Abetalipoproteinemia

Mendelian MONDO:0008692 Pathograph 44 Hypobetalipoproteinemia Intestinal Disorder Hereditary Peripheral Neuropathy

Abetalipoproteinemia is a severe autosomal recessive disorder of apoB-containing lipoprotein assembly and secretion caused by biallelic MTTP pathogenic variants. Loss of microsomal triglyceride transfer protein function prevents normal chylomicron export from enterocytes and VLDL export from hepatocytes, producing absent or extremely low apoB-containing lipoproteins, hypocholesterolemia, hypotriglyceridemia, fat malabsorption, and secondary fat-soluble vitamin deficiency. Infants typically present with failure to thrive, diarrhea, vomiting, steatorrhea, acanthocytosis, and abnormal lipid studies; untreated individuals can later develop retinal, neurologic, hematologic, hepatic, and coagulation complications. Management centers on a low-fat diet, essential fatty acid intake, and high-dose fat-soluble vitamin supplementation.

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1
Inheritance
7
Pathophys.
30
Phenotypes
1
Hypotheses
44
Pathograph
1
Genes
3
Treatments
7
References
1
Deep Research
1
Hyp. Reports
👪

Inheritance

1
Autosomal Recessive HP:0000007
Autosomal recessive inheritance
Show evidence (2 references)
ORPHA:14 SUPPORT Other
"Autosomal recessive"
Orphanet classifies Abetalipoproteinemia inheritance as autosomal recessive.
PMID:30358967 SUPPORT Human Clinical
"inherited in an autosomal recessive"
GeneReviews states that abetalipoproteinemia is inherited in an autosomal recessive manner.
◈

Mechanistic Hypotheses

1
Canonical MTTP ApoB-Lipoprotein Assembly Model
canonical_mttp_lipoprotein_assembly_model CANONICAL
Biallelic MTTP pathogenic variants impair MTP function, preventing assembly and secretion of apoB-containing chylomicrons and VLDL particles. This produces absent circulating apoB lipoproteins, intestinal fat malabsorption, and fat-soluble vitamin deficiency that drives retinal, neurologic, hematologic, and coagulation manifestations.
Retained as CANONICAL. The 2026 openscientist hypothesis-search report (kb/hypotheses/Abetalipoproteinemia/canonical_mttp_lipoprotein_assembly_model) reviewed 82 papers and found zero refutations of the MTP loss-of-function pathway. Three qualifications refine the canonical model: (1) MTP operates as an obligate heterodimer with PDI and disease-causing truncations selectively disrupt this interaction; (2) local MTP expression in retinal pigment epithelium and ganglion cells suggests a tissue-autonomous component to ABL retinopathy beyond systemic vitamin E deficiency; and (3) hypomorphic MTTP alleles retain partial function and produce attenuated phenotypes with detectable apoB48 secretion, demonstrating a genotype-phenotype gradient. Pharmacological MTP inhibition with lomitapide and viral inhibition by HCV core protein independently recapitulate the canonical pathway.
Deep research
OpenScientist citations 32 citations 2026-05-23T01:43:14.704225
Show evidence (12 references)
PMID:24288038 SUPPORT Human Clinical
"improper packaging and secretion of apolipoprotein (apo)"
This review identifies defective apoB-lipoprotein packaging and secretion as the root mechanism.
PMID:30522860 SUPPORT Human Clinical
"export apolipoprotein B-containing lipoproteins from both the intestine and the"
This clinical lipid-absorption study supports defective intestinal and hepatic apoB-lipoprotein export.
PMID:1439810 SUPPORT Human Clinical
"MTP activity and the 88-kilodalton component of MTP were present in intestinal biopsy samples from eight control individuals but were absent in four abetalipoproteinemic subjects."
Foundational 1992 discovery directly measured absent MTP protein and enzymatic activity in human intestinal biopsies from ABL patients, establishing MTP loss as the molecular basis of the disease.
+ 9 more references
⚙

