Portal Hypertension, Noncirrhotic, 2 (PHNC2 / NCPH2) — Comprehensive Disease Report

Disease: Portal Hypertension, Noncirrhotic, 2 MONDO: MONDO:0030397 · OMIM: #619463 · Causal gene: GIMAP5 (HGNC:18005) Evidence base: Aggregated disease-level resources (OMIM, MONDO, HPO, gnomAD, UniProt) plus individual-patient reports (~21 patients published to date). Fewer than ~25 molecularly confirmed patients worldwide; all conclusions rest on small case series, a landmark human+mouse mechanistic study, and rodent models.

Summary (Answer to the Research Question)

Portal Hypertension, Noncirrhotic, 2 (PHNC2) is a rare autosomal-recessive disorder caused by biallelic loss-of-function variants in GIMAP5, a small organellar GTPase of the immunity-associated protein (IAN) family expressed selectively in lymphocytes and endothelial cells. Loss of GIMAP5 produces a two-arm disease: (1) a hepatic vascular arm in which GIMAP5-deficient liver sinusoidal endothelial cells (LSECs) fail to maintain their identity (via reduced GATA4), undergo capillarization, and cause noncirrhotic (porto-sinusoidal) portal hypertension; and (2) an immune arm with lymphopenia, autoimmune cytopenias, and recurrent infections. A unifying biochemical lesion is pathological accumulation of long-chain ceramides (GIMAP5 normally restrains CK2-driven ceramide synthase activity), driving cellular senescence in both endothelium and lymphocytes. Presentation is typically in childhood with splenomegaly, thrombocytopenia, esophageal varices, and elevated transaminases, without cirrhosis.

1. Disease Information

Overview. PHNC2 is a Mendelian cause of idiopathic/noncirrhotic portal hypertension, now classified within the spectrum of porto-sinusoidal vascular disorder (PSVD). It is distinctive because portal hypertension arises from a primary endothelial defect rather than from hepatocellular injury or cirrhosis, and it co-occurs with an inborn error of immunity.

Key identifiers - MONDO: MONDO:0030397 ("portal hypertension, noncirrhotic, 2"; synonym NCPH2) - OMIM: #619463 (phenotype) - UMLS: C5561948 · MedGen: 1794158 - Gene: GIMAP5 — HGNC:18005; NCBI Gene 55340; Ensembl ENSG00000196329; UniProt Q96F15; gene MIM 608086; cytoband 7q36.1 - ICD-10: K76.6 (portal hypertension; no PHNC2-specific code) · ICD-11: DB98.5 region (non-cirrhotic portal hypertension/idiopathic; no specific code) - MeSH: most closely "Hypertension, Portal" (D006975); no PHNC2-specific MeSH - Orphanet: no PHNC2-specific ORPHA; overlaps "Idiopathic non-cirrhotic portal hypertension"/PSVD

Synonyms / alternative names: NCPH2; GIMAP5 deficiency; GIMAP5-related noncirrhotic portal hypertension; GIMAP5-related porto-sinusoidal vascular disorder; (historically discussed with "idiopathic noncirrhotic portal hypertension," INCPH). Note: PHNC1 (INCPH1, OMIM 617068) is a distinct entity caused by DGUOK (26874653).

Data provenance: Disease-level ontologies/aggregators + individual patient case reports/series (human clinical), complemented by mouse and rat model data and in-vitro mechanistic studies.

2. Etiology

Primary cause — genetic (monogenic). Biallelic (homozygous or compound-heterozygous) loss-of-function variants in GIMAP5. "we demonstrate homozygous damaging mutations in GIMAP5, a small organellar GTPase, in four families with unexplained portal hypertension" (Drzewiecki et al., 33956074).

Genetic risk factors - Causal variants: recessive GIMAP5 alleles (see §4). Disease requires two damaged alleles. - Consanguinity is a major contributor: three of four index families were consanguineous (first-cousin unions) (33956074). - Founder/recurrent allele: p.Leu204Pro recurs across independent reports and is relatively common (gnomAD AF ≈2.1×10⁻³), so it is the most likely allele to appear in homozygous or compound-heterozygous state.

