3-36993574-G-A

Position:

• chr3-36993574-G-A

Variant summary

Our verdict is Likely pathogenic. Variant got 8 ACMG points: 10P and 2B. PM2 PP5_Very_Strong BP4 BP7

The ENST00000231790.8(MLH1):​c.27G>A​(p.Arg9=) variant causes a synonymous change involving the alteration of a non-conserved nucleotide. The variant was absent in control chromosomes in GnomAD project. In-silico tool predicts a benign outcome for this variant. Variant has been reported in ClinVar as Likely pathogenic (★★). Synonymous variant affecting the same amino acid position (i.e. R9R) has been classified as Likely benign.

• Frequency: Genomes: not found (cov: 33)
• Consequence: MLH1 ENST00000231790.8 synonymous
• Clinical Significance: Likely pathogenic criteria provided, multiple submitters, no conflicts P:5
• Conservation: PhyloP100: 1.73

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 Likely_pathogenic. Variant got 8 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• PP5: Variant 3-36993574-G-A is Pathogenic according to our data. Variant chr3-36993574-G-A is described in ClinVar as [Likely_pathogenic]. Clinvar id is 186982.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.
• BP4: Computational evidence support a benign effect (BayesDel_noAF=-0.36). . Strength limited to SUPPORTING due to the PP5.
• BP7: Synonymous conserved (PhyloP=1.73 with no splicing effect.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
MLH1	NM_000249.4	c.27G>A	p.Arg9=	synonymous_variant	1/19	ENST00000231790.8	NP_000240.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
MLH1	ENST00000231790.8	c.27G>A	p.Arg9=	synonymous_variant	1/19	1	NM_000249.4	ENSP00000231790	P1

Frequencies

GnomAD3 genomes Cov.: 33

GnomAD4 exome Cov.: 31

GnomAD4 genome Cov.: 33

ClinVar

Significance: Likely pathogenic

Submissions summary: Pathogenic:5

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

Baylor Genetics

Jan 05, 2024

- -

Hereditary nonpolyposis colon cancer Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

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

Jul 08, 2024

Variant summary: MLH1 c.27G>A alters a non-conserved nucleotide resulting in a synonymous change. Consensus agreement among computation tools predict no significant impact on normal splicing. However, these predictions have yet to be confirmed by functional studies. The variant was absent in 251448 control chromosomes. c.27G>A has been reported in the literature in multiple individuals from a family affected with colorectal cancer (Leclerc_2018, Ward_2013). This variant also co-occurred with two pathogenic variants in CHEK2 and HOXB13 in a patient with multiple cancers including colon cancer, ovarium cancer, endometrium cancer and and CLL (Wallander_2021). These data indicate that the variant is likely to be associated with disease. To our knowledge, no experimental evidence demonstrating an impact on protein function has been reported. The following publications have been ascertained in the context of this evaluation (PMID: 29790873, 34711244, 22878509). ClinVar contains an entry for this variant (Variation ID: 186982). Based on the evidence outlined above, the variant was classified as likely pathogenic. -

not provided Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Clinical Genetics Laboratory, Skane University Hospital Lund

Mar 25, 2024

- -

Hereditary nonpolyposis colorectal neoplasms Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

Dec 14, 2022

This variant is not present in population databases (gnomAD no frequency). 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. Algorithms developed to predict the effect of sequence changes on RNA splicing suggest that this variant is not likely to affect RNA splicing. ClinVar contains an entry for this variant (Variation ID: 186982). This variant has been observed in individuals with Lynch syndrome-associated tumors and Lynch syndrome (PMID: 22878509, 29790873; Invitae). It has also been observed to segregate with disease in related individuals. This sequence change affects codon 9 of the MLH1 mRNA. It is a 'silent' change, meaning that it does not change the encoded amino acid sequence of the MLH1 protein. -

Hereditary cancer-predisposing syndrome Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Ambry Genetics

Jan 31, 2024

The c.27G>A variant (also known as p.R9R), located in coding exon 1 of the MLH1 gene, results from a G to A substitution at nucleotide position 27. This nucleotide substitution does not change the arginine at codon 9. This alteration was detected along with low-level constitutional MLH1 promoter methylation in a Caucasian male with 3 colorectal cancers, one of which demonstrated high microsatellite instability (MSI-H) with loss of MLH1 protein expression on immunohistochemistry (IHC). The father and mother of this proband were both diagnosed with colorectal cancer as well as a son, who died at age 22 from colorectal cancer. The son also carried the c.27G>A variant allele along with low-level constitutional MLH1 promoter methylation; however, two affected maternal family members did not carry this alteration and were negative for constitutional MLH1 promoter methylation indicating the variant allele may have been paternally inherited (Ward RL et al. Genet. Med. 2013 Jan;15:25-35). This alteration was also reported in a French family that fulfilled Amsterdam I criteria and exhibited low-level constitutional MLH1 promoter methylation. Four family members, two diagnosed with colorectal cancer and two with colorectal adenomas, carried the c.27G>A allele along with low-level constitutional MLH1 promoter methylation. This alteration was identified in another unrelated individual in this study who was diagnosed with colorectal cancer as well as endometrial cancer and had constitutional MLH1 promoter methylation (Leclerc J et al. Genet. Med. 2018 12;20:1589-1599). In our clinical cohort, this alteration also segregated with low-level constitutional MLH1 promoter methylation and disease in families meeting clinical diagnostic criteria for Lynch syndrome (Ambry internal data). This variant was not reported in population-based cohorts in the Genome Aggregation Database (gnomAD). This nucleotide position is not well conserved in available vertebrate species. In silico splice site analysis predicts that this alteration will not have any significant effect on splicing. RNA studies have demonstrated this alteration does not result in abnormal splicing in the set of samples tested (Ambry internal data). Based on the majority of available evidence to date, this variant is likely to be pathogenic. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_noAF	Benign	-0.36
CADD	Benign	14
DANN	Benign	0.94
RBP_binding_hub_radar		0.0
RBP_regulation_power_radar		1.6

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: rs759680369; hg19: chr3-37035065;