MLH1 Constitutional Epimutation Screening Requires Highly Sensitive Assays to Identify Lynch Syndrome Patients With...

Area of Science:

• Genetics
• Cancer Biology
• Molecular Diagnostics

Background:

• Lynch syndrome is a hereditary cancer predisposition syndrome.
• Constitutional epimutations of the MLH1 gene, caused by promoter methylation, are an alternative cause of Lynch syndrome.
• These epimutations can be mosaic with varying methylation levels in carriers.

Purpose of the Study:

• To evaluate the utility of a highly sensitive droplet digital methyl-specific PCR (ddMSP) assay for detecting low-level MLH1 constitutional epimutations.
• To assess the diagnostic yield of MLH1 epimutation screening in patients with MLH1-methylated tumors diagnosed before age 61.

Main Methods:

• A series of 142 patients with MLH1-methylated tumors diagnosed before age 61 were analyzed.
• A specific and highly sensitive ddMSP assay was employed to detect low-level MLH1 methylation (<1%).
• Validation analyses confirmed the constitutional origin of detected methylation.

Main Results:

• Six patients with very low MLH1 methylation levels (<1%) were identified using ddMSP, who were missed by standard pyrosequencing.
• These patients, along with those identified by pyrosequencing, represented 13.1% of the cohort diagnosed with Lynch syndrome.
• The diagnosis of Lynch syndrome led to altered clinical follow-up for these patients.

Conclusions:

• Highly sensitive assays like ddMSP are crucial for systematic MLH1 epimutation screening in patients with MLH1-methylated tumors diagnosed before age 61.
• Implementing sensitive screening increases Lynch syndrome diagnoses, improving patient management and genetic counseling.
• Constitutional MLH1 epimutations are a significant, often overlooked, cause of Lynch syndrome.