rs267607844

Positions:

• chr3-37042265-C-A
• chr3-37042265-C-G
• chr3-37042265-C-T

Variant summary

Our verdict is Pathogenic. Variant got 10 ACMG points: 10P and 0B. PM2 PP5_Very_Strong

The NM_000249.4(MLH1):​c.1668-3C>A variant causes a splice region, intron 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. 3/3 splice prediction tools predicting alterations to normal splicing. Variant has been reported in ClinVar as Likely pathogenic (★★★).

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 0.000024 (0 hom.)
  • Failed GnomAD Quality Control
• Consequence: MLH1 NM_000249.4 splice_region, intron
• Scores: Splicing: ADA: 0.9995
• Clinical Significance: Likely pathogenic reviewed by expert panel P:1 U:2
• Conservation: PhyloP100: 3.30

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 10 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• PP5: Variant 3-37042265-C-A is Pathogenic according to our data. Variant chr3-37042265-C-A is described in ClinVar as [Likely_pathogenic]. Clinvar id is 89829.Status of the report is reviewed_by_expert_panel, 3 stars. Variant chr3-37042265-C-A is described in Lovd as [Likely_pathogenic]. Variant chr3-37042265-C-A is described in Lovd as [Pathogenic].

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
MLH1	NM_000249.4	c.1668-3C>A		splice_region_variant, intron_variant		ENST00000231790.8	NP_000240.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
MLH1	ENST00000231790.8	c.1668-3C>A		splice_region_variant, intron_variant		1	NM_000249.4	ENSP00000231790.3

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome Data not reliable, filtered out with message: AS_VQSR AF: 0.0000237 AC: 34 AN: 1437474 Hom.: 0 Cov.: 29 AF XY: 0.0000265 AC XY: 19 AN XY: 716444

Gnomad4 AFR exome AF: 0.0000910

Gnomad4 AMR exome AF: 0.00

Gnomad4 ASJ exome AF: 0.00

Gnomad4 EAS exome AF: 0.00

Gnomad4 SAS exome AF: 0.00

Gnomad4 FIN exome AF: 0.0000188

Gnomad4 NFE exome AF: 0.0000248

Gnomad4 OTH exome AF: 0.0000335

GnomAD4 genome Cov.: 32

ClinVar

Significance: Likely pathogenic

Submissions summary: Pathogenic:1 Uncertain:2

Revision: reviewed by expert panel

Submissions by phenotype

Lynch syndrome Pathogenic:1

Likely pathogenic, reviewed by expert panel

curation

International Society for Gastrointestinal Hereditary Tumours (InSiGHT)

Oct 18, 2018

Exon 15 skipping shown in minigene & RT-PCR & possibly 2 MSI tumours (1 from Dieumegard et al 2000 & 1 from UMD) -

Carcinoma of colon Uncertain:1

Uncertain significance, no assertion criteria provided

clinical testing

Department of Pathology and Laboratory Medicine, Sinai Health System

-

The c.1668-3C>A variant has been reported in the literature in 1/68 proband chromosomes of an individual with incomplete HNPCC. This patient showed a strong family history of CRC, but was missing at least one HNPCC criterion. The variant was not found in any of the 192 control chromosomes tested. The tumor from this patient was MSI positive, lacked IHC MLH1 staining, and was found to exhibit LOH (Dieumegard_2000_10732761). The variant is located in the 3' splice region but does not affect the invariant -1 and -2 positions. However, positions -3 and -5 to -12 are part of the splicing consensus sequence and variants involving these positions sometimes affect splicing, increasing the likelihood that this variant has clinical significance Computational prediction software (SpliceSiteFinder, MaxEntScan, NNSPLICE, GeneSplicer, HumanSpliceFinder) predicts a greater than 10% difference in splicing in 2 of 5 different programs. However, this information is not predictive enough to rule out pathogenicity. In summary, based on above information, the clinical significance of this variant cannot be determined with certainty at this time. This variant is classified as a Variant of Unknown Significance. -

Hereditary cancer-predisposing syndrome Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Ambry Genetics

Jul 20, 2021

The c.1668-3C>A intronic variant results from a C to A substitution 3 nucleotides upstream from coding exon 15 in the MLH1 gene. This variant has been reported in a female diagnosed with endometrial cancer at age 48, rectal cancer at age 56, and three colon cancers at ages 63, 65, and 67. One colon tumor was MSI-H and exhibited loss of MLH1 on immunohistochemistry. Family history consisted of colorectal cancer in two relatives, endometrial cancer, and breast cancer (Dieumegard B et al. Br. J. Cancer, 2000 Feb;82:871-80). This nucleotide position is well conserved in available vertebrate species. In silico splice site analysis predicts that this alteration will weaken the native splice acceptor site. Since supporting evidence is limited at this time, the clinical significance of this alteration remains unclear. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_noAF	Benign	-0.18
CADD	Benign	19
DANN	Benign	0.95

Splicing

Name	Calibrated prediction	Score	Prediction
dbscSNV1_ADA	Pathogenic	1.0
dbscSNV1_RF	Pathogenic	0.88
SpliceAI score (max)		0.70		Details are displayed if max score is > 0.2
DS_AL_spliceai		0.70		Position offset: 3

Find out detailed SpliceAI scores and Pangolin per-transcript scores at spliceailookup.broadinstitute.org

Publications

LitVar

Other links and lift over

dbSNP: rs267607844; hg19: chr3-37083756;