Pathophysiology

7
MTTP Loss of Function
Pathogenic variants in MTTP reduce or abolish microsomal triglyceride transfer protein function. MTP normally forms a lipid-transfer complex with protein disulfide isomerase; loss of the functional 97-kDa subunit or missense variants that disrupt the complex prevent normal apoB particle biogenesis.
triglyceride transport link lipoprotein metabolic process link
lipid transfer activity link apolipoprotein binding link
Downstream
Impaired ApoB Lipoprotein Assembly and Secretion MTTP loss prevents the lipid-transfer activity required to assemble and secrete apoB-containing lipoproteins.
Show evidence (4 references)
ORPHA:14 SUPPORT Other
"MTTP | microsomal triglyceride transfer protein | hgnc:7467 | Disease-causing germline mutation(s) in"
Orphanet records MTTP as a disease-causing gene for Abetalipoproteinemia.
PMID:10946006 SUPPORT Human Clinical
"mutations of the MTP gene have been screened in 4"
Patient mutation screening supports MTTP variants as the human genetic cause of ABL.
PMID:10946006 SUPPORT In Vitro
"displayed negligible MTP activity."
COS-1 expression testing supports loss of MTP activity for a disease-associated MTTP missense variant.
+ 1 more reference
Impaired ApoB Lipoprotein Assembly and Secretion
Defective MTP activity prevents assembly and secretion of apoB-containing particles, including intestinal chylomicrons and hepatic VLDL. The resulting absence of apoB-containing lipoproteins causes severe hypocholesterolemia, hypotriglyceridemia, and low LDL cholesterol.
enterocyte link hepatocyte link
chylomicron assembly link very-low-density lipoprotein particle assembly link lipid transport link
Downstream
Fat and Fat-Soluble Vitamin Malabsorption Loss of chylomicron export impairs intestinal absorption and transport of dietary fat and fat-soluble vitamins.
Absent apoB-containing lipoproteins Failure to assemble and secrete chylomicron, VLDL, and LDL particles is observed as absent apoB-containing lipoproteins.
Abnormal circulating apolipoprotein concentration Failure to secrete apoB-containing particles causes abnormal circulating apolipoprotein concentration.
Hypocholesterolemia Loss of LDL/VLDL particles causes markedly decreased circulating cholesterol.
Decreased LDL cholesterol concentration Defective apoB-lipoprotein secretion causes absent or extremely low LDL cholesterol.
Decreased HDL cholesterol concentration The ABL lipid phenotype can include decreased HDL cholesterol; the intervening mechanism is not specified in the cited clinical sources.
Hypotriglyceridemia Loss of chylomicron and VLDL secretion produces very low circulating triglycerides.
Acanthocytic Hematologic Manifestations Severe apoB-lipoprotein depletion is clinically associated with acanthocytosis and related hematologic abnormalities.
Hepatic Steatosis and Laboratory Abnormalities Failed hepatic VLDL export promotes hepatic lipid retention and downstream hepatic steatosis or liver-laboratory abnormalities.
Show evidence (2 references)
PMID:24288038 SUPPORT Human Clinical
"chylomicrons, very low density lipoprotein and low density lipoprotein."
The review states that apoB-containing chylomicrons, VLDL, and LDL are virtually absent.
PMID:30522860 SUPPORT Human Clinical
"undetectable concentrations of apolipoprotein B, extremely low levels of"
This supports the characteristic apoB and LDL biochemical depletion downstream of MTTP variants.
Fat and Fat-Soluble Vitamin Malabsorption
Absent intestinal chylomicron formation impairs absorption and transport of dietary fat and fat-soluble vitamins. This causes steatorrhea, chronic diarrhea, failure to thrive, and decreased circulating vitamins A, D, E, and K; vitamin K deficiency can prolong coagulation measures.
intestinal lipid absorption link
Downstream
Fat malabsorption Defective chylomicron export produces abnormal gastrointestinal fat absorption.
Steatorrhea Fat malabsorption leads to fat-rich stools.
Chronic diarrhea Fat malabsorption contributes to chronic diarrhea in infancy.
Failure to thrive Malabsorption and inadequate caloric utilization contribute to growth failure.
Reduced circulating vitamin A concentration Fat-soluble vitamin malabsorption lowers circulating vitamin A.
Decreased circulating vitamin D concentration Fat-soluble vitamin malabsorption lowers circulating vitamin D.
Decreased circulating vitamin E concentration Fat-soluble vitamin malabsorption lowers circulating vitamin E.
Low fat-soluble vitamin concentrations Fat-soluble vitamin malabsorption produces decreased vitamin A, D, E, and K concentrations that require surveillance.