Environmental risk factors. None established. No toxin, infection, diet, or occupational exposure is required for disease; the phenotype is genetically determined. (Of note, acquired phenocopies of noncirrhotic portal hypertension exist — e.g., didanosine/thioguanine exposure, oxaliplatin — but these are not PHNC2.)

Protective factors. No genetic or environmental protective factors are defined. At the population level GIMAP5 is LOF-tolerant (gnomAD pLI = 0.003; observed/expected LOF = 8/9.9), so monoallelic carriers are generally healthy — heterozygosity is effectively "protective" relative to the biallelic state.

Gene–environment interactions. A 2026 report raised the hypothesis that partial (monoallelic) GIMAP5 deficiency might subtly predispose to localized vascular anomalies under specific environmental/epigenetic conditions via multi-hit mechanisms — the dizygotic twin carrying a single p.Leu204Pro allele showed a localized fibro-adipose vascular anomaly but no immune defect (42358996). This remains speculative.

3. Phenotypes (with HPO terms, type, and frequency)

Onset is typically in infancy/childhood; severity is variable; the hepatic disease is chronic and progressive.

Age of onset: neonatal–childhood (pediatric); portal hypertension complications and immune features generally manifest in the first two decades. Progression: progressive liver/vascular disease (one patient developed worsening coagulopathy and direct hyperbilirubinemia after shunt surgery) (33956074). Quality-of-life impact: substantial — recurrent variceal bleeding risk, transfusion-dependent cytopenias, infection susceptibility, growth/activity limitation, and the burden of surveillance endoscopy and possible transplantation. No formal EQ-5D/SF-36/PROMIS data exist for this ultra-rare disease.

4. Genetic / Molecular Information

Causal gene: GIMAP5 (GTPase, IMAP family member 5) — HGNC:18005; NCBI Gene 55340; Ensembl ENSG00000196329; UniProt Q96F15 (307 aa); gene MIM 608086; 7q36.1 (GRCh38 chr7:150,722,253–150,750,033, + strand). Part of the IAN GTPase cluster on 7q36.1; read-through transcript with upstream GIMAP1 exists. Aliases: IAN5, IAN4L1, IROD, NCPH2.

Protein architecture: GIMAP5 is a small AIG1-type guanine-nucleotide-binding (G) domain GTPase (InterPro IPR006703; Pfam PF04548 "AIG1 family"; PROSITE PS51720), belonging to the P-loop NTPase superfamily (IPR027417) and the GTPase GIMA/IAN/Toc family (IPR045058), with a C-terminal transmembrane anchor targeting it to lysosomal/endosomal membranes. The reported missense substitutions (I47T, P109L, L204P, L223P) map to/near this G-domain and are predicted to destabilize the fold and abolish GTPase function, consistent with the observed absent protein for null combinations.

Pathogenic variants (all germline, all loss-of-function / recessive):

• Variant classification (ACMG/AMP): the recurrent alleles are treated as pathogenic/likely pathogenic given segregation, absent/abolished protein, and functional data; many other GIMAP5 entries in ClinVar are VUS or large 7q copy-number changes not specific to PHNC2.
• Variant types: predominantly missense; at least one nonsense (R214*). No pathogenic large structural rearrangement specific to PHNC2 is established (7q CNVs in ClinVar are contiguous-gene events, not PHNC2).
• Functional consequence: loss of function — e.g., compound-het L204P/R214 yields absent GIMAP5 protein* on immunoblot (42358996). No gain-of-function or dominant-negative mechanism.
• Somatic vs germline: exclusively germline.

Modifier genes. None formally proven. Mechanistically, GIMAP5 stability requires the lysosomal MFSD1–GLMP complex (38055739), so MFSD1/GLMP are candidate biological modifiers; downstream GATA4 and GSK3β/CK2/ceramide-synthase nodes modulate phenotype in models.

Epigenetic information / chromosomal abnormalities. No disease-specific DNA-methylation or histone signature reported. Contiguous 7q36 deletions/duplications affect GIMAP5 among many genes but are not the mechanism of PHNC2.

