# NM_000071.3(CBS):c.840G>A (p.Val280=)

https://sugi.bio/variant/cbs-p-val280

## Summary

**CBS p.Val280= (c.840G>A)** is classified **Likely benign** in CBS (ClinVar, Multiple submitters, 3 submitters; last evaluated 2025-12-30). Absent from gnomAD v4.1; Associated with familial thoracic aortic aneurysm and aortic dissection.

**At a glance:** Likely benign · review: Multiple submitters · rsID rs1060500682 · 3 submitters · 1 linked condition · absent from gnomAD v4.1

## For patients & families {#patients}

This is a change in the CBS gene that is classified as likely benign — not considered disease-causing, submitted by 3 submitters, and is linked to familial thoracic aortic aneurysm and aortic dissection.

*Reference information, not medical advice, and not a prediction for any individual. A genetic counselor or clinician can interpret what it means for you and your family.*

|  |  |
| --- | --- |
| Typical inheritance (of this condition) | Autosomal dominant |
| Age of onset (of this condition) | Adolescent, Adult, Childhood |
| Clinical trials | 2 registered for this condition — see ClinicalTrials.gov |
| Diagnostic panels | CBS is a diagnostic-grade gene on 11 Genomics England panels |

**Commonly reported features of Familial thoracic aortic aneurysm and aortic dissection** (across patients with this condition; presentation varies — frequencies from Orphanet):

- Cutis marmorata — Very frequent (99-80%)
- Abnormality of connective tissue — Very frequent (99-80%)
- Cystic medial necrosis of the aorta — Very frequent (99-80%)
- Abnormality iris morphology — Frequent (79-30%)
- Hypertension — Frequent (79-30%)
- Cardiomegaly — Frequent (79-30%)
- Aortic regurgitation — Frequent (79-30%)
- Coronaryartery atherosclerosis — Frequent (79-30%)

**Support & next steps:** [Condition overview & support (NIH GARD)](https://rarediseases.info.nih.gov/diseases/0002249/index) · [Find a genetic counselor (NSGC)](https://findageneticcounselor.nsgc.org/).

## Identity {#identity}

| Field | Value |
| --- | --- |
| Gene | [CBS](https://sugi.bio/atlas/gene/CBS/) |
| Protein change (HGVS p.) | p.Val280= |
| Coding change (HGVS c.) | c.840G>A |
| MANE Select transcript | [NM_000071](https://www.ncbi.nlm.nih.gov/nuccore/NM_000071) |
| dbSNP | [rs1060500682](https://www.ncbi.nlm.nih.gov/snp/rs1060500682/) |
| Variant type | single nucleotide variant |
| Location | chr21:43063067-43063067 (GRCh38) |
| ClinVar | [VCV405374](https://www.ncbi.nlm.nih.gov/clinvar/variation/405374/) |

**All HGVS expressions:** `LRG_777:g.17864G>A`, `LRG_777t1:c.840G>A`, `NC_000021.8:g.44483177C>T`, `NC_000021.9:g.43063067C>T`, `NG_008938.1:g.17864G>A`, `NM_000071.3:c.840G>A`, `NM_001178008.3:c.840G>A`, `NM_001178009.3:c.840G>A`, `NM_001320298.2:c.840G>A`, `NM_001321072.1:c.525G>A`

## Computational & population evidence {#evidence}

**Concordance:** Mixed / partial computational evidence (see below).

- **Missense predictors (AlphaMissense/REVEL/SaProt) do not apply** to this variant type — they score amino-acid substitutions only. For non-missense variants the computational signal comes from conservation (below), not from a missing predictor score.
- Conservation: phyloP 0.091, GERP 0.024, phastCons 0.921 — not a conserved position (phyloP < 0.1, ACGS BP7 cut)
- CADD: **PHRED 11.57**. No single ClinGen-calibrated threshold exists and the expert panels that use CADD disagree — GUCY2D/AIPL1 require ≥ 20.0 for an untranslated-region variant, ABCA4 ≥ 28.1 for a synonymous or indel variant, the Pulmonary Hypertension panel imports Pejaver 2022's missense-calibrated numbers, and the Antibody Deficiencies panel declines CADD entirely for PIK3CD. CADD v1.7 also incorporates Zoonomia phyloP, so it partly re-expresses the conservation above. *Descriptive; no threshold applied.*
- SpliceAI: **below the reporting threshold**. This position is scored for a different substitution (C>A, Δ0.43 acceptor gain), so this allele was evaluated and its deltas all fell under Δ0.2 — a prediction of no splicing effect for this allele, not a gap in our data. *No ACMG code assigned.*
- Population frequency: **absent from gnomAD v4.1** — a rarity signal (ACMG PM2-supporting), not evidence of pathogenicity on its own.

*Computational predictors are not independent (ClinGen Variant Classification guidance): AlphaMissense (Cheng et al. 2023) carries the ACMG weight for missense and conservation (phyloP/GERP/phastCons) for non-missense; REVEL (Pejaver-2022 calibrated strength bands) and SaProt (Su et al. 2023, structure-aware, ClinVar-independent protein language model, raw LLR) are shown as orthogonal agreement signals, not additive. For frequency, the gnomAD v4.1 grpmax filtering allele frequency (FAF95) is ClinGen's designated BA1/BS1 input (gnomAD v4 guidance v3.0, June 2025); BA1/BS1 thresholds are disease-specific, not a blanket 5%. Predictions, not a clinical determination.*

## Gene constraint & dosage {#gene-context}


Curated gene–disease validity (ClinGen):

- **classic homocystinuria** — Definitive (AR)

## Protein context {#protein}

Residue **280** lies in a β-strand.

