rs35045067

Positions:

• chr3-37048557-A-C
• chr3-37048557-A-G
• chr3-37048557-A-T

Variant summary

Our verdict is Likely pathogenic. Variant got 7 ACMG points: 7P and 0B. PM2 PM5 PP3_Moderate PP5

The NM_000249.4(MLH1):​c.1937A>C​(p.Tyr646Ser) 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 Conflicting classifications of pathogenicity (no stars). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. Y646C) has been classified as Pathogenic.

• Frequency: Genomes: not found (cov: 31)
• Consequence: MLH1 NM_000249.4 missense
• Clinical Significance: Conflicting classifications of pathogenicity criteria provided, conflicting classifications P:1 U:1
• Conservation: PhyloP100: 8.94

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 7 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• PM5: Other missense variant is known to change same aminoacid residue: Variant chr3-37048557-A-G is described in Lovd as [Pathogenic].
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.926
• PP5: Variant 3-37048557-A-C is Pathogenic according to our data. Variant chr3-37048557-A-C is described in ClinVar as [Conflicting_classifications_of_pathogenicity]. Clinvar id is 237324.We mark this variant Likely_pathogenic, oryginal submissions are: {Likely_pathogenic=1, Uncertain_significance=1}.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
MLH1	NM_000249.4	c.1937A>C	p.Tyr646Ser	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.1937A>C	p.Tyr646Ser	missense_variant	17/19	1	NM_000249.4	ENSP00000231790	P1

Frequencies

GnomAD3 genomes Cov.: 31

GnomAD4 exome Cov.: 31

GnomAD4 genome Cov.: 31

ClinVar

Significance: Conflicting classifications of pathogenicity

Submissions summary: Pathogenic:1 Uncertain:1

Revision: criteria provided, conflicting classifications

Submissions by phenotype

Hereditary cancer-predisposing syndrome Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Ambry Genetics

Oct 01, 2021

The p.Y646S variant (also known as c.1937A>C), located in coding exon 17 of the MLH1 gene, results from an A to C substitution at nucleotide position 1937. The tyrosine at codon 646 is replaced by serine, an amino acid with dissimilar properties. This variant has been identified in a proband(s) who met Amsterdam I/II criteria for Lynch syndrome and tumor demonstrated high microsatellite instability with loss of PMS2 expression by immunohistochemistry (Ambry internal data). In addition, this variant has been identified in a proband whose Lynch syndrome-associated tumor demonstrated loss of MLH1 and PMS2 expression by immunohistochemistry (Ambry internal data). Based on an internal structural analysis, Y646S replaces a large, hydrophobic residue with a smaller residue which disrupts packing and creates a cavity in the core of the protein, thereby disrupting the local structure to a higher degree than comparable nearby pathogenic variants. 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 majority of available evidence to date, this variant is likely to be pathogenic. -

Hereditary nonpolyposis colorectal neoplasms Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

Dec 07, 2015

In summary, this is a novel missense change with uncertain impact on protein function. It has been classified as a Variant of Uncertain Significance. Algorithms developed to predict the effect of missense changes on protein structure and function (SIFT, PolyPhen-2, Align-GVGD) all suggest that this variant is likely to be disruptive, but these predictions have not been confirmed by published functional studies. This variant is not present in population databases (ExAC no frequency) and has not been reported in the literature. This sequence change replaces tyrosine with serine at codon 646 of the MLH1 protein (p.Tyr646Ser). The tyrosine residue is highly conserved and there is a large physicochemical difference between tyrosine and serine. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	0.65
BayesDel_addAF	Pathogenic	0.48	D
BayesDel_noAF	Pathogenic	0.46
CADD	Pathogenic	26
DANN	Uncertain	0.99
DEOGEN2	Pathogenic	0.93	D;.;.;.;.;.
Eigen	Pathogenic	0.96
Eigen_PC	Pathogenic	0.91
FATHMM_MKL	Pathogenic	0.98	D
LIST_S2	Uncertain	0.89	D;D;.;.;.;D
M_CAP	Pathogenic	0.59	D
MetaRNN	Pathogenic	0.93	D;D;D;D;D;D
MetaSVM	Pathogenic	0.97	D
MutationAssessor	Pathogenic	3.7	H;.;.;.;.;.
MutationTaster	Benign	1.0	D;D;D;D;D;D
PrimateAI	Uncertain	0.65	T
PROVEAN	Pathogenic	-8.2	D;D;D;D;D;D
REVEL	Pathogenic	0.92
Sift	Uncertain	0.0030	D;D;D;D;D;D
Sift4G	Uncertain	0.0060	D;D;D;D;D;D
Polyphen		1.0	D;.;.;.;.;.
Vest4		0.83
MutPred		0.71		Loss of catalytic residue at Y646 (P = 0.0273);.;.;.;.;.;
MVP		0.95
MPC		0.48
ClinPred		1.0	D
GERP RS		5.8
RBP_binding_hub_radar		0.0
RBP_regulation_power_radar		1.1
Varity_R		0.99
gMVP		0.92

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.020		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: rs35045067; hg19: chr3-37090048;