# NM_000293.3(PHKB):c.2304_2305del (p.Arg768fs)

https://sugi.bio/variant/phkb-p-arg768fs

## Summary

**PHKB p.Arg768fs (c.2304_2305del)** is classified **Pathogenic/Likely pathogenic** in PHKB (ClinVar, Multiple submitters, 2 submitters; last evaluated 2025-11-20). Very rare (popmax 8.48e-05%, nfe); Associated with glycogen storage disease IXb.

**At a glance:** Pathogenic/Likely pathogenic · review: Multiple submitters · 2 submitters · 1 linked condition · very rare (popmax 8.48e-05%, nfe)

## For patients & families {#patients}

This is a change in the PHKB gene that is considered likely disease-causing, submitted by 2 submitters, and is linked to glycogen storage disease IXb.

*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 recessive |
| Age of onset (of this condition) | Childhood |
| Clinical trials | 2 registered for this condition — see ClinicalTrials.gov |
| Diagnostic panels | PHKB is a diagnostic-grade gene on 8 Genomics England panels |

**Commonly reported features of Glycogen storage disease due to liver and muscle phosphorylase kinase deficiency** (across patients with this condition; presentation varies — frequencies from Orphanet):

- Hypertriglyceridemia — Very frequent (99-80%)
- Hepatomegaly — Very frequent (99-80%)
- Postnatal growth retardation — Very frequent (99-80%)
- Abnormal enzyme/coenzyme activity — Very frequent (99-80%)
- Hepatic fibrosis — Frequent (79-30%)
- Elevated circulating hepatic transaminase concentration — Frequent (79-30%)
- Hypercholesterolemia — Frequent (79-30%)
- Fasting hypoglycemia — Frequent (79-30%)

**Support & next steps:** [Condition overview & support (NIH GARD)](https://rarediseases.info.nih.gov/diseases/0016711/index) · [Find a genetic counselor (NSGC)](https://findageneticcounselor.nsgc.org/).

## Identity {#identity}

| Field | Value |
| --- | --- |
| Gene | [PHKB](https://sugi.bio/atlas/gene/PHKB/) |
| Protein change (HGVS p.) | p.Arg768fs |
| Coding change (HGVS c.) | c.2304_2305del |
| MANE Select transcript | [NM_000293](https://www.ncbi.nlm.nih.gov/nuccore/NM_000293) |
| Variant type | Microsatellite |
| Location | chr16:47663697-47663698 (GRCh38) |
| ClinVar | [VCV3580747](https://www.ncbi.nlm.nih.gov/clinvar/variation/3580747/) |

**All HGVS expressions:** `NC_000016.10:g.47663698AG[2]`, `NC_000016.9:g.47697609AG[2]`, `NG_016598.1:g.207400AG[2]`, `NM_000293.3:c.2304_2305del`, `NM_001031835.3:c.2283_2284del`, `NM_001363837.1:c.2304_2305del`

## 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 1.53, GERP -2.4, phastCons 1 — weakly conserved position
- Molecular consequence: **frameshift** — a predicted loss-of-function variant. Gene population constraint: LOEUF 0.792, pLI 1.2179e-07. *Descriptive; not an applied PVS1 code.*
- Nonsense-mediated decay: the premature termination codon is **in exon 24 of 31**, so the transcript is predicted to undergo NMD.
- CADD: **PHRED 34.0**. 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: **not assessed** — the release is built from a substitutions-only source, so it holds no microsatellite variants. That is a property of the dataset, not of the variant, and is not evidence against a splicing effect.
- Population frequency (gnomAD v4.1): grpmax **8.48e-05%** (nfe) · 1/1,178,884 in the highest group · 3/1,612,664 alleles overall — very rare (popmax 8.48e-05%, nfe).

| Ancestry group | Allele frequency | 1 in |
| --- | --- | --- |
| Ashkenazi Jewish (not grpmax-eligible) | 0.00676% | 14,795 |
| European (non-Finnish) (grpmax) | 8.48e-05% | 1,178,884 |

Ashkenazi Jewish shows a higher raw frequency than the grpmax group. gnomAD excludes bottlenecked groups — Finnish, Ashkenazi Jewish, Amish and "Remaining individuals" — from grpmax, because founder effects make their frequencies unrepresentative for filtering. The table is sorted by frequency, so an excluded group can sit above the grpmax row.

