13-32319076-G-T

Position:

• chr13-32319076-G-T

Variant summary

Our verdict is Uncertain significance. Variant got 4 ACMG points: 4P and 0B. PVS1_Moderate PM2

The NM_000059.4(BRCA2):​c.68-1G>T variant causes a splice acceptor change. The variant was absent in control chromosomes in GnomAD project. In-silico tool predicts a pathogenic outcome for this variant. 3/3 splice prediction tools predicting alterations to normal splicing. Variant has been reported in ClinVar as Uncertain significance (★★).

• Frequency: Genomes: not found (cov: 33)
• Consequence: BRCA2 NM_000059.4 splice_acceptor
• Scores: Splicing: ADA: 1.000
• Clinical Significance: Uncertain significance criteria provided, multiple submitters, no conflicts P:1 U:4
• Conservation: PhyloP100: 7.06

Genes affected

BRCA2 (HGNC:1101): (BRCA2 DNA repair associated) Inherited mutations in BRCA1 and this gene, BRCA2, confer increased lifetime risk of developing breast or ovarian cancer. Both BRCA1 and BRCA2 are involved in maintenance of genome stability, specifically the homologous recombination pathway for double-strand DNA repair. The largest exon in both genes is exon 11, which harbors the most important and frequent mutations in breast cancer patients. The BRCA2 gene was found on chromosome 13q12.3 in human. The BRCA2 protein contains several copies of a 70 aa motif called the BRC motif, and these motifs mediate binding to the RAD51 recombinase which functions in DNA repair. BRCA2 is considered a tumor suppressor gene, as tumors with BRCA2 mutations generally exhibit loss of heterozygosity (LOH) of the wild-type allele. [provided by RefSeq, May 2020]

ACMG classification

Verdict is Uncertain_significance. Variant got 4 ACMG points.

• PVS1: Splicing +-2 bp (donor or acceptor) variant, product NOT destroyed by NMD, known LOF gene, truncates exone, which is 0.02417861 fraction of the gene. Cryptic splice site detected, with MaxEntScore 8.4, offset of 6, new splice context is: ttttttttaaatatatttAGgac. Cryptic site results in inframe change. If cryptic site found is not functional and variant results in exon loss, it results in inframe change.
• PM2: Very rare variant in population databases, with high coverage

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
BRCA2	NM_000059.4	c.68-1G>T		splice_acceptor_variant		ENST00000380152.8	NP_000050.3

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
BRCA2	ENST00000380152.8	c.68-1G>T		splice_acceptor_variant		5	NM_000059.4	ENSP00000369497	A2

Frequencies

GnomAD3 genomes Cov.: 33

GnomAD4 exome Cov.: 32

GnomAD4 genome Cov.: 33

Bravo AF: 0.00000378

ClinVar

Significance: Uncertain significance

Submissions summary: Pathogenic:1 Uncertain:4

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Hereditary cancer-predisposing syndrome Uncertain:2

Uncertain significance, criteria provided, single submitter	clinical testing	Color Diagnostics, LLC DBA Color Health	Jan 11, 2022	This variant is located in intron 2 of the BRCA2 gene. It is predicted to abolish the intron 2 splice acceptor site at the AG dinucleotide at the 3' terminus of the intron. However, there is an alternative AG dinucleotide at c.72_73, which if used is predicted to cause a 6-basepair deletion (r.68_73del) and an in-frame deletion of 2 amino acids. RNA studies on similar canonical splice acceptor site variants, c.68-1G>A and c.68-2A>G, reported aberrant splicing with the major product being the predicted in-frame deletion of the first six 6 nucleotides in exon 3 (PMID: 32641407, 33469799). This variant has not been reported in individuals affected with hereditary cancer in the literature. This variant has not been identified 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. -
Uncertain significance, criteria provided, single submitter	clinical testing	Ambry Genetics	Oct 25, 2021	The c.68-1G>T intronic variant results from a G to T substitution one nucleotide upstream from coding exon 2 of the BRCA2 gene. This nucleotide position is highly conserved in available vertebrate species. In silico splice site analysis predicts that this alteration will weaken the native splice acceptor site and will result in the creation or strengthening of a novel splice acceptor site. RNA studies have demonstrated that close match alterations BRCA2 c.68-2A>G and BRCA2 c.68-1G>A, which have the same predicted RNA effect as this variant, result in substantial expression of multiple abnormal transcripts including a splice variant which is predicted to result in an in-frame loss of two amino acids as well as one that results in skipping of coding exon 2 (also known as exon 3 in the literature (Ambry internal data; Nix P et al. Fam Cancer, 2021 Jan; personal communication). The loss of coding exon 2 of is strongly associated with hereditary breast and ovarian cancer phenotype based on multifactorial analysis (Caputo SM et al. Oncotarget, 2018 Apr;9:17334-17348); however the functional and clinical impact of the small in-frame loss is unknown. Downstream functional studies showed that close-match alteration BRCA2 c.68-2A>G was able to rescue the growth defect in BRCA2-null mouse embryonic stem cells and that these surviving cells maintained partial activity in a homology directed DNA repair assay (personal communication). BRCA2 c.68-2A>G is also identified in patients who collectively have a phenotype that is not consistent with a high risk BRCA2 pathogenic variant (Nix P et al. Fam Cancer, 2021 Jan). Since supporting evidence is conflicting at this time, the clinical significance of this alteration remains unclear. It cannot yet be ruled out that this variant may be hypomorphic and present with reduced risks and/or biallelic phenotype. -

