioma originalInglés
Número de artículo171
PublicaciónClinical Epigenetics
EstadoPublicada - 28 nov. 2019

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