# NM_205861.3(DHDDS):c.961C>T (p.Arg321Ter)

https://sugi.bio/variant/dhdds-p-arg321ter

## Summary

**DHDDS p.Arg321Ter (c.961C>T)** is classified **Uncertain significance** in DHDDS (ClinVar, Multiple submitters, 2 submitters; last evaluated 2022-08-31). Very rare (popmax 0.00223%, eas); Associated with retinitis pigmentosa 59.

**At a glance:** Uncertain significance · review: Multiple submitters · rsID rs754188985 · 2 submitters · 1 linked condition · very rare (popmax 0.00223%, eas)

## For patients & families {#patients}

This is a change in the DHDDS gene that is currently of uncertain significance — a definitive interpretation has not yet been established, submitted by 2 submitters, and is linked to retinitis pigmentosa 59.

*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.*

**Support & next steps:** [Condition overview & support (NIH GARD)](https://rarediseases.info.nih.gov/diseases/0015724/index) · [Find a genetic counselor (NSGC)](https://findageneticcounselor.nsgc.org/).

## Identity {#identity}

| Field | Value |
| --- | --- |
| Gene | [DHDDS](https://sugi.bio/atlas/gene/DHDDS/) |
| Protein change (HGVS p.) | p.Arg321Ter |
| Coding change (HGVS c.) | c.961C>T |
| MANE Select transcript | [NM_205861](https://www.ncbi.nlm.nih.gov/nuccore/NM_205861) |
| dbSNP | [rs754188985](https://www.ncbi.nlm.nih.gov/snp/rs754188985/) |
| Variant type | single nucleotide variant |
| Location | chr1:26469090-26469090 (GRCh38) |
| ClinVar | [VCV2169166](https://www.ncbi.nlm.nih.gov/clinvar/variation/2169166/) |

**All HGVS expressions:** `NC_000001.10:g.26795581C>T`, `NC_000001.11:g.26469090C>T`, `NG_029786.1:g.41809C>T`, `NM_001243564.2:c.859C>T`, `NM_001243565.2:c.844C>T`, `NM_001319959.2:c.682C>T`, `NM_024887.4:c.964C>T`, `NM_205861.3:c.961C>T`

## 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 and, for splice-region changes, SpliceAI (below), not from a missing predictor score.
- SpliceAI predicts **donor gain** (Δ 0.29) — a splice-altering prediction on an uncertain variant — a signal for review
- Conservation: phyloP 0.333, GERP -3.31, phastCons 0.989 — weakly conserved position
- Molecular consequence: **nonsense (stop-gain)** — a predicted loss-of-function variant. the gene is **loss-of-function-intolerant** (LOEUF 0.536, pLI 0.90959), supporting a loss-of-function disease mechanism. *Descriptive; not an applied PVS1 code.*
- Nonsense-mediated decay: the premature termination codon is **in the last exon (9 of 9)** — predicted to **escape NMD**, so the truncated protein is likely expressed. An input to PVS1, not an applied code.
- CADD: **PHRED 38.0**. 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 deltas (raw): acceptor loss **0.00**, donor loss **0.00**, acceptor gain **0.00**, donor gain **0.29**. Largest is donor gain.
- SpliceAI deltas (masked): acceptor loss **0.00**, donor loss **0.00**, acceptor gain **0.00**, donor gain **0.29**.
- Pangolin: Δ**0.76** (gain), gain 0.76 / loss 0.00. Agrees with SpliceAI. An independent predictor to SpliceAI — a different model trained on different data. *Descriptive; ClinGen's SVI calibration covers SpliceAI, not Pangolin, so no ACMG code is assigned.*
- Population frequency (gnomAD v4.1): grpmax **0.00223%** (eas) · FAF95 0.000292% · FAF99 0.000211% · 1/44,876 in the highest group · 9/1,460,818 alleles overall — very rare (popmax 0.00223%, eas).

| Ancestry group | Allele frequency | 1 in |
| --- | --- | --- |
| East Asian (grpmax) | 0.00223% | 44,876 |
| European (non-Finnish) | 0.000678% | 147,505 |

