chr18-23544456-C-A

Variant names:

• chr18-23544456-C-A
• rs1555634452
• NM_000271.5:c.2018G>T

Variant summary

Our verdict is Likely pathogenic. The variant received 9 ACMG points: 9P and 0B. PM1 PM2 PP2 PP3_Strong

The NM_000271.5(NPC1):​c.2018G>T​(p.Gly673Val) variant causes a missense change involving the alteration of a conserved nucleotide. The variant allele was found at a frequency of 0.00000137 in 1,461,844 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a pathogenic outcome for this variant. Variant has been reported in ClinVar as Uncertain significance (★).

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 0.0000014 (0 hom.)
• Consequence: NPC1 NM_000271.5 missense
• Clinical Significance: Uncertain significance criteria provided, single submitter U:2
• Conservation: PhyloP100: 7.90
• Publications: 0 publications found

Genes affected

NPC1 (HGNC:7897): (NPC intracellular cholesterol transporter 1) This gene encodes a large protein that resides in the limiting membrane of endosomes and lysosomes and mediates intracellular cholesterol trafficking via binding of cholesterol to its N-terminal domain. It is predicted to have a cytoplasmic C-terminus, 13 transmembrane domains, and 3 large loops in the lumen of the endosome - the last loop being at the N-terminus. This protein transports low-density lipoproteins to late endosomal/lysosomal compartments where they are hydrolized and released as free cholesterol. Defects in this gene cause Niemann-Pick type C disease, a rare autosomal recessive neurodegenerative disorder characterized by over accumulation of cholesterol and glycosphingolipids in late endosomal/lysosomal compartments.[provided by RefSeq, Aug 2009]

NPC1 Gene-Disease associations (from GenCC):

• Niemann-Pick disease, type C1

  Inheritance: AR Classification: DEFINITIVE, STRONG Submitted by: ClinGen, Laboratory for Molecular Medicine, Labcorp Genetics (formerly Invitae), G2P, Genomics England PanelApp, Myriad Women’s Health
• Niemann-Pick disease type C, adult neurologic onset

  Inheritance: AR Classification: SUPPORTIVE Submitted by: Orphanet
• Niemann-Pick disease type C, juvenile neurologic onset

  Inheritance: AR Classification: SUPPORTIVE Submitted by: Orphanet
• Niemann-Pick disease type C, late infantile neurologic onset

  Inheritance: AR Classification: SUPPORTIVE Submitted by: Orphanet
• Niemann-Pick disease type C, severe early infantile neurologic onset

  Inheritance: AR Classification: SUPPORTIVE Submitted by: Orphanet
• Niemann-Pick disease type C, severe perinatal form

  Inheritance: AR Classification: SUPPORTIVE Submitted by: Orphanet

ACMG classification

Our verdict: Likely_pathogenic. The variant received 9 ACMG points.

• PM1: In a hotspot region, there are 3 aminoacids with missense pathogenic changes in the window of +-8 aminoacids around while only 0 benign, 4 uncertain in NM_000271.5
• PM2: Very rare variant in population databases, with high coverage
• PP2: Missense variant in the gene, where a lot of missense mutations are associated with disease in ClinVar. The gene has 171 curated pathogenic missense variants (we use a threshold of 10). The gene has 18 curated benign missense variants. Gene score misZ: 1.0917 (below the threshold of 3.09). Trascript score misZ: 1.706 (below the threshold of 3.09). GenCC associations: The gene is linked to Niemann-Pick disease, type C1, Niemann-Pick disease type C, severe early infantile neurologic onset, Niemann-Pick disease type C, late infantile neurologic onset, Niemann-Pick disease type C, adult neurologic onset, Niemann-Pick disease type C, juvenile neurologic onset, Niemann-Pick disease type C, severe perinatal form.
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.996

Variant Effect in Transcripts

ACMG analysis was done for transcript: NM_000271.5. 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
	NPC1	NM_000271.5	MANE Select	c.2018G>T	p.Gly673Val	missense	Exon 13 of 25	NP_000262.2

