21-43071985-G-A

Position:

• chr21-43071985-G-A

Variant summary

Our verdict is Likely benign. Variant got -5 ACMG points: 0P and 5B. BP4_Strong BP6

The NM_000071.3(CBS):​c.209C>T​(p.Pro70Leu) variant causes a missense, splice region change involving the alteration of a non-conserved nucleotide. In-silico tool predicts a benign outcome for this variant. 17/23 in silico tools predict a benign outcome for this variant. 3/3 splice prediction tools predict no significant impact on normal splicing. Variant has been reported in ClinVar as Conflicting classifications of pathogenicity (no stars). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. P70R) has been classified as Uncertain significance.

• Frequency: Genomes: not found (cov: 0)
• Consequence: CBS NM_000071.3 missense, splice_region
• Scores: Splicing: ADA: 0.0003986
• Clinical Significance: Conflicting classifications of pathogenicity criteria provided, conflicting classifications U:2 B:1
• Conservation: PhyloP100: -0.529

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 Likely_benign. Variant got -5 ACMG points.

• BP4: Computational evidence support a benign effect (MetaRNN=0.02443254).
• BP6: Variant 21-43071985-G-A is Benign according to our data. Variant chr21-43071985-G-A is described in ClinVar as [Conflicting_classifications_of_pathogenicity]. Clinvar id is 212841.We mark this variant Likely_benign, oryginal submissions are: {Likely_benign=1, Uncertain_significance=2}.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
CBS	NM_000071.3	c.209C>T	p.Pro70Leu	missense_variant, splice_region_variant	3/17	ENST00000398165.8

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
CBS	ENST00000398165.8	c.209C>T	p.Pro70Leu	missense_variant, splice_region_variant	3/17	1	NM_000071.3	P1

Frequencies

GnomAD3 genomes Cov.: 0

GnomAD3 exomes AF: 0.0000440 AC: 11 AN: 249920 Hom.: 0 AF XY: 0.0000296 AC XY: 4 AN XY: 135238

Gnomad AFR exome AF: 0.000369

Gnomad AMR exome AF: 0.00

Gnomad ASJ exome AF: 0.00

Gnomad EAS exome AF: 0.000163

Gnomad SAS exome AF: 0.0000327

Gnomad FIN exome AF: 0.00

Gnomad NFE exome AF: 0.00000891

Gnomad OTH exome AF: 0.00

GnomAD4 exome Cov.: 0

GnomAD4 genome Cov.: 0

Alfa AF: 0.0000497 Hom.: 0

ExAC AF: 0.0000576 AC: 7

Asia WGS AF: 0.000577 AC: 2 AN: 3478

EpiCase AF: 0.0000545

EpiControl AF: 0.00

ClinVar

Significance: Conflicting classifications of pathogenicity

Submissions summary: Uncertain:2 Benign:1

Revision: criteria provided, conflicting classifications

Submissions by phenotype

Familial thoracic aortic aneurysm and aortic dissection Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Ambry Genetics

Mar 10, 2020

The p.P70L variant (also known as c.209C>T), located in coding exon 1 of the CBS gene, results from a C to T substitution at nucleotide position 209. The amino acid change results in proline to leucine at codon 70, an amino acid with similar properties. This variant resulted in intermediate growth in one yeast growth assay (Mayfield JA et al. Genetics, 2012 Apr;190:1309-23). This amino acid position is poorly conserved in available vertebrate species. In addition, this alteration is predicted to be tolerated by in silico analysis. Since supporting evidence is limited at this time, the clinical significance of this alteration remains unclear. -

HYPERHOMOCYSTEINEMIA, THROMBOTIC, CBS-RELATED Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

Aug 16, 2022

This sequence change replaces proline, which is neutral and non-polar, with leucine, which is neutral and non-polar, at codon 70 of the CBS protein (p.Pro70Leu). This variant is present in population databases (rs2229413, gnomAD 0.03%). This variant has not been reported in the literature in individuals affected with CBS-related conditions. ClinVar contains an entry for this variant (Variation ID: 212841). Algorithms developed to predict the effect of missense changes on protein structure and function output the following: SIFT: "Tolerated"; PolyPhen-2: "Benign"; Align-GVGD: "Class C0". The leucine amino acid residue is found in multiple mammalian species, which suggests that this missense change does not adversely affect protein function. Experimental studies have shown that this missense change affects CBS function (PMID: 22267502). 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 available evidence is currently insufficient to determine the role of this variant in disease. Therefore, it has been classified as a Variant of Uncertain Significance. -

not specified Benign:1

Likely benign, criteria provided, single submitter

clinical testing

GeneDx

Dec 17, 2014

This variant is considered likely benign or benign based on one or more of the following criteria: it is a conservative change, it occurs at a poorly conserved position in the protein, it is predicted to be benign by multiple in silico algorithms, and/or has population frequency not consistent with disease. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Benign	0.055
BayesDel_addAF	Benign	-0.23	T
BayesDel_noAF	Benign	-0.26
CADD	Benign	0.19
DANN	Benign	0.39
DEOGEN2	Benign	0.35	T;T;T;T;.
Eigen	Benign	-1.9
Eigen_PC	Benign	-1.9
FATHMM_MKL	Benign	0.025	N
LIST_S2	Benign	0.64	.;.;.;T;T
M_CAP	Benign	0.080	D
MetaRNN	Benign	0.024	T;T;T;T;T
MetaSVM	Benign	-0.31	T
MutationAssessor	Benign	-1.2	N;N;N;N;.
MutationTaster	Benign	1.0	N;N;N;N;N;N;N;N;N;N
PrimateAI	Benign	0.26	T
PROVEAN	Benign	-0.22	N;N;N;N;N
REVEL	Uncertain	0.32
Sift	Benign	0.66	T;T;T;T;T
Sift4G	Benign	0.70	T;T;T;T;T
Polyphen		0.0	B;B;B;B;.
Vest4		0.092
MVP		0.19
MPC		0.35
ClinPred		0.0036	T
GERP RS		-11
Varity_R		0.21
gMVP		0.21

Splicing

Name	Calibrated prediction	Score	Prediction
dbscSNV1_ADA	Benign	0.00040
dbscSNV1_RF	Benign	0.22
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

Publications

LitVar

Other links and lift over

dbSNP: rs2229413; hg19: chr21-44492095; COSMIC: COSV61444000; COSMIC: COSV61444000;