5. Environmental Information

• Environmental factors / toxins: none required or established for PHNC2. (Toxic/drug-induced noncirrhotic portal hypertension — e.g., didanosine, thioguanine, arsenic, vinyl chloride, oxaliplatin — are separate acquired phenocopies to exclude.)
• Lifestyle factors: not applicable to disease causation.
• Infectious agents: not causal. However, because of the immune arm, patients suffer recurrent/severe viral infections as a consequence of the disease (e.g., severe viral infections in the proband, 42358996). CHEBI/pathogen exposure is downstream, not upstream.

6. Mechanism / Pathophysiology

Ordered causal chain (initiating lesion → clinical manifestation)

1. Biallelic loss-of-function variants in GIMAP5 lead to loss/instability of the GIMAP5 GTPase (compounded by loss of the stabilizing lysosomal MFSD1–GLMP–GIMAP5 complex). (demonstrated)
2. GIMAP5 loss results in failure to restrain protein kinase CK2, which leads to over-activation of ceramide synthases and pathological accumulation of long-chain ceramides. (demonstrated in T cells; inferred in endothelium)
3. Ceramide overaccumulation leads to cellular senescence / organelle (mitochondrial) dysfunction in GIMAP5-expressing cells — endothelial cells and lymphocytes. (demonstrated)

Branch A — hepatic vascular (portal hypertension): 4a. In liver sinusoidal endothelial cells (LSECs), GIMAP5 loss results in reduced GATA4 (the transcription factor required for LSEC specification). (demonstrated by scRNA-seq positioning GIMAP5 upstream of GATA4) 5a. Reduced GATA4 leads to loss of LSEC identity → capillarization (loss of fenestrae, acquisition of a basement membrane, CD34 positivity) and reduction of macrovascular hepatic endothelial cells. (demonstrated in humans and mice) 6a. Sinusoidal capillarization / porto-sinusoidal remodeling (with nodular regenerative hyperplasia and obliterative portal venopathy — venules absent in portal areas) increases intrahepatic vascular resistance. (demonstrated histologically) 7a. Increased resistance results in noncirrhotic portal hypertension → splenomegaly, esophageal varices, ascites, variceal bleeding; thrombocytopenia via hypersplenism. (clinical)

Branch B — immune (lymphopenia/autoimmunity): 4b. In lymphocytes, GIMAP5 loss (via ceramide, impaired mitochondrial/ER Ca²⁺ homeostasis, ER-stress/CHOP apoptosis, and constitutive GSK3β activity restricting c-Myc/NFATc1) leads to spontaneous T- and NK-cell apoptosis / impaired proliferation. (demonstrated in rat/mouse and patient cells) 5b. Lymphopenia and immune dysregulation result in recurrent infections, autoimmune cytopenias, T-cell exhaustion, and atypical memory B-cell expansion. (clinical)

Key point (branch independence): The hepatic vascular disease is cell-intrinsic to endothelium and lymphocyte-independent — endothelial-specific Gimap5 deletion reproduces capillarization, and Gimap5^sph/sph;Rag1⁻/⁻ mice (lacking T/B cells) still develop the liver phenotype (33956074). This predicts HSCT will not reverse established portal hypertension.

Category detail

• Molecular pathways: CK2 → ceramide-synthase/sphingolipid pathway (GO:0006672 ceramide metabolic process); GATA4-dependent endothelial specification; GSK3β signaling (Wnt/insulin-adjacent) controlling c-Myc and NFATc1; NF-κB/MAPK dysregulation in Gimap5-mutant T cells (16584774).
• Cellular processes: anti-apoptotic function (GO:0043066 negative regulation of apoptotic process); cellular senescence (GO:0090398); T-cell homeostasis (GO:0043029); endothelial cell differentiation (GO:0045446); autophagy/lysosomal biology.
• Protein dysfunction: loss of a small AIG1-type G-domain GTPase (Pfam PF04548; InterPro IPR006703; GO:0003924 GTPase activity; GO:0005525 GTP binding); missense variants in/around the G-domain destabilize/abolish the protein (loss of function).
• Metabolic/lipidomic changes: accumulation of long-chain ceramides (CHEBI:17761 ceramide) — a defining metabolic signature.
• Immune involvement: combined features of immunodeficiency (lymphopenia, infection) and autoimmunity (cytopenias) — an inborn error of immunity.
• Tissue-damage mechanism: endothelial capillarization/senescence → sinusoidal fibrosis-independent remodeling; progressive liver dysfunction.
• Molecular profiling: single-cell RNA-seq of GIMAP5-deficient mouse liver documented replacement of LSECs by capillarized endothelial cells and placed GIMAP5 upstream of GATA4 (33956074); T-cell proteomics/lipidomics documented the CK2–ceramide axis (38172257).

