9-21971156-G-C

Position:

• chr9-21971156-G-C

Variant summary

Our verdict is Uncertain significance. Variant got 4 ACMG points: 8P and 4B. PM1 PM5 PP3_Strong BS2

The NM_000077.5(CDKN2A):​c.203C>G​(p.Ala68Gly) variant causes a missense change involving the alteration of a conserved nucleotide. The variant allele was found at a frequency of 0.00000902 in 1,441,598 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a pathogenic 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. A68L) has been classified as Likely pathogenic.

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 0.0000090 (0 hom.)
• Consequence: CDKN2A NM_000077.5 missense
• Clinical Significance: Uncertain significance criteria provided, multiple submitters, no conflicts U:5
• Conservation: PhyloP100: 9.23

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]

CDKN2A (HGNC:):

ACMG classification

Verdict is Uncertain_significance. Variant got 4 ACMG points.

• PM1: In a repeat ANK 2 (size 28) in uniprot entity CDN2A_HUMAN there are 15 pathogenic changes around while only 3 benign (83%) in NM_000077.5
• PM5: Other missense variant is known to change same aminoacid residue: Variant chrnull-null-null-null is described in UniProt as null.
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.979
• BS2: High AC in GnomAdExome4 at 13 AD gene.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
CDKN2A	NM_000077.5	c.203C>G	p.Ala68Gly	missense_variant	2/3	ENST00000304494.10	NP_000068.1
CDKN2A	NM_058195.4	c.246C>G	p.Arg82Arg	synonymous_variant	2/3	ENST00000579755.2	NP_478102.2

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
CDKN2A	ENST00000304494.10	c.203C>G	p.Ala68Gly	missense_variant	2/3	1	NM_000077.5	ENSP00000307101.5
CDKN2A	ENST00000579755.2	c.246C>G	p.Arg82Arg	synonymous_variant	2/3	1	NM_058195.4	ENSP00000462950.1

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD3 exomes AF: 0.00000473 AC: 1 AN: 211516 Hom.: 0 AF XY: 0.00000847 AC XY: 1 AN XY: 118042

Gnomad AFR exome AF: 0.00

Gnomad AMR exome AF: 0.00

Gnomad ASJ exome AF: 0.00

Gnomad EAS exome AF: 0.00

Gnomad SAS exome AF: 0.00

Gnomad FIN exome AF: 0.00

Gnomad NFE exome AF: 0.0000106

Gnomad OTH exome AF: 0.00

GnomAD4 exome AF: 0.00000902 AC: 13 AN: 1441598 Hom.: 0 Cov.: 31 AF XY: 0.00000976 AC XY: 7 AN XY: 717166

Gnomad4 AFR exome AF: 0.00

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: 0.00

Gnomad4 NFE exome AF: 0.0000108

Gnomad4 OTH exome AF: 0.0000167

GnomAD4 genome Cov.: 32

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:5

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	Jul 26, 2022	The CDKN2A locus encodes two different gene products, p16INK4a and p14ARF (https://www.ncbi.nlm.nih.gov/books/NBK7030/). This missense variant replaces alanine with glycine at codon 68 of the CDKN2A (p16INK4A) protein. Computational prediction suggests that this variant may have deleterious impact on protein structure and function (internally defined REVEL score threshold >= 0.7, PMID: 27666373). To our knowledge, functional studies have not been reported for this variant. This variant has not been reported in individuals affected with hereditary cancer in the literature. This variant has been identified in 1/211516 chromosomes 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, 2023	The p.A68G variant (also known as c.203C>G), located in coding exon 2 of the CDKN2A gene, results from a C to G substitution at nucleotide position 203. The alanine at codon 68 is replaced by glycine, an amino acid with similar properties. This amino acid position is highly conserved in available vertebrate species. In addition, the in silico prediction for this alteration is deleterious. Since supporting evidence is limited at this time, the clinical significance of this alteration remains unclear. -

not specified Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Women's Health and Genetics/Laboratory Corporation of America, LabCorp

May 19, 2022

Variant summary: CDKN2A c.203C>G (p.Ala68Gly) results in a non-conservative amino acid change in the encoded protein sequence. Five of five in-silico tools predict a damaging effect of the variant on protein function. The variant allele was found at a frequency of 4.7e-06 in 211516 control chromosomes (gnomAD). The available data on variant occurrences in the general population are insufficient to allow any conclusion about variant significance. c.203C>G has been reported in the literature in individuals affected with Melanoma (Taylor_2016), however, this report does not provide unequivocal conclusions about association of the variant with Cutaneous Malignant Melanoma. Tang_2003 examined the structural stability of the p16 product and discovered the variant was as stable as wild-type in both water and Urea. This information does not allow convincing conclusions about the variant effect on patient phenotype. Two ClinVar submitters have assessed the variant since 2014: both classified the variant as of uncertain significance. Based on the evidence outlined above, the variant was classified as uncertain significance. -

not provided Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Quest Diagnostics Nichols Institute San Juan Capistrano

Oct 13, 2023

- -

Familial melanoma Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

Jun 04, 2022

This sequence change replaces alanine, which is neutral and non-polar, with glycine, which is neutral and non-polar, at codon 68 of the CDKN2A (p16INK4a) protein (p.Ala68Gly). This variant is present in population databases (no rsID available, gnomAD 0.001%). This variant has not been reported in the literature in individuals affected with CDKN2A (p16INK4a)-related conditions. ClinVar contains an entry for this variant (Variation ID: 628976). 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. This variant disrupts the p.Ala68 amino acid residue in CDKN2A (p16INK4a). Other variant(s) that disrupt this residue have been determined to be pathogenic (PMID: 8710906, 9425228, 11075991, 18983535, 21462282, 25780468). This suggests that this residue is clinically significant, and that variants that disrupt this residue are likely to be disease-causing. 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
AlphaMissense	Benign	0.32
BayesDel_addAF	Pathogenic	0.26	D
BayesDel_noAF	Pathogenic	0.14
CADD	Uncertain	25
DANN	Uncertain	1.0
DEOGEN2	Uncertain	0.44	T;T;.;.;.;.;T;.
Eigen	Uncertain	0.66
Eigen_PC	Uncertain	0.62
FATHMM_MKL	Pathogenic	0.99	D
LIST_S2	Uncertain	0.97	D;D;.;D;.;D;D;D
M_CAP	Pathogenic	0.82	D
MetaRNN	Pathogenic	0.98	D;D;D;D;D;D;D;D
MetaSVM	Uncertain	0.49	D
PrimateAI	Uncertain	0.55	T
PROVEAN	Uncertain	-3.8	D;.;.;D;.;.;.;.
REVEL	Pathogenic	0.81
Sift	Uncertain	0.013	D;.;.;D;.;.;.;.
Sift4G	Pathogenic	0.0	D;D;D;D;D;D;D;D
Polyphen		1.0	D;.;.;.;.;.;.;.
Vest4		0.60
MutPred		0.80		Gain of catalytic residue at A68 (P = 0.0678);Gain of catalytic residue at A68 (P = 0.0678);.;Gain of catalytic residue at A68 (P = 0.0678);.;.;.;.;
MVP		0.94
MPC		1.2
ClinPred		0.96	D
GERP RS		5.8
Varity_R		0.57
gMVP		0.82

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.010		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: rs1060501260; hg19: chr9-21971155; COSMIC: COSV58700174; COSMIC: COSV58700174;