Vitamin E-Linked Neurologic and Retinal Injury Persistent deficiency of fat-soluble vitamins contributes to retinal degeneration and neurologic injury.
Vitamin K-Related Coagulation Abnormality Fat-soluble vitamin malabsorption includes vitamin K deficiency, which can increase INR and prolong coagulation testing.
Show evidence (2 references)
ORPHA:14 SUPPORT Other
"A severe, familial hypobetalipoproteinemia characterized by permanently low levels (below the 5th percentile) of apolipoprotein B and LDL cholesterol, and by growth delay, malabsorption, hepatomegaly, and neurological and neuromuscular manifestations."
Orphanet definition links hypobetalipoproteinemia with growth delay and malabsorption.
PMID:30358967 SUPPORT Human Clinical
"Malabsorption of fat-soluble vitamins (A, D, E, and K) can"
GeneReviews supports fat-soluble vitamin malabsorption as a consequence of the disorder.
Vitamin E-Linked Neurologic and Retinal Injury
Persistent fat-soluble vitamin deficiency, especially vitamin E deficiency, is associated with progressive retinal degeneration and neuromuscular disease. Untreated individuals can develop loss of night and color vision, abnormal retinal pigmentation, loss of deep tendon reflexes, posterior column sensory dysfunction, dysarthria, ataxia, neuropathy, and myopathy.
Downstream
Abnormality of the nervous system Vitamin deficiency contributes to neurologic manifestations.
Progressive visual loss Retinal degeneration causes progressive visual loss.
Color vision defect Retinal involvement can impair color vision.
Nyctalopia Retinal involvement can cause night blindness.
Abnormal retinal pigmentation Untreated retinal disease produces abnormal retinal pigmentation.
Areflexia Neuromuscular involvement includes progressive loss of reflexes.
Ataxia Neuromuscular involvement can cause ataxia.
Dysarthria Neuromuscular involvement can cause dysarthria.
Impaired vibratory sensation Posterior column and sensory involvement can impair vibratory sensation.
Myalgia Neuromuscular involvement can include myopathy and muscle pain.
Show evidence (2 references)
PMID:24288038 SUPPORT Human Clinical
"malabsorption of lipid-soluble vitamins leading to retinal degeneration,"
This review links lipid-soluble vitamin malabsorption to retinal degeneration.
PMID:18611256 SUPPORT Human Clinical
"development of atypical retinitis pigmentosa, coagulopathy, posterior column"
Long-term clinical cases and review link fat-soluble vitamin deficiency to retinal, coagulation, and neurologic complications.
Acanthocytic Hematologic Manifestations
ApoB-lipoprotein absence and altered lipid transport are associated with acanthocytosis on blood smear and hematologic manifestations including anemia, reticulocytosis, hemolysis, and hyperbilirubinemia.
Downstream
Acanthocytosis Altered red-cell membrane morphology causes acanthocytosis.
Anemia Hematologic involvement can include anemia.
Reticulocytosis Hemolysis can increase reticulocytes.
Hyperbilirubinemia Hemolysis can increase bilirubin.
Show evidence (2 references)
PMID:30358967 SUPPORT Human Clinical
"Hematologic manifestations may include acanthocytosis (irregularly spiculated"
GeneReviews supports acanthocytosis as part of the hematologic phenotype.
PMID:24288038 SUPPORT Human Clinical
"Clinical diagnosis is based on signs and symptoms, acanthocytosis"
This review identifies acanthocytosis as a diagnostic sign.
Hepatic Steatosis and Laboratory Abnormalities
Hepatic involvement can include hepatomegaly, hepatic steatosis, mild transaminase elevation, hypoalbuminemia, and rarely progression to fibrosis or cirrhosis. Hepatic steatosis is recognized in clinical reviews and is monitored during follow-up.
hepatocyte link
Downstream
Hepatomegaly Hepatic lipid handling defects can manifest as hepatomegaly.
Hepatic steatosis Impaired hepatic apoB-lipoprotein export contributes to hepatic steatosis.
Hypoalbuminemia Hepatic and malabsorptive involvement can be accompanied by hypoalbuminemia.
Show evidence (2 references)
PMID:24288038 SUPPORT Human Clinical
"neuropathy and coagulopathy. Hepatic steatosis is also common."
This review supports hepatic steatosis as a common hepatic manifestation.
PMID:30358967 SUPPORT Human Clinical
"liver function tests (AST, ALT, GGT, total and"
GeneReviews recommends surveillance of liver tests, supporting clinically relevant hepatic involvement.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Abetalipoproteinemia Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
●

