Open AccessContribution of MLH 1 constitutional methylation for Lynch syndrome diagnosis in patients with tumor MLH 1 downregulation
Author(s) -
Pinto Diana,
Pinto Carla,
Guerra Joana,
Pinheiro Manuela,
Santos Rui,
Vedeld Hege Marie,
Yohannes Zeremariam,
Peixoto Ana,
Santos Catarina,
Pinto Pedro,
Lopes Paula,
Lothe Ragnhild,
Lind Guro Elisabeth,
Henrique Rui,
Teixeira Manuel R.
Publication year - 2018
Publication title -
cancer medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.403
H-Index - 53
ISSN - 2045-7634
DOI - 10.1002/cam4.1285
Subject(s) - lynch syndrome , biology , methylation , dna methylation , germline , gene silencing , germline mutation , epigenetics , mutation , cancer research , gene , dna mismatch repair , cancer , genetics , microbiology and biotechnology , gene expression , colorectal cancer
Constitutional epimutation of the two major mismatch repair genes, MLH 1 and MSH 2 , has been identified as an alternative mechanism that predisposes to the development of Lynch syndrome. In the present work, we aimed to investigate the prevalence of MLH 1 constitutional methylation in colorectal cancer ( CRC ) patients with abnormal expression of the MLH 1 protein in their tumors. In a series of 38 patients who met clinical criteria for Lynch syndrome genetic testing, with loss of MLH 1 expression in the tumor and with no germline mutations in the MLH 1 gene (35/38) or with tumors presenting the BRAF p.Val600Glu mutation (3/38), we screened for constitutional methylation of the MLH 1 gene promoter using methylation‐specific multiplex ligation‐dependent probe amplification ( MS ‐ MLPA ) in various biological samples. We found four (4/38; 10.5%) patients with constitutional methylation in the MLH 1 gene promoter. RNA studies demonstrated decreased MLH 1 expression in the cases with constitutional methylation when compared with controls. We could infer the mosaic nature of MLH 1 constitutional hypermethylation in tissues originated from different embryonic germ layers, and in one family we could show that it occurred de novo. We conclude that constitutional MLH 1 methylation occurs in a significant proportion of patients who have loss of MLH 1 protein expression in their tumors and no MLH 1 pathogenic germline mutation. Furthermore, we provide evidence that MLH 1 constitutional hypermethylation is the molecular mechanism behind about 3% of Lynch syndrome families diagnosed in our institution, especially in patients with early onset or multiple primary tumors without significant family history.