NM_000249.4:c.1668-1G>A

Variant names:

• chr3-37042267-G-A
• rs267607845
• NM_000249.4:c.1668-1G>A

Variant summary

Our verdict is Pathogenic. The variant received 18 ACMG points: 18P and 0B. PVS1 PM2 PP5_Very_Strong

The NM_000249.4(MLH1):​c.1668-1G>A variant causes a splice acceptor, intron change involving the alteration of a conserved nucleotide. The variant allele was found at a frequency of 0.00000207 in 1,448,254 control chromosomes in the GnomAD database, with no homozygous occurrence. 3/3 splice prediction tools predicting alterations to normal splicing. Variant has been reported in ClinVar as Likely pathogenic (★★★).

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 0.0000021 (0 hom.)
• Consequence: MLH1 NM_000249.4 splice_acceptor, intron
• Scores: Splicing: ADA: 1.000
• Clinical Significance: Likely pathogenic reviewed by expert panel P:9 U:1
• Conservation: PhyloP100: 8.93
• Publications: 9 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.

• PVS1: Splicing +-2 bp (donor or acceptor) variant, LoF is a know mechanism of disease, No cryptic splice site detected. Exon removal results in frameshift change.
• PM2: Very rare variant in population databases, with high coverage
• PP5: Variant 3-37042267-G-A is Pathogenic according to our data. Variant chr3-37042267-G-A is described in ClinVar as Likely_pathogenic. ClinVar VariationId is 89826.Status of the report is reviewed_by_expert_panel, 3 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
MLH1	NM_000249.4	c.1668-1G>A		splice_acceptor_variant, intron_variant	Intron 14 of 18	ENST00000231790.8	NP_000240.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
MLH1	ENST00000231790.8	c.1668-1G>A		splice_acceptor_variant, intron_variant	Intron 14 of 18	1	NM_000249.4	ENSP00000231790.3

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome AF: 0.00000207 AC: 3 AN: 1448254 Hom.: 0 Cov.: 29 AF XY: 0.00 AC XY: 0 AN XY: 721404

African (AFR) AF: 0.00 AC: 0 AN: 33212

American (AMR) AF: 0.00 AC: 0 AN: 44700

Ashkenazi Jewish (ASJ) AF: 0.00 AC: 0 AN: 26046

East Asian (EAS) AF: 0.00 AC: 0 AN: 39658

South Asian (SAS) AF: 0.00 AC: 0 AN: 86044

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 53382

Middle Eastern (MID) AF: 0.00 AC: 0 AN: 5754

European-Non Finnish (NFE) AF: 0.00000273 AC: 3 AN: 1099486

Other (OTH) AF: 0.00 AC: 0 AN: 59972

GnomAD4 genome Cov.: 32

Alfa AF: 0.0000107 Hom.: 0

ClinVar

Significance: Likely pathogenic

Submissions summary: Pathogenic:9 Uncertain:1

Revision: reviewed by expert panel

Submissions by phenotype

Lynch syndrome Pathogenic:3

Jun 21, 2019

International Society for Gastrointestinal Hereditary Tumours (InSiGHT)

Significance: Likely pathogenic

Review Status: reviewed by expert panel

Collection Method: curation

Interrupts canonical donor splice site -

Apr 19, 2019

Laboratory for Molecular Medicine, Mass General Brigham Personalized Medicine

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

The c.1668-1G>A variant in MLH1 has been reported in at least 4 individuals with Lynch Syndrome (Lamberti 2006, Arnold 2009, Pérez-Carbonell 2012, Shirts 2016) and was found to segregate with disease in 2 additional affected individuals in one family (Arnold 2009). This variant was absent from large population studies. This variant occurs in the invariant region (+/- 1,2) of the splice consensus sequence and has been observed to cause altered splicing leading to an abnormal or absent protein (Arnold 2009, Pérez-Carbonell 2012). Heterozygous loss of function of the MLH1 gene is an established disease mechanism in Lynch Syndrome. Additionally, this variant has been classified as Likely pathogenic on Sep 5, 2013 by the ClinGen-approved InSiGHT panel (ClinVar SCV000106296.2). In summary, this variant meets criteria to be classified as pathogenic for Lynch Syndrome in an autosomal dominant manner. ACMG/AMP criteria applied: PM2, PS4_Supporting, PVS1. -

May 01, 2018

University of Washington Department of Laboratory Medicine, University of Washington

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

MLH1 NM_000249.3:c.1668-1G>A was observed in one family with several cases of early-onset colon and endometrial cancer (Shirts et al 2016, PMID 26845104). It was also seen as an apparent passenger mutation in a tumor with other somatic mutations apparently responsible for the observed MSI status, reducing the likelihood of pathogenicity (Shirts et al 2018, PMID 29887214). This has been reported as likely pathogenic by the InSiGHT consortium and as pathogenic by several laboratories. We currently consider this variant to be likely pathogenic. -

