3-37014544-C-T
Variant summary
Our verdict is Likely pathogenic. Variant got 6 ACMG points: 6P and 0B. PM5PP3_Strong
The NM_000249.4(MLH1):c.790C>T(p.His264Tyr) variant causes a missense, splice region change. The variant allele was found at a frequency of 0.0000141 in 1,558,108 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a pathogenic outcome for this variant. 2/3 splice prediction tools predicting alterations to normal splicing. 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. H264R) has been classified as Pathogenic.
Frequency
Consequence
NM_000249.4 missense, splice_region
Scores
Clinical Significance
Conservation
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ACMG classification
Verdict is Likely_pathogenic. Variant got 6 ACMG points.
Transcripts
RefSeq
Ensembl
Frequencies
GnomAD3 genomes AF: 0.0000197 AC: 3AN: 152106Hom.: 0 Cov.: 33
GnomAD3 exomes AF: 0.0000160 AC: 4AN: 250062Hom.: 0 AF XY: 0.0000222 AC XY: 3AN XY: 135222
GnomAD4 exome AF: 0.0000135 AC: 19AN: 1406002Hom.: 0 Cov.: 24 AF XY: 0.0000228 AC XY: 16AN XY: 702876
GnomAD4 genome AF: 0.0000197 AC: 3AN: 152106Hom.: 0 Cov.: 33 AF XY: 0.0000135 AC XY: 1AN XY: 74290
ClinVar
Submissions by phenotype
Hereditary cancer-predisposing syndrome Uncertain:2
This missense variant replaces histidine with tyrosine at codon 264 of the MLH1 protein. Computational prediction suggests that this variant may have deleterious impact on protein structure and function (internally defined REVEL score threshold >= 0.7, PMID: 27666373). Functional studies report conflicting results for this variant. One study assaying DNA damage tolerance found this variant to be functional (PMID: 30998989), while another study assaying DNA repair activity in mouse cells reported this variant as pathogenic (PMID: 31784484). This variant has been reported in individuals affected with colorectal cancer (PMID: 10413423, 30998989). This variant has been identified in 5/281464 chromosomes in the general population by the Genome Aggregation Database (gnomAD). The available evidence is insufficient to determine the role of this variant in disease conclusively. Therefore, this variant is classified as a Variant of Uncertain Significance. -
The p.H264Y variant (also known as c.790C>T), located in coding exon 9 of the MLH1 gene, results from a C to T substitution at nucleotide position 790. The amino acid change results in histidine to tyrosine at codon 264, an amino acid with similar properties. However, this change occurs in the last base pair of coding exon 9, which makes it likely to have some effect on normal mRNA splicing. RNA studies have demonstrated that this alteration does not result in abnormal splicing in the set of samples tested (Ambry internal data). In one functional study, the p.H264Y variant demonstrated restored cytotoxicity to methylation damage in a human colorectal cancer cell line; however, the mean survival score was between those of known damaging and neutral alterations leading to the tentative classification of "potentially neutral" (Bouvet D et al. Gastroenterology. 2019 08;157(2):421-431). This alteration has been reported in a Chinese male diagnosed with a MSI-H colorectal cancer at age 30y which demonstrated absent MLH1 protein expression on IHC. However, authors note that this alteration was detected in conjunction with the MLH1 p.T117M mutation, presumably on the same chromosome (in cis) as this patient's affected mother was also found to carry both alterations (Chan TL et al. J. Natl. Cancer Inst., 1999 Jul;91:1221-6; Lucci-Cordisco E et al. Cancer Biomark, 2006;2:11-27; Yuen ST et al. Oncogene, 2002 Oct;21:7585-92). This amino acid position is highly conserved in available vertebrate species. In addition, this alteration is predicted to be deleterious by in silico analysis. Since supporting evidence is limited at this time, the clinical significance of this alteration remains unclear. -
not specified Uncertain:1
Variant summary: MLH1 c.790C>T (p.His264Tyr) results in a conservative amino acid change located in the DNA mismatch repair protein, S5 domain 2-like domain (IPR013507) of the encoded protein sequence. Four of five in-silico tools predict a damaging effect of the variant on protein function. Despite the variant being located at the last nucleotide position in exon 9, 5/5 computational tools predict no significant impact on normal splicing. Additionally, no truncated protein product was detected in a patient sample carrying the variant, supporting the lack of impact of this variant on splicing (Chan_1999). The variant allele was found at a frequency of 1.6e-05 in 250062 control chromosomes (gnomAD). The available data on variant occurrences in the general population are insufficient to allow any conclusion about variant significance. c.790C>T has been reported in the literature in a mother and son with colorectal cancer who also carried another pathogenic variant MLH1 c.350C>T (p.T117M), providing supporting evidence for a benign role (Chan_1999, Yuen_2002). One publication reports experimental evidence evaluating an impact on protein function, however, does not allow convincing conclusions about the variant effect (Bouvet_2019). Three submitters have provided clinical-significance assessments for this variant to ClinVar after 2014 without evidence for independent evaluation. All laboratories classified the variant as uncertain significance. Based on the evidence outlined above, the variant was classified as uncertain significance. -
