3-37050630-T-TA

Position:

• chr3-37050630-T-TA

Variant summary

Our verdict is Pathogenic. Variant got 18 ACMG points: 18P and 0B. PVS1 PM2 PP5_Very_Strong

The ENST00000231790.8(MLH1):​c.2249dup​(p.Tyr750Ter) variant causes a stop gained, frameshift change involving the alteration of a conserved nucleotide. The variant was absent in control chromosomes in GnomAD project. Variant has been reported in ClinVar as Pathogenic (★★). Synonymous variant affecting the same amino acid position (i.e. Y750Y) has been classified as Likely benign.

• Frequency: Genomes: not found (cov: 32)
• Consequence: MLH1 ENST00000231790.8 stop_gained, frameshift
• Clinical Significance: Pathogenic criteria provided, multiple submitters, no conflicts P:2
• Conservation: PhyloP100: 9.00

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]

ACMG classification

Verdict is Pathogenic. Variant got 18 ACMG points.

• PVS1: Loss of function variant, product does not undergo nonsense mediated mRNA decay. Variant is located in the 3'-most exon, not predicted to undergo nonsense mediated mRNA decay. There are 21 pathogenic variants in the truncated region.
• PM2: Very rare variant in population databases, with high coverage
• PP5: Variant 3-37050630-T-TA is Pathogenic according to our data. Variant chr3-37050630-T-TA is described in ClinVar as [Pathogenic]. Clinvar id is 237334.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
MLH1	NM_000249.4	c.2249dup	p.Tyr750Ter	stop_gained, frameshift_variant	19/19	ENST00000231790.8	NP_000240.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
MLH1	ENST00000231790.8	c.2249dup	p.Tyr750Ter	stop_gained, frameshift_variant	19/19	1	NM_000249.4	ENSP00000231790	P1

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome Cov.: 31

GnomAD4 genome Cov.: 32

ClinVar

Significance: Pathogenic

Submissions summary: Pathogenic:2

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Hereditary nonpolyposis colorectal neoplasms Pathogenic:1

Pathogenic, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

Jan 04, 2018

This sequence change results in a premature translational stop signal in the MLH1 gene (p.Tyr750*). While this is not anticipated to result in nonsense mediated decay, it is expected to delete the last 7 amino acids of the MLH1 protein. This truncation affects the highly conserved C-terminal domain responsible for MLH1 constitutive dimerization with PMS2 (PMID: 12799449, 16338176, 20533529). A different truncating variant downstream of this variant (p.Lys751Serfs*3) has been reported in individuals affected with Lynch syndrome and has been determined to be pathogenic (PMID: 24802709, 8797773, 27295708, 18566915, 18931482). This suggests that deletion of this region of the MLH1 protein is causative of disease. Loss-of-function variants in MLH1 are known to be pathogenic (PMID: 15713769, 24362816). For these reasons, this variant has been classified as Pathogenic. This variant is not present in population databases (ExAC no frequency). A different variant (c.2250C>G) giving rise to the same protein effect observed here (p.Tyr750*) has been reported in an individual affected with Lynch syndrome (PMID: 10422993). Experimental studies show that this change significantly affects PMS2-MLH1 dimerization and mismatch repair activity (PMID: 16338176, 20533529), indicating that this residue may be critical for protein function. This variant has not been reported in the literature in individuals with MLH1-related disease. ClinVar contains an entry for this variant (Variation ID: 237334). -

Hereditary cancer-predisposing syndrome Pathogenic:1

Pathogenic, criteria provided, single submitter

clinical testing

Ambry Genetics

Aug 28, 2020

The c.2249dupA pathogenic mutation, located in coding exon 19 of the MLH1 gene, results from a duplication of A at nucleotide position 2249. This changes the amino acid from a tyrosine to a stop codon within coding exon 19 (p.Y750*). This alteration occurs at the 3' terminus of theMLH1 gene, is not expected to trigger nonsense-mediated mRNA decay, and only impacts the last 7 amino acids of the protein. However, premature stop codons are typically deleterious in nature and the impacted region is critical for protein function based on an internal structural analysis which suggests that this variant perturbs a known functional domain responsible for binding to as well as stabilizing PMS2 and removes a terminal cysteine residue shown to be involved in metal binding as part of a functional domain in PMS2 (Ambry internal data; Mohd AB et al. DNA Repair (Amst.) 2006 Mar;5(3):347-61; Smith CE et al. PLoS Genet. 2013 Oct;9(10):e1003869; Gueneau E et al. Nat. Struct. Mol. Biol. 2013 Apr;20:461-8). Another alteration resulting in a similar truncation at amino acid 750, p.Y750* (c.2250C>G), has been detected in families meeting Amsterdam I/II criteria for Lynch syndrome and was reported to have reduced interaction with PMS2 as well as deficient relative mismatch repair activity (Syngal S et al. JAMA, 1999 Jul;282:247-53; Yuan Y et al. Jpn. J. Clin. Oncol., 2004 Nov;34:660-6; Wang XL et al. World J. Gastroenterol., 2006 Jul;12:4074-7; Mueller J et al. Cancer Res., 2009 Sep;69:7053-61; Kosinski J et al. Hum. Mutat., 2010 Aug;31:975-82). As such, this alteration is interpreted as a disease-causing mutation. -

Computational scores

Source: dbNSFP v4.3

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: rs878853787; hg19: chr3-37092121;