15-89321196-C-T

Position:

• chr15-89321196-C-T

Variant summary

Our verdict is Likely pathogenic. Variant got 9 ACMG points: 9P and 0B. PM1 PM5 PP3_Strong PP5

The ENST00000268124.11(POLG):​c.2663G>A​(p.Gly888Asp) variant causes a missense change involving the alteration of a conserved nucleotide. The variant allele was found at a frequency of 0.00000479 in 1,461,876 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a pathogenic outcome for this variant. 12/21 in silico tools predict a damaging outcome for this variant. Variant has been reported in ClinVar as Conflicting classifications of pathogenicity (no stars). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. G888C) has been classified as Uncertain significance.

• Frequency:
  • Genomes: not found (cov: 33)
  • Exomes 𝑓: 0.0000048 (0 hom.)
• Consequence: POLG ENST00000268124.11 missense
• Clinical Significance: Conflicting classifications of pathogenicity criteria provided, conflicting classifications P:2 U:1
• Conservation: PhyloP100: 7.57

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:):

ACMG classification

Verdict is Likely_pathogenic. Variant got 9 ACMG points.

• PM1: In a hotspot region, there are 5 aminoacids with missense pathogenic changes in the window of +-8 aminoacids around while only 0 benign, 11 uncertain in ENST00000268124.11
• PM5: Other missense variant is known to change same aminoacid residue: Variant chr15-89321197-C-T is described in ClinVar as [Pathogenic]. Clinvar id is 619332.Status of the report is criteria_provided_single_submitter, 1 stars.
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.994
• PP5: Variant 15-89321196-C-T is Pathogenic according to our data. Variant chr15-89321196-C-T is described in ClinVar as [Conflicting_classifications_of_pathogenicity]. Clinvar id is 239379.We mark this variant Likely_pathogenic, oryginal submissions are: {Likely_pathogenic=1, Pathogenic=1, Uncertain_significance=1}.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
POLG	NM_002693.3	c.2663G>A	p.Gly888Asp	missense_variant	17/23	ENST00000268124.11	NP_002684.1
POLGARF	NM_001406557.1	c.*1935G>A		3_prime_UTR_variant	17/23		NP_001393486.1
POLG	NM_001126131.2	c.2663G>A	p.Gly888Asp	missense_variant	17/23		NP_001119603.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
POLG	ENST00000268124.11	c.2663G>A	p.Gly888Asp	missense_variant	17/23	1	NM_002693.3	ENSP00000268124	P1

Frequencies

GnomAD3 genomes Cov.: 33

GnomAD4 exome AF: 0.00000479 AC: 7 AN: 1461876 Hom.: 0 Cov.: 35 AF XY: 0.00000413 AC XY: 3 AN XY: 727244

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: 0.00000540

Gnomad4 OTH exome AF: 0.0000166

GnomAD4 genome Cov.: 33

ClinVar

Significance: Conflicting classifications of pathogenicity

Submissions summary: Pathogenic:2 Uncertain:1

Revision: criteria provided, conflicting classifications

Submissions by phenotype

Progressive sclerosing poliodystrophy Pathogenic:1 Uncertain:1

Uncertain significance, criteria provided, single submitter	clinical testing	Labcorp Genetics (formerly Invitae), Labcorp	Mar 19, 2016	In summary, this variant is a rare missense change with uncertain impact on protein function. While it is absent from the population and reported in affected individuals, the available evidence is currently insufficient to determine its role in disease. Therefore, it has been classified as a Variant of Uncertain Significance. 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, but these predictions have not been confirmed by published functional studies. This variant has been reported in combination with a pathogenic variant in an individual affected with a POLG-related disease (PMID: 21880868). This variant is not present in population databases (ExAC no frequency). This sequence change replaces glycine with aspartic acid at codon 888 of the POLG protein (p.Gly888Asp). The glycine residue is highly conserved and there is a moderate physicochemical difference between glycine and aspartic acid. -
Pathogenic, criteria provided, single submitter	clinical testing	Wong Mito Lab, Molecular and Human Genetics, Baylor College of Medicine	Oct 01, 2018	The NM_002693.2:c.2663G>A (NP_002684.1:p.Gly888Asp) [GRCH38: NC_000015.10:g.89321196C>T] variant in POLG gene is interpretated to be a Pathogenic based on ACMG guidelines (PMID: 25741868). This variant meets the following evidence codes reported in the ACMG-guideline. PS1:This variation causes same amino-acid change as an established pathogenic variant. PM1:This variant is in mutational hot spot or a well-studied functional domain without benign variation. PM2:This variant is absent in key population databases. PM3:Detected in trans with a pathogenic variant for Mitochondrial DNA depletion syndrome 4A (Alpers type) which is a recessive disorder. PP1:This variant is co-segregated with Mitochondrial DNA depletion syndrome 4A (Alpers type) in multiple affected family members. PP2:This is a missense variant in POLG with a low rate of benign and high rate of pathogenic missense variations. PP3:Computational evidence/predictors indicate the variant has deleterious effect on POLG structure, function, or protein-protein interaction. PP4:Patient's phenotype or family history is highly specific for POLG. Based on the evidence criteria codes applied, the variant is suggested to be Pathogenic. -

