21-43062952-C-T

Position:

• chr21-43062952-C-T

Variant summary

Our verdict is Pathogenic. Variant got 10 ACMG points: 10P and 0B. PVS1_Moderate PP5_Very_Strong

The NM_000071.3(CBS):​c.954+1G>A variant causes a splice donor, intron change. In-silico tool predicts a pathogenic outcome for this variant. 3/3 splice prediction tools predicting alterations to normal splicing. Variant has been reported in ClinVar as Likely pathogenic (★★).

• Frequency: Genomes: not found (cov: 0)
• Consequence: CBS NM_000071.3 splice_donor, intron
• Scores: Splicing: ADA: 0.9999
• Clinical Significance: Pathogenic/Likely pathogenic criteria provided, multiple submitters, no conflicts P:5
• Conservation: PhyloP100: 6.85

Genes affected

CBS (HGNC:1550): (cystathionine beta-synthase) The protein encoded by this gene acts as a homotetramer to catalyze the conversion of homocysteine to cystathionine, the first step in the transsulfuration pathway. The encoded protein is allosterically activated by adenosyl-methionine and uses pyridoxal phosphate as a cofactor. Defects in this gene can cause cystathionine beta-synthase deficiency (CBSD), which can lead to homocystinuria. This gene is a major contributor to cellular hydrogen sulfide production. Multiple alternatively spliced transcript variants have been found for this gene. [provided by RefSeq, Feb 2016]

CBS (HGNC:):

ACMG classification

Verdict is Pathogenic. Variant got 10 ACMG points.

• PVS1: Splicing +-2 bp (donor or acceptor) variant, product NOT destroyed by NMD, known LOF gene, truncates exone, which is 0.07548309 fraction of the gene. No cryptic splice site detected. Exon removal is inframe change.
• PP5: Variant 21-43062952-C-T is Pathogenic according to our data. Variant chr21-43062952-C-T is described in ClinVar as [Likely_pathogenic]. Clinvar id is 371568.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars. Variant chr21-43062952-C-T is described in Lovd as [Pathogenic].

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
CBS	NM_000071.3	c.954+1G>A		splice_donor_variant, intron_variant		ENST00000398165.8	NP_000062.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
CBS	ENST00000398165.8	c.954+1G>A		splice_donor_variant, intron_variant		1	NM_000071.3	ENSP00000381231.4

Frequencies

GnomAD3 genomes Cov.: 0

GnomAD4 exome Cov.: 0

GnomAD4 genome Cov.: 0

ClinVar

Significance: Pathogenic/Likely pathogenic

Submissions summary: Pathogenic:5

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Classic homocystinuria Pathogenic:3

Pathogenic, no assertion criteria provided	clinical testing	Natera, Inc.	Oct 01, 2021	- -
Pathogenic, criteria provided, single submitter	clinical testing	Baylor Genetics	Jul 09, 2022	- -
Pathogenic, criteria provided, single submitter	clinical testing	Counsyl	Oct 19, 2016	- -

HYPERHOMOCYSTEINEMIA, THROMBOTIC, CBS-RELATED Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

Apr 10, 2022

This sequence change affects a donor splice site in intron 10 of the CBS gene. It is expected to disrupt RNA splicing. Variants that disrupt the donor or acceptor splice site typically lead to a loss of protein function (PMID: 16199547), and loss-of-function variants in CBS are known to be pathogenic (PMID: 10338090, 12124992). This variant is not present in population databases (gnomAD no frequency). Disruption of this splice site has been observed in individual(s) with cystathionine beta-synthase deficiency (PMID: 12007221, 12124992). This variant is also known as IVS8+1G>A. ClinVar contains an entry for this variant (Variation ID: 371568). Studies have shown that disruption of this splice site is associated with altered splicing resulting in an unknown protein product impact (PMID: 12007221). 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. -

Homocystinuria Pathogenic:1

Pathogenic, criteria provided, single submitter

clinical testing

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

Jul 30, 2020

Variant summary: CBS c.954+1G>A is located in a canonical splice-site and is predicted to affect mRNA splicing resulting in a significantly altered protein due to either exon skipping, shortening, or inclusion of intronic material. Several computational tools predict a significant impact on normal splicing: Four predict the variant abolishes a 5' splicing donor site. The variant was absent in 251124 control chromosomes (gnomAD). c.954+1G>A has been reported in the literature in individuals affected with Homocystinuria (e.g. Kraus_1999, Gaustadnes_2002). These data indicate that the variant is likely to be associated with disease. A ClinVar submitter (evaluation after 2014) cites the variant as pathogenic. Based on the evidence outlined above, the variant was classified as pathogenic. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Pathogenic	0.24	D
BayesDel_noAF	Uncertain	0.11
CADD	Pathogenic	32
DANN	Uncertain	0.99
Eigen	Pathogenic	0.89
Eigen_PC	Uncertain	0.65
FATHMM_MKL	Uncertain	0.93	D
GERP RS		4.7

Splicing

Name	Calibrated prediction	Score	Prediction
dbscSNV1_ADA	Pathogenic	1.0
dbscSNV1_RF	Pathogenic	0.93
SpliceAI score (max)		0.99		Details are displayed if max score is > 0.2
DS_DG_spliceai		0.23		Position offset: -3
DS_DL_spliceai		0.99		Position offset: 1

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

Publications

LitVar

Other links and lift over

dbSNP: rs1057517373; hg19: chr21-44483062;