*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}

**DHDDS** population constraint: LOEUF 0.536, pLI 0.90959, missense-Z 1.7803. *Lower LOEUF and higher pLI indicate a gene that tolerates loss-of-function poorly; ClinGen dosage is the curated haploinsufficiency call.*

Curated gene–disease validity (ClinGen):

- **DHDDS-CDG** — Definitive (AR)

## Protein context {#protein}

Residue **321** lies in a UniProt-annotated variant site (in rp59; in a patient with congenital disorder of glycosylation); an α-helix.

AlphaFold model confidence (whole protein): pLDDT 95.01, 90% of residues very-high.

**9 experimental structure(s)** (PDB): [6W2L](https://www.rcsb.org/structure/6W2L), [6Z1N](https://www.rcsb.org/structure/6Z1N), [7PAX](https://www.rcsb.org/structure/7PAX), [7PAY](https://www.rcsb.org/structure/7PAY), [7PB0](https://www.rcsb.org/structure/7PB0), [7PB1](https://www.rcsb.org/structure/7PB1).

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

*Describes the biological roles of DHDDS (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:** DHDDS's established molecular role includes ditrans,polycis-polyprenyl diphosphate synthase [(2E,6E)-farnesyl diphosphate specific] activity. In Reactome, DHDDS is annotated in disease pathway(s) including **Defective DHDDS causes RP59**.

**Disease mechanism (Reactome):** DHDDS loss or alteration is curated in [Defective DHDDS causes RP59](https://reactome.org/content/detail/R-HSA-4755609).

### Pathways affected {#pathways}

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

| Pathway (Reactome) | Evidence |
| --- | --- |
| ⚕ [Defective DHDDS causes RP59](https://reactome.org/content/detail/R-HSA-4755609) | curated |
| [Synthesis of dolichyl-phosphate](https://reactome.org/content/detail/R-HSA-446199) | curated |

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

**Molecular function:** ditrans,polycis-polyprenyl diphosphate synthase [(2E,6E)-farnesyl diphosphate specific] activity.

**Biological process:** dolichyl diphosphate biosynthetic process, dolichyl monophosphate biosynthetic process.

## Clinical significance {#significance}

**Uncertain significance** — review status Multiple submitters *(criteria provided, multiple submitters, no conflicts)*, last evaluated 2022-08-31.

**Submitter consensus:** unanimous (2/2 Uncertain significance).

**Submission history:** 2 submissions (2021–2022); classifications have been stable.

### Submitter classifications {#submitters}

| Submitter | Classification | Review | Method | Date |
| --- | --- | --- | --- | --- |
| Labcorp Genetics (formerly Invitae), Labcorp | Uncertain significance | criteria provided, single submitter | clinical testing | 2022-08-31 |
| Blueprint Genetics | Uncertain significance | criteria provided, single submitter | clinical testing | 2021-04-02 |

## Associated conditions {#conditions}

[retinitis pigmentosa 59](https://sugi.bio/atlas/disease/retinitis-pigmentosa-59/).

**Reported phenotype names (ClinVar):** Retinitis pigmentosa 59, not provided, none provided.

## Similar variants {#similar}

Related DHDDS variant pages (same residue, condition, or type): [DHDDS p.Arg321Gln](/variant/dhdds-p-arg321gln), [DHDDS p.Arg321Pro](/variant/dhdds-p-arg321pro), [DHDDS c.658-2A>G](/variant/dhdds-c-658-minus-2a-g), [DHDDS p.Arg205Gln](/variant/dhdds-p-arg205gln), [DHDDS p.Arg211Gln](/variant/dhdds-p-arg211gln), [DHDDS p.Arg37Cys](/variant/dhdds-p-arg37cys), [DHDDS p.Arg37His](/variant/dhdds-p-arg37his), [DHDDS p.Arg37Ser](/variant/dhdds-p-arg37ser).

### 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 2169166). 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.*