rs1555279223

Positions:

• chr13-48303987-G-GCCGCCC

Variant summary

Our verdict is Uncertain significance. Variant got 2 ACMG points: 2P and 0B. PM2

The NM_000321.3(RB1):​c.78_83dupGCCCCC​(p.Pro27_Pro28dup) variant causes a disruptive inframe insertion change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.000000743 in 1,346,554 control chromosomes in the GnomAD database, with no homozygous occurrence. Variant has been reported in ClinVar as Uncertain significance (★★).

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 7.4e-7 (0 hom.)
• Consequence: RB1 NM_000321.3 disruptive_inframe_insertion
• Clinical Significance: Uncertain significance criteria provided, multiple submitters, no conflicts U:2
• Conservation: PhyloP100: 0.858

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 (HGNC:):

ACMG classification

Verdict is Uncertain_significance. Variant got 2 ACMG points.

• PM2: Very rare variant in population databases, with high coverage

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
RB1	NM_000321.3	c.78_83dupGCCCCC	p.Pro27_Pro28dup	disruptive_inframe_insertion	1/27	ENST00000267163.6	NP_000312.2
RB1	NM_001407165.1	c.78_83dupGCCCCC	p.Pro27_Pro28dup	disruptive_inframe_insertion	1/27		NP_001394094.1
RB1	NM_001407166.1	c.78_83dupGCCCCC	p.Pro27_Pro28dup	disruptive_inframe_insertion	1/17		NP_001394095.1
RB1	NM_001407167.1	c.78_83dupGCCCCC	p.Pro27_Pro28dup	disruptive_inframe_insertion	1/3		NP_001394096.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
RB1	ENST00000267163.6	c.78_83dupGCCCCC	p.Pro27_Pro28dup	disruptive_inframe_insertion	1/27	1	NM_000321.3	ENSP00000267163.4

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome AF: 7.43e-7 AC: 1 AN: 1346554 Hom.: 0 Cov.: 31 AF XY: 0.00000151 AC XY: 1 AN XY: 664122

Gnomad4 AFR exome AF: 0.00

Gnomad4 AMR exome AF: 0.0000325

Gnomad4 ASJ exome AF: 0.00

Gnomad4 EAS exome AF: 0.00

Gnomad4 SAS exome AF: 0.00

Gnomad4 FIN exome AF: 0.00

Gnomad4 NFE exome AF: 0.00

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 32

Bravo AF: 0.00000378

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:2

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Retinoblastoma Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

Jul 14, 2022

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. Experimental studies and prediction algorithms are not available or were not evaluated, and the functional significance of this variant is currently unknown. ClinVar contains an entry for this variant (Variation ID: 527901). This variant has not been reported in the literature in individuals affected with RB1-related conditions. This variant is not present in population databases (gnomAD no frequency). This variant, c.78_83dup, results in the insertion of 2 amino acid(s) of the RB1 protein (p.Pro28_Pro29dup), but otherwise preserves the integrity of the reading frame. -

Hereditary cancer-predisposing syndrome Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Ambry Genetics

May 27, 2022

The c.78_83dupGCCCCC variant (also known as p.P28_P29dup), located in coding exon 1 of the RB1 gene, results from an in-frame duplication of GCCCCC at nucleotide positions 78 to 83. This results in the duplication of 2 extra residues (PP) between codons 28 and 29. This amino acid region is well conserved in available vertebrate species. In addition, this alteration is predicted to be neutral by in silico analysis (Choi Y et al. PLoS ONE. 2012; 7(10):e46688). Since supporting evidence is limited at this time, the clinical significance of this alteration remains unclear. -

Computational scores

Source: dbNSFP v4.3

Splicing

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

Publications

LitVar

Other links and lift over

dbSNP: rs1555279223; hg19: chr13-48878123;