NM_000127.3:c.992_993delCCinsAT

Variant names:

• chr8-117837171-GG-AT
• NM_000127.3:c.992_993delCCinsAT
• EXT1 p.Ala331Asp

Variant summary

Our verdict is Likely pathogenic. The variant received 7 ACMG points: 7P and 0B. PS1 PM1 PP3

The NM_000127.3(EXT1):​c.992_993delCCinsAT​(p.Ala331Asp) variant causes a missense change involving the alteration of a conserved nucleotide. The variant was absent in control chromosomes in GnomAD project. It is difficult to determine the true allele frequency of this variant because it is of type MNV, and the frequency of such variant types in population databases may be underestimated and unreliable. No clinical diagnostic laboratories have submitted clinical-significance assessments for this variant to ClinVar. Another nucleotide change resulting in the same amino acid substitution has been previously reported as Pathogenic in ClinVar.

• Frequency: Genomes: not found (cov: 32)
• Consequence: EXT1 NM_000127.3 missense
• Clinical Significance: Not reported in ClinVar
• Conservation: PhyloP100: 10.0
• 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: Likely_pathogenic. The variant received 7 ACMG points.

• PS1: Transcript NM_000127.3 (EXT1) is affected with MISSENSE_VARIANT having same AA change as one Pathogenic present in ClinVar.
• PM1: In a hotspot region, there are 5 aminoacids with missense pathogenic changes in the window of +-8 aminoacids around while only 1 benign, 6 uncertain in NM_000127.3
• PP3: No computational evidence supports a deleterious effect, but strongly conserved according to phyloP

Variant Effect in Transcripts

ACMG analysis was done for transcript: NM_000127.3. You can select a different transcript below to see updated ACMG assignments.

RefSeq Transcripts

Sel.	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	EXT1	NM_000127.3	MANE Select	c.992_993delCCinsAT	p.Ala331Asp	missense	N/A	NP_000118.2

Ensembl Transcripts

Sel.	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	EXT1	ENST00000378204.7	TSL:1 MANE Select	c.992_993delCCinsAT	p.Ala331Asp	missense	N/A	ENSP00000367446.3	Q16394
	EXT1	ENST00000436216.2	TSL:3	n.359_360delCCinsAT		non_coding_transcript_exon	Exon 2 of 6	ENSP00000400372.1	H7C1H6
	EXT1	ENST00000684189.1		n.459_460delCCinsAT		non_coding_transcript_exon	Exon 2 of 11

Frequencies

GnomAD3 genomes Cov.: 32

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

GnomAD4 genome Cov.: 32

ClinVar

Not reported in ClinVar

Computational scores

Source: dbNSFP v4.9

Name	Calibrated prediction	Score	Prediction
PhyloP100		10

Splicing

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

MaxEntScan Visualizer can be used to analyze the impact of this mutation on the neighboring sequence.

Other links and lift over

hg19: chr8-118849410;