NM_000531.6:c.663G>T

Variant names:

• chrX-38403740-G-T
• NM_000531.6:c.663G>T

Variant summary

Our verdict is Pathogenic. Variant got 14 ACMG points: 14P and 0B. PM2 PP3_Strong PP5_Very_Strong

The NM_000531.6(OTC):​c.663G>T​(p.Lys221Asn) variant causes a missense, splice region change involving the alteration of a conserved nucleotide. The variant was absent in control chromosomes in GnomAD project. In-silico tool predicts a pathogenic outcome for this variant. 3/3 splice prediction tools predicting alterations to normal splicing. Variant has been reported in ClinVar as Likely pathogenic (★★).

• Frequency: Genomes: not found (cov: 23)
• Consequence: OTC NM_000531.6 missense, splice_region
• Scores: Splicing: ADA: 1.000
• Clinical Significance: Pathogenic/Likely pathogenic criteria provided, multiple submitters, no conflicts P:2
• Conservation: PhyloP100: 7.72

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]

ENSG00000250349 (HGNC:):

ACMG classification

Verdict is Pathogenic. Variant got 14 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, max_spliceai. No scorers claiming Uncertain. No scorers claiming Benign.
• PP5: Variant X-38403740-G-T is Pathogenic according to our data. Variant chrX-38403740-G-T is described in ClinVar as [Likely_pathogenic]. Clinvar id is 1804689.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
OTC	NM_000531.6	c.663G>T	p.Lys221Asn	missense_variant, splice_region_variant	Exon 6 of 10	ENST00000039007.5	NP_000522.3
OTC	NM_001407092.1	c.663G>T	p.Lys221Asn	missense_variant, splice_region_variant	Exon 8 of 12		NP_001394021.1
OTC	XM_017029556.2	c.663G>T	p.Lys221Asn	missense_variant, splice_region_variant	Exon 6 of 9		XP_016885045.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
OTC	ENST00000039007.5	c.663G>T	p.Lys221Asn	missense_variant, splice_region_variant	Exon 6 of 10	1	NM_000531.6	ENSP00000039007.4
ENSG00000250349	ENST00000465127.1	c.172-262381G>T		intron_variant	Intron 3 of 8	5		ENSP00000417050.1

Frequencies

GnomAD3 genomes Cov.: 23

GnomAD4 exome Cov.: 30

GnomAD4 genome Cov.: 23

ClinVar

Significance: Pathogenic/Likely pathogenic

Submissions summary: Pathogenic:2

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Ornithine carbamoyltransferase deficiency Pathogenic:2

Nov 13, 2022

Women's Health and Genetics/Laboratory Corporation of America, LabCorp

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Variant summary: OTC c.663G>T (p.Lys221Asn) results in a non-conservative amino acid change located in the Aspartate/ornithine carbamoyltransferase, Asp/Orn-binding domain (IPR006131) of the encoded protein sequence. Four of five in-silico tools predict a damaging effect of the variant on protein function. Several computational tools predict a significant impact on normal splicing: One predicts the variant abolishes the canonical 5' splicing donor site and three predict the variant weakens the same canonical 5' splicing donor site. Two predict the variant creates a new cryptic 3' acceptor site. However, these predictions have yet to be confirmed by functional studies. The variant was absent in 182871 control chromosomes (gnomAD). c.663G>T has been reported in the literature in a female carrier affected with Ornithine Transcarbamylase Deficiency (Kim_2006). These data do not allow any conclusion about variant significance. Experimental evidence evaluating the impact of the variant on protein function using COS-1 cells showed that the variant protein had 0% residual activity (Kim_2006). No clinical diagnostic laboratories have submitted clinical-significance assessments for this variant to ClinVar after 2014. Based on the evidence outlined above, the variant was classified as likely pathogenic. -

May 13, 2023

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

For these reasons, this variant has been classified as Pathogenic. Variants that disrupt the consensus splice site are a relatively common cause of aberrant splicing (PMID: 17576681, 9536098). Algorithms developed to predict the effect of sequence changes on RNA splicing suggest that this variant may disrupt the consensus splice site. Experimental studies have shown that this missense change affects OTC function (PMID: 17041896). 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: 1804689). This missense change has been observed in individual(s) with ornithine transcarbamylase deficiency (PMID: 16786505, 17041896; Invitae). This variant is not present in population databases (gnomAD no frequency). This sequence change replaces lysine, which is basic and polar, with asparagine, which is neutral and polar, at codon 221 of the OTC protein (p.Lys221Asn). This variant also falls at the last nucleotide of exon 6, which is part of the consensus splice site for this exon. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Benign	0.32
BayesDel_addAF	Pathogenic	0.28	D
BayesDel_noAF	Pathogenic	0.16
CADD	Pathogenic	34
DANN	Uncertain	1.0
DEOGEN2	Pathogenic	0.93	D
FATHMM_MKL	Pathogenic	0.99	D
LIST_S2	Uncertain	0.93	D
M_CAP	Pathogenic	0.77	D
MetaRNN	Pathogenic	0.97	D
MetaSVM	Pathogenic	1.1	D
MutationAssessor	Pathogenic	2.9	M
PrimateAI	Uncertain	0.57	T
PROVEAN	Uncertain	-2.8	D
REVEL	Pathogenic	0.85
Sift	Uncertain	0.022	D
Sift4G	Benign	0.064	T
Polyphen		0.98	D
Vest4		0.72
MutPred		0.80		Loss of ubiquitination at K221 (P = 0.0116);
MVP		0.96
MPC		1.2
ClinPred		0.97	D
GERP RS		5.9
Varity_R		0.94
gMVP		0.93

Splicing

Name	Calibrated prediction	Score	Prediction
dbscSNV1_ADA	Pathogenic	1.0
dbscSNV1_RF	Pathogenic	1.0
SpliceAI score (max)		0.94		Details are displayed if max score is > 0.2
DS_DL_spliceai		0.94		Position offset: 0

Find out detailed SpliceAI scores and Pangolin per-transcript scores at spliceailookup.broadinstitute.org

Publications

No publications associated with this variant yet.

Other links and lift over

hg19: chrX-38262993; COSMIC: COSV50004993; COSMIC: COSV50004993;