Hereditary cancer-predisposing syndrome Pathogenic:3

May 19, 2021

Ambry Genetics

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

The c.1668-1G>A intronic pathogenic mutation results from a G to A substitution one nucleotide upstream from coding exon 15 of the MLH1 gene. This alteration has been previously reported in several individuals with colorectal cancers demonstrating microsatellite instability and absent MLH1 and/or PMS2 IHC staining, including individuals meeting Amsterdam criteria (Taylor CF, et al. Hum. Mutat. 2003 Dec; 22(6):428-33; Piñol V, et al. JAMA 2005 Apr; 293(16):1986-94; Lamberti C, et al. Digestion 2006 ; 74(1):58-67; Pérez-Carbonell L, et al. Gut 2012 Jun; 61(6):865-72; Walker M et al. Br J Surg, 2007 Dec;94:1567-71). One splicing assay using cell lines from mutation carriers found that this alteration results in out-of-frame skipping of exon 15 (Arnold S, et al. Hum. Mutat. 2009 May; 30(5):757-70). In silico splice site analysis predicts that this alteration will weaken the native splice acceptor site; however, direct evidence is insufficient at this time (Ambry internal data). In addition to the clinical data presented in the literature, alterations that disrupt the canonical splice site are expected to cause aberrant splicing, resulting in an abnormal protein or a transcript that is subject to nonsense-mediated mRNA decay. As such, this alteration is classified as a disease-causing mutation. -

Jan 26, 2018

Academic Department of Medical Genetics, University of Cambridge

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: research

Application of AMCG guidelines 2015. Used other ClinVar submission evidence where relevant. Loss of heterozygosity in tumours or immunohistochemistry abnormalities considered functional evidence of pathogenicity. -

Jan 01, 2022

Color Diagnostics, LLC DBA Color Health

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This variant causes a G to A nucleotide substitution at the -1 position of intron 14 of the MLH1 gene. Functional RNA studies have shown that this variant causes out-of-frame deletion of exon 15 (PMID: 2707453). This variant is expected to result in an absent or non-functional protein product. This variant has been reported in individuals affected with Lynch syndrome or colorectal cancer with tumors showing microsatellite instability and loss of MLH1 protein expression (PMID: 2707453, 15855432, 17095871, 19267393, 21868491). This variant has not been identified in the general population by the Genome Aggregation Database (gnomAD). Loss of MLH1 function is a known mechanism of disease (clinicalgenome.org). Based on the available evidence, this variant is classified as Pathogenic. -

Colorectal cancer, hereditary nonpolyposis, type 2 Pathogenic:2

Oct 17, 2024

Molecular Pathology, Peter Maccallum Cancer Centre

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

- -

Jul 21, 2023

Myriad Genetics, Inc.

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This variant is considered pathogenic. This variant occurs within a consensus splice junction and is predicted to result in abnormal mRNA splicing of either an out-of-frame exon or an in-frame exon necessary for protein stability and/or normal function. This variant is strongly associated with more severe personal and family histories of cancer, typical for individuals with pathogenic variants in this gene [PMID: 27363726]. -

Hereditary nonpolyposis colorectal neoplasms Pathogenic:1

Mar 14, 2023

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This sequence change affects an acceptor splice site in intron 14 of the MLH1 gene. RNA analysis indicates that disruption of this splice site induces altered splicing and may result in an absent or disrupted protein product. This variant is not present in population databases (gnomAD no frequency). Disruption of this splice site has been observed in individual(s) with Lynch syndrome (PMID: 14635101, 15855432, 17095871, 19267393, 21868491). ClinVar contains an entry for this variant (Variation ID: 89826). Studies have shown that disruption of this splice site results in exon skipping and introduces a premature termination codon (PMID: 19267393). The resulting mRNA is expected to undergo nonsense-mediated decay. For these reasons, this variant has been classified as Pathogenic. -

not provided Uncertain:1

-

Department of Pathology and Laboratory Medicine, Sinai Health System

Significance: Uncertain significance

Review Status: no assertion criteria provided

Collection Method: clinical testing

- -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Pathogenic	0.63	D
BayesDel_noAF	Pathogenic	0.42
CADD	Pathogenic	34
DANN	Uncertain	1.0
Eigen	Pathogenic	1.2
Eigen_PC	Pathogenic	1.1
FATHMM_MKL	Pathogenic	0.99	D
PhyloP100		8.9
ClinPred		0.99	D
GERP RS		5.4
Mutation Taster		=0/100	disease causing (ClinVar)

Splicing

Name	Calibrated prediction	Score	Prediction
dbscSNV1_ADA	Pathogenic	1.0
dbscSNV1_RF	Pathogenic	0.93
SpliceAI score (max)		0.71		Details are displayed if max score is > 0.2
DS_AL_spliceai		0.71		Position offset: 1

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

Other links and lift over

dbSNP: rs267607845; hg19: chr3-37083758;