3-37017508-C-G

Variant names:

• chr3-37017508-C-G
• rs63751194
• NM_000249.4:c.793C>G

Variant summary

Our verdict is Pathogenic. The variant received 18 ACMG points: 18P and 0B. PM1 PM2 PM5 PP3_Strong PP5_Very_Strong

The NM_000249.4(MLH1):​c.793C>G​(p.Arg265Gly) variant causes a missense, splice region change involving the alteration of a conserved nucleotide. The variant was absent in control chromosomes in GnomAD project. In-silico tool predicts a pathogenic outcome for this variant. 1/1 splice prediction tools predict no significant impact on normal splicing. Variant has been reported in ClinVar as Likely pathogenic (★★). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. R265H) has been classified as Likely benign.

• Frequency: Genomes: not found (cov: 32)
• Consequence: MLH1 NM_000249.4 missense, splice_region
• Clinical Significance: Pathogenic/Likely pathogenic criteria provided, multiple submitters, no conflicts P:5
• Conservation: PhyloP100: 7.28
• Publications: 64 publications found

Genes affected

MLH1 (HGNC:7127): (mutL homolog 1) The protein encoded by this gene can heterodimerize with mismatch repair endonuclease PMS2 to form MutL alpha, part of the DNA mismatch repair system. When MutL alpha is bound by MutS beta and some accessory proteins, the PMS2 subunit of MutL alpha introduces a single-strand break near DNA mismatches, providing an entry point for exonuclease degradation. The encoded protein is also involved in DNA damage signaling and can heterodimerize with DNA mismatch repair protein MLH3 to form MutL gamma, which is involved in meiosis. This gene was identified as a locus frequently mutated in hereditary nonpolyposis colon cancer (HNPCC). [provided by RefSeq, Aug 2017]

MLH1 Gene-Disease associations (from GenCC):

• Lynch syndrome

  Inheritance: AD Classification: DEFINITIVE, SUPPORTIVE Submitted by: G2P, ClinGen, Orphanet
• Lynch syndrome 2

  Inheritance: AD Classification: DEFINITIVE, STRONG Submitted by: Ambry Genetics, Genomics England PanelApp
• Muir-Torre syndrome

  Inheritance: AD Classification: DEFINITIVE, STRONG, MODERATE, SUPPORTIVE Submitted by: Genomics England PanelApp, Ambry Genetics, G2P, Orphanet
• mismatch repair cancer syndrome 1

  Inheritance: AR Classification: DEFINITIVE, STRONG, SUPPORTIVE Submitted by: Ambry Genetics, G2P, Labcorp Genetics (formerly Invitae), Orphanet, ClinGen
• Lynch syndrome 1

  Inheritance: AD Classification: STRONG Submitted by: Labcorp Genetics (formerly Invitae)
• ovarian cancer

  Inheritance: AD Classification: STRONG Submitted by: Genomics England PanelApp
• malignant pancreatic neoplasm

  Inheritance: AD Classification: MODERATE Submitted by: Genomics England PanelApp
• rhabdomyosarcoma

  Inheritance: AR Classification: MODERATE Submitted by: Genomics England PanelApp
• prostate cancer

  Inheritance: AD Classification: LIMITED Submitted by: Ambry Genetics
• breast cancer

  Inheritance: AD Classification: NO_KNOWN Submitted by: Ambry Genetics
• hereditary breast carcinoma

  Inheritance: AD Classification: NO_KNOWN Submitted by: ClinGen

ACMG classification

Our verdict: Pathogenic. The variant received 18 ACMG points.

