rs1555975756

Variant names:

• chrX-38401693-G-A
• rs1555975756
• NM_000531.6:c.540+265G>A

Variant summary

Our verdict is Pathogenic. The variant received 11 ACMG points: 11P and 0B. PM2 PP3 PP5_Very_Strong

The NM_000531.6(OTC):​c.540+265G>A variant causes a intron change involving the alteration of a non-conserved nucleotide. The variant was absent in control chromosomes in GnomAD project. In-silico tool predicts a benign outcome for this variant. Variant has been reported in ClinVar as Pathogenic (★★).

• Frequency: Genomes: not found (cov: 23)
• Consequence: OTC NM_000531.6 intron
• Clinical Significance: Pathogenic criteria provided, multiple submitters, no conflicts P:12
• Conservation: PhyloP100: 0.539
• Publications: 7 publications found

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]

OTC Gene-Disease associations (from GenCC):

• ornithine carbamoyltransferase deficiency

  Inheritance: XL Classification: DEFINITIVE, STRONG, SUPPORTIVE Submitted by: Labcorp Genetics (formerly Invitae), ClinGen, G2P, Laboratory for Molecular Medicine, Orphanet

ENSG00000250349 (HGNC:):

ACMG classification

Our verdict: Pathogenic. The variant received 11 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• PP3: Splicing predictors support a deleterious effect. Scorers claiming Pathogenic: max_spliceai. No scorers claiming Uncertain. No scorers claiming Benign.
• PP5: Variant X-38401693-G-A is Pathogenic according to our data. Variant chrX-38401693-G-A is described in ClinVar as Pathogenic. ClinVar VariationId is 449382.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Variant Effect in Transcripts

ACMG analysis was done for transcript: NM_000531.6. You can select a different transcript below to see updated ACMG assignments.

RefSeq Transcripts

Selected	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	OTC	NM_000531.6	MANE Select	c.540+265G>A		intron	N/A	NP_000522.3
	OTC	NM_001407092.1		c.540+265G>A		intron	N/A	NP_001394021.1

Ensembl Transcripts

Selected	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	OTC	ENST00000039007.5	TSL:1 MANE Select	c.540+265G>A		intron	N/A	ENSP00000039007.4
	ENSG00000250349	ENST00000465127.1	TSL:5	c.172-264428G>A		intron	N/A	ENSP00000417050.1
	OTC	ENST00000713758.1		c.540+265G>A		intron	N/A	ENSP00000519059.1

Frequencies

GnomAD3 genomes Cov.: 23

We have no GnomAD4 exomes data on this position. Probably position not covered by the project.

GnomAD4 genome Cov.: 23

Alfa AF: 0.00 Hom.: 0

ClinVar

Significance: Pathogenic

Submissions summary: Pathogenic:12

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Ornithine carbamoyltransferase deficiency Pathogenic:10

Oct 07, 2024

Genomic Medicine Center of Excellence, King Faisal Specialist Hospital and Research Centre

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Sep 16, 2020

Natera, Inc.

Significance: Pathogenic

Review Status: no assertion criteria provided

Collection Method: clinical testing

Mar 08, 2023

Color Diagnostics, LLC DBA Color Health

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This variant causes a G to A nucleotide substitution at the +265 position of intron 5 of the OTC gene. This variant has been reported in three male neonates clinically diagnosed with OTC deficiency (PMID: 18204299, 18440262, 34014569), as well as in seven females affected with late-onset OTC deficiency (PMID: 33489762) and episodic OTC deficiency (PMID: 34014569). This variant has not been identified in the general population by the Genome Aggregation Database (gnomAD). RT-PCR analyses of patient-derived RNA have shown that a new splice acceptor site created by this variant is paired with a cryptic splice donor site located 135 nucleotides downstream, resulting in the inclusion of the 135-nucleotide intronic sequence between exons 5 and 6 of the OTC transcript with a premature stop of translation at codon 184 (PMID: 18204299, 18440262). This variant is expected to result in an absent or nonfunctional protein product. Loss of OTC function is a known mechanism of disease (clinicalgenome.org). Based on the available evidence, this variant is classified as Pathogenic.