Ensembl Transcripts

Selected	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	NPC1	ENST00000269228.10	TSL:1 MANE Select	c.2018G>T	p.Gly673Val	missense	Exon 13 of 25	ENSP00000269228.4
	NPC1	ENST00000591051.1	TSL:2	c.1094G>T	p.Gly365Val	missense	Exon 6 of 18	ENSP00000467636.1
	NPC1	ENST00000540608.5	TSL:2	n.1932G>T		non_coding_transcript_exon	Exon 11 of 16

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome AF: 0.00000137 AC: 2 AN: 1461844 Hom.: 0 Cov.: 32 AF XY: 0.00000138 AC XY: 1 AN XY: 727216

⚠️ The allele balance in gnomAD version 4 Exomes is significantly skewed from the expected value of 0.5.

African (AFR) AF: 0.00 AC: 0 AN: 33478

American (AMR) AF: 0.00 AC: 0 AN: 44716

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: 86240

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 53420

Middle Eastern (MID) AF: 0.00 AC: 0 AN: 5768

European-Non Finnish (NFE) AF: 0.00000180 AC: 2 AN: 1111990

Other (OTH) AF: 0.00 AC: 0 AN: 60396

⚠️ The allele balance in gnomAD4 Exomes is highly skewed from 0.5 (p-value = 0), which strongly suggests a high chance of mosaicism in these individuals.

GnomAD4 genome Cov.: 32

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:2

Revision: criteria provided, single submitter

Submissions by phenotype

not specified Uncertain:1

Apr 11, 2024

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

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Variant summary: NPC1 c.2018G>T (p.Gly673Val) results in a non-conservative amino acid change located in the Sterol-sensing domain (IPR000731) of the encoded protein sequence. Five of five in-silico tools predict a damaging effect of the variant on protein function. The variant was absent in 251388 control chromosomes. The available data on variant occurrences in the general population are insufficient to allow any conclusion about variant significance. c.2018G>T has been reported in the literature in individuals affected with Niemann-Pick Disease Type C (Garver_2010, Park_2003). These data do not allow any conclusion about variant significance. To our knowledge, no experimental evidence demonstrating an impact on protein function has been reported. The following publications have been ascertained in the context of this evaluation (PMID: 19744920, 12955717). ClinVar contains an entry for this variant (Variation ID: 554148). Based on the evidence outlined above, the variant was classified as uncertain significance.

Niemann-Pick disease, type C1 Uncertain:1

Sep 27, 2017

Counsyl

Significance: Uncertain significance

Review Status: no assertion criteria provided

Collection Method: clinical testing

This submission and the accompanying classification are no longer maintained by the submitter. For more information on current observations and classification, please contact variantquestions@myriad.com.

Computational scores

Source: dbNSFP v4.9

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	0.94
BayesDel_addAF	Pathogenic	0.57	D
BayesDel_noAF	Pathogenic	0.58
CADD	Uncertain	25
DANN	Uncertain	1.0
DEOGEN2	Pathogenic	0.98	D
Eigen	Pathogenic	0.94
Eigen_PC	Pathogenic	0.81
FATHMM_MKL	Pathogenic	0.99	D
LIST_S2	Pathogenic	0.98	D
M_CAP	Pathogenic	0.79	D
MetaRNN	Pathogenic	1.0	D
MetaSVM	Pathogenic	1.1	D
MutationAssessor	Pathogenic	3.8	H
PhyloP100		7.9
PrimateAI	Uncertain	0.70	T
PROVEAN	Pathogenic	-9.0	D
REVEL	Pathogenic	0.96
Sift	Uncertain	0.0020	D
Sift4G	Pathogenic	0.0	D
Polyphen		1.0	D
Vest4		0.99
MutPred		0.96		Loss of helix (P = 0.2271)
MVP		0.99
MPC		1.0
ClinPred		1.0	D
GERP RS		5.8
RBP_binding_hub_radar		0.0
RBP_regulation_power_radar		1.7
Varity_R		0.99
gMVP		0.96
Mutation Taster		=2/98	disease causing

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: rs1555634452; hg19: chr18-21124420;