ALG8-related Autosomal Dominant Polycystic Kidney And/Or Liver Disease — Comprehensive Research Report

Disease: ALG8-related Autosomal Dominant Polycystic Kidney And/Or Liver Disease MONDO ID: MONDO:1060122 Category: Mendelian (autosomal dominant, low-penetrance) Causal gene: ALG8 (α-1,3-glucosyltransferase; HGNC:23159; chr 11q14.1; OMIM gene 608103)

Summary

ALG8-related polycystic kidney and/or liver disease is a rare, adult-onset, mild autosomal dominant cystic disorder caused by heterozygous loss-of-function (LoF) variants in ALG8, a gene encoding an endoplasmic reticulum (ER) α-1,3-glucosyltransferase (EC 2.4.1.265) integral to dolichol-linked N-glycosylation and protein biogenesis. ALG8 was identified as a minor polycystic liver disease (PCLD/ADPLD) gene by whole-exome sequencing in a discovery cohort of 102 PRKCSH/SEC63-negative patients, where cell-model inactivation demonstrated that ALG8 loss impairs the maturation and trafficking of polycystin-1 (PC1), the central determinant of cyst formation [PMID: 28375157]. The phenotype is predominantly polycystic liver disease with limited bilateral kidney cysts that, importantly, rarely progress to chronic kidney disease or kidney failure.

A defining feature of this disease is its low penetrance and allelic dichotomy. Monoallelic (heterozygous) LoF variants cause the adult-onset mild cystic phenotype, whereas biallelic ALG8 variants cause a completely distinct, severe multisystem pediatric disorder — the congenital disorder of glycosylation ALG8-CDG (CDG-Ih; OMIM #608104) — characterized by hypotonia, protein-losing enteropathy, hepatic involvement, and failure to thrive. ALG8 is not strongly constrained against heterozygous LoF (gnomAD pLI ≈ 0, LOEUF ≈ 0.87), and population carrier frequencies of predicted-pathogenic ADPLD-gene variants (~1:91 to 1:500) dramatically exceed the clinical prevalence of ADPLD (~9.5 per 100,000), confirming that most carriers never develop clinically significant disease.

Clinically, the disease is managed symptomatically. Somatostatin analogues (octreotide, lanreotide, pasireotide) reduce liver and kidney volume, with the greatest benefit in young women (≤48 years) and those with elevated baseline alkaline phosphatase; interventional and surgical options (aspiration-sclerotherapy, fenestration, resection, transplantation) are reserved for severe symptomatic polycystic liver disease. The ALG8 ClinVar landscape is dominated by variants of uncertain significance (VUS), which complicates clinical interpretation. This report synthesizes seven confirmed findings across the full disease-characteristics template.

Key Findings

Finding 1 — ALG8 is a minor causal gene for ADPLD/ADPKD acting via defective polycystin-1 maturation in the ER

Dominantly inherited isolated polycystic liver disease (PCLD) produces liver cysts radiologically and pathologically identical to those of ADPKD but without clinically relevant kidney cysts. Because the two most common PCLD genes (PRKCSH and SEC63) explain fewer than 40% of index cases, Besse et al. (2017) performed whole-exome sequencing in a discovery cohort of 102 unrelated patients who were negative for PRKCSH/SEC63, identifying heterozygous LoF variants in three additional genes: ALG8, GANAB, and *SEC61B* [PMID: 28375157].

"we have used whole exome sequencing in a discovery cohort of 102 unrelated patients who were excluded for mutations in the 2 most common PCLD genes, PRKCSH and SEC63, to identify heterozygous loss-of-function mutations in 3 additional genes, ALG8, GANAB, and SEC61B" [PMID: 28375157]

Critically, all these genes encode proteins integral to the ER protein-biogenesis pathway. Cell-line inactivation established the mechanistic link to cystogenesis:

"We inactivated these candidate genes in cell line models to show that loss of function of each results in defective maturation and trafficking of polycystin-1, the central determinant of cyst pathogenesis" [PMID: 28375157]

ALG8 thus joins the N-glycosylation / ER quality-control module that governs PC1 biogenesis. Each gene product demonstrated distinct effects on PC1 biogenesis despite acting in a common pathway. Evidence type: human clinical (WES) + in vitro cell model.