Phenotypes

30
Blood 2
Anemia FREQUENT Anemia (HP:0001903)
Show evidence (1 reference)
ORPHA:14 SUPPORT Other
"HP:0001903 | Anemia | Frequent (79-30%)"
Orphanet records anemia as frequent.
Reticulocytosis FREQUENT Reticulocytosis (HP:0001923)
Show evidence (1 reference)
ORPHA:14 SUPPORT Other
"HP:0001923 | Reticulocytosis | Frequent (79-30%)"
Orphanet records reticulocytosis as frequent.
Digestive 4
Steatorrhea VERY_FREQUENT Steatorrhea (HP:0002570)
Show evidence (1 reference)
ORPHA:14 SUPPORT Other
"HP:0002570 | Steatorrhea | Very frequent (99-80%)"
Orphanet records steatorrhea as very frequent.
Chronic diarrhea FREQUENT Chronic diarrhea (HP:0002028)
Show evidence (2 references)
ORPHA:14 SUPPORT Other
"HP:0002028 | Chronic diarrhea | Frequent (79-30%)"
Orphanet records chronic diarrhea as frequent.
PMID:30358967 SUPPORT Human Clinical
"with failure to thrive, diarrhea, vomiting, and malabsorption of fat."
GeneReviews supports diarrhea as part of the typical infant presentation.
Hepatomegaly OCCASIONAL Hepatomegaly (HP:0002240)
Show evidence (1 reference)
ORPHA:14 SUPPORT Other
"HP:0002240 | Hepatomegaly | Occasional (29-5%)"
Orphanet records hepatomegaly as occasional.
Hepatic steatosis OCCASIONAL Hepatic steatosis (HP:0001397)
Show evidence (2 references)
ORPHA:14 SUPPORT Other
"HP:0001397 | Hepatic steatosis | Occasional (29-5%)"
Orphanet records hepatic steatosis as occasional.
PMID:24288038 SUPPORT Human Clinical
"neuropathy and coagulopathy. Hepatic steatosis is also common."
This review supports hepatic steatosis as a common manifestation.
Eye 4
Progressive visual loss FREQUENT Progressive visual loss (HP:0000529)
Show evidence (1 reference)
ORPHA:14 SUPPORT Other
"HP:0000529 | Progressive visual loss | Frequent (79-30%)"
Orphanet records progressive visual loss as frequent.
Color vision defect FREQUENT Color vision defect (HP:0000551)
Show evidence (2 references)
ORPHA:14 SUPPORT Other
"HP:0000551 | Color vision defect | Frequent (79-30%)"
Orphanet records color vision defect as frequent.
PMID:30358967 SUPPORT Human Clinical
"with progressive loss of night vision and/or color vision in adulthood."
GeneReviews supports acquired loss of color vision as a retinal manifestation.
Nyctalopia FREQUENT Nyctalopia (HP:0000662)
Show evidence (2 references)
ORPHA:14 SUPPORT Other
"HP:0000662 | Nyctalopia | Frequent (79-30%)"
Orphanet records nyctalopia as frequent.
PMID:30358967 SUPPORT Human Clinical
"with progressive loss of night vision and/or color vision in adulthood."
GeneReviews supports night vision loss as a retinal manifestation.
Abnormal retinal pigmentation FREQUENT Abnormal retinal pigmentation (HP:0007703)
Show evidence (1 reference)
ORPHA:14 SUPPORT Other
"HP:0007703 | Abnormality of retinal pigmentation | Frequent (79-30%)"
Orphanet records abnormal retinal pigmentation as frequent.
Metabolism 2
Decreased HDL cholesterol concentration FREQUENT Decreased HDL cholesterol concentration (HP:0003233)
Show evidence (1 reference)
ORPHA:14 SUPPORT Other
"HP:0003233 | Decreased HDL cholesterol concentration | Frequent (79-30%)"