*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}

**PHKB** population constraint: LOEUF 0.792, pLI 1.2179e-07, missense-Z 0.87257; ClinGen dosage — haploinsufficiency gene assoc. with recessive phenotype, 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):

- **glycogen storage disease IXb** — Definitive (AR)

## Protein context {#protein}

Residue **768** lies in the 'calmodulin-binding' region; an α-helix.

AlphaFold model confidence (whole protein): pLDDT 87.06, 64% of residues very-high.

**6 experimental structure(s)** (PDB): [8JFK](https://www.rcsb.org/structure/8JFK), [8JFL](https://www.rcsb.org/structure/8JFL), [8XYA](https://www.rcsb.org/structure/8XYA), [8Z5P](https://www.rcsb.org/structure/8Z5P), [8Z5Q](https://www.rcsb.org/structure/8Z5Q), [8Z5T](https://www.rcsb.org/structure/8Z5T).

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

*Describes the biological roles of PHKB (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.*


### Pathways affected {#pathways}

PHKB participates in **1 Reactome pathway** (⚕ = disease pathway):

| Pathway (Reactome) | Evidence |
| --- | --- |
| [Glycogen breakdown (glycogenolysis)](https://reactome.org/content/detail/R-HSA-70221) | electronic |

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

**Biological process:** glycogen catabolic process.

## Clinical significance {#significance}

**Pathogenic/Likely pathogenic** — review status Multiple submitters *(criteria provided, multiple submitters, no conflicts)*, last evaluated 2025-11-20.

**Submitter consensus:** conflicting (1 Likely pathogenic, 1 Pathogenic).

**Submission history:** 2 submissions (2024–2025); classifications have differed over time.

### Submitter classifications {#submitters}

| Submitter | Classification | Review | Method | Date |
| --- | --- | --- | --- | --- |
| Fulgent Genetics, Fulgent Genetics | Likely pathogenic | criteria provided, single submitter | clinical testing | 2024-06-01 |
| Labcorp Genetics (formerly Invitae), Labcorp | Pathogenic | criteria provided, single submitter | clinical testing | 2025-11-20 |

## Associated conditions {#conditions}

[glycogen storage disease IXb](https://sugi.bio/atlas/disease/glycogen-storage-disease-ixb/).

**Reported phenotype names (ClinVar):** Glycogen storage disease IXb, GLYCOGENOSIS OF LIVER AND MUSCLE, AUTOSOMAL RECESSIVE, GSD IXb, PHOSPHORYLASE KINASE DEFICIENCY OF LIVER AND MUSCLE, AUTOSOMAL RECESSIVE.

## Similar variants {#similar}

Related PHKB variant pages (same residue, condition, or type): [PHKB p.Glu820del](/variant/phkb-p-glu820del), [PHKB p.Gly124fs](/variant/phkb-p-gly124fs), [PHKB p.Ser289_His290insTer](/variant/phkb-p-ser289-his290inster), [PHKB c.1126+1GTAA[3]](/variant/phkb-c-1126-plus-1gtaa-3), [PHKB c.1126+30_1126+52del](/variant/phkb-c-1126-plus-30-1126-plus-52del), [PHKB c.1364-11_1364-9del](/variant/phkb-c-1364-minus-11-1364-minus-9del), [PHKB c.1881-13_1881-10del](/variant/phkb-c-1881-minus-13-1881-minus-10del), [PHKB c.2336+22_2336+24del](/variant/phkb-c-2336-plus-22-2336-plus-24del).

### Data sources & attribution {#sources}

ClinVar (NCBI — public domain, built 2026-10-14); 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 2026-10-14); 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 3580747). 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.*