GO / CL / CHEBI suggestions: GO:0003924, GO:0005525, GO:0043066, GO:0090398, GO:0006672, GO:0045446, GO:0043029; CL:1000488 (liver sinusoidal endothelial cell), CL:0000115 (endothelial cell), CL:0000084 (T cell), CL:0000623 (NK cell), CL:0000182 (hepatocyte); CHEBI:17761 (ceramide).

7. Anatomical Structures Affected

• Organ level (primary): liver (UBERON:0002107) — specifically the hepatic sinusoid (UBERON:0001281) and portal venous system/portal vein (UBERON:0002017). Digestive/hepatobiliary and cardiovascular (portal venous) systems are primarily involved.
• Secondary organ involvement: spleen (UBERON:0002106) — splenomegaly/hypersplenism; esophagus (UBERON:0001043) — varices; bone marrow (UBERON:0002371) and lymphoid organs — lymphopenia, extramedullary hematopoiesis (in models); gastrointestinal tract (variceal bleeding).
• Tissue/cell level: vascular endothelium, chiefly liver sinusoidal endothelial cells (CL:1000488); T lymphocytes (CL:0000084) and NK cells (CL:0000623); hepatocytes secondarily; platelets (consumed peripherally).
• Subcellular level: GIMAP5 localizes to the lysosomal membrane (GO:0005765) and multivesicular body/endosome membrane (GO:0032585) (UniProt Q96F15); older studies also implicated ER (GO:0005783) and mitochondria (GO:0005739) in T-cell survival/Ca²⁺ handling.
• Localization / lateralization: intra-abdominal, bilateral/diffuse hepatic involvement; not lateralized.

8. Temporal Development

• Onset: congenital-to-pediatric; portal hypertension and immune manifestations usually emerge in infancy through adolescence. Onset pattern is insidious/chronic (portal hypertension often detected via splenomegaly/thrombocytopenia or a variceal bleed).
• Progression: chronic, progressive hepatic vascular disease; can advance to decompensation (coagulopathy, hyperbilirubinemia) despite shunting (33956074). Immune disease can be episodic (autoimmune cytopenia flares, intercurrent infections).
• Disease course/duration: lifelong; no spontaneous remission of the vascular disease. Immune cytopenias can be treatment-induced remission (e.g., sirolimus) (42358996).
• Critical periods / intervention windows: early molecular diagnosis enables variceal surveillance/prophylaxis, infection prophylaxis, and consideration of HSCT before irreversible organ damage; the endothelial disease may have an early window before established capillarization/portal hypertension (inferred).

9. Inheritance and Population

• Inheritance: Autosomal recessive (HP:0000007). Recurrence risk 25% for siblings of an affected proband.
• Penetrance: appears high/complete for biallelic LOF (all reported biallelic individuals affected), though phenotypic expressivity is variable (severity, relative weight of hepatic vs immune features).
• Genetic anticipation / mosaicism: not applicable / not reported.
• Consanguinity: a major factor — most index families are consanguineous (33956074).
• Founder / recurrent allele: p.Leu204Pro (AF ≈2.1×10⁻³) recurs and drives a disproportionate share of cases; no formal founder haplotype study published.
• Carrier frequency: GIMAP5 is LOF-tolerant (gnomAD pLI=0.003); heterozygous carriers are healthy. Aggregate carrier frequency is low but non-trivial where p.L204P is present.
• Epidemiology: ultra-rare — on the order of ~20–25 molecularly confirmed patients reported worldwide (≥4 families in the founding study plus subsequent case reports/series, ~21 patients reviewed by 2026). No reliable prevalence/incidence estimate (well under 1/1,000,000). Reported patients are geographically diverse (Turkey, Europe, China, North America).
• Sex ratio: no established skew (autosomal recessive). Age distribution: pediatric-predominant at diagnosis.

