chr13-48473388-G-T

Variant names:

• chr13-48473388-G-T
• rs374157786
• NM_000321.3:c.2518G>T

Variant summary

Our verdict is Uncertain significance. The variant received 3 ACMG points: 3P and 0B. PM2 PP3

The NM_000321.3(RB1):​c.2518G>T​(p.Gly840Trp) variant causes a missense, splice region change. The variant allele was found at a frequency of 0.00000213 in 1,409,502 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 Uncertain significance (★★). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. G840R) has been classified as Likely benign.

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 0.0000021 (0 hom.)
• Consequence: RB1 NM_000321.3 missense, splice_region
• Scores: Splicing: ADA: 0.9932
• Clinical Significance: Uncertain significance criteria provided, multiple submitters, no conflicts U:2
• Conservation: PhyloP100: 6.97
• Publications: 2 publications found

Genes affected

RB1 (HGNC:9884): (RB transcriptional corepressor 1) The protein encoded by this gene is a negative regulator of the cell cycle and was the first tumor suppressor gene found. The encoded protein also stabilizes constitutive heterochromatin to maintain the overall chromatin structure. The active, hypophosphorylated form of the protein binds transcription factor E2F1. Defects in this gene are a cause of childhood cancer retinoblastoma (RB), bladder cancer, and osteogenic sarcoma. [provided by RefSeq, Jul 2008]

RB1 Gene-Disease associations (from GenCC):

• hereditary retinoblastoma

  Inheritance: AD Classification: DEFINITIVE, STRONG, SUPPORTIVE Submitted by: Labcorp Genetics (formerly Invitae), Orphanet, G2P, Ambry Genetics
• retinoblastoma

  Inheritance: AD Classification: DEFINITIVE Submitted by: ClinGen
• melanoma

  Inheritance: AD Classification: MODERATE Submitted by: Ambry Genetics

ACMG classification

Our verdict: Uncertain_significance. The variant received 3 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• PP3: Splicing predictors support a deleterious effect. Scorers claiming Pathogenic: dbscSNV1_ADA, dbscSNV1_RF. No scorers claiming Uncertain. Scorers claiming Benign: max_spliceai.

Variant Effect in Transcripts

ACMG analysis was done for transcript: NM_000321.3. You can select a different transcript below to see updated ACMG assignments.

RefSeq Transcripts

Selected	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	RB1	NM_000321.3	MANE Select	c.2518G>T	p.Gly840Trp	missense splice_region	Exon 24 of 27	NP_000312.2
	RB1	NM_001407165.1		c.2518G>T	p.Gly840Trp	missense splice_region	Exon 24 of 27	NP_001394094.1

Ensembl Transcripts

Selected	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	RB1	ENST00000267163.6	TSL:1 MANE Select	c.2518G>T	p.Gly840Trp	missense splice_region	Exon 24 of 27	ENSP00000267163.4
	RB1	ENST00000467505.6	TSL:1	n.*1886G>T		splice_region non_coding_transcript_exon	Exon 19 of 22	ENSP00000434702.1
	RB1	ENST00000467505.6	TSL:1	n.*1886G>T		3_prime_UTR	Exon 19 of 22	ENSP00000434702.1

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome AF: 0.00000213 AC: 3 AN: 1409502 Hom.: 0 Cov.: 28 AF XY: 0.00000142 AC XY: 1 AN XY: 703954

African (AFR) AF: 0.00 AC: 0 AN: 32188

American (AMR) AF: 0.00 AC: 0 AN: 44564

Ashkenazi Jewish (ASJ) AF: 0.00 AC: 0 AN: 25768

East Asian (EAS) AF: 0.00 AC: 0 AN: 39268

South Asian (SAS) AF: 0.00 AC: 0 AN: 85142

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 52740

Middle Eastern (MID) AF: 0.00 AC: 0 AN: 5052

European-Non Finnish (NFE) AF: 0.00000281 AC: 3 AN: 1066186

Other (OTH) AF: 0.00 AC: 0 AN: 58594

GnomAD4 genome Cov.: 32

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:2

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Retinoblastoma Uncertain:1

Jul 12, 2022

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This variant is not present in population databases (gnomAD no frequency). This sequence change replaces glycine, which is neutral and non-polar, with tryptophan, which is neutral and slightly polar, at codon 840 of the RB1 protein (p.Gly840Trp). This variant has not been reported in the literature in individuals affected with RB1-related conditions. ClinVar contains an entry for this variant (Variation ID: 1004878). 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. 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.

Hereditary cancer-predisposing syndrome Uncertain:1

Jun 03, 2023

Ambry Genetics

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: clinical testing

The p.G840W variant (also known as c.2518G>T), located in coding exon 24 of the RB1 gene, results from a G to T substitution at nucleotide position 2518. The glycine at codon 840 is replaced by tryptophan, an amino acid with highly dissimilar properties. This amino acid position is conserved. 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.

Computational scores

Source: dbNSFP v4.9

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	0.83
BayesDel_addAF	Pathogenic	0.42	D
BayesDel_noAF	Pathogenic	0.37
CADD	Pathogenic	34
DANN	Uncertain	0.99
DEOGEN2	Pathogenic	0.81	D
Eigen	Pathogenic	0.78
Eigen_PC	Pathogenic	0.79
FATHMM_MKL	Pathogenic	0.99	D
LIST_S2	Uncertain	0.94	D
M_CAP	Uncertain	0.14	D
MetaRNN	Pathogenic	0.84	D
MetaSVM	Uncertain	0.69	D
MutationAssessor	Benign	1.8	L
PhyloP100		7.0
PrimateAI	Uncertain	0.78	T
PROVEAN	Uncertain	-2.7	D
REVEL	Pathogenic	0.79
Sift	Uncertain	0.0010	D
Sift4G	Uncertain	0.0020	D
Polyphen		1.0	D
Vest4		0.89
MutPred		0.60		Loss of disorder (P = 0.0073)
MVP		0.97
MPC		1.4
ClinPred		1.0	D
GERP RS		5.7
RBP_binding_hub_radar		0.0
RBP_regulation_power_radar		1.7
Varity_R		0.70
gMVP		0.74
Mutation Taster		=24/76	disease causing

Splicing

Name	Calibrated prediction	Score	Prediction
dbscSNV1_ADA	Pathogenic	0.99
dbscSNV1_RF	Pathogenic	0.89
SpliceAI score (max)		0.090		Details are displayed if max score is > 0.2

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

Other links and lift over

dbSNP: rs374157786; hg19: chr13-49047524; COSMIC: COSV104565292;