Colorectal cancer, hereditary nonpolyposis, type 2 Uncertain:1
This MLH1 missense variant has been reported in a mother and son who were both affected with colorectal cancer, and both of them had a second MLH1 variant (c.350C>T; p.Thr117Met) that is known to be pathogenic. c.790C>T (rs63751597) is rare (<0.1%) in a large population dataset (gnomAD v2.1.1: 5/281464 total alleles; 0.002%; no homozygotes). It has been reported in ClinVar (Variation ID 90367). Two bioinformatic tools queried predict that this substitution would be damaging, and the histidine residue at this position is evolutionarily conserved across most of the species assessed. However, assays studying the effect of this variant on protein function have been inconclusive, with one study suggesting the variant is neutral and another suggesting a pathogenic role. While this variant changes the last nucleotide of exon 9, it is not predicted to affect normal exon 9 splicing, and at least one experimental study supports the lack of an effect on splicing. We consider the clinical significance of c.790C>T in MLH1 to be uncertain at this time. -
Lynch syndrome 1 Uncertain:1
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Lynch syndrome Uncertain:1
This missense variant replaces histidine with tyrosine at codon 264 of the MLH1 protein. Computational prediction suggests that this variant may have deleterious impact on protein structure and function (internally defined REVEL score threshold >= 0.7, PMID: 27666373). Functional studies report conflicting results for this variant. One study assaying DNA damage tolerance found this variant to be functional (PMID: 30998989), while another study assaying DNA repair activity in mouse cells reported this variant as pathogenic (PMID: 31784484). This variant has been reported in individuals affected colorectal cancer (PMID: 10413423, 30998989). This variant has been identified in 5/281464 chromosomes in the general population by the Genome Aggregation Database (gnomAD). The available evidence is insufficient to determine the role of this variant in disease conclusively. Therefore, this variant is classified as a Variant of Uncertain Significance. -
MLH1-related disorder Uncertain:1
The MLH1 c.790C>T variant is predicted to result in the amino acid substitution p.His264Tyr. This variant has been reported in cis with a pathogenic MLH1 variant in a child and their mother, both with colorectal cancer (Chan et al. 1999. PubMed ID: 10413423). In vitro functional studies demonstrate a minimal effect on mismatch repair activity; however the mean survival score was potentially neutral and methylation tolerance showed minimal or no evidence of pathogenicity (Bouvet et al. 2019. PubMed ID: 30998989; Houlleberghs et al. 2019. PubMed ID: 31784484). It is interpreted as uncertain in ClinVar with multiple submitters in agreement (https://www.ncbi.nlm.nih.gov/clinvar/variation/90367/). This variant is reported in 0.0098% of alleles in individuals of South Asian descent in gnomAD. At this time, the clinical significance of this variant is uncertain due to the absence of conclusive functional and genetic evidence. -
not provided Uncertain:1
Not observed at significant frequency in large population cohorts (gnomAD); In silico analysis supports that this missense variant has a deleterious effect on protein structure/function; Observed in an individual and parent both with colorectal cancer who both also carried a pathogenic MLH1 variant (Chan et al., 1999); This variant is associated with the following publications: (PMID: 27498913, 23760103, 17192056, 12386821, 18383312, 34426522, 22753075, 21153778, 35031544, 31784484, 23403630, 10956410, 10413423, 30998989) -
Hereditary breast ovarian cancer syndrome Uncertain:1
. According to the ACMG standard criteria we chose these criteria: PM2 (supporting pathogenic): popmax:AFR popmax AF:4.82905e-05 popmax AC:2, PP3 (supporting pathogenic): CADD:29.9 REVEL: 0.911 BayesDEL:0.409449 -
Hereditary nonpolyposis colorectal neoplasms Benign:1
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Computational scores
Source:
Splicing
Find out detailed SpliceAI scores and Pangolin per-transcript scores at