8-117819743-AGGG-AGG

Variant names:

• chr8-117819743-AG-A
• rs886039355
• NM_000127.3:c.1468delC

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.1468delC​(p.Leu490TrpfsTer9) variant causes a frameshift change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.00000137 in 1,461,120 control chromosomes in the GnomAD database, with no homozygous occurrence. Variant has been reported in ClinVar as Pathogenic (★★). Variant results in nonsense mediated mRNA decay.

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 0.0000014 (0 hom.)
• Consequence: EXT1 NM_000127.3 frameshift
• Clinical Significance: Pathogenic criteria provided, multiple submitters, no conflicts P:3
• Conservation: PhyloP100: 3.06
• Publications: 7 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 8-117819743-AG-A is Pathogenic according to our data. Variant chr8-117819743-AG-A is described in ClinVar as [Pathogenic]. Clinvar id is 265130.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.1468delC	p.Leu490TrpfsTer9	frameshift_variant	Exon 6 of 11	ENST00000378204.7	NP_000118.2

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
EXT1	ENST00000378204.7	c.1468delC	p.Leu490TrpfsTer9	frameshift_variant	Exon 6 of 11	1	NM_000127.3	ENSP00000367446.3
EXT1	ENST00000437196.1	n.*359delC		non_coding_transcript_exon_variant	Exon 5 of 10	5		ENSP00000407299.1
EXT1	ENST00000684189.1	n.935delC		non_coding_transcript_exon_variant	Exon 6 of 11
EXT1	ENST00000437196.1	n.*359delC		3_prime_UTR_variant	Exon 5 of 10	5		ENSP00000407299.1

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome AF: 0.00000137 AC: 2 AN: 1461120 Hom.: 0 Cov.: 31 AF XY: 0.00000138 AC XY: 1 AN XY: 726864

African (AFR) AF: 0.00 AC: 0 AN: 33464

American (AMR) AF: 0.00 AC: 0 AN: 44724

Ashkenazi Jewish (ASJ) AF: 0.00 AC: 0 AN: 26136

East Asian (EAS) AF: 0.00 AC: 0 AN: 39700

South Asian (SAS) AF: 0.00 AC: 0 AN: 86224

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 53418

Middle Eastern (MID) AF: 0.00 AC: 0 AN: 5128

European-Non Finnish (NFE) AF: 0.00000180 AC: 2 AN: 1111994

Other (OTH) AF: 0.00 AC: 0 AN: 60332

GnomAD4 genome Cov.: 32

ClinVar

Significance: Pathogenic

Submissions summary: Pathogenic:3

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Chondrosarcoma;CN263289:Exostoses, multiple, type 1 Pathogenic:1

-

Juno Genomics, Hangzhou Juno Genomics, Inc

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

PM2_Supporting+PVS1+PS4_Supporting+PP4 -

Multiple congenital exostosis Pathogenic:1

Jul 26, 2024

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This sequence change creates a premature translational stop signal (p.Leu490Trpfs*9) in the EXT1 gene. It is expected to result in an absent or disrupted protein product. Loss-of-function variants in EXT1 are known to be pathogenic (PMID: 10679937, 11391482, 19810120). This variant is not present in population databases (gnomAD no frequency). This premature translational stop signal has been observed in individuals with multiple exostoses (PMID: 10713884, 17301954). ClinVar contains an entry for this variant (Variation ID: 265130). For these reasons, this variant has been classified as Pathogenic. -

not provided Pathogenic:1

Oct 12, 2015

GeneDx

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

The c.1468delC pathogenic variant in the EXT1 gene has been reported previously in association with hereditary multiple exostoses (Dobson-Stone et al., 2000; Signori et al., 2007; Sarrión et al., 2013). The deletion causes a frameshift starting with codon Leucine 490, changes this amino acid to a Tryptophan residue and creates a premature Stop codon at position 9 of the new reading frame, denoted p.Leu490TrpfsX9. This pathogenic variant is predicted to cause loss of normal protein function either through protein truncation or nonsense-mediated mRNA decay. The c.1468delC 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. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
PhyloP100		3.1
Mutation Taster		=2/198	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: rs886039355; hg19: chr8-118831982;