Nov 09, 2021

MGZ Medical Genetics Center

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

May 04, 2022

Mendelics

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

May 22, 2024

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This sequence change falls in intron 5 of the OTC gene. It does not directly change the encoded amino acid sequence of the OTC protein. The frequency data for this variant in the population databases is considered unreliable, as metrics indicate insufficient coverage at this position in the gnomAD database. This variant has been observed in individual(s) with ornithine transcarbamylase (OTC) deficiency (PMID: 18204299, 18440262, 33489762). ClinVar contains an entry for this variant (Variation ID: 449382). Algorithms developed to predict the effect of sequence changes on RNA splicing suggest that this variant may create or strengthen a splice site. For these reasons, this variant has been classified as Pathogenic.

Mar 11, 2024

Rady Children's Institute for Genomic Medicine, Rady Children's Hospital San Diego

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This variant is also referred to as IVS5+265G>A in the literature. This intronic variant is located 265 nucleotides downstream of the exon 5 intron 5 boundary. Multiple splice prediction tools suggest this variant is not likely to interfere with normal splicing. However, OTC mRNA in the liver of an affected individual showed a 135-nt insertion between exons 5 and 6, creating a novel splice acceptor site. This novel splice acceptor site produced a novel exon structure, from the intron sequence together with downstream cryptic splicing donor sites, which was subsequently incorporated into OTC mRNA (PMID: 18204299). This variant has been previously reported as a de novo change in male and female individuals with ornithine transcarbamylase deficiency (PMID: 18204299, 33272297, 34014569, 33489762). Functional studies demonstrated that the c.540+265G>A variant results in decreased enzyme levels (PMID: 34014569). The c.540+265G>A variant is absent from the gnomAD population database and thus is presumed to be rare. Based on the available evidence, c.540+265G>A is classified as Pathogenic.

Jul 19, 2023

All of Us Research Program, National Institutes of Health

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This variant causes a G to A nucleotide substitution at the +265 position of intron 5 of the OTC gene. This variant has been reported in three male neonates clinically diagnosed with OTC deficiency (PMID: 18204299, 18440262, 34014569), as well as in seven females affected with late-onset OTC deficiency (PMID: 33489762) and episodic OTC deficiency (PMID: 34014569). This variant has not been identified in the general population by the Genome Aggregation Database (gnomAD). RT-PCR analyses of patient-derived RNA have shown that a new splice acceptor site created by this variant is paired with a cryptic splice donor site located 135 nucleotides downstream, resulting in the inclusion of the 135-nucleotide intronic sequence between exons 5 and 6 of the OTC transcript with a premature stop of translation at codon 184 (PMID: 18204299, 18440262). This variant is expected to result in an absent or nonfunctional protein product. Loss of OTC function is a known mechanism of disease (clinicalgenome.org). Based on the available evidence, this variant is classified as Pathogenic.

Jan 01, 2016

Centre for Mendelian Genomics, University Medical Centre Ljubljana

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This variant was classified as: Pathogenic.

Jun 07, 2024

Revvity Omics, Revvity

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

not provided Pathogenic:1

Mar 22, 2022

GeneDx

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Non-canonical splice site variant demonstrated to result in loss of normal function through nonsense-mediated mRNA decay (Ogino et al. 2007; Engel et al. 2008); No data available from control populations to assess the frequency of this variant; This variant is associated with the following publications: (PMID: 18440262, 34014569, 19823873, 28771251, 33272297, 33489762, 18204299)

Protein avoidance;C4023070:Abnormal circulating ornithine concentration;C5574662:Hyperammonemia Pathogenic:1

Jan 01, 2017

Centre for Mendelian Genomics, University Medical Centre Ljubljana

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Computational scores

Source: dbNSFP v4.9

Name	Calibrated prediction	Score	Prediction
BayesDel_noAF	Benign	-0.85
CADD	Benign	22
DANN	Benign	0.36
PhyloP100		0.54
Mutation Taster		=38/62	disease causing (ClinVar)

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.65		Details are displayed if max score is > 0.2
DS_AG_spliceai		0.65		Position offset: 2

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

Other links and lift over

dbSNP: rs1555975756; hg19: chrX-38260946;