chrX-38411982-A-G

Position:

• chrX-38411982-A-G

Variant summary

Our verdict is Pathogenic. Variant got 16 ACMG points: 16P and 0B. PM1 PM2 PP3_Strong PP5_Very_Strong

The NM_000531.6(OTC):​c.988A>G​(p.Arg330Gly) 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 (★★). Synonymous variant affecting the same amino acid position (i.e. R330R) has been classified as Likely benign.

• Frequency: Genomes: not found (cov: 23)
• Consequence: OTC NM_000531.6 missense
• Clinical Significance: Pathogenic/Likely pathogenic criteria provided, multiple submitters, no conflicts P:3
• Conservation: PhyloP100: 6.72

Genes affected

OTC (HGNC:8512): (ornithine transcarbamylase) This nuclear gene encodes a mitochondrial matrix enzyme. The encoded protein is involved in the urea cycle which functions to detoxify ammonia into urea for excretion. Mutations in this enzyme lead to ornithine transcarbamylase deficiency, which causes hyperammonemia. [provided by RefSeq, May 2022]

ACMG classification

Verdict is Pathogenic. Variant got 16 ACMG points.

• PM1: In a hotspot region, there are 4 aminoacids with missense pathogenic changes in the window of +-8 aminoacids around while only 1 benign, 5 uncertain in NM_000531.6
• PM2: Very rare variant in population databases, with high coverage
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.996
• PP5: Variant X-38411982-A-G is Pathogenic according to our data. Variant chrX-38411982-A-G is described in ClinVar as [Likely_pathogenic]. Clinvar id is 97376.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
OTC	NM_000531.6	c.988A>G	p.Arg330Gly	missense_variant	9/10	ENST00000039007.5
OTC	NM_001407092.1	c.988A>G	p.Arg330Gly	missense_variant	11/12

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
OTC	ENST00000039007.5	c.988A>G	p.Arg330Gly	missense_variant	9/10	1	NM_000531.6	P1
OTC	ENST00000643344.1	c.*738A>G		3_prime_UTR_variant, NMD_transcript_variant	10/11

Frequencies

GnomAD3 genomes Cov.: 23

GnomAD4 exome Cov.: 29

GnomAD4 genome Cov.: 23

ClinVar

Significance: Pathogenic/Likely pathogenic

Submissions summary: Pathogenic:3

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

not provided Pathogenic:2

Pathogenic, no assertion criteria provided	literature only	GenMed Metabolism Lab	-	- -
Likely pathogenic, criteria provided, single submitter	clinical testing	GeneDx	Nov 16, 2015	The R330G variant has been published previously as a pathogenic variant in patients with ornithine transcarbamylase (OTC) deficiency (Tuchman et al. 1997; McCullough et al. 2000; Nagasaka et al. 2013). The R330G variant was not observed in approximately 6500 individuals of European and African American ancestry in the NHLBI Exome Sequencing Project, indicating it is not a common benign variant in these populations. The R330G variant is a non-conservative amino acid substitution, which is likely to impact secondary protein structure as these residues differ in polarity, charge, size and/or other properties. This substitution occurs at a position that is conserved across species, and in silico analysis predicts this variant is probably damaging to the protein structure/function. Furthermore, missense variants in nearby residues (E326K, W332R, M335I) have been reported in the Human Gene Mutation Database in association with OTC deficiency (Stenson et al., 2014), supporting the functional importance of this region of the protein. Therefore, we interpret the R330C variant to be likely pathogenic; however, the possibility that it is benign cannot be excluded. -

Ornithine carbamoyltransferase deficiency Pathogenic:1

Pathogenic, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

May 09, 2021

For these reasons, this variant has been classified as Pathogenic. Advanced modeling of protein sequence and biophysical properties (such as structural, functional, and spatial information, amino acid conservation, physicochemical variation, residue mobility, and thermodynamic stability) performed at Invitae indicates that this missense variant is expected to disrupt OTC protein function. This variant has been observed in individual(s) with ornithine transcarbamylase deficiency (PMID: 9266388, 10946359, Invitae). ClinVar contains an entry for this variant (Variation ID: 97376). This variant is not present in population databases (ExAC no frequency). This sequence change replaces arginine with glycine at codon 330 of the OTC protein (p.Arg330Gly). The arginine residue is highly conserved and there is a moderate physicochemical difference between arginine and glycine. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	0.99
BayesDel_addAF	Pathogenic	0.72	D
BayesDel_noAF	Pathogenic	0.79
CADD	Pathogenic	28
DANN	Uncertain	1.0
DEOGEN2	Pathogenic	0.94	D
FATHMM_MKL	Uncertain	0.96	D
LIST_S2	Uncertain	0.95	D
M_CAP	Pathogenic	0.88	D
MetaRNN	Pathogenic	1.0	D
MetaSVM	Pathogenic	1.0	D
MutationAssessor	Pathogenic	4.5	H
MutationTaster	Benign	1.0	D
PrimateAI	Pathogenic	0.80	T
PROVEAN	Pathogenic	-6.5	D
REVEL	Pathogenic	0.99
Sift	Pathogenic	0.0	D
Sift4G	Pathogenic	0.0	D
Polyphen		1.0	D
Vest4		0.99
MutPred		0.98		Loss of stability (P = 0.051);
MVP		1.0
MPC		1.3
ClinPred		1.0	D
GERP RS		5.2
Varity_R		0.99
gMVP		1.0

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.040		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: rs72558478; hg19: chrX-38271235;