Orphanet records decreased HDL cholesterol concentration as frequent.
Hypoalbuminemia FREQUENT Hypoalbuminemia (HP:0003073)
Show evidence (1 reference)
ORPHA:14 SUPPORT Other
"HP:0003073 | Hypoalbuminemia | Frequent (79-30%)"
Orphanet records hypoalbuminemia as frequent.
Nervous System 4
Abnormality of the nervous system VERY_FREQUENT Abnormality of the nervous system (HP:0000707)
Show evidence (1 reference)
ORPHA:14 SUPPORT Other
"HP:0000707 | Abnormality of the nervous system | Very frequent (99-80%)"
Orphanet records nervous-system abnormality as very frequent.
Areflexia FREQUENT Areflexia (HP:0001284)
Show evidence (2 references)
ORPHA:14 SUPPORT Other
"HP:0001284 | Areflexia | Frequent (79-30%)"
Orphanet records areflexia as frequent.
PMID:30358967 SUPPORT Human Clinical
"deep tendon reflexes, vibratory sense, and proprioception; muscle weakness;"
GeneReviews describes progressive loss of deep tendon reflexes in untreated individuals.
Ataxia OCCASIONAL Ataxia (HP:0001251)
Show evidence (2 references)
ORPHA:14 SUPPORT Other
"HP:0001251 | Ataxia | Occasional (29-5%)"
Orphanet records ataxia as an occasional phenotype.
PMID:30358967 SUPPORT Human Clinical
"dysarthria; and ataxia typically manifest"
GeneReviews describes ataxia among neuromuscular findings in untreated individuals.
Dysarthria OCCASIONAL Dysarthria (HP:0001260)
Show evidence (2 references)
ORPHA:14 SUPPORT Other
"HP:0001260 | Dysarthria | Occasional (29-5%)"
Orphanet records dysarthria as an occasional phenotype.
PMID:30358967 SUPPORT Human Clinical
"dysarthria; and ataxia typically manifest"
GeneReviews describes dysarthria among neuromuscular findings in untreated individuals.
Constitutional 1
Myalgia FREQUENT Myalgia (HP:0003326)
Show evidence (1 reference)
ORPHA:14 SUPPORT Other
"HP:0003326 | Myalgia | Frequent (79-30%)"
Orphanet records myalgia as frequent.
Growth 1
Failure to thrive FREQUENT Failure to thrive (HP:0001508)
Show evidence (1 reference)
ORPHA:14 SUPPORT Other
"HP:0001508 | Failure to thrive | Frequent (79-30%)"
Orphanet records failure to thrive as frequent.
Other 12
Abnormal circulating apolipoprotein concentration VERY_FREQUENT Abnormal circulating apolipoprotein concentration (HP:0025201)
Show evidence (1 reference)
ORPHA:14 SUPPORT Other
"HP:0025201 | Abnormal circulating apolipoprotein concentration | Very frequent (99-80%)"
Orphanet records abnormal circulating apolipoprotein concentration as very frequent.
Hypocholesterolemia FREQUENT Hypocholesterolemia (HP:0003146)
Show evidence (2 references)
ORPHA:14 SUPPORT Other
"HP:0003146 | Hypocholesterolemia | Frequent (79-30%)"
Orphanet records hypocholesterolemia as frequent.
PMID:24288038 SUPPORT Human Clinical
"are rare diseases characterized by hypocholesterolemia and"
This review describes hypocholesterolemia as a core feature.
Decreased LDL cholesterol concentration FREQUENT Decreased LDL cholesterol concentration (HP:0003563)
Show evidence (2 references)
ORPHA:14 SUPPORT Other
"HP:0003563 | Decreased LDL cholesterol concentration | Frequent (79-30%)"