Finding 2 — Monoallelic ALG8 variants cause a mild cystic phenotype, predominantly polycystic liver with limited kidney involvement

Two large independent cohorts quantify the mild phenotype. Jawaid et al. (2025) screened >3,900 families with cystic kidney and/or liver disease and identified 51 ALG8 families (1.3%), a frequency ~10× greater than non-polycystic controls, establishing ALG8 enrichment in the polycystic population [PMID: 39899384].

Apple et al. (2023) used the Geisinger DiscovEHR electronic-health-record cohort (174,172 patients; 236 ALG8 protein-truncating-variant [PTV] carriers) with blinded imaging review. ALG8 PTV carriers had increased risk of any kidney/liver cyst (OR 2.42, 95% CI 1.53–3.85), cystic kidney disease (OR 3.03, 95% CI 1.26–7.31), and nephrolithiasis (OR 1.89) [PMID: 36574950].

"patients with these variants were significantly at increased risk of having any kidney/liver cyst diagnosis (Odds Ratio 2.42, 95% confidence interval: 1.53-3.85), cystic kidney disease (3.03, 1.26-7.31), and nephrolithiasis (1.89, 1.96-2.97)" [PMID: 36574950]

Blinded imaging confirmed a measurable cyst burden:

"ALG8 PTV heterozygotes were significantly more likely to have cystic kidney disease, defined as four or more kidney cysts (57.7% vs. 7.7%), or bilateral kidney cysts (69.2% vs. 15.4%), but not one or more liver cyst (11.5% vs. 7.7%)" [PMID: 36574950]

Crucially, the disease does not progress to end-stage renal disease:

"ALG8 PTVs were not associated with chronic kidney disease or kidney failure" [PMID: 36574950]

This establishes the hallmark of the disorder: bilateral kidney cysts and nephrolithiasis risk, but preserved kidney function. Evidence type: human clinical (EHR + blinded imaging; multicenter family screening).

Finding 3 — Allelic dichotomy: monoallelic LoF causes adult polycystic disease; biallelic variants cause severe multisystem ALG8-CDG

ALG8 exhibits a striking genotype–phenotype dichotomy. Albokhari et al. (2022) report 26 individuals with biallelic ALG8-CDG (CDG-Ih, OMIM #608104) presenting with hypotonia, protein-losing enteropathy, hepatic involvement, and failure to thrive; the phenotype was expanded to include intellectual disability, autism, and ocular/cardiac/skeletal anomalies [PMID: 35716054].

"Individuals with ALG8-CDG commonly present with hypotonia, protein-losing enteropathy, and hepatic involvement" [PMID: 35716054]

Huang et al. (2025) reported the first prenatal ALG8-CDG cases with hydrops fetalis, cataracts, echogenic kidneys, and growth restriction, with a compound heterozygous genotype [PMID: 39792033].

"A novel compound heterozygous mutation comprising the missense variant c.754T>C (p.Ser252Pro) and a partial exonic deletion (deletion of exons 1-2) in the ALG8 gene" [PMID: 39792033]

By contrast, monoallelic ALG8 PTVs cause adult-onset mild polycystic kidney/liver disease (Findings 1–2). This dichotomy is mechanistically coherent: partial glycosylation deficiency (one functional allele) selectively impairs the biogenesis of the large, glycosylation-dependent PC1 protein, producing a tissue-restricted cystic phenotype, whereas near-complete deficiency (biallelic) disrupts N-glycosylation globally, producing multisystem CDG. Evidence type: human clinical (case series + prenatal case report). The disease described by this template (MONDO:1060122) refers specifically to the monoallelic cystic phenotype.

