chr15-89333096-C-G

Position:

• chr15-89333096-C-G

Variant summary

Our verdict is Uncertain significance. Variant got 4 ACMG points: 4P and 0B. PM2 PP3_Moderate

The NM_002693.3(POLG):​c.659G>C​(p.Trp220Ser) variant causes a missense, splice region change involving the alteration of a conserved nucleotide. The variant allele was found at a frequency of 0.00000657 in 152,220 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a pathogenic outcome for this variant. 13/23 in silico tools predict a damaging outcome for this variant. 2/3 splice prediction tools predicting alterations to normal splicing. Variant has been reported in ClinVar as Uncertain significance (★).

• Frequency: Genomes: 𝑓 0.0000066 (0 hom., cov: 34)
• Consequence: POLG NM_002693.3 missense, splice_region
• Scores: Splicing: ADA: 0.9999
• Clinical Significance: Uncertain significance criteria provided, single submitter U:1
• Conservation: PhyloP100: 7.68

Genes affected

POLG (HGNC:9179): (DNA polymerase gamma, catalytic subunit) Mitochondrial DNA polymerase is heterotrimeric, consisting of a homodimer of accessory subunits plus a catalytic subunit. The protein encoded by this gene is the catalytic subunit of mitochondrial DNA polymerase. The encoded protein contains a polyglutamine tract near its N-terminus that may be polymorphic. Defects in this gene are a cause of progressive external ophthalmoplegia with mitochondrial DNA deletions 1 (PEOA1), sensory ataxic neuropathy dysarthria and ophthalmoparesis (SANDO), Alpers-Huttenlocher syndrome (AHS), and mitochondrial neurogastrointestinal encephalopathy syndrome (MNGIE). Two transcript variants encoding the same protein have been found for this gene. [provided by RefSeq, Jul 2008]

POLGARF (HGNC:56246): (POLG alternative reading frame) This gene uses the same transcript as the POLG gene but has a CUG start codon and an alternate reading frame that makes a 260 aa protein. This protein is distinct from POLG isoforms and may interact with P32 (also known as C1QBP), a mitochondrial matrix protein thought to be involved in the expression of mitochondrial genome-encoded proteins. POLGARF protein may bind P32 and sequester it in the nucleolus. Interestingly, some disease-causing mutations thought to be in POLG may instead be associated with POLGARF. [provided by RefSeq, May 2022]

ACMG classification

Verdict is Uncertain_significance. Variant got 4 ACMG points.

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

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
POLG	NM_002693.3	c.659G>C	p.Trp220Ser	missense_variant, splice_region_variant	2/23	ENST00000268124.11	NP_002684.1
POLGARF	NM_001406557.1	c.714G>C	p.Leu238=	splice_region_variant, synonymous_variant	2/23		NP_001393486.1
POLG	NM_001126131.2	c.659G>C	p.Trp220Ser	missense_variant, splice_region_variant	2/23		NP_001119603.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
POLG	ENST00000268124.11	c.659G>C	p.Trp220Ser	missense_variant, splice_region_variant	2/23	1	NM_002693.3	ENSP00000268124	P1
POLGARF	ENST00000706918.1	c.714G>C	p.Leu238=	splice_region_variant, synonymous_variant	1/2			ENSP00000516626	P1

Frequencies

GnomAD3 genomes AF: 0.00000657 AC: 1 AN: 152220 Hom.: 0 Cov.: 34

Gnomad AFR AF: 0.00

Gnomad AMI AF: 0.00

Gnomad AMR AF: 0.0000654

Gnomad ASJ AF: 0.00

Gnomad EAS AF: 0.00

Gnomad SAS AF: 0.00

Gnomad FIN AF: 0.00

Gnomad MID AF: 0.00

Gnomad NFE AF: 0.00

Gnomad OTH AF: 0.00

GnomAD4 exome Cov.: 31

GnomAD4 genome AF: 0.00000657 AC: 1 AN: 152220 Hom.: 0 Cov.: 34 AF XY: 0.0000134 AC XY: 1 AN XY: 74364

Gnomad4 AFR AF: 0.00

Gnomad4 AMR AF: 0.0000654

Gnomad4 ASJ AF: 0.00

Gnomad4 EAS AF: 0.00

Gnomad4 SAS AF: 0.00

Gnomad4 FIN AF: 0.00

Gnomad4 NFE AF: 0.00

Gnomad4 OTH AF: 0.00

Bravo AF: 0.0000113

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:1

Revision: criteria provided, single submitter

Submissions by phenotype

Progressive sclerosing poliodystrophy Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

Jun 03, 2023

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. Variants that disrupt the consensus splice site are a relatively common cause of aberrant splicing (PMID: 17576681, 9536098). An algorithm developed to predict the effect of missense changes on protein structure and function (PolyPhen-2) suggests that this variant is likely to be disruptive. ClinVar contains an entry for this variant (Variation ID: 405580). This variant has not been reported in the literature in individuals affected with POLG-related conditions. This variant is not present in population databases (gnomAD no frequency). This sequence change replaces tryptophan, which is neutral and slightly polar, with serine, which is neutral and polar, at codon 220 of the POLG protein (p.Trp220Ser). This variant also falls at the last nucleotide of exon 2, which is part of the consensus splice site for this exon. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	0.92
BayesDel_addAF	Pathogenic	0.51	D
BayesDel_noAF	Pathogenic	0.49
CADD	Pathogenic	35
DANN	Uncertain	0.99
DEOGEN2	Pathogenic	0.92	D;D
Eigen	Pathogenic	0.86
Eigen_PC	Pathogenic	0.77
FATHMM_MKL	Pathogenic	0.99	D
LIST_S2	Uncertain	0.92	.;D
M_CAP	Pathogenic	0.54	D
MetaRNN	Pathogenic	0.99	D;D
MetaSVM	Pathogenic	1.0	D
MutationAssessor	Pathogenic	4.0	H;H
MutationTaster	Benign	1.0	D;D
PrimateAI	Uncertain	0.75	T
PROVEAN	Pathogenic	-13	D;D
REVEL	Pathogenic	0.91
Sift	Pathogenic	0.0	D;D
Sift4G	Pathogenic	0.0010	D;D
Polyphen		1.0	D;D
Vest4		0.94
MutPred		0.87		Gain of disorder (P = 0.0203);Gain of disorder (P = 0.0203);
MVP		0.98
MPC		0.76
ClinPred		1.0	D
GERP RS		4.6
RBP_binding_hub_radar		0.92
RBP_regulation_power_radar		2.7
Varity_R		0.99
gMVP		0.96

Splicing

Name	Calibrated prediction	Score	Prediction
dbscSNV1_ADA	Pathogenic	1.0
dbscSNV1_RF	Pathogenic	0.98
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: rs1004988362; hg19: chr15-89876327;