rs757347527

chr21-43058855-G-A

Variant summary

Our verdict is Uncertain significance. Variant got 2 ACMG points: 4P and 2B. PM1 PM5 BP4_Moderate

The NM_000071.3(CBS):c.1337C>T(p.Ala446Val) variant causes a missense change involving the alteration of a non-conserved nucleotide. In-silico tool predicts a benign outcome for this variant. Variant has been reported in ClinVar as Uncertain significance (★). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. A446S) has been classified as Likely pathogenic.

• Frequency: Genomes: not found (cov: 0)
• Consequence: CBS NM_000071.3 missense
• Clinical Significance: Uncertain significance criteria provided, single submitter U:2
• Conservation: PhyloP100: 0.508

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 Uncertain_significance. Variant got 2 ACMG points.

• PM1: In a hotspot region, there are 3 aminoacids with missense pathogenic changes in the window of +-8 aminoacids around while only 1 benign, 7 uncertain in NM_000071.3
• PM5: Other missense variant is known to change same aminoacid residue: Variant chrnull-null-null-null is described in UniProt as null.
• BP4: Computational evidence support a benign effect (MetaRNN=0.12953463).

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
CBS	NM_000071.3	c.1337C>T	p.Ala446Val	missense_variant	14/17	ENST00000398165.8

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
CBS	ENST00000398165.8	c.1337C>T	p.Ala446Val	missense_variant	14/17	1	NM_000071.3	P1

Frequencies

GnomAD3 genomes Cov.: 0

GnomAD3 exomes AF: 0.0000179 AC: 3 AN: 167316 Hom.: 0 AF XY: 0.0000113 AC XY: 1 AN XY: 88762

Gnomad AFR exome AF: 0.00

Gnomad AMR exome AF: 0.00

Gnomad ASJ exome AF: 0.00

Gnomad EAS exome AF: 0.000161

Gnomad SAS exome AF: 0.00

Gnomad FIN exome AF: 0.0000673

Gnomad NFE exome AF: 0.00

Gnomad OTH exome AF: 0.00

GnomAD4 exome Cov.: 0

GnomAD4 genome Cov.: 0

ExAC AF: 0.00000852 AC: 1

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:2

Revision: criteria provided, single submitter

Submissions by phenotype

Classic homocystinuria Uncertain:1

Uncertain significance, no assertion criteria provided

clinical testing

Natera, Inc.

Oct 28, 2019

- -

HYPERHOMOCYSTEINEMIA, THROMBOTIC, CBS-RELATED Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Invitae

Jul 18, 2022

This sequence change replaces alanine, which is neutral and non-polar, with valine, which is neutral and non-polar, at codon 446 of the CBS protein (p.Ala446Val). 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 variant has not been reported in the literature in individuals affected with CBS-related conditions. ClinVar contains an entry for this variant (Variation ID: 568107). 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 valine amino acid residue is found in multiple mammalian species, which suggests that this missense change does not adversely affect protein function. Algorithms developed to predict the effect of sequence changes on RNA splicing suggest that this variant may create or strengthen a 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. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Benign	0.076
BayesDel_addAF	Uncertain	0.048	T
BayesDel_noAF	Benign	-0.17
Cadd	Uncertain	24
Dann	Uncertain	0.99
DEOGEN2	Uncertain	0.60	D;D;D;D
Eigen	Benign	-0.39
Eigen_PC	Benign	-0.38
FATHMM_MKL	Benign	0.17	N
M_CAP	Benign	0.024	T
MetaRNN	Benign	0.13	T;T;T;T
MetaSVM	Benign	-1.1	T
MutationAssessor	Benign	-0.14	N;N;N;N
MutationTaster	Benign	0.94	D;D;D;D;D;D;D;D;D;D;D;D
PrimateAI	Benign	0.37	T
PROVEAN	Benign	1.4	N;N;N;N
REVEL	Benign	0.19
Sift	Benign	0.32	T;T;T;T
Sift4G	Benign	0.32	T;T;T;T
Polyphen		0.0010	B;B;B;B
Vest4		0.33
MutPred		0.53		Gain of sheet (P = 0.0344);Gain of sheet (P = 0.0344);Gain of sheet (P = 0.0344);Gain of sheet (P = 0.0344);
MVP		0.64
MPC		0.35
ClinPred		0.086	T
GERP RS		1.2
Varity_R		0.21
gMVP		0.53

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.97		Details are displayed if max score is > 0.2
DS_DG_spliceai		0.97		Position offset: 2

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

Publications

LitVar

Other links and lift over

dbSNP: rs757347527; hg19: chr21-44478965;