10. Diagnostics

Genetic testing (definitive): - Whole-exome sequencing (WES) or whole-genome sequencing (WGS) identifying biallelic GIMAP5 variants is the diagnostic gold standard (high-depth WES used in the founding study; 33956074). GeneMatcher/trio exome aids ultra-rare gene discovery. - Single-gene / panel testing: GIMAP5 can be included on PSVD / noncirrhotic portal hypertension and inborn errors of immunity gene panels; targeted testing for the recurrent p.L204P is reasonable in consanguineous pedigrees. - CMA/karyotype/FISH: not primary; only relevant to exclude contiguous 7q36 CNVs. Mitochondrial/repeat-expansion testing not applicable. - Confirmatory functional test: GIMAP5 protein immunoblot (absent protein confirms LOF) and flow-cytometric immunophenotyping (T/NK lymphopenia, T-cell exhaustion, atypical memory B cells) (42358996).

Clinical/laboratory workup (supportive, to characterize the phenotype): - Labs: CBC (thrombocytopenia, cytopenias), transaminases (elevated), GGT (elevated), bilirubin/coagulation (with progression), lymphocyte subsets. LOINC-codable. - Liver histology (PSVD pattern): nodular regenerative hyperplasia, CD34-positive capillarized LSECs, obliterative portal venopathy (absent portal venules), no cirrhosis/significant fibrosis (33956074). SNOMED CT: nodular regenerative hyperplasia of liver. - Endoscopy: upper GI endoscopy for esophageal/gastric varices. - Imaging: ultrasound/Doppler, CT/MRI showing splenomegaly, portosystemic collaterals, patent portal vein (excluding portal/splanchnic vein thrombosis); transient elastography typically discordant with severe portal hypertension (low fibrosis vs high pressure).

Diagnostic criteria / differential. No PHNC2-specific criteria; diagnosis = PSVD/noncirrhotic portal hypertension features + biallelic GIMAP5. Differential diagnosis: cirrhosis of any cause; portal/splenic vein thrombosis (extrahepatic); congenital hepatic fibrosis; schistosomiasis; drug/toxin-induced NRH (didanosine, thioguanine, oxaliplatin); other genetic PSVD/INCPH genes — DGUOK (PHNC1/INCPH1), KCNN3, FCHSD1, FOPV, TRMT5, HRG, and syndromic causes (Adams–Oliver, telomere biology disorders, cystic fibrosis, Turner, Williams–Beuren) (review 38900412). GIMAP5's accompanying immunodeficiency/autoimmunity is a key distinguishing clue.

Screening (asymptomatic): cascade/carrier testing of relatives; prenatal/preimplantation testing in known families (see §13).

11. Outcome / Prognosis

• Survival/mortality: guarded in severe cases. In the founding cohort, three affected individuals in one kindred were deceased, two dying from complications of portal hypertension; one patient died at 17 with recurrent infections (33956074). No formal 5-/10-year survival statistics exist (too few patients).
• Morbidity: recurrent variceal bleeding, refractory/transfusion-dependent cytopenias, infection susceptibility, progressive liver dysfunction (coagulopathy, hyperbilirubinemia), and risk of extramedullary hematopoiesis (models). Hepatocellular carcinoma (HP:0001402) is listed as a potential long-term risk.
• Recovery potential: the vascular disease does not spontaneously remit; portosystemic shunting improves varices but does not halt underlying liver disease (33956074). Immune cytopenias can respond well to immunomodulation.
• Prognostic factors: degree of portal hypertension/hepatic decompensation; severity of immunodeficiency and infection burden; genotype (null/absent protein alleles such as R214 may predict more complete deficiency). Prognostic biomarker candidate:* long-chain ceramide accumulation (mechanistic; not clinically validated).

12. Treatment

No disease-specific approved therapy exists; management is organ-directed and, increasingly, mechanism-informed.

A. Portal-hypertension / hepatic care (standard of care): - Endoscopic variceal band ligation and nonselective beta-blockers (e.g., propranolol/carvedilol) for variceal prophylaxis (NCIT: Propranolol C692; Endoscopic Variceal Ligation). - Portosystemic shunt surgery / TIPS — improved varices/collaterals in a reported patient (33956074) (NCIT: Transjugular Intrahepatic Portosystemic Shunt). - Ascites management (diuretics/sodium restriction); liver transplantation for end-stage disease (NCIT: Liver Transplantation C15356) — rational because the defect is intrahepatic-endothelial.

