21-43072174-TG-TGG

Variant names:

• chr21-43072174-T-TG
• rs748695461
• NM_000071.3:c.19dupC

Variant summary

Our verdict is Pathogenic. Variant got 16 ACMG points: 16P and 0B. PVS1 PP5_Very_Strong

The NM_000071.3(CBS):​c.19dupC​(p.Gln7ProfsTer30) variant causes a frameshift change involving the alteration of a non-conserved nucleotide. Variant has been reported in ClinVar as Pathogenic (★★).

• Frequency: Genomes: not found (cov: 0)
• Consequence: CBS NM_000071.3 frameshift
• Clinical Significance: Pathogenic criteria provided, multiple submitters, no conflicts P:9
• Conservation: PhyloP100: 0.0790

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]

ACMG classification

Verdict is Pathogenic. Variant got 16 ACMG points.

• PVS1: Loss of function variant, product does not undergo nonsense mediated mRNA decay. Variant located near the start codon (<100nt), not predicted to undergo nonsense mediated mRNA decay. There are 172 pathogenic variants in the truncated region.
• PP5: Variant 21-43072174-T-TG is Pathogenic according to our data. Variant chr21-43072174-T-TG is described in ClinVar as [Pathogenic]. Clinvar id is 371345.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
CBS	NM_000071.3	c.19dupC	p.Gln7ProfsTer30	frameshift_variant	Exon 3 of 17	ENST00000398165.8	NP_000062.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
CBS	ENST00000398165.8	c.19dupC	p.Gln7ProfsTer30	frameshift_variant	Exon 3 of 17	1	NM_000071.3	ENSP00000381231.4

Frequencies

GnomAD3 genomes Cov.: 0

GnomAD3 exomes AF: 0.00000411 AC: 1 AN: 243178 Hom.: 0 AF XY: 0.00000752 AC XY: 1 AN XY: 132972

Gnomad AFR exome AF: 0.00

Gnomad AMR exome AF: 0.00

Gnomad ASJ exome AF: 0.00

Gnomad EAS exome AF: 0.0000547

Gnomad SAS exome AF: 0.00

Gnomad FIN exome AF: 0.00

Gnomad NFE exome AF: 0.00

Gnomad OTH exome AF: 0.00

GnomAD4 exome Cov.: 0

GnomAD4 genome Cov.: 0

ClinVar

Significance: Pathogenic

Submissions summary: Pathogenic:9

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Classic homocystinuria Pathogenic:5

Mar 15, 2024

Baylor Genetics

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

- -

Sep 02, 2016

Counsyl

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

- -

Nov 05, 2021

Fulgent Genetics, Fulgent Genetics

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

- -

Nov 05, 2021

Genetics and Molecular Pathology, SA Pathology

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

- -

Oct 14, 2020

Natera, Inc.

Significance: Pathogenic

Review Status: no assertion criteria provided

Collection Method: clinical testing

- -

HYPERHOMOCYSTEINEMIA, THROMBOTIC, CBS-RELATED Pathogenic:1

Jan 04, 2024

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.Gln7Profs*30) in the CBS gene. It is expected to result in an absent or disrupted protein product. Loss-of-function variants in CBS are known to be pathogenic (PMID: 10338090, 12124992). The frequency data for this variant in the population databases is considered unreliable, as metrics indicate poor data quality at this position in the gnomAD database. This premature translational stop signal has been observed in individuals with CBS deficiency (PMID: 10338090, 12124992). ClinVar contains an entry for this variant (Variation ID: 371345). For these reasons, this variant has been classified as Pathogenic. -

not provided Pathogenic:1

May 31, 2022

GeneDx

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Frameshift variant predicted to result in protein truncation or nonsense mediated decay in a gene for which loss of function is a known mechanism of disease; Not observed at significant frequency in large population cohorts (gnomAD); This variant is associated with the following publications: (PMID: 10338090, 31589614, 25218699) -

CBS-related disorder Pathogenic:1

Jul 01, 2024

PreventionGenetics, part of Exact Sciences

Significance: Pathogenic

Review Status: no assertion criteria provided

Collection Method: clinical testing

The CBS c.19dupC variant is predicted to result in a frameshift and premature protein termination (p.Gln7Profs*30). This variant has been reported in both the homozygous and compound heterozygous states in multiple individuals with homocystinuria (referred to as 19insC in Kraus et al. 1999. PubMed ID: 10338090; Gaustadnes et al. 2002. PubMed ID: 12124992; Janosík et al. 2001. PubMed ID: 11359213; Alcaide et al. 2014. PubMed ID: 25218699). This variant is reported in 0.0055% of alleles in individuals of East Asian descent in gnomAD. Frameshift variants in CBS are expected to be pathogenic. This variant is interpreted as pathogenic. -

Homocystinuria Pathogenic:1

Apr 26, 2019

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

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Variant summary: CBS c.19dupC (p.Gln7ProfsX30) results in a premature termination codon, predicted to cause a truncation of the encoded protein or absence of the protein due to nonsense mediated decay, which are commonly known mechanisms for disease. The variant allele was found at a frequency of 4.1e-06 in 243178 control chromosomes (gnomAD). c.19dupC has been reported in the literature in multiple homozygote and compound heterozygote individuals affected with Homocystinuria (Alcaide_2015, Gaustadnes_2002). These data indicate that the variant is very likely to be associated with disease. A compound heterozygote affected individual was found to have <10% CBS activity (Alcaide_2015). Three ClinVar submisions from clinical diagnostic laboratories (evaluation after 2014) cite the variant as pathogenic. Based on the evidence outlined above, the variant was classified as pathogenic. -

Computational scores

Source: dbNSFP v4.3

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

Publications

LitVar

Other links and lift over

dbSNP: rs748695461; hg19: chr21-44492284;