| Domain | Key finding/statistic | Evidence type | Ontology suggestions |
|---|---|---|---|
| Identity/etiology | Chylomicron retention disease (CRD; Anderson disease) is an ultra-rare, autosomal-recessive intestinal lipid-malabsorption disorder caused principally by biallelic **SAR1B** loss-of-function variants; estimated prevalence is **<1 per 1,000,000** (pqac-00000000, pqac-00000005) | Aggregated disease resource; human molecular evidence | MONDO:0009528; chylomicron retention disease; Anderson disease |
| Core phenotype frequencies | In a molecularly confirmed 16-patient cohort/literature synthesis: diarrhea **100%**, steatorrhea **85%**, failure to thrive **80%**, abdominal distension **65%**, vomiting **60%**, elevated CK **60%**, vitamin E deficiency **95%**, vitamin A deficiency **70%**, and vitamin D and K deficiencies **45% each** (pqac-00000009) | Human clinical cohort and literature review | Chronic diarrhea; steatorrhea; failure to thrive; abdominal distension; vomiting; elevated serum creatine kinase; fat-soluble-vitamin deficiency |
| Lipid signature | Low total cholesterol, LDL-C, and HDL-C occurred in **100%** of the summarized genotyped cases; triglycerides were normal in **90%**, and the oral fat-load response was negative in **100%** (pqac-00000009) | Human biochemical evidence | Hypocholesterolemia; decreased LDL cholesterol; decreased HDL cholesterol; normal circulating triglyceride concentration |
| Diagnostic signature | Typical combination: infancy-onset fat malabsorption, total/LDL cholesterol near **50% of normal**, moderately low HDL, normal triglycerides, absent postprandial chylomicrons/apoB-48, white duodenal mucosa, and enterocytes distended by lipid droplets or membrane-bound chylomicron-like particles; confirm with biallelic **SAR1B** variants (pqac-00000001, pqac-00000012, pqac-00000015) | Human laboratory, endoscopic, histopathologic, and genetic evidence | Absent postprandial chylomicrons; lipid accumulation in enterocytes; white intestinal mucosa; small-intestinal biopsy |
| Mechanism | SEC12-mediated GDP–GTP exchange activates SAR1B at ER exit sites; SAR1B recruits SEC23–SEC24 and SEC13–SEC31 COPII coats. Pathogenic dysfunction blocks pre-chylomicron ER-to-Golgi trafficking and/or Golgi fusion, causing enterocyte lipid retention and reduced intestinal lipid export (pqac-00000025, pqac-00000026) | Human genetics plus biochemical and cell-biological evidence | GO:0006888 ER-to-Golgi vesicle-mediated transport; COPII-coated ER-to-Golgi transport vesicle; GTPase activity; protein transport |
| Secondary mechanisms | SAR1B-deficient Caco-2/15 cells have reduced chylomicron and HDL formation, impaired cholesterol efflux, and increased lipid peroxidation; oxidative stress, inflammation, and ER stress are plausible downstream contributors, but their clinical importance remains incompletely established (pqac-00000008, pqac-00000017, pqac-00000027) | In-vitro evidence; review-level inference for human complications | Oxidative stress; endoplasmic-reticulum stress; inflammatory response; cholesterol efflux |
| Genetics/variants | **SAR1B** (formerly **SARA2**; chromosome **5q31.1**) has eight exons. Representative disease variants include frameshift **p.Leu28Argfs*7** and **p.Asp48Thrfs*17**, nonsense **p.Glu122***, exon-2 deletion, and missense **p.Asp137Asn**, **p.Ser179Arg**, and **p.Gly185Val** (pqac-00000002, pqac-00000021, pqac-00000024) | Human germline molecular evidence and functional modeling | SAR1B; secretion-associated Ras-related GTPase 1B; germline pathogenic variant; loss of function |
| Modifiers/expressivity | Clinical severity varies even among variants predicted to abolish function. Increased intestinal **SAR1A** expression does not fully compensate; a co-occurring **PCSK9 p.Leu21dup** variant showed no clear additional effect. Proposed modifiers such as **APOB**, **MTTP**, and **ABCG5/ABCG8** remain unproven (pqac-00000006, pqac-00000021, pqac-00000024) | Human expression data; candidate-modifier inference | Variable expressivity; SAR1A; PCSK9; APOB; MTTP; ABCG5; ABCG8 |
| Treatment doses | Supportive therapy includes restriction of long-chain fat, adequate calories, optional medium-chain triglycerides, omega-6 at **3–5% of energy**, omega-3 at **0.5–1%**, vitamin E **50 IU/kg/day**, vitamin A **15,000 IU/day**, vitamin K **15 mg/week**, and vitamin D **800–1,200 IU/day** or age-adjusted intermittent dosing. Doses require biochemical and toxicity monitoring (pqac-00000010, pqac-00000011) | Expert guideline based on literature and two-center experience | Low-fat diet; medium-chain triglyceride supplementation; vitamin E supplementation; vitamin A supplementation; vitamin D supplementation; vitamin K supplementation; dietary counseling |
| Surveillance | Annual childhood assessment: growth, gastrointestinal and neurologic symptoms, diet, lipid profile, liver enzymes, fat-soluble vitamins, essential fatty acids, CBC, and CK. After age 10, liver ultrasound and neurologic, muscular, ophthalmologic, and bone assessment approximately every three years; adult echocardiography every three years was proposed (pqac-00000010, pqac-00000011) | Expert guideline/clinical practice recommendation | Growth monitoring; liver ultrasonography; ophthalmologic examination; neurologic examination; bone densitometry; echocardiography |
| Models/recent research | CRISPR Sar1b-mutant/deletion mice reproduce steatorrhea, malabsorption, failed chylomicron secretion, hypocholesterolemia, and hypoalphalipoproteinemia; homozygous states are usually embryonic/neonatal lethal. An **8-week, 60%-fat diet** exposed genotype- and sex-dependent lipid, insulin, hepatic-steatosis, fatty-acid, and ER-stress effects; females were relatively protected (pqac-00000016, pqac-00000017, pqac-00000018, pqac-00000019) | Genetically engineered mouse models; 2023 experimental study | Mus musculus; high-fat diet; intestinal lipid accumulation; hepatic steatosis; insulin resistance; ER stress |
| Prognosis | Gastrointestinal symptoms often improve rapidly with fat restriction, but fat intolerance persists and steatorrhea did not adapt after about five years. Early treatment was associated with absence of clinical/electrophysiologic neuro-ophthalmologic complications in **12/16** patients; delayed diagnosis can lead to permanent growth, neurologic, retinal, muscular, cardiac, hepatic, or skeletal morbidity (pqac-00000003, pqac-00000009, pqac-00000011) | Longitudinal human cohorts and expert synthesis | Growth delay; peripheral neuropathy; ataxia; retinopathy; myopathy; cardiomyopathy; hepatic steatosis; reduced bone mineralization |


*Table: Compact evidence table summarizing the identity, phenotype frequencies, diagnostic signature, molecular mechanism, genetics, management, models, and prognosis of chylomicron retention disease. Evidence types and suggested ontology concepts are included for knowledge-base annotation.*