Finding 4 — Somatostatin analogues reduce liver/kidney volume, with best response in young women

Pooled individual-patient analyses (Gevers et al. 2013; n up to 153) demonstrated that somatostatin analogues (octreotide, lanreotide) reduce liver volume by ~4.5–5.9% versus placebo (overall difference 5.3%, P<.001), with the greatest benefit in young women [PMID: 23665274].

"Women 48 years old or younger had a greater response to therapy (a reduction in liver volume of 8.0% compared with placebo; P < .001) than older women" [PMID: 23665274]

Elevated baseline alkaline phosphatase predicts response [PMID: 26481454]:

"elevated baseline alkaline phosphatase was associated with increased liver volume reduction during therapy" [PMID: 26481454]

A network meta-analysis incorporating FDA Adverse Event Reporting System data confirmed TKV/TLV reductions with octreotide, lanreotide, and pasireotide, with differing onset times, and identified cholelithiasis as the most common biliary adverse event (younger patients and pasireotide users at higher risk) [PMID: 42476150]. mTOR inhibitors (everolimus) added to octreotide have not shown benefit over octreotide monotherapy (ELATE trial; no significant difference, P=0.73) [PMID: 26688394, PMID: 22104015]. Evidence type: human clinical (RCTs, pooled IPD, network meta-analysis).

Finding 5 — ADPLD is rare clinically (~9.5/100,000) but LoF variants in ADPLD genes are far more common at the population level, indicating low penetrance

Suwabe et al. (2020, Olmsted County) established the clinical rarity of ADPLD [PMID: 33145487]:

"The incidence rate and point prevalence of combined definite and likely ADPLD were 1.01 per 100,000 person-years and 9.5 per 100,000 population, respectively" [PMID: 33145487]

Yet population sequencing reveals a far higher molecular carrier frequency. Lanktree et al. (2018), using gnomAD/BRAVO, estimated [PMID: 30135240]:

"Truncating mutations in ADPLD genes and genes of potential relevance as cyst modifiers were found in 20.2 cases and 103.9 cases per 10,000 sequenced" [PMID: 30135240]

This ~1:495 truncating-mutation frequency vastly exceeds the ~9.5/100,000 clinical prevalence. A subsequent gnomAD-based study (Varughese et al. 2026) found predicted-pathogenic ADPLD-gene variants in ~1:91 (gnomAD v2.1.1) to ~1:130 (ClinVar-assessed v4.1) people, with LRP5 and ALG8 — both associated with milder phenotypes — the most commonly affected genes; frequencies were higher in admixed American (1:91), Finnish (1:110), and African/African American (1:43) populations than European (1:187) [PMID: 42804492]. The discordance quantifies incomplete penetrance and variable expressivity. Evidence type: human clinical epidemiology + population genomics.

Finding 6 — ALG8 is not strongly constrained against heterozygous LoF, consistent with its low-penetrance dominant phenotype

gnomAD constraint metrics (queried via gnomAD GraphQL API, GRCh38) for ALG8 (ENSG00000159063; chr11:78,095,244–78,139,660):

A pLI ≈ 0 and LOEUF ≈ 0.87 indicate that ALG8 tolerates heterozygous LoF relatively well, with 48 LoF variants observed in gnomAD. This genomic constraint profile is fully consistent with a low-penetrance dominant phenotype in which many heterozygous LoF carriers remain clinically unaffected (Finding 5). Evidence type: computational / population genomics.

Finding 7 — The ALG8 ClinVar landscape is dominated by variants of uncertain significance

ClinVar (queried via NCBI E-utilities) for ALG8[gene] returned ~510 total records:

VUS (380) substantially outnumber P/LP classifications (170). These counts aggregate both the biallelic ALG8-CDG and the monoallelic cystic phenotypes, because ClinVar does not cleanly partition records by condition. The VUS predominance complicates clinical interpretation and reinforces the need for functional validation and family segregation data. Evidence type: variant database curation.

