18-23533352-T-G

Variant names:

• chr18-23533352-T-G
• rs1208252513
• NM_000271.5:c.3754+3A>C

Variant summary

Our verdict is Uncertain significance. The variant received 4 ACMG points: 4P and 0B. PM2 PP3 PP5

The NM_000271.5(NPC1):​c.3754+3A>C variant causes a splice region, intron change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.00000137 in 1,461,478 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a benign outcome for this variant. 3/3 splice prediction tools predicting alterations to normal splicing. Variant has been reported in ClinVar as Conflicting classifications of pathogenicity (no stars).

• Frequency:
  • Genomes: not found (cov: 33)
  • Exomes 𝑓: 0.0000014 (0 hom.)
• Consequence: NPC1 NM_000271.5 splice_region, intron
• Scores: Splicing: ADA: 0.9928
• Clinical Significance: Conflicting classifications of pathogenicity criteria provided, conflicting classifications P:1 U:3
• Conservation: PhyloP100: 1.74
• Publications: 1 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: Uncertain_significance. The variant received 4 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• PP3: Splicing predictors support a deleterious effect. Scorers claiming Pathogenic: dbscSNV1_ADA, dbscSNV1_RF, max_spliceai. No scorers claiming Uncertain. No scorers claiming Benign.
• PP5: Variant 18-23533352-T-G is Pathogenic according to our data. Variant chr18-23533352-T-G is described in ClinVar as Conflicting_classifications_of_pathogenicity. ClinVar VariationId is 555325.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
NPC1	NM_000271.5	c.3754+3A>C		splice_region_variant, intron_variant	Intron 24 of 24	ENST00000269228.10	NP_000262.2

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
NPC1	ENST00000269228.10	c.3754+3A>C		splice_region_variant, intron_variant	Intron 24 of 24	1	NM_000271.5	ENSP00000269228.4

Frequencies

GnomAD3 genomes Cov.: 33

GnomAD2 exomes AF: 0.00000398 AC: 1 AN: 251358 AF XY: 0.00000736

Gnomad AFR exome AF: 0.00

Gnomad AMR exome AF: 0.0000289

Gnomad ASJ exome AF: 0.00

Gnomad EAS exome AF: 0.00

Gnomad FIN exome AF: 0.00

Gnomad NFE exome AF: 0.00

Gnomad OTH exome AF: 0.00

GnomAD4 exome AF: 0.00000137 AC: 2 AN: 1461478 Hom.: 0 Cov.: 31 AF XY: 0.00000138 AC XY: 1 AN XY: 727086

African (AFR) AF: 0.00 AC: 0 AN: 33476

American (AMR) AF: 0.0000447 AC: 2 AN: 44724

Ashkenazi Jewish (ASJ) AF: 0.00 AC: 0 AN: 26130

East Asian (EAS) AF: 0.00 AC: 0 AN: 39694

South Asian (SAS) AF: 0.00 AC: 0 AN: 86250

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 53408

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

European-Non Finnish (NFE) AF: 0.00 AC: 0 AN: 1111650

Other (OTH) AF: 0.00 AC: 0 AN: 60378

GnomAD4 genome Cov.: 33

Alfa AF: 0.0000312 Hom.: 0

Bravo AF: 0.00000378

ClinVar

Significance: Conflicting classifications of pathogenicity

Submissions summary: Pathogenic:1 Uncertain:3

Revision: criteria provided, conflicting classifications

Submissions by phenotype

Niemann-Pick disease, type C1 Pathogenic:1 Uncertain:2

Feb 11, 2024

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This sequence change falls in intron 24 of the NPC1 gene. It does not directly change the encoded amino acid sequence of the NPC1 protein. It affects a nucleotide within the consensus splice site. This variant is present in population databases (no rsID available, gnomAD 0.003%). This variant has been observed in individual(s) with clinical features of Niemann-Pick disease type C (PMID: 26981555; Invitae). In at least one individual the data is consistent with being in trans (on the opposite chromosome) from a pathogenic variant. ClinVar contains an entry for this variant (Variation ID: 555325). Variants that disrupt the consensus splice site are a relatively common cause of aberrant splicing (PMID: 17576681, 9536098). Algorithms developed to predict the effect of sequence changes on RNA splicing suggest that this variant may disrupt the consensus splice site. In summary, the currently available evidence indicates that the variant is pathogenic, but additional data are needed to prove that conclusively. Therefore, this variant has been classified as Likely Pathogenic. -

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Neuberg Centre For Genomic Medicine, NCGM

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: clinical testing

The splice site c.3754+3A>C variant has not been reported previously as a pathogenic variant nor as a benign variant, to our knowledge. The variant has allele frequency 0.0004% in gnomAD exomes and novel (not in any individuals) in 1000 Genomes. This variant has been reported to the ClinVar database as Uncertain Significance. For these reasons, this variant has been classified as Uncertain Significance (VUS). -

Nov 28, 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. -

Inborn genetic diseases Uncertain:1

Dec 23, 2021

Ambry Genetics

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: clinical testing

The c.3754+3A>C intronic alteration consists of a A to C substitution nucleotides after coding exon 24 in the NPC1 gene. Based on insufficient or conflicting evidence, the clinical significance of this alteration remains unclear. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_noAF	Benign	-0.39
CADD	Benign	22
DANN	Benign	0.89
PhyloP100		1.7
PromoterAI		0.039	Neutral
Mutation Taster		=4/96	disease causing

Splicing

Name	Calibrated prediction	Score	Prediction
dbscSNV1_ADA	Pathogenic	0.99
dbscSNV1_RF	Pathogenic	0.89
SpliceAI score (max)		0.92		Details are displayed if max score is > 0.2
DS_DL_spliceai		0.92		Position offset: 3

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

Other links and lift over

dbSNP: rs1208252513; hg19: chr18-21113316;