rs1554601476

Variant names:

• chr8-118110192-G-GT
• rs1554601476
• NM_000127.3:c.854dupA

Variant summary

Our verdict is Pathogenic. The variant received 18 ACMG points: 18P and 0B. PVS1 PM2 PP5_Very_Strong

The NM_000127.3(EXT1):​c.854dupA​(p.His285GlnfsTer4) variant causes a frameshift change involving the alteration of a conserved nucleotide. The variant was absent in control chromosomes in GnomAD project. Variant has been reported in ClinVar as Pathogenic (★★). Synonymous variant affecting the same amino acid position (i.e. H285H) has been classified as Likely benign. Variant results in nonsense mediated mRNA decay.

• Frequency: Genomes: not found (cov: 32)
• Consequence: EXT1 NM_000127.3 frameshift
• Clinical Significance: Pathogenic criteria provided, multiple submitters, no conflicts P:2
• Conservation: PhyloP100: 7.89
• Publications: 0 publications found

Genes affected

EXT1 (HGNC:3512): (exostosin glycosyltransferase 1) This gene encodes an endoplasmic reticulum-resident type II transmembrane glycosyltransferase involved in the chain elongation step of heparan sulfate biosynthesis. Mutations in this gene cause the type I form of multiple exostoses. [provided by RefSeq, Jul 2008]

EXT1 Gene-Disease associations (from GenCC):

• exostoses, multiple, type 1

  Inheritance: AD Classification: DEFINITIVE, STRONG Submitted by: Labcorp Genetics (formerly Invitae), G2P, ClinGen
• chondrosarcoma

  Inheritance: AD Classification: STRONG Submitted by: Genomics England PanelApp
• hereditary multiple osteochondromas

  Inheritance: AD Classification: SUPPORTIVE Submitted by: Orphanet

ACMG classification

Our verdict: Pathogenic. The variant received 18 ACMG points.

• PVS1: Loss of function variant, product undergoes nonsense mediated mRNA decay. LoF is a known mechanism of disease.
• PM2: Very rare variant in population databases, with high coverage
• PP5: Variant 8-118110192-G-GT is Pathogenic according to our data. Variant chr8-118110192-G-GT is described in ClinVar as Pathogenic. ClinVar VariationId is 423050.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
EXT1	NM_000127.3	c.854dupA	p.His285GlnfsTer4	frameshift_variant	Exon 1 of 11	ENST00000378204.7	NP_000118.2

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
EXT1	ENST00000378204.7	c.854dupA	p.His285GlnfsTer4	frameshift_variant	Exon 1 of 11	1	NM_000127.3	ENSP00000367446.3
EXT1	ENST00000436216.2	n.221dupA		non_coding_transcript_exon_variant	Exon 1 of 6	3		ENSP00000400372.1
EXT1	ENST00000437196.1	n.73+781dupA		intron_variant	Intron 1 of 9	5		ENSP00000407299.1

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome Cov.: 31

GnomAD4 genome Cov.: 32

ClinVar

Significance: Pathogenic

Submissions summary: Pathogenic:2

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Multiple congenital exostosis Pathogenic:1

Jun 19, 2018

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. Loss-of-function variants in EXT1 are known to be pathogenic (PMID: 10679937, 11391482, 19810120). This variant has not been reported in the literature in individuals with EXT1-related disease. ClinVar contains an entry for this variant (Variation ID: 423050). This variant is not present in population databases (ExAC no frequency). This sequence change creates a premature translational stop signal (p.His285Glnfs*4) in the EXT1 gene. It is expected to result in an absent or disrupted protein product. -

not provided Pathogenic:1

Jan 05, 2017

GeneDx

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

The c.854dupA pathogenic variant in the EXT1 gene causes a frameshift starting with codon Histidine 285, changes this amino acid to a Glutamine residue and creates a premature Stop codon at position 4 of the new reading frame, denoted p.His285GlnfsX4. This pathogenic variant is predicted to cause loss of normal protein function either through protein truncation or nonsense-mediated mRNA decay. The variant was not observed in approximately 6,500 individuals of European and African American ancestry in the NHLBI Exome Sequencing Project, indicating it is not a common benign variant in these populations. Although this pathogenic variant has not been previously reported to our knowledge, its presence is consistent with the diagnosis of hereditary multiple exostoses. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
PhyloP100		7.9
Mutation Taster		=0/200	disease causing (ClinVar)

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

Other links and lift over

dbSNP: rs1554601476; hg19: chr8-119122431;