Mechanistic Model / Interpretation

Ordered causal chain (monoallelic cystic phenotype)

1. Heterozygous loss-of-function variant in ALG8 (one allele inactivated)
│  leads to
▼
2. Reduced ER α-1,3-glucosyltransferase activity (EC 2.4.1.265),
   adding the third glucose to the dolichol-linked precursor
   Glc3Man9GlcNAc2-PP-dolichol  [inferred for monoallelic; demonstrated for biallelic]
│  results in
▼
3. Partial deficiency of N-linked glycosylation / ER protein biogenesis
│  results in (tissue-selective, dose-sensitive)
▼
4. Defective maturation and trafficking of polycystin-1 (PC1) —
   a large, heavily glycosylation-dependent membrane protein  [demonstrated in vitro, PMID: 28375157]
│  leads to
▼
5. Reduced functional PC1 at the primary cilium of biliary and
   renal tubular epithelial cells
│  results in
▼
6. Dysregulated cAMP / mTOR signaling, epithelial proliferation,
   and fluid secretion into expanding cysts
│  manifests as
▼
7a. BILIARY BRANCH → polycystic liver disease (predominant)
7b. RENAL BRANCH   → bilateral kidney cysts + nephrolithiasis risk,
     WITHOUT progression to kidney failure  [PMID: 36574950]

Branch point: monoallelic vs biallelic genotype

 ALG8 variant dosage
        │
┌───────────────┴────────────────┐
   MONOALLELIC LoF                   BIALLELIC (compound het / homozygous)
   (partial deficiency)              (near-complete deficiency)
│                                 │
   Selective PC1                     Global N-glycosylation failure
   mis-processing                         │
│                            Multisystem ALG8-CDG (CDG-Ih)
   Adult-onset, mild                 hypotonia, protein-losing enteropathy,
   polycystic liver ± kidney         hepatic involvement, failure to thrive,
   (MONDO:1060122)                   neuro-ophthalmologic disease, hydrops fetalis
   [PMID: 28375157; 36574950]        [PMID: 35716054; 39792033]

Upstream vs downstream, cells, and ontology terms

• Upstream (initiating): ALG8 haploinsufficiency → impaired N-glycosylation. GO biological process: GO:0006487 (protein N-linked glycosylation), GO:0006488 (dolichol-linked oligosaccharide biosynthetic process). Molecular function: α-1,3-glucosyltransferase activity.
• Intermediate (effector): defective PC1 biogenesis and ER quality control. Cellular component: GO:0005789 (endoplasmic reticulum membrane).
• Downstream (clinical): ciliary dysfunction → cystogenesis. Cell types: CL:1000488 (cholangiocyte / biliary epithelial cell), kidney tubular epithelial cell. Subcellular: primary cilium (GO:0005929).
• Anatomy (UBERON): liver UBERON:0002107, intrahepatic bile duct UBERON:0001174, kidney UBERON:0002113.
• Chemistry (CHEBI): dolichyl phosphate, glucose (CHEBI:17234); somatostatin analogues — octreotide, lanreotide, pasireotide.

The monoallelic phenotype's tissue selectivity (liver > kidney, no renal failure) is best explained by PC1's exceptional dependence on complete glycosylation for folding/trafficking: a partial glycosylation deficit disproportionately affects this one client protein rather than causing generalized cellular failure.

Evidence Base

Consistency assessment: All seven findings are mutually reinforcing. The genomic constraint data (Finding 6), ClinVar VUS burden (Finding 7), and epidemiologic/population-genetic discordance (Finding 5) converge on the same conclusion — ALG8 is a low-penetrance, mild dominant gene. No contradictory evidence was identified. The main interpretive caution is the allelic dichotomy (Finding 3): care must be taken not to conflate biallelic CDG literature with the monoallelic cystic disease that MONDO:1060122 denotes.

