rs120074120

Variant names:

• chr11-6391853-T-A
• rs120074120
• NM_000543.5:c.788T>A

Variant summary

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

The NM_000543.5(SMPD1):​c.788T>A​(p.Leu263*) variant causes a stop gained change. The variant allele was found at a frequency of 0.000000684 in 1,461,550 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 Pathogenic (★★). Synonymous variant affecting the same amino acid position (i.e. L263L) has been classified as Likely benign. Variant results in nonsense mediated mRNA decay.

• Frequency:
  • Genomes: not found (cov: 31)
  • Exomes 𝑓: 6.8e-7 (0 hom.)
• Consequence: SMPD1 NM_000543.5 stop_gained
• Clinical Significance: Pathogenic criteria provided, multiple submitters, no conflicts P:4
• Conservation: PhyloP100: 5.68
• Publications: 3 publications found

Genes affected

SMPD1 (HGNC:11120): (sphingomyelin phosphodiesterase 1) The protein encoded by this gene is a lysosomal acid sphingomyelinase that converts sphingomyelin to ceramide. The encoded protein also has phospholipase C activity. Defects in this gene are a cause of Niemann-Pick disease type A (NPA) and Niemann-Pick disease type B (NPB). Multiple transcript variants encoding different isoforms have been identified. [provided by RefSeq, Jul 2010]

SMPD1 Gene-Disease associations (from GenCC):

• acid sphingomyelinase deficiency

  Inheritance: AR Classification: DEFINITIVE Submitted by: ClinGen
• Niemann-Pick disease

  Inheritance: AR Classification: DEFINITIVE Submitted by: Myriad Women’s Health
• Niemann-Pick disease type A

  Inheritance: AR Classification: DEFINITIVE, STRONG, SUPPORTIVE Submitted by: Genomics England PanelApp, Orphanet, G2P
• Niemann-Pick disease type B

  Inheritance: AR Classification: STRONG, SUPPORTIVE Submitted by: Genomics England PanelApp, Orphanet, Labcorp Genetics (formerly Invitae)

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 11-6391853-T-A is Pathogenic according to our data. Variant chr11-6391853-T-A is described in ClinVar as Pathogenic. ClinVar VariationId is 2984.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
SMPD1	NM_000543.5	c.788T>A	p.Leu263*	stop_gained	Exon 2 of 6	ENST00000342245.9	NP_000534.3

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
SMPD1	ENST00000342245.9	c.788T>A	p.Leu263*	stop_gained	Exon 2 of 6	1	NM_000543.5	ENSP00000340409.4

Frequencies

GnomAD3 genomes Cov.: 31

GnomAD2 exomes AF: 0.00000400 AC: 1 AN: 250022 AF XY: 0.00000738

Gnomad AFR exome AF: 0.00

Gnomad AMR exome AF: 0.00

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: 6.84e-7 AC: 1 AN: 1461550 Hom.: 0 Cov.: 37 AF XY: 0.00000138 AC XY: 1 AN XY: 727130

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

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: 0.0000116 AC: 1 AN: 86258

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 53204

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

European-Non Finnish (NFE) AF: 0.00 AC: 0 AN: 1111894

Other (OTH) AF: 0.00 AC: 0 AN: 60390

GnomAD4 genome Cov.: 31

ExAC AF: 0.00000824 AC: 1

ClinVar

Significance: Pathogenic

Submissions summary: Pathogenic:4

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Niemann-Pick disease, type A Pathogenic:2

Mar 17, 2017

Natera, Inc.

Significance: Pathogenic

Review Status: no assertion criteria provided

Collection Method: clinical testing

- -

Jan 01, 1992

OMIM

Significance: Pathogenic

Review Status: no assertion criteria provided

Collection Method: literature only

- -

Niemann-Pick disease, type A;C0268243:Niemann-Pick disease, type B Pathogenic:1

Sep 19, 2023

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.Leu263*) in the SMPD1 gene. It is expected to result in an absent or disrupted protein product. Loss-of-function variants in SMPD1 are known to be pathogenic (PMID: 12369017, 15221801). This variant is present in population databases (rs120074120, gnomAD 0.003%). This premature translational stop signal has been observed in individuals with Niemann-Pick disease (PMID: 1618760, 27338287). This variant is also known as L261X. ClinVar contains an entry for this variant (Variation ID: 2984). For these reasons, this variant has been classified as Pathogenic. -

Sphingomyelin/cholesterol lipidosis Pathogenic:1

Jan 22, 2020

Broad Center for Mendelian Genomics, Broad Institute of MIT and Harvard

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: curation

The p.Leu263Ter variant in SMPD1 (also known as p.Leu261Ter due to a difference in cDNA numbering) has been reported in 1 individual of Indian descent with Niemann-Pick disease (PMID: 1618760) and has been identified in 0.003% (1/30614) of South Asian chromosomes by the Genome Aggregation Database (gnomAD, http://gnomad.broadinstitute.org; dbSNP rs120074120). Although this variant has been seen in the general population, its frequency is low enough to be consistent with a recessive carrier frequency. This variant has also been reported in ClinVar (VariaitonID: 2984) as Pathogenic by OMIM. In vitro functional studies provide some evidence that the p.Leu263Ter variant may impact protein activity (PMID: 1618760). However, these types of assays may not accurately represent biological function. This nonsense variant leads to a premature termination codon at position 263, which is predicted to lead to a truncated or absent protein. Loss of function of the SMPD1 gene is an established disease mechanism in autosomal recessive Niemann-Pick disease. The presence of this variant in an affected homozygote increases the likelihood that the p.Leu263Ter variant is pathogenic (PMID: 1618760). The phenotype of an individual homozygous for this variant is highly specific for Niemann-Pick disease based on acid sphingomyelinase activity being <10% of normal (PMID: 1618760). In summary, this variant meets criteria to be classified as pathogenic for Niemann-Pick disease in an autosomal recessive manner based on the prediction that it causes loss of function, in vitro functional studies, its presence in a homozygous individual, and the phenotype of a patient with the variant being highly specific for disease. ACMG/AMP Criteria applied: PVS1, PS3, PM2, PM3_supporting, PP4 (Richards 2015). -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Pathogenic	0.55	D
BayesDel_noAF	Pathogenic	0.62
CADD	Pathogenic	40
DANN	Uncertain	0.99
Eigen	Pathogenic	0.80
Eigen_PC	Uncertain	0.66
FATHMM_MKL	Pathogenic	0.98	D
PhyloP100		5.7
Vest4		0.93
GERP RS		5.0
PromoterAI		-0.035	Neutral
Mutation Taster		=0/200	disease causing (ClinVar)

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.010		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: rs120074120; hg19: chr11-6413083;