3-37050632-CAA-CA

Position:

• chr3-37050632-CAA-CA

Variant summary

Our verdict is Pathogenic. Variant got 14 ACMG points: 14P and 0B. PVS1_Strong PM2 PP5_Very_Strong

The NM_000249.4(MLH1):​c.2253delA​(p.Val752fs) variant causes a 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 Likely pathogenic (★★).

• Frequency: Genomes: not found (cov: 32)
• Consequence: MLH1 NM_000249.4 frameshift
• Clinical Significance: Pathogenic/Likely 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]

MLH1 (HGNC:):

ACMG classification

Verdict is Pathogenic. Variant got 14 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 4 pathogenic variants in the truncated region.
• PM2: Very rare variant in population databases, with high coverage
• PP5: Variant 3-37050632-CA-C is Pathogenic according to our data. Variant chr3-37050632-CA-C is described in ClinVar as [Likely_pathogenic]. Clinvar id is 578789.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.2253delA	p.Val752fs	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.2253delA	p.Val752fs	frameshift_variant	19/19	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: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

May 01, 2018

This sequence change deletes 1 nucleotide from exon 19 of the MLH1 mRNA (c.2253delA), causing a frameshift at codon 752. This is expected to replace the last five amino acids of the MLH1 protein with 30 random amino acids, creating a new downstream translational stop signal that extends the length of the protein by 25 amino acids. While this is not anticipated to result in nonsense mediated decay, it is expected to result in a disrupted MLH1 protein. This variant is not present in population databases (ExAC no frequency). This variant has not been reported in the literature in individuals with MLH1-related disease. While no functional studies have been performed to test the effect of this particular variant on MLH1 protein function or stability, it affects the highly conserved C-terminal domain (CTD) responsible for MLH1 constitutive dimerization with PMS2 (PMID: 12799449, 16338176, 20533529). Different frameshift variants including c.2269dup, located downstream of this variant have been determined to be pathogenic (PMID: 8128251, 9697702, 12810663, 14985405, Invitae). This suggests that disruption of this region of the MLH1 protein is causative of disease. For these reasons, this variant has been classified as Pathogenic. -

Hereditary cancer-predisposing syndrome Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Ambry Genetics

Dec 28, 2018

The c.2253delA variant, located in coding exon 19 of the MLH1 gene, results from a deletion of one nucleotide at nucleotide position 2253, causing a translational frameshift with a predicted alternate stop codon (p.V752Sfs*31). Frameshifts are typically deleterious in nature, however, this frameshift occurs at the 3' terminus of MLH1, is not expected to trigger nonsense-mediated mRNA decay, and results in the elongation of the protein by 25 amino acids. Structural analysis shows that this alteration perturbs a known functional domain responsible for binding to PMS2 and removes a cysteine residue shown to be involved in metal binding as part of a functional domain in PMS2 (Mohd AB et al. DNA Repair (Amst.) 2006 Mar;5(3):347-61; Smith CE et al. PLoS Genet. 2013 Oct;9(10):e1003869). A different frameshift variant (c.2252_2253dupAA), located at the same location as this variant, has been identified in an HNPCC patient who fulfilled Bethesda guidelines with tumor analysis revealing MSI-H and loss of MLH1 by IHC (Pistorius SR et al. Int J Colorectal Dis 2000 Nov;15(5-6):255-63). This amino acid position is highly conserved in available vertebrate species. Based on the majority of available evidence to date, this variant is likely to be pathogenic. -

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: rs267607901; hg19: chr3-37092123;