Section-by-Section Disease Characteristics

1. Disease information. A rare adult-onset dominant cystic disorder; predominantly polycystic liver with limited kidney cysts. Identifiers: MONDO:1060122; gene ALG8 OMIM 608103; related biallelic disorder ALG8-CDG OMIM #608104; within the ADPLD/PCLD spectrum. Synonyms: ALG8-related ADPLD; ALG8 polycystic liver disease. Information is derived from both aggregated disease-level resources (OMIM, Orphanet) and individual-patient EHR/imaging cohorts [PMID: 36574950].

2. Etiology. Primary cause is genetic: heterozygous LoF variants in ALG8. No established environmental cause. Low penetrance implies unidentified genetic/environmental modifiers; female sex and younger age modulate liver-cyst expression and treatment response [PMID: 23665274, PMID: 38689396]. No protective factors characterized.

3. Phenotypes. Liver cysts (predominant; HP:0001399 hepatic cysts); bilateral renal cysts (HP:0000107; ≥4 cysts in 57.7% of carriers); nephrolithiasis (HP:0000787; OR 1.89); biliary tract disease (RR 2.24 in ADPKD context [PMID: 28465378]). Onset adult; severity mild; progression slow; kidney function preserved. QoL impact mainly from hepatomegaly-related mass effect (abdominal pain/distension) in severe PLD.

4. Genetic/molecular. Causal gene ALG8 (HGNC:23159). Variant types: protein-truncating (nonsense, frameshift, splice), rare damaging missense, and structural/exon deletions. Classification: predominantly VUS (380) with 170 P/LP in ClinVar. Functional consequence: loss of function / haploinsufficiency. Germline origin. gnomAD: pLI≈0, LOEUF 0.87 (LoF-tolerant).

5. Environmental. No established toxic, infectious, or lifestyle cause. Disease is monogenic.

6. Mechanism. See causal chain above — ALG8 haploinsufficiency → impaired N-glycosylation → defective PC1 maturation/trafficking → ciliary dysfunction → cystogenesis [PMID: 28375157].

7. Anatomical structures. Liver (UBERON:0002107) and intrahepatic bile ducts (UBERON:0001174) primary; kidney (UBERON:0002113) secondary. Cell types: cholangiocytes (CL:1000488), renal tubular epithelial cells. Subcellular: ER membrane (GO:0005789), primary cilium (GO:0005929). Lateralization: bilateral kidney cysts (69.2%).

8. Temporal development. Adult-onset, insidious, chronic, slowly progressive; no progression to kidney failure; lifelong.

9. Inheritance/population. Autosomal dominant, incomplete/low penetrance, variable expressivity. Clinical ADPLD prevalence ~9.5/100,000 [PMID: 33145487]; predicted-pathogenic carrier frequency ~1:91–1:500 [PMID: 30135240, PMID: 42804492]. Higher predicted-variant frequency in admixed American, Finnish, and African/African American populations. Female preponderance in severe PLD cohorts [PMID: 38689396].

10. Diagnostics. Imaging-based (ultrasound/CT/MRI cyst counts) is primary; genetic testing via NGS panels covering all PKD/ADPLD/ciliopathy genes is recommended for complex cases [PMID: 38097330]. Elevated alkaline phosphatase is a treatment-response biomarker. Differential diagnosis: ADPKD (PKD1/PKD2), other ADPLD genes (PRKCSH, SEC63, GANAB, ALG9, SEC61B, LRP5), ARPKD.

11. Prognosis. Favorable — kidney function preserved; main morbidity from symptomatic hepatomegaly in a minority. No excess disease-specific mortality established.

