# NM_000038.6(APC):c.163_164insG (p.Ile55fs)

https://sugi.bio/variant/apc-p-ile55fs

## Summary

**APC p.Ile55fs (c.163_164insG)** is classified **Pathogenic** in APC (ClinVar, Multiple submitters, 3 submitters; last evaluated 2025-10-02). No gnomAD frequency available for this variant; Associated with hereditary neoplastic syndrome.

**At a glance:** Pathogenic · review: Multiple submitters · rsID rs1554069524 · 3 submitters · 2 linked conditions · no gnomAD frequency available for this variant

## For patients & families {#patients}

This is a change in the APC gene that is considered disease-causing, submitted by 3 submitters, and is linked to hereditary neoplastic syndrome.

*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.*

|  |  |
| --- | --- |
| Clinical trials | 31 registered for this condition — see ClinicalTrials.gov |

**Support & next steps:** [Condition overview & support (NIH GARD)](https://rarediseases.info.nih.gov/diseases/0019921/index) · [Find a genetic counselor (NSGC)](https://findageneticcounselor.nsgc.org/).

## Identity {#identity}

| Field | Value |
| --- | --- |
| Gene | [APC](https://sugi.bio/atlas/gene/APC/) |
| Protein change (HGVS p.) | p.Ile55fs |
| Coding change (HGVS c.) | c.163_164insG |
| MANE Select transcript | [NM_000038](https://www.ncbi.nlm.nih.gov/nuccore/NM_000038) |
| dbSNP | [rs1554069524](https://www.ncbi.nlm.nih.gov/snp/rs1554069524/) |
| Variant type | Insertion |
| Location | chr5:112766353-112766354 (GRCh38) |
| ClinVar | [VCV486772](https://www.ncbi.nlm.nih.gov/clinvar/variation/486772/) |

**All HGVS expressions:** `LRG_130:g.78833_78834insG`, `NC_000005.10:g.112766353_112766354insG`, `NC_000005.9:g.112102050_112102051insG`, `NG_008481.4:g.78833_78834insG`, `NM_000038.6:c.163_164insG`, `NM_001127510.3:c.163_164insG`, `NM_001127511.3:c.193_194insG`, `NM_001354895.2:c.163_164insG`, `NM_001354896.2:c.163_164insG`, `NM_001354897.2:c.193_194insG`, `NM_001354898.2:c.88_89insG`, `NM_001354899.2:c.163_164insG`, `NM_001354900.2:c.-15_-14insG`, `NM_001354901.2:c.-15_-14insG`, `NM_001354902.2:c.193_194insG`, `NM_001354903.2:c.163_164insG`, `NM_001354904.2:c.88_89insG`, `NM_001354905.2:c.-15_-14insG`, `NM_001354906.2:c.-873_-872insG`

## Computational & population evidence {#evidence}

**Concordance:** 1 independent predictor **concordant** with the ClinVar classification.

- **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 11.119, phastCons 1 — highly conserved position (PP3-type support)
- Molecular consequence: **frameshift** — a predicted loss-of-function variant. ClinGen curates **sufficient evidence for haploinsufficiency** in this gene (constraint LOEUF 0.321, pLI 1), supporting a loss-of-function disease mechanism. *Descriptive; not an applied PVS1 code.*
- Nonsense-mediated decay: the premature termination codon is **in exon 3 of 16**, so the transcript is predicted to undergo NMD.
- SpliceAI: **not assessed** — the release is built from a substitutions-only source, so it holds no insertion variants. That is a property of the dataset, not of the variant, and is not evidence against a splicing effect.
- Population frequency: **no gnomAD frequency available for this variant** — rarity (ACMG PM2) and BA1/BS1 cannot be assessed for this variant.

*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}

**APC** population constraint: LOEUF 0.321, pLI 1, missense-Z 0.7981; ClinGen dosage — haploinsufficiency 3/3, triplosensitivity 0/3. *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):

- **gastric adenocarcinoma and proximal polyposis of the stomach** — Definitive (AD)
- **classic or attenuated familial adenomatous polyposis** — Definitive (AD)

## Protein context {#protein}


**31 experimental structure(s)** (PDB): [1DEB](https://www.rcsb.org/structure/1DEB), [1EMU](https://www.rcsb.org/structure/1EMU), [1JPP](https://www.rcsb.org/structure/1JPP), [1M5I](https://www.rcsb.org/structure/1M5I), [1T08](https://www.rcsb.org/structure/1T08), [1TH1](https://www.rcsb.org/structure/1TH1).

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

*Describes the biological roles of APC (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:** APC's established molecular role includes beta-catenin binding. In Reactome, APC is annotated in disease pathway(s) including **APC truncation mutants are not K63 polyubiquitinated**, **APC truncation mutants have impaired AXIN binding**.

**Disease mechanism (Reactome):** APC loss or alteration is curated in [APC truncation mutants are not K63 polyubiquitinated](https://reactome.org/content/detail/R-HSA-5467333), [APC truncation mutants have impaired AXIN binding](https://reactome.org/content/detail/R-HSA-5467337), [AXIN missense mutants destabilize the destruction complex](https://reactome.org/content/detail/R-HSA-5467340).