Orphanet records decreased LDL cholesterol concentration as frequent.
PMID:30358967 SUPPORT Human Clinical
"proband with absent or extremely low LDL-cholesterol, triglyceride, and"
GeneReviews describes absent or extremely low LDL cholesterol as a diagnostic biochemical feature.
Hypotriglyceridemia FREQUENT Hypotriglyceridemia (HP:0012153)
Show evidence (1 reference)
ORPHA:14 SUPPORT Other
"HP:0012153 | Hypotriglyceridemia | Frequent (79-30%)"
Orphanet records hypotriglyceridemia as frequent.
Fat malabsorption VERY_FREQUENT Fat malabsorption (HP:0002630)
Show evidence (1 reference)
ORPHA:14 SUPPORT Other
"HP:0002630 | Fat malabsorption | Very frequent (99-80%)"
Orphanet records fat malabsorption as very frequent.
Reduced circulating vitamin A concentration FREQUENT Reduced circulating vitamin A concentration (HP:0004905)
Show evidence (1 reference)
ORPHA:14 SUPPORT Other
"HP:0004905 | Low levels of vitamin A | Frequent (79-30%)"
Orphanet records low vitamin A levels as frequent.
Decreased circulating vitamin D concentration FREQUENT Decreased circulating vitamin D concentration (HP:0100512)
Show evidence (1 reference)
ORPHA:14 SUPPORT Other
"HP:0100512 | Low levels of vitamin D | Frequent (79-30%)"
Orphanet records low vitamin D levels as frequent.
Decreased circulating vitamin E concentration VERY_FREQUENT Decreased circulating vitamin E concentration (HP:0100513)
Show evidence (1 reference)
ORPHA:14 SUPPORT Other
"HP:0100513 | Low levels of vitamin E | Very frequent (99-80%)"
Orphanet records low vitamin E levels as very frequent.
Acanthocytosis VERY_FREQUENT Acanthocytosis (HP:0001927)
Show evidence (2 references)
ORPHA:14 SUPPORT Other
"HP:0001927 | Acanthocytosis | Very frequent (99-80%)"
Orphanet records acanthocytosis as very frequent.
PMID:30358967 SUPPORT Human Clinical
"Hematologic manifestations may include acanthocytosis (irregularly spiculated"
GeneReviews supports acanthocytosis as a hematologic manifestation.
Hyperbilirubinemia FREQUENT Hyperbilirubinemia (HP:0002904)
Show evidence (1 reference)
ORPHA:14 SUPPORT Other
"HP:0002904 | Hyperbilirubinemia | Frequent (79-30%)"
Orphanet records hyperbilirubinemia as frequent.
Impaired vibratory sensation OCCASIONAL Impaired vibratory sensation (HP:0002495)
Show evidence (2 references)
ORPHA:14 SUPPORT Other
"HP:0002495 | Impaired vibratory sensation | Occasional (29-5%)"
Orphanet records impaired vibratory sensation as an occasional phenotype.
PMID:30358967 SUPPORT Human Clinical
"deep tendon reflexes, vibratory sense, and proprioception; muscle weakness;"
GeneReviews describes progressive loss of vibratory sense in untreated individuals.
Prolonged prothrombin time OCCASIONAL Prolonged prothrombin time (HP:0008151)
Show evidence (2 references)
ORPHA:14 SUPPORT Other
"HP:0008151 | Prolonged prothrombin time | Occasional (29-5%)"
Orphanet records prolonged prothrombin time as occasional.
PMID:30358967 SUPPORT Human Clinical
"result in an increased international normalized ratio (INR)."
GeneReviews links fat-soluble vitamin malabsorption to increased INR.
🧬