AlphaFold model confidence (whole protein): pLDDT 90.15, 75% of residues very-high.

**28 experimental structure(s)** (PDB): [1JBQ](https://www.rcsb.org/structure/1JBQ), [1M54](https://www.rcsb.org/structure/1M54), [4COO](https://www.rcsb.org/structure/4COO), [4L0D](https://www.rcsb.org/structure/4L0D), [4L27](https://www.rcsb.org/structure/4L27), [4L28](https://www.rcsb.org/structure/4L28) — incl. mutant structure 4L27.

## What this gene does {#gene-function}

*Describes the biological roles of CBS (the gene this variant disrupts) — not effects measured for this specific variant. A damaging variant is expected to affect these functions and pathways; the degree depends on the variant.*

**How this variant is thought to act:** CBS's established molecular role includes cystathionine beta-synthase activity.


### Pathways affected {#pathways}

CBS participates in **2 Reactome pathways** (⚕ = disease pathway):

| Pathway (Reactome) | Evidence |
| --- | --- |
| [Cysteine formation from homocysteine](https://reactome.org/content/detail/R-HSA-1614603) | curated |
| [Metabolism of ingested SeMet, Sec, MeSec into H2Se](https://reactome.org/content/detail/R-HSA-2408508) | electronic |

### Molecular function & processes (GO — experimentally supported) {#go}

**Molecular function:** cystathionine beta-synthase activity, oxygen binding, enzyme binding, heme binding, pyridoxal phosphate binding, ubiquitin protein ligase binding.

**Biological process:** L-serine metabolic process, L-serine catabolic process, L-cysteine biosynthetic process, L-cysteine catabolic process, DNA protection, L-homocysteine catabolic process.

## Clinical significance {#significance}

**Likely benign** — review status Multiple submitters *(criteria provided, multiple submitters, no conflicts)*, last evaluated 2025-12-30.

**Submitter consensus:** unanimous (3/3 Likely benign).

**Submission history:** 3 submissions (2016–2025); classifications have been stable.

### Submitter classifications {#submitters}

| Submitter | Classification | Review | Method | Date |
| --- | --- | --- | --- | --- |
| Ambry Genetics | Likely benign | criteria provided, single submitter | clinical testing | 2016-02-17 |
| Labcorp Genetics (formerly Invitae), Labcorp | Likely benign | criteria provided, single submitter | clinical testing | 2025-12-30 |
| Blueprint Genetics | Likely benign | criteria provided, single submitter | clinical testing | 2021-06-07 |

## Associated conditions {#conditions}

[familial thoracic aortic aneurysm and aortic dissection](https://sugi.bio/atlas/disease/familial-thoracic-aortic-aneurysm-and-aortic-dissection/).

**Reported phenotype names (ClinVar):** Familial thoracic aortic aneurysm and aortic dissection, HYPERHOMOCYSTEINEMIA, THROMBOTIC, CBS-RELATED, not specified, AllHighlyPenetrant, Thoracic aortic aneurysms and dissections.

## Similar variants {#similar}

Related CBS variant pages (same residue, condition, or type): [CBS p.Val280Met](/variant/cbs-p-val280met), [CBS c.1224-2A>C](/variant/cbs-c-1224-minus-2a-c), [CBS c.954+1G>A](/variant/cbs-c-954-plus-1g-a), [CBS p.Ala114Val](/variant/cbs-p-ala114val), [CBS p.Ala288Thr](/variant/cbs-p-ala288thr), [CBS p.Ala331Glu](/variant/cbs-p-ala331glu), [CBS p.Arg121His](/variant/cbs-p-arg121his), [CBS p.Arg125Gln](/variant/cbs-p-arg125gln).

### Data sources & attribution {#sources}

ClinVar (NCBI — public domain, built 2026-10-11); gnomAD v4.1 (Broad Institute, built 2026-10-06); AlphaMissense (Cheng et al. 2023, © Google DeepMind — CC BY 4.0, built 2026-01-27); REVEL (Ioannidis et al. 2016 — ODbL, built 2026-07-13); SaProt (Su et al. 2023 — MIT, built 2026-07-14); SpliceAI (Illumina — free for non-commercial use, built 2026-10-13); CADD (Rentzsch et al. 2019, University of Washington — free for non-commercial use, built 2026-10-10); Conservation (phyloP/phastCons/GERP) (UCSC hg38 470-way mammal (Hiller Lab) + Ensembl Compara, built 2026-07-12); gnomAD Non-coding Constraint (Gnocchi) (Chen et al. 2024, Broad Institute — CC0, built 2026-10-11); gnomAD Regional Missense Constraint (Broad Institute — CC0, built 2026-10-13); Pangolin (Zeng & Li 2022 — CC BY 4.0, built 2026-10-11); Repeat regions (UCSC — RepeatMasker, TRF, segmental duplications, built 2026-10-11); ClinGen (ClinGen, built 2026-09-22); UniProt (CC BY 4.0); Reactome / GO (CC BY 4.0, built 2026-09-23); MaveDB (per-record license, built 2026-10-11); CIViC (CC0, built 2026-09-22); Orphanet (Orphanet, built 2026-06-12)

*Primary record: NCBI ClinVar (variation 405374). Classifications reflect these databases as of the page's build date and may change. Free reference use — not medical advice; consult the primary submitters and a clinician.*