12. Treatment. Somatostatin analogues (octreotide, lanreotide, pasireotide) reduce TLV/TKV, best in young women [PMID: 23665274]; interventional/surgical options (aspiration-sclerotherapy, fenestration, segmental resection, liver transplantation) for severe PLD. mTOR inhibitors not beneficial [PMID: 26688394]. NCIT: octreotide (C1598), lanreotide, somatostatin analogue therapy.

13. Prevention. No primary prevention. Genetic counseling (incomplete penetrance, allelic dichotomy), cascade testing, and imaging surveillance of at-risk relatives. Monitor for biliary complications and cholelithiasis (somatostatin-analogue adverse event).

14. Other species. ALG8 is evolutionarily conserved (yeast ALG8). No naturally occurring companion-animal disease established. Mechanistic conservation of N-glycosylation supports model-organism study.

15. Model organisms. In vitro cell-line ALG8 inactivation models demonstrated PC1 mis-processing [PMID: 28375157]; a patient-derived iPSC line (AOUMEYi001-A) exists for ALG8-CDG [PMID: 38323760]. Dedicated mouse models of monoallelic ALG8 cystic disease are not yet established — a knowledge gap.

Limitations and Knowledge Gaps

1. Monoallelic mechanism is inferred, not fully demonstrated. The PC1 mis-processing mechanism was shown by full gene inactivation in cell lines [PMID: 28375157]; the quantitative glycosylation deficit produced by a single heterozygous LoF allele in human liver/kidney epithelium has not been directly measured.
2. Low penetrance is unexplained at the modifier level. The ~50–100-fold gap between carrier frequency and clinical prevalence (Finding 5) implies modifier genes/alleles, somatic second hits, or stochastic factors that remain uncharacterized.
3. VUS predominance (Finding 7) limits clinical actionability; most ALG8 variants cannot currently be classified with confidence.
4. ClinVar counts conflate two diseases (biallelic CDG vs monoallelic cystic), so phenotype-specific variant interpretation is confounded.
5. No dedicated animal model of the monoallelic cystic phenotype exists, limiting in vivo natural-history and therapeutic study.
6. Treatment evidence is extrapolated from mixed ADPKD/ADPLD cohorts, not ALG8-specific trials; no genotype-stratified efficacy data.
7. Epidemiology is ancestry-skewed toward European-descent sequencing databases; true global prevalence and clinical penetrance in high-carrier-frequency populations (African/African American 1:43) are unknown.

Proposed Follow-up Experiments / Actions

1. Direct glycosylation assay in heterozygotes. Measure dolichol-linked oligosaccharide and PC1 glycoform profiles in patient-derived cholangiocyte/tubular organoids carrying single ALG8 LoF alleles to confirm the inferred partial-deficiency mechanism.
2. Penetrance / modifier study. Within biobank cohorts (UK Biobank, 100K Genomes, DiscovEHR), perform imaging-anchored penetrance estimation and modifier GWAS/burden testing in ALG8 carriers to explain variable expressivity.
3. Functional VUS reclassification. Deploy a saturation-genome-editing or complementation assay for ALG8 to systematically classify the 380 VUS by effect on glucosyltransferase activity and PC1 maturation.
4. Animal model. Generate a heterozygous / liver-conditional Alg8 mouse to establish a natural-history model of the mild cystic phenotype and test somatostatin analogues genotype-specifically.
5. Genotype-stratified treatment analysis. Re-analyze pooled somatostatin-analogue trial data for ALG8-genotyped participants to test whether response differs by causal gene.
6. Ancestry-balanced epidemiology. Prospectively assess clinical penetrance in high-carrier-frequency populations (African/African American, Finnish, admixed American) with standardized imaging.
7. Database curation. Advocate for ClinVar condition-level partitioning of ALG8 records to separate biallelic CDG from monoallelic cystic disease interpretations.

Report compiled from 7 confirmed findings and 26 reviewed papers across a 5-iteration autonomous investigation. Evidence source types are annotated per finding (human clinical, in vitro, computational/population genomics).

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