Genetic Associations

1
MTTP pathogenic variants (Causative biallelic pathogenic variants)
Autosomal recessive inheritance
Show evidence (2 references)
ORPHA:14 SUPPORT Other
"MTTP | microsomal triglyceride transfer protein | hgnc:7467 | Disease-causing germline mutation(s) in"
Orphanet records MTTP as a disease-causing germline gene for Abetalipoproteinemia.
PMID:30358967 SUPPORT Human Clinical
"biallelic pathogenic variants in MTTP"
GeneReviews supports biallelic MTTP pathogenic variants as diagnostic for Abetalipoproteinemia.
💊

Treatments

3
Low-fat diet with long-chain fatty acid avoidance
Action: dietary intervention MAXO:0000088
Prescribed dietary fat restriction reduces steatorrhea and limits the load of long-chain fatty acids that cannot be normally transported by chylomicrons.
Mechanism Target:
MODULATES Fat and Fat-Soluble Vitamin Malabsorption — Low-fat diet reduces symptoms caused by defective intestinal chylomicron-mediated lipid transport.
Show evidence (1 reference)
PMID:24288038 SUPPORT Human Clinical
"Mainstays of treatment include adherence to a low-fat"
The review identifies low-fat diet as a mainstay of treatment.
Show evidence (2 references)
PMID:30358967 SUPPORT Human Clinical
"low-fat diet (10%-20% of total calories from fat); oral"
GeneReviews gives the dietary fat target for treatment.
PMID:30358967 SUPPORT Human Clinical
"particularly those rich in long-chain fatty acids."
GeneReviews recommends avoiding fatty foods, especially those rich in long-chain fatty acids.
Fat-soluble vitamin supplementation
Action: nutritional supplementation MAXO:0000106
High-dose supplementation with vitamins A, D, E, and K is used to prevent or limit retinal, neurologic, hematologic, and coagulation complications.
Mechanism Target:
RESTORES Fat and Fat-Soluble Vitamin Malabsorption — Supplementation replaces fat-soluble vitamins that are poorly absorbed and transported.
Show evidence (1 reference)
PMID:30358967 SUPPORT Human Clinical
"Most complications can be prevented through institution"
GeneReviews states most complications can be prevented by low-fat diet plus fat-soluble vitamin supplementation.
INHIBITS Vitamin E-Linked Neurologic and Retinal Injury — Vitamin supplementation, especially vitamin E, is intended to prevent or halt neurologic and retinal complications.
Show evidence (1 reference)
PMID:18611256 SUPPORT Human Clinical
"Treatment appears to have been associated with arrest of the neuropathy"
Long-term treated cases support vitamin supplementation as associated with arrest of neuropathy and other complications.
Show evidence (2 references)
PMID:30358967 SUPPORT Human Clinical
"polyunsaturated fatty acids, as tolerated); supplementation with vitamin A"
GeneReviews recommends supplementation with fat-soluble vitamins beginning with vitamin A.
PMID:18611256 SUPPORT Human Clinical
"high oral doses of fat soluble vitamins, including vitamin E over the last three"
Long-term cases describe high-dose fat-soluble vitamin treatment including vitamin E.
Essential fatty acid supplementation
Action: nutritional supplementation MAXO:0000106
Small amounts of oils rich in polyunsaturated fatty acids are used as tolerated to provide essential fatty acids despite overall dietary fat restriction.
Mechanism Target:
MODULATES Fat and Fat-Soluble Vitamin Malabsorption — Essential fatty acid supplementation balances deficiency risk against fat intolerance.
Show evidence (1 reference)
PMID:30358967 SUPPORT Human Clinical
"essential fatty acid supplementation (up to 1 teaspoon per day of oils rich in"
GeneReviews recommends oral essential fatty acid supplementation as tolerated.
Show evidence (1 reference)
PMID:24288038 SUPPORT Human Clinical
"supplementation with essential fatty acids and high oral doses of fat"
The management review lists essential fatty acid supplementation as a mainstay of treatment.
🔬