B. Immune-directed therapy: - Sirolimus (rapamycin; mTOR inhibitor) achieved sustained remission of autoimmune cytopenias (42358996) (NCIT: Sirolimus C1212). - Supportive: IVIG, targeted antimicrobial/antiviral prophylaxis, vaccination as tolerated (NCIT: Intravenous Immunoglobulin Therapy). - Allogeneic hematopoietic stem cell transplantation (HSCT) is considered definitive for the immune/hematologic disease (NCIT: Hematopoietic Stem Cell Transplantation C15431), but — because the liver disease is endothelial-intrinsic and lymphocyte-independent — HSCT is not expected to reverse established portal hypertension; the risk/benefit must be weighed carefully (42358996).

C. Experimental / mechanism-based (preclinical): - GSK3 inhibitors rescued patient T-cell proliferation in vitro (29382851). - CK2 inhibitors + ceramide-synthase inhibitors rescued GIMAP5-deficient T cells by preventing ceramide overaccumulation (38172257) — a candidate for future targeted therapy. - Gene/RNA therapy: none developed; conceptually attractive given recessive LOF and endothelial/lymphoid expression (not yet in trials). No NCT registrations identified.

Pharmacogenomics: none disease-specific. Personalized approach: genotype/phenotype-guided balancing of liver-directed vs immune-directed (sirolimus) vs HSCT strategies.

13. Prevention

• Primary prevention: not possible for the genetic disease itself; preconception genetic counseling in consanguineous/known-carrier families, with carrier testing, prenatal diagnosis, and preimplantation genetic testing (PGT-M) to prevent affected births (autosomal recessive, 25% recurrence).
• Secondary prevention (early detection): molecular diagnosis enables variceal surveillance endoscopy, monitoring of platelet counts/liver tests, and early immune monitoring; cascade genetic screening of at-risk relatives.
• Tertiary prevention (complication avoidance): beta-blockers/band ligation to prevent variceal hemorrhage; infection prophylaxis and vaccination; timely immunomodulation for cytopenias; transplant planning.
• Immunization/public-health/environmental measures: standard immunizations (with attention to live-vaccine caution in immunodeficiency); no vector/sanitation measures apply (non-infectious etiology).
• Counseling: genetic counseling is central given recessive inheritance and consanguinity.

14. Other Species / Natural Disease

• Taxonomy of affected/model species: human Homo sapiens (NCBI:txid9606); Mus musculus (NCBI:txid10090); Rattus norvegicus (NCBI:txid10116). GIMAP5 orthologs are also studied in chicken (Gallus gallus, NCBI:txid9031; PMIDs 31579581, 32147998).
• Orthologous genes: mouse Gimap5 (NCBI Gene 14468; MGI), rat Gimap5 (RGD). Mechanisms (anti-apoptotic GTPase, lymphocyte survival) are evolutionarily conserved across rodents and birds.
• Natural (spontaneous) animal disease: the BioBreeding diabetes-prone (BB-DP) rat carries a spontaneous Gimap5 frameshift (lyp) allele causing T-cell lymphopenia and autoimmune type 1 diabetes (PMIDs 17655828, 19007993) — a naturally occurring model of GIMAP5 deficiency, though its hallmark is autoimmune diabetes rather than portal hypertension. No specific companion-animal PHNC2 (no OMIA entry for GIMAP5 portal hypertension identified).
• Comparative pathology: rodents recapitulate lymphopenia and liver pathology; the portal-hypertension/LSEC-capillarization phenotype is specifically demonstrated in mouse (endothelial-intrinsic).
• Zoonotic potential: none (genetic, non-transmissible).

15. Model Organisms

Mouse (Mus musculus; MGI) — primary PHNC2 model: - Germline Gimap5 knockout / sph (sphinx) ENU allele: impaired peripheral T-cell survival, disrupted NK/NKT development, chronic hepatic hematopoiesis, hepatocyte apoptosis and liver failure, median survival ~15 weeks (18796632). - Endothelial-cell-conditional Gimap5 deletion: reproduces LSEC capillarization — the most faithful model of the human portal-hypertension mechanism (33956074). - Epistasis models: Gimap5^sph/sph;Rag1⁻/⁻ mice (no T/B cells) still develop liver disease → portal hypertension is lymphocyte-independent (33956074). - Complex/humanized biology: Mfsd1, Glmp, and Gimap5 germline knockouts each cause lymphopenia, liver pathology, and extramedullary hematopoiesis, defining the stabilizing MFSD1–GLMP–GIMAP5 complex (38055739). - Mechanistic mouse models: GSK3β-axis studies (29382851); ceramide/CK2 senescence pathway (38172257).