Mitochondrial disease Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Victorian Clinical Genetics Services, Murdoch Childrens Research Institute

Oct 10, 2024

Based on the classification scheme VCGS_Germline_v1.3.5, this variant is classified as Likely pathogenic. Following criteria are met: 0102 - Loss of function is a known mechanism of disease in this gene and is associated with mitochondrial disease (MONDO#0044970), POLG-related. (I) 0108 - This gene is associated with both recessive and dominant disease. Variants are usually inherited in a recessive manner, however progressive external ophthalmoplegia can also be dominant when heterozygous variants are located in the highly conserved active site of motif B of the polymerase domain (PMID: 30451971). (I) 0115 - Variants in this gene are known to have variable expressivity (PMID: 20301791). (I) 0200 - Variant is predicted to result in a missense amino acid change from glycine to aspartic acid. (I) 0251 - This variant is heterozygous. (I) 0304 - Variant is present in gnomAD (v4) <0.01 (7 heterozygotes, 0 homozygotes). (SP) 0501 - Missense variant consistently predicted to be damaging by multiple in silico tools or highly conserved with a major amino acid change. (SP) 0600 - Variant is located in the annotated DNA_pol_gammaA domain (NCBI). (I) 0708 - Other missense variants comparable to the one identified in this case have conflicting previous evidence for pathogenicity. An alternative change, p.(Gly888Ser), has been reported as pathogenic in a compound heterozygous individual with Alpers syndrome (ClinVar, PMID: 17923349). Two other alternative changes, p.(Gly888Arg) and p.(Gly888Cys), have been reported as VUS by clinical laboratories in ClinVar. (I) 0802 - This variant has moderate previous evidence of pathogenicity in unrelated individuals. This variant has been identified in three unrelated individuals, all of whom have a second POLG variant and a diagnosis or Alpers syndrome or suspected mitochondrial disorder (PMIDs: 21880868, 22980518, 21167499, ClinVar). It has also been reported as a VUS by a clinical laboratory in ClinVar, however, the variant was present in a heterozygous state with no second POLG variant identified (personal communicaiton). (SP) 0905 - No published segregation evidence has been identified for this variant. (I) 1007 - No published functional evidence has been identified for this variant. (I) 1208 - Inheritance information for this variant is not currently available in this individual. (I) Legend: (SP) - Supporting pathogenic, (I) - Information, (SB) - Supporting benign -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	1.0
BayesDel_addAF	Pathogenic	0.57	D
BayesDel_noAF	Pathogenic	0.58
CADD	Pathogenic	29
DANN	Uncertain	1.0
DEOGEN2	Pathogenic	0.97	D;D
Eigen	Pathogenic	0.94
Eigen_PC	Pathogenic	0.86
FATHMM_MKL	Pathogenic	0.97	D
LIST_S2	Pathogenic	1.0	.;D
M_CAP	Pathogenic	0.67	D
MetaRNN	Pathogenic	0.99	D;D
MetaSVM	Pathogenic	1.1	D
MutationAssessor	Pathogenic	3.2	M;M
MutationTaster	Benign	1.0	D;D
PrimateAI	Pathogenic	0.87	D
PROVEAN	Pathogenic	-6.9	D;D
REVEL	Pathogenic	0.97
Sift	Pathogenic	0.0	D;D
Sift4G	Pathogenic	0.0	D;D
Polyphen		1.0	D;D
Vest4		0.99
MutPred		0.94		Gain of phosphorylation at T885 (P = 0.1044);Gain of phosphorylation at T885 (P = 0.1044);
MVP		0.99
MPC		0.75
ClinPred		1.0	D
GERP RS		5.2
RBP_binding_hub_radar		0.0
RBP_regulation_power_radar		1.8
Varity_R		0.95
gMVP		0.94

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.0		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: rs878854560; hg19: chr15-89864427;