• PM1: In a hotspot region, there are 3 aminoacids with missense pathogenic changes in the window of +-8 aminoacids around while only 2 benign, 48 uncertain in NM_000249.4
• PM2: Very rare variant in population databases, with high coverage
• PM5: Other missense variant is known to change same aminoacid residue: Variant chr3-37017509-G-C is described in ClinVar as Likely_pathogenic. ClinVar VariationId is 433856.Status of the report is reviewed_by_expert_panel, 3 stars.
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.957
• PP5: Variant 3-37017508-C-G is Pathogenic according to our data. Variant chr3-37017508-C-G is described in ClinVar as Pathogenic/Likely_pathogenic. ClinVar VariationId is 801205.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
MLH1	NM_000249.4	c.793C>G	p.Arg265Gly	missense_variant, splice_region_variant	Exon 10 of 19	ENST00000231790.8	NP_000240.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
MLH1	ENST00000231790.8	c.793C>G	p.Arg265Gly	missense_variant, splice_region_variant	Exon 10 of 19	1	NM_000249.4	ENSP00000231790.3

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome Cov.: 31

GnomAD4 genome Cov.: 32

ClinVar

Significance: Pathogenic/Likely pathogenic

Submissions summary: Pathogenic:5

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Colorectal cancer, hereditary nonpolyposis, type 2 Pathogenic:1

Jul 18, 2023

Myriad Genetics, Inc.

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This variant is considered likely pathogenic. Functional studies indicate this variant impacts protein function [Myriad internal data]. This variant is expected to disrupt protein structure [Myriad internal data].

Hereditary nonpolyposis colon cancer Pathogenic:1

Dec 30, 2024

Women's Health and Genetics/Laboratory Corporation of America, LabCorp

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Variant summary: MLH1 c.793C>G (p.Arg265Gly) results in a non-conservative amino acid change located in the N-terminal domain (IPR002099) of the encoded protein sequence. Five of five in-silico tools predict a damaging effect of the variant on protein function. As the variant is located in the exonic splice region near the intron 9 splicing acceptor site, several computational tools predict a significant impact on normal splicing: Two predict the variant weakens the canonical 3' splicing acceptor site. Internal RNA analysis reports experimental evidence that this variant affects mRNA splicing resulting in skipping of exon 10 and exon 10-11 in a smaller proportion of transcripts, each of which would result in an out-of frame outcome (internal data). Other variant(s) that disrupt this residue have also been determined to be pathogenic with a similar impact on exon skipping, supporting a critical relevance to function. The variant was absent in 251460 control chromosomes. c.793C>G has been reported in the literature in individuals affected with Lynch Syndrome/Hereditary Nonpolyposis Colorectal Cancer (example, Mork_2019, Feng_2024). The following publications have been ascertained in the context of this evaluation (PMID: 39109916, 31101557). ClinVar contains an entry for this variant (Variation ID: 801205). Based on the evidence outlined above, the variant was classified as pathogenic.

not provided Pathogenic:1

Aug 21, 2025

Quest Diagnostics Nichols Institute San Juan Capistrano

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

The MLH1 c.793C>G (p.Arg265Gly) variant has been reported in the published literature in individuals with colorectal cancer where tumors showed microsatellite instability and loss of MLH1 and PMS2 protein expression on immunohistochemistry (PMID: 31101557 (2019), personal communication with Ambry Genetics regarding Clinvar ID: 801205). The variant has also been identified as a somatic variant in individuals with colorectal cancer (PMIDs: 25111426 (2014) and 39109916 (2024)). This variant has not been reported in large, multi-ethnic general populations (Genome Aggregation Database, http://gnomad.broadinstitute.org). Analysis of this variant using bioinformatics tools for the prediction of the effect of amino acid changes on protein structure and function yielded predictions that this variant is damaging. Based on the available information, this variant is classified as likely pathogenic.

