rs63749792

Positions:

• chr3-37048538-C-A
• chr3-37048538-C-G
• chr3-37048538-C-T

Variant summary

Our verdict is Pathogenic. Variant got 16 ACMG points: 16P and 0B. PM2 PM5 PP3_Strong PP5_Very_Strong

The NM_000249.4(MLH1):​c.1918C>A​(p.Pro640Thr) variant causes a missense 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. 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. P640L) has been classified as Benign.

• Frequency: Genomes: not found (cov: 31)
• Consequence: MLH1 NM_000249.4 missense
• Clinical Significance: Pathogenic/Likely pathogenic criteria provided, multiple submitters, no conflicts P:3 U:1
• Conservation: PhyloP100: 7.39

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 (HGNC:):

ACMG classification

Verdict is Pathogenic. Variant got 16 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• PM5: Other missense variant is known to change same aminoacid residue: Variant chr3-37048539-C-T is described in Lovd as [Pathogenic].
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.985
• PP5: Variant 3-37048538-C-A is Pathogenic according to our data. Variant chr3-37048538-C-A is described in ClinVar as [Likely_pathogenic]. Clinvar id is 492688.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars. Variant chr3-37048538-C-A is described in Lovd as [Pathogenic].

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
MLH1	NM_000249.4	c.1918C>A	p.Pro640Thr	missense_variant	17/19	ENST00000231790.8	NP_000240.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
MLH1	ENST00000231790.8	c.1918C>A	p.Pro640Thr	missense_variant	17/19	1	NM_000249.4	ENSP00000231790.3

Frequencies

GnomAD3 genomes Cov.: 31

GnomAD4 exome Cov.: 31

GnomAD4 genome Cov.: 31

ClinVar

Significance: Pathogenic/Likely pathogenic

Submissions summary: Pathogenic:3 Uncertain:1

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Colorectal cancer, hereditary nonpolyposis, type 2 Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Myriad Genetics, Inc.

Jul 24, 2023

This variant is considered likely pathogenic. This variant has been reported in multiple individuals with clinical features of gene-specific disease [PMID: 36454741, 16341804, 24933000, Myriad internal data]. This variant is expected to disrupt protein structure [Myriad internal data]. Functional studies indicate this variant impacts protein function [PMID: 23403630]. -

Hereditary nonpolyposis colorectal neoplasms Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

Nov 15, 2022

In summary, the currently available evidence indicates that the variant is pathogenic, but additional data are needed to prove that conclusively. Therefore, this variant has been classified as Likely Pathogenic. This variant disrupts the p.Pro640 amino acid residue in MLH1. Other variant(s) that disrupt this residue have been determined to be pathogenic (PMID: 16276679, 16341804, 21404117, 23403630). This suggests that this residue is clinically significant, and that variants that disrupt this residue are likely to be disease-causing. Experimental studies have shown that this missense change affects MLH1 function (PMID: 17510385). Advanced modeling of protein sequence and biophysical properties (such as structural, functional, and spatial information, amino acid conservation, physicochemical variation, residue mobility, and thermodynamic stability) performed at Invitae indicates that this missense variant is expected to disrupt MLH1 protein function. ClinVar contains an entry for this variant (Variation ID: 492688). This variant has not been reported in the literature in individuals affected with MLH1-related conditions. This variant is not present in population databases (gnomAD no frequency). This sequence change replaces proline, which is neutral and non-polar, with threonine, which is neutral and polar, at codon 640 of the MLH1 protein (p.Pro640Thr). -

Hereditary cancer-predisposing syndrome Pathogenic:1

Pathogenic, criteria provided, single submitter

clinical testing

Ambry Genetics

May 17, 2024

The p.P640T variant (also known as c.1918C>A), located in coding exon 17 of the MLH1 gene, results from a C to A substitution at nucleotide position 1918. The proline at codon 640 is replaced by threonine, an amino acid with highly similar properties. This variant was identified as germline in two Tunisian individuals diagnosed with colorectal cancer at ages 39 and 55, respectively. Their tumors demonstrated loss of MLH1 and PMS2 expression by IHC and MLH1 loss of heterozygosity (LOH) (Ben Sghaier R et al. Fam Cancer, 2019 07;18:343-348). This variant has been identified in the homozygous state in an individual who met clinical criteria for constitutional mismatch repair deficiency syndrome (CMMRD) (Akrout F et al. Front Oncol, 2023 Aug;13:1195814).Based on internal structural analysis, this variant is moderately destabilizing and more disrupting to the MLH1 C-terminal domain than another nearby pathogenic variant. This 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. In addition, this alteration is predicted to be deleterious by in silico analysis. Based on the supporting evidence, this variant is interpreted as a disease-causing mutation. -

not specified Uncertain:1

Uncertain significance, no assertion criteria provided

clinical testing

Mayo Clinic Laboratories, Mayo Clinic

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Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	0.94
BayesDel_addAF	Pathogenic	0.55	D
BayesDel_noAF	Pathogenic	0.56
CADD	Uncertain	25
DANN	Uncertain	1.0
DEOGEN2	Pathogenic	0.95	D;.;.;.;.;.
Eigen	Pathogenic	1.0
Eigen_PC	Pathogenic	0.96
FATHMM_MKL	Pathogenic	0.99	D
LIST_S2	Uncertain	0.96	D;D;.;.;.;D
M_CAP	Pathogenic	0.47	D
MetaRNN	Pathogenic	0.98	D;D;D;D;D;D
MetaSVM	Pathogenic	1.1	D
MutationAssessor	Pathogenic	3.7	H;.;.;.;.;.
PrimateAI	Uncertain	0.65	T
PROVEAN	Pathogenic	-7.8	D;D;D;D;D;D
REVEL	Pathogenic	0.98
Sift	Pathogenic	0.0	D;D;D;D;D;D
Sift4G	Pathogenic	0.0	D;D;D;D;D;D
Polyphen		1.0	D;.;.;.;.;.
Vest4		0.96
MutPred		0.89		Gain of sheet (P = 0.0073);.;.;.;.;.;
MVP		0.98
MPC		0.43
ClinPred		1.0	D
GERP RS		5.8
Varity_R		0.97
gMVP		0.90

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.0		Details are displayed if max score is > 0.2

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

Publications

LitVar

Other links and lift over

dbSNP: rs63749792; hg19: chr3-37090029;