16-8797926-G-C

Position:

• chr16-8797926-G-C

Variant summary

Our verdict is Pathogenic. Variant got 18 ACMG points: 18P and 0B. PM1 PM2 PM5 PP3_Strong PP5_Very_Strong

The NM_000303.3(PMM2):​c.44G>C​(p.Gly15Ala) variant causes a missense change. The variant was absent in control chromosomes in GnomAD project. In-silico tool predicts a pathogenic outcome for this variant. Variant has been reported in ClinVar as Likely pathogenic (★★). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. G15E) has been classified as Likely pathogenic.

• Frequency: Genomes: not found (cov: 33)
• Consequence: PMM2 NM_000303.3 missense
• Clinical Significance: Conflicting classifications of pathogenicity criteria provided, conflicting classifications P:4 U:1
• Conservation: PhyloP100: 6.86

Genes affected

PMM2 (HGNC:9115): (phosphomannomutase 2) The protein encoded by this gene catalyzes the isomerization of mannose 6-phosphate to mannose 1-phosphate, which is a precursor to GDP-mannose necessary for the synthesis of dolichol-P-oligosaccharides. Mutations in this gene have been shown to cause defects in glycoprotein biosynthesis, which manifests as carbohydrate-deficient glycoprotein syndrome type I. [provided by RefSeq, Jul 2008]

ACMG classification

Verdict is Pathogenic. Variant got 18 ACMG points.

• PM1: In a chain Phosphomannomutase 2 (size 244) in uniprot entity PMM2_HUMAN there are 79 pathogenic changes around while only 2 benign (98%) in NM_000303.3
• 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.
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.99
• PP5: Variant 16-8797926-G-C is Pathogenic according to our data. Variant chr16-8797926-G-C is described in ClinVar as [Likely_pathogenic]. Clinvar id is 553249.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
PMM2	NM_000303.3	c.44G>C	p.Gly15Ala	missense_variant	1/8	ENST00000268261.9	NP_000294.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
PMM2	ENST00000268261.9	c.44G>C	p.Gly15Ala	missense_variant	1/8	1	NM_000303.3	ENSP00000268261	P1

Frequencies

GnomAD3 genomes Cov.: 33

GnomAD4 exome Cov.: 32

GnomAD4 genome Cov.: 33

Bravo AF: 0.00000756

ClinVar

Significance: Conflicting classifications of pathogenicity

Submissions summary: Pathogenic:4 Uncertain:1

Revision: criteria provided, conflicting classifications

Submissions by phenotype

PMM2-congenital disorder of glycosylation Pathogenic:4 Uncertain:1

Pathogenic, criteria provided, single submitter	clinical testing	Centre for Inherited Metabolic Diseases, Karolinska University Hospital	Apr 02, 2020	- -
Uncertain significance, criteria provided, single submitter	clinical testing	Counsyl	Aug 08, 2017	- -
Likely pathogenic, criteria provided, single submitter	clinical testing	Labcorp Genetics (formerly Invitae), Labcorp	Dec 19, 2019	This variant disrupts the p.Gly15 amino acid residue in PMM2. Other variant(s) that disrupt this residue have been observed in individuals with PMM2-related conditions (PMID: 12626389, 28454995, Invitae), which suggests that this may be a clinically significant amino acid residue. Algorithms developed to predict the effect of missense changes on protein structure and function are either unavailable or do not agree on the potential impact of this missense change (SIFT: "Deleterious"; PolyPhen-2: "Benign"; Align-GVGD: "Class C0"). This variant has been observed in individual(s) with clinical features of PMM2-congenital disorder of glycosylation (Invitae). In at least one individual the data is consistent with the variant being in trans (on the opposite chromosome) from a pathogenic variant. ClinVar contains an entry for this variant (Variation ID: 553249). This variant is not present in population databases (ExAC no frequency). This sequence change replaces glycine with alanine at codon 15 of the PMM2 protein (p.Gly15Ala). The glycine residue is highly conserved and there is a small physicochemical difference between glycine and alanine. In summary, the currently available evidence indicates that the variant is pathogenic, but additional data are needed to prove that conclusively. Therefore, this variant has been classified as Likely Pathogenic. -
Pathogenic, criteria provided, single submitter	clinical testing	Women's Health and Genetics/Laboratory Corporation of America, LabCorp	Aug 30, 2024	Variant summary: PMM2 c.44G>C (p.Gly15Ala) 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 frequency data for this variant in gnomAD is considered unreliable, as metrics indicate poor data quality at this position. c.44G>C has been reported in the literature in individuals affected with Congenital Disorder Of Glycosylation Type 1a (example:Baker_2019, Starosta_2021, Stranneheim_2021) . These data indicate that the variant is likely to be associated with disease. A different variant affecting the same codon has been classified as pathogenic by our lab (c.43G>A, p.Gly15Arg), supporting the critical relevance of codon 15 to PMM2 protein function. The following publications have been ascertained in the context of this evaluation (PMID: 33413482, 30577886, 33726816). ClinVar contains an entry for this variant (Variation ID: 553249). Based on the evidence outlined above, the variant was classified as pathogenic. -
Likely pathogenic, criteria provided, single submitter	clinical testing	Baylor Genetics	Feb 12, 2024	- -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	0.89
BayesDel_addAF	Pathogenic	0.57	D
BayesDel_noAF	Pathogenic	0.58
CADD	Pathogenic	30
DANN	Uncertain	1.0
DEOGEN2	Pathogenic	0.96	D;.
Eigen	Pathogenic	0.94
Eigen_PC	Pathogenic	0.84
FATHMM_MKL	Uncertain	0.95	D
LIST_S2	Pathogenic	0.99	D;D
M_CAP	Pathogenic	0.68	D
MetaRNN	Pathogenic	0.99	D;D
MetaSVM	Pathogenic	0.94	D
MutationAssessor	Pathogenic	3.7	H;.
MutationTaster	Benign	0.62	D;D;D;D;D
PrimateAI	Pathogenic	0.83	D
PROVEAN	Pathogenic	-4.8	D;D
REVEL	Pathogenic	0.97
Sift	Uncertain	0.0010	D;D
Sift4G	Uncertain	0.0020	D;D
Polyphen		0.99	D;.
Vest4		0.90
MutPred		0.94		Loss of phosphorylation at T16 (P = 0.2491);Loss of phosphorylation at T16 (P = 0.2491);
MVP		0.97
MPC		0.013
ClinPred		1.0	D
GERP RS		4.8
RBP_binding_hub_radar		0.0
RBP_regulation_power_radar		1.7
Varity_R		0.91
gMVP		0.91

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: rs958073558; hg19: chr16-8891783;