rs66469337

Positions:

• chrX-38421050-T-C
• chrX-38421050-T-G

Variant summary

Our verdict is Likely pathogenic. Variant got 7 ACMG points: 7P and 0B. PM2 PM5 PP3_Moderate PP5

The NM_000531.6(OTC):​c.1033T>C​(p.Tyr345His) 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 Conflicting classifications of pathogenicity (no stars). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. Y345C) has been classified as Likely pathogenic.

• Frequency: Genomes: not found (cov: 23)
• Consequence: OTC NM_000531.6 missense
• Clinical Significance: Conflicting classifications of pathogenicity criteria provided, conflicting classifications P:2 U:1
• Conservation: PhyloP100: 6.65

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 Likely_pathogenic. Variant got 7 ACMG points.

• 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, 0.928
• PP5: Variant X-38421050-T-C is Pathogenic according to our data. Variant chrX-38421050-T-C is described in ClinVar as [Conflicting_classifications_of_pathogenicity]. Clinvar id is 97100.We mark this variant Likely_pathogenic, oryginal submissions are: {Uncertain_significance=1, Pathogenic=1}.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
OTC	NM_000531.6	c.1033T>C	p.Tyr345His	missense_variant	10/10	ENST00000039007.5	NP_000522.3
OTC	NM_001407092.1	c.1033T>C	p.Tyr345His	missense_variant	12/12		NP_001394021.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
OTC	ENST00000039007.5	c.1033T>C	p.Tyr345His	missense_variant	10/10	1	NM_000531.6	ENSP00000039007	P1
OTC	ENST00000643344.1	c.*783T>C		3_prime_UTR_variant, NMD_transcript_variant	11/11			ENSP00000496606

Frequencies

GnomAD3 genomes Cov.: 23

GnomAD4 exome Cov.: 27

GnomAD4 genome Cov.: 23

ClinVar

Significance: Conflicting classifications of pathogenicity

Submissions summary: Pathogenic:2 Uncertain:1

Revision: criteria provided, conflicting classifications

Submissions by phenotype

Ornithine carbamoyltransferase deficiency Pathogenic:1 Uncertain:1

Pathogenic, criteria provided, single submitter	clinical testing	Labcorp Genetics (formerly Invitae), Labcorp	Mar 15, 2022	This variant is not present in population databases (gnomAD no frequency). This sequence change replaces tyrosine, which is neutral and polar, with histidine, which is basic and polar, at codon 345 of the OTC protein (p.Tyr345His). This missense change has been observed in individuals with ornithine transcarbamylase deficiency (PMID: 16786505, 18662984, 29123827; Invitae). For these reasons, this variant has been classified as Pathogenic. This variant disrupts the p.Tyr345 amino acid residue in OTC. Other variant(s) that disrupt this residue have been observed in individuals with OTC-related conditions (PMID: 1480464, 10946359), 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 (SIFT, PolyPhen-2, Align-GVGD) all suggest that this variant is likely to be tolerated. ClinVar contains an entry for this variant (Variation ID: 97100). -
Uncertain significance, criteria provided, single submitter	clinical testing	Revvity Omics, Revvity	Feb 03, 2023	- -

not provided Pathogenic:1

Pathogenic, no assertion criteria provided

literature only

GenMed Metabolism Lab

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Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Uncertain	0.38
BayesDel_addAF	Pathogenic	0.55	D
BayesDel_noAF	Pathogenic	0.56
CADD	Benign	22
DANN	Uncertain	0.99
DEOGEN2	Benign	0.38	T
FATHMM_MKL	Pathogenic	0.98	D
LIST_S2	Uncertain	0.90	D
M_CAP	Pathogenic	0.54	D
MetaRNN	Pathogenic	0.93	D
MetaSVM	Pathogenic	0.82	D
MutationAssessor	Benign	1.3	L
MutationTaster	Benign	1.0	D
PrimateAI	Uncertain	0.69	T
PROVEAN	Benign	-0.84	N
REVEL	Pathogenic	0.67
Sift	Benign	0.24	T
Sift4G	Benign	0.31	T
Polyphen		0.042	B
Vest4		0.68
MutPred		0.83		Gain of disorder (P = 0.0233);
MVP		0.98
MPC		0.53
ClinPred		0.83	D
GERP RS		5.3
Varity_R		0.57
gMVP		0.87

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: rs66469337; hg19: chrX-38280303;