chr9-21974757-C-A

Position:

• chr9-21974757-C-A

Variant summary

Our verdict is Uncertain significance. Variant got 5 ACMG points: 6P and 1B. PM1 PM2 PM5 BP4

The NM_000077.5(CDKN2A):​c.71G>T​(p.Arg24Leu) variant causes a missense 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. 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. R24C) has been classified as Likely pathogenic.

• Frequency: Genomes: not found (cov: 32)
• Consequence: CDKN2A NM_000077.5 missense
• Clinical Significance: Uncertain significance criteria provided, multiple submitters, no conflicts U:3
• Conservation: PhyloP100: 0.147

Genes affected

CDKN2A (HGNC:1787): (cyclin dependent kinase inhibitor 2A) This gene generates several transcript variants which differ in their first exons. At least three alternatively spliced variants encoding distinct proteins have been reported, two of which encode structurally related isoforms known to function as inhibitors of CDK4 kinase. The remaining transcript includes an alternate first exon located 20 Kb upstream of the remainder of the gene; this transcript contains an alternate open reading frame (ARF) that specifies a protein which is structurally unrelated to the products of the other variants. This ARF product functions as a stabilizer of the tumor suppressor protein p53 as it can interact with, and sequester, the E3 ubiquitin-protein ligase MDM2, a protein responsible for the degradation of p53. In spite of the structural and functional differences, the CDK inhibitor isoforms and the ARF product encoded by this gene, through the regulatory roles of CDK4 and p53 in cell cycle G1 progression, share a common functionality in cell cycle G1 control. This gene is frequently mutated or deleted in a wide variety of tumors, and is known to be an important tumor suppressor gene. [provided by RefSeq, Sep 2012]

ACMG classification

Verdict is Uncertain_significance. Variant got 5 ACMG points.

• PM1: In a repeat ANK 1 (size 29) in uniprot entity CDN2A_HUMAN there are 5 pathogenic changes around while only 0 benign (100%) in NM_000077.5
• PM2: Very rare variant in population databases, with high coverage
• PM5: Other missense variant is known to change same aminoacid residue: Variant chrnull-null-null-null is described in UniProt as null.
• BP4: Computational evidence support a benign effect (MetaRNN=0.3171221).

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
CDKN2A	NM_000077.5	c.71G>T	p.Arg24Leu	missense_variant	1/3	ENST00000304494.10	NP_000068.1
CDKN2A	NM_058195.4	c.194-3549G>T		intron_variant		ENST00000579755.2	NP_478102.2

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
CDKN2A	ENST00000304494.10	c.71G>T	p.Arg24Leu	missense_variant	1/3	1	NM_000077.5	ENSP00000307101	P2
CDKN2A	ENST00000579755.2	c.194-3549G>T		intron_variant		1	NM_058195.4	ENSP00000462950

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome Cov.: 32

GnomAD4 genome Cov.: 32

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:3

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Melanoma and neural system tumor syndrome Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Baylor Genetics

Dec 28, 2023

- -

Hereditary cancer-predisposing syndrome Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Ambry Genetics

Nov 04, 2022

The p.R24L variant (also known as c.71G>T), located in coding exon 1 of the CDKN2A gene, results from a G to T substitution at nucleotide position 71. The arginine at codon 24 is replaced by leucine, an amino acid with dissimilar properties. This amino acid position is not well conserved in available vertebrate species. In addition, this alteration is predicted to be tolerated by in silico analysis. Since supporting evidence is limited at this time, the clinical significance of this alteration remains unclear. -

Familial melanoma Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

Sep 24, 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. This variant disrupts the p.Arg24 amino acid residue in CDKN2A (p16INK4a). Other variant(s) that disrupt this residue have been determined to be pathogenic (PMID: 8570179, 9516223, 11595726, 20340136, 21462282, 23190892). This suggests that this residue is clinically significant, and that variants that disrupt this residue are likely to be disease-causing. 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 tolerated. ClinVar contains an entry for this variant (Variation ID: 532272). This variant has not been reported in the literature in individuals affected with CDKN2A (p16INK4a)-related conditions. This variant is not present in population databases (gnomAD no frequency). This sequence change replaces arginine, which is basic and polar, with leucine, which is neutral and non-polar, at codon 24 of the CDKN2A (p16INK4a) protein (p.Arg24Leu). -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Benign	0.30
BayesDel_addAF	Benign	-0.027	T
BayesDel_noAF	Benign	-0.28
CADD	Benign	17
DANN	Uncertain	1.0
DEOGEN2	Uncertain	0.43	T;T;.
Eigen	Benign	-0.23
Eigen_PC	Benign	-0.33
FATHMM_MKL	Benign	0.28	N
LIST_S2	Benign	0.13	T;T;T
M_CAP	Uncertain	0.14	D
MetaRNN	Benign	0.32	T;T;T
MetaSVM	Benign	-0.91	T
MutationTaster	Benign	1.0	N;N;N;N;N;N;N;N;N
PrimateAI	Uncertain	0.52	T
PROVEAN	Uncertain	-2.8	D;.;D
REVEL	Benign	0.25
Sift	Benign	0.28	T;.;T
Sift4G	Benign	0.28	T;T;T
Polyphen		0.77	P;.;.
Vest4		0.12
MutPred		0.53		Loss of methylation at R22 (P = 0.0396);Loss of methylation at R22 (P = 0.0396);Loss of methylation at R22 (P = 0.0396);
MVP		0.87
MPC		0.49
ClinPred		0.77	D
GERP RS		3.0
Varity_R		0.22
gMVP		0.90

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.020		Details are displayed if max score is > 0.2

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

Publications

LitVar

Other links and lift over

dbSNP: rs104894097; hg19: chr9-21974756;