### Pathways affected {#pathways}

APC participates in **15 Reactome pathways** (⚕ = disease pathway):

| Pathway (Reactome) | Evidence |
| --- | --- |
| ⚕ [APC truncation mutants are not K63 polyubiquitinated](https://reactome.org/content/detail/R-HSA-5467333) | curated |
| ⚕ [APC truncation mutants have impaired AXIN binding](https://reactome.org/content/detail/R-HSA-5467337) | curated |
| ⚕ [AXIN missense mutants destabilize the destruction complex](https://reactome.org/content/detail/R-HSA-5467340) | curated |
| ⚕ [CTNNB1 S33 mutants aren't phosphorylated](https://reactome.org/content/detail/R-HSA-5358747) | curated |
| ⚕ [CTNNB1 S37 mutants aren't phosphorylated](https://reactome.org/content/detail/R-HSA-5358749) | curated |
| ⚕ [CTNNB1 S45 mutants aren't phosphorylated](https://reactome.org/content/detail/R-HSA-5358751) | curated |
| ⚕ [CTNNB1 T41 mutants aren't phosphorylated](https://reactome.org/content/detail/R-HSA-5358752) | curated |
| ⚕ [Signaling by GSK3beta mutants](https://reactome.org/content/detail/R-HSA-5339716) | curated |
| ⚕ [Truncations of AMER1 destabilize the destruction complex](https://reactome.org/content/detail/R-HSA-5467348) | curated |
| [Apoptotic cleavage of cellular proteins](https://reactome.org/content/detail/R-HSA-111465) | curated |
| [Beta-catenin phosphorylation cascade](https://reactome.org/content/detail/R-HSA-196299) | curated |
| [Deactivation of the beta-catenin transactivating complex](https://reactome.org/content/detail/R-HSA-3769402) | curated |
| [Degradation of beta-catenin by the destruction complex](https://reactome.org/content/detail/R-HSA-195253) | curated |
| [Ovarian tumor domain proteases](https://reactome.org/content/detail/R-HSA-5689896) | curated |
| [Disassembly of the destruction complex and recruitment of AXIN to the membrane](https://reactome.org/content/detail/R-HSA-4641262) | electronic |

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

**Molecular function:** beta-catenin binding, microtubule binding, protein kinase regulator activity, protein kinase binding, ubiquitin protein ligase binding, gamma-catenin binding.

**Biological process:** mitotic cytokinesis, DNA damage response, negative regulation of microtubule depolymerization, mitotic spindle assembly checkpoint signaling, negative regulation of cell population proliferation, insulin receptor signaling pathway.

## Clinical significance {#significance}

**Pathogenic** — review status Multiple submitters *(criteria provided, multiple submitters, no conflicts)*, last evaluated 2025-10-02.

**Submitter consensus:** unanimous (3/3 Pathogenic).

**Submission history:** 3 submissions (2019–2025); classifications have been stable.

### Submitter classifications {#submitters}

| Submitter | Classification | Review | Method | Date |
| --- | --- | --- | --- | --- |
| Myriad Genetics, Inc. | Pathogenic | criteria provided, single submitter | clinical testing | 2023-04-24 |
| Ambry Genetics | Pathogenic | criteria provided, single submitter | clinical testing | 2025-10-02 |
| Labcorp Genetics (formerly Invitae), Labcorp | Pathogenic | criteria provided, single submitter | clinical testing | 2019-03-28 |

## Associated conditions {#conditions}

[hereditary neoplastic syndrome](https://sugi.bio/atlas/disease/hereditary-neoplastic-syndrome/), [familial adenomatous polyposis 1](https://sugi.bio/atlas/disease/familial-adenomatous-polyposis-1/).

**Reported phenotype names (ClinVar):** Hereditary cancer-predisposing syndrome, Familial adenomatous polyposis 1, Tumor predisposition, Hereditary Cancer Syndrome, Hereditary neoplastic syndrome, Neoplastic Syndromes, Hereditary, FAMILIAL ADENOMATOUS POLYPOSIS 1, ATTENUATED, POLYPOSIS, ADENOMATOUS INTESTINAL.

## Similar variants {#similar}

Related APC variant pages (same residue, condition, or type): [APC p.Gln55Lys](/variant/apc-p-gln55lys), [APC p.Ile55Val](/variant/apc-p-ile55val), [APC p.Gln55Arg](/variant/apc-p-gln55arg), [APC p.Gln55His](/variant/apc-p-gln55his), [APC p.Gln55Ter](/variant/apc-p-gln55ter), [APC p.Ile55Phe](/variant/apc-p-ile55phe), [APC p.Ile55Thr](/variant/apc-p-ile55thr), [APC p.Ile55=](/variant/apc-p-ile55).

### Data sources & attribution {#sources}

ClinVar (NCBI — public domain, built 2026-10-14); gnomAD v4.1 (Broad Institute, built 2026-10-14); 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 2026-10-14); 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 486772). 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.*