Hereditary nonpolyposis colorectal neoplasms Pathogenic:1

Jan 22, 2025

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This sequence change replaces arginine, which is basic and polar, with glycine, which is neutral and non-polar, at codon 265 of the MLH1 protein (p.Arg265Gly). RNA analysis indicates that this missense change induces altered splicing and may result in an absent or altered protein product. This variant is not present in population databases (gnomAD no frequency). This missense change has been observed in individual(s) with colorectal cancer (PMID: 31101557). ClinVar contains an entry for this variant (Variation ID: 801205). Invitae Evidence Modeling of protein sequence and biophysical properties (such as structural, functional, and spatial information, amino acid conservation, physicochemical variation, residue mobility, and thermodynamic stability) indicates that this missense variant is expected to disrupt MLH1 protein function with a positive predictive value of 95%. Studies have shown that this missense change results in skipping of exon 10, and produces a non-functional protein and/or introduces a premature termination codon (internal data). Other variant(s) that result in skipping of exon 10 have been determined to be pathogenic (PMID: 26247049; internal data). This suggests that this variant may also be clinically significant and likely to be disease-causing. For these reasons, this variant has been classified as Pathogenic.

Hereditary cancer-predisposing syndrome Pathogenic:1

Jan 31, 2025

Ambry Genetics

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

The p.R265G pathogenic mutation (also known as c.793C>G), located in coding exon 10 of the MLH1 gene, results from a C to G substitution at nucleotide position 793. The arginine at codon 265 is replaced by glycine, an amino acid with dissimilar properties. This variant has been identified in multiple families diagnosed with Lynch syndrome (Mork ME et al. Cancer Genet. 2019 06;235-236:77-83; Ambry internal data).This variant has been identified in a proband(s) whose Lynch syndrome-associated tumor demonstrated loss of MLH1 and PMS2 expression by immunohistochemistry (Ambry internal data). Another alteration at the same codon, p.R265S (c.793C>A), has been identified in multiple individuals with Lynch/HNPCC-related cancers (Zavodna K et al. Neoplasma. 2006;53:269-76; Alemayehu A et al. Genes Chromosomes Cancer. 2008 Oct;47:906-14; Hardt K et al. Fam. Cancer. 2011 Jun;10:273-84; Ferguson SE et al. Cancer. 2014 Dec;120:3932-9), and has been shown to be deleterious in several functional assays (Wanat JJ et al. Hum. Mol. Genet. 2007 Feb;16:445-52; Drost M et al. Hum. Mutat. 2010 Mar;31:247-53; van der Klift HM et al. Mol Genet Genomic Med. 2015 Jul;3:327-45; Soukarieh O et al. PLoS Genet. 2016 Jan;12:e1005756). The p.R265G variant is considered to be rare based on population cohorts in the Genome Aggregation Database (gnomAD). This amino acid position is highly conserved in available vertebrate species. This alteration is predicted to be deleterious by in silico analysis. Based on the supporting evidence, this alteration is interpreted as a disease-causing mutation.

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	1.0
BayesDel_addAF	Pathogenic	0.57	D
BayesDel_noAF	Pathogenic	0.59
CADD	Pathogenic	31
DANN	Uncertain	1.0
DEOGEN2	Pathogenic	0.90	D;.;.;.;.;.;.
Eigen	Pathogenic	1.1
Eigen_PC	Pathogenic	1.0
FATHMM_MKL	Pathogenic	1.0	D
LIST_S2	Pathogenic	0.99	D;D;.;.;.;D;D
M_CAP	Pathogenic	0.79	D
MetaRNN	Pathogenic	0.96	D;D;D;D;D;D;D
MetaSVM	Pathogenic	0.94	D
MutationAssessor	Pathogenic	4.8	H;.;.;.;.;.;.
PhyloP100		7.3
PrimateAI	Uncertain	0.65	T
PROVEAN	Pathogenic	-7.0	D;D;D;D;D;D;D
REVEL	Pathogenic	0.96
Sift	Pathogenic	0.0	D;D;D;D;D;D;D
Sift4G	Pathogenic	0.0	D;D;D;D;D;D;D
Vest4		0.98
ClinPred		1.0	D
GERP RS		5.7
Varity_R		0.99
gMVP		0.93
Mutation Taster		=0/100	disease causing

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.16		Details are displayed if max score is > 0.2

Find out detailed SpliceAI scores and Pangolin per-transcript scores at spliceailookup.broadinstitute.org

Other links and lift over

dbSNP: rs63751194; hg19: chr3-37058999;