Malignant tumor of breast Pathogenic:1

Pathogenic, no assertion criteria provided

clinical testing

Department of Pathology and Laboratory Medicine, Sinai Health System

-

The c.68-1G>T variant was not identified in the literature, nor was it identified in the dbSNP, NHLBI Exome Sequencing Project (Exome Variant Server), Exome Aggregation Consortium (ExAC), LOVD, COSMIC, ClinVar, GeneInsight COGR, BIC or UMD. The c.68-1G>T variant is predicted to cause abnormal splicing because the nucleotide substitution occurs in the invariant region of the splice consensus sequence. In addition, 4 of 5 in silico or computational prediction software programs (SpliceSiteFinder, MaxEntScan, NNSPLICE, GeneSplicer, HumanSpliceFinder) predict a greater than 10% difference in splicing. In summary, based on the above information, this variant meets our laboratory’s criteria to be classified as pathogenic. -

not provided Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

GeneDx

Jul 05, 2023

Canonical splice site variant predicted to result in the in-frame skipping of exon 3, which is also a naturally-occurring isoform (Diez et al., 2007; Muller et al., 2011); Not observed at significant frequency in large population cohorts (gnomAD); Has not been previously published as pathogenic or benign to our knowledge; Also known as 296-1G>T; This variant is associated with the following publications: (PMID: 21939546, 17971607, 19609323, 32641407, 33469799, 29937994) -

Hereditary breast ovarian cancer syndrome Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

Sep 26, 2023

This sequence change affects an acceptor splice site in intron 2 of the BRCA2 gene. RNA analysis indicates that disruption of this splice site induces altered splicing and likely results in the loss of 2 amino acid residue(s), but is expected to preserve the integrity of the reading-frame. This variant is not present in population databases (gnomAD no frequency). This variant has not been reported in the literature in individuals affected with BRCA2-related conditions. ClinVar contains an entry for this variant (Variation ID: 409412). Studies have shown that disruption of this splice site results in the activation of a cryptic splice site in exon 3 (PMID: 32641407, 33469799; Invitae). In summary, the available evidence is currently insufficient to determine the role of this variant in disease. Therefore, it has been classified as a Variant of Uncertain Significance. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Pathogenic	0.37	D
BayesDel_noAF	Pathogenic	0.29
CADD	Pathogenic	35
DANN	Uncertain	1.0
Eigen	Pathogenic	1.1
Eigen_PC	Pathogenic	0.99
FATHMM_MKL	Pathogenic	0.98	D
MutationTaster	Benign	1.0	D;D
GERP RS		5.7

Splicing

Name	Calibrated prediction	Score	Prediction
dbscSNV1_ADA	Pathogenic	1.0
dbscSNV1_RF	Pathogenic	0.94
SpliceAI score (max)		0.98		Details are displayed if max score is > 0.2
DS_AG_spliceai		0.98		Position offset: 7
DS_AL_spliceai		0.97		Position offset: 1

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

Publications

LitVar

Other links and lift over

dbSNP: rs1060502376; hg19: chr13-32893213; COSMIC: COSV104430643; COSMIC: COSV104430643;