Rat (Rattus norvegicus; RGD): BB-DP (lyp/lyp) and congenic lines — spontaneous Gimap5 frameshift; robust model of T-cell lymphopenia, ER-stress/CHOP apoptosis, mitochondrial Ca²⁺ dysregulation, and autoimmune diabetes (PMIDs 17655828, 19424493, 19007993, 21502331).

In vitro / cellular: patient T cells (proliferation defect rescued by GSK3 inhibitors), Jurkat/HEK overexpression studies, and primary LSEC analyses.

Phenotype recapitulation & limitations: rodents faithfully model the immune arm (lymphopenia, autoimmunity) and, in mouse endothelial-specific/whole-body models, the hepatic vascular arm (capillarization, portal hypertension). Limitations: the BB-DP rat's dominant phenotype is autoimmune diabetes (not seen as a core human PHNC2 feature); mouse whole-body nulls have very short lifespans complicating chronic-disease study; hepatocellular carcinoma risk and human-specific variant effects are not fully captured. Resources: MGI (mouse Gimap5), RGD (rat Gimap5, BB rat), IMPC/IMSR for alleles.

Supported vs. Refuted Hypotheses

Supported: - PHNC2 is caused by biallelic LOF GIMAP5 variants, autosomal recessive (33956074). - Portal hypertension arises from GATA4-dependent LSEC capillarization, an endothelial-intrinsic, lymphocyte-independent mechanism (33956074). - A unifying CK2–ceramide senescence pathway links hepatic and immune disease (38172257). - Disease is multisystem (portal hypertension + immunodeficiency/autoimmunity) with childhood onset (PMIDs 33956074, 42358996).

Refuted / not supported: - PHNC2 is not due to cirrhosis, fibrosis, or portal/splanchnic vein thrombosis (explicitly excluded; 33956074). - Not caused by DGUOK (that is the distinct PHNC1/INCPH1, 26874653). - No environmental/infectious cause is required; heterozygous carriers are unaffected.

Limitations and Future Directions

• Very small N (~20–25 patients) limits penetrance, expressivity, natural-history, prognosis, and QoL precision.
• Genotype–phenotype relationships (e.g., missense vs null alleles; the recurrent p.L204P; possible monoallelic vascular predisposition) need larger cohorts.
• Therapeutic priorities: validate CK2/ceramide-synthase and GSK3 inhibition clinically; define whether early HSCT alters liver outcomes; assess liver transplantation outcomes; explore endothelial-directed or gene-based therapy.
• Registry/omics: a dedicated PSVD-genetics registry and hepatic single-cell/lipidomic profiling in patients would refine mechanism and biomarkers.

Key References (PMID)

• 33956074 Drzewiecki et al., J Exp Med 2021 — GIMAP5 maintains liver endothelial cell homeostasis and prevents portal hypertension (disease-defining).
• 38172257 Park et al., Nat Immunol 2024 — GIMAP5 deficiency reveals a ceramide-driven longevity/senescence pathway.
• 38055739 Zhong et al., PNAS 2023 — MFSD1–GLMP–GIMAP5 complex in lymphocyte survival and liver homeostasis.
• 42358996 Moratti et al., Front Immunol 2026 — clinical spectrum, sirolimus, HSCT dilemmas (compound-het L204P/R214*).
• 29382851 Patterson et al., Nat Commun 2018 — Gimap5–GSK3β; first human LOF patient.
• 18796632 Schulteis et al., Blood 2008 — Gimap5-KO mouse liver failure/lymphopenia.
• 38900412 Ciriaci et al., Hepatology 2026 — genetic predisposition to PSVD (differential/gene list).
• 26874653 Vilarinho et al., 2016 — DGUOK in INCPH1 (distinct PHNC1).