Biochemical Markers

2
Absent apoB-containing lipoproteins (DECREASED)
Context: ApoB-containing lipoproteins including chylomicrons, VLDL, and LDL are absent or virtually absent.
Pathograph Readouts
Readout Of Impaired ApoB Lipoprotein Assembly and Secretion Negative Diagnostic
Absent or extremely low apoB-containing lipoproteins report failed apoB particle assembly and secretion.
Show evidence (1 reference)
PMID:24288038 SUPPORT Human Clinical
"virtually absent apo B-containing lipoproteins, including"
The review supports absent apoB-containing lipoproteins as the diagnostic biochemical readout of failed apoB-particle assembly.
Show evidence (1 reference)
PMID:24288038 SUPPORT Human Clinical
"virtually absent apo B-containing lipoproteins, including"
The review supports absent apoB-containing lipoproteins as a diagnostic biochemical finding.
Low fat-soluble vitamin concentrations (DECREASED)
Context: Vitamin A, D, E, and K levels are reduced due to fat malabsorption and require surveillance.
Pathograph Readouts
Readout Of Fat and Fat-Soluble Vitamin Malabsorption Negative Monitoring
Lower fat-soluble vitamin concentrations track impaired intestinal absorption and replacement needs.
Show evidence (1 reference)
PMID:30358967 SUPPORT Human Clinical
"fat-soluble vitamin levels"
GeneReviews recommends monitoring fat-soluble vitamin levels, supporting them as readouts of the malabsorption branch.
Show evidence (1 reference)
PMID:30358967 SUPPORT Human Clinical
"Malabsorption of fat-soluble vitamins (A, D, E, and K) can"
GeneReviews directly supports fat-soluble vitamin malabsorption as a biochemical consequence of the disease.
{ }

Source YAML

click to show 
name: Abetalipoproteinemia
creation_date: '2026-05-04T05:21:52Z'
updated_date: '2026-05-21T20:10:55Z'
category: Mendelian
description: >
  Abetalipoproteinemia is a severe autosomal recessive disorder of
  apoB-containing lipoprotein assembly and secretion caused by biallelic MTTP
  pathogenic variants. Loss of microsomal triglyceride transfer protein
  function prevents normal chylomicron export from enterocytes and VLDL export
  from hepatocytes, producing absent or extremely low apoB-containing
  lipoproteins, hypocholesterolemia, hypotriglyceridemia, fat malabsorption,
  and secondary fat-soluble vitamin deficiency. Infants typically present with
  failure to thrive, diarrhea, vomiting, steatorrhea, acanthocytosis, and
  abnormal lipid studies; untreated individuals can later develop retinal,
  neurologic, hematologic, hepatic, and coagulation complications. Management
  centers on a low-fat diet, essential fatty acid intake, and high-dose
  fat-soluble vitamin supplementation.
disease_term:
  preferred_term: abetalipoproteinemia
  term:
    id: MONDO:0008692
    label: abetalipoproteinemia
notes: >-
  ORPHA:14 cross-references Abetalipoproteinemia to MONDO:0008692 with an Exact
  mapping and also lists ICD-10:E78.6, ICD-11:5C81.1, MeSH:D000012,
  MedDRA:10083851, OMIM:200100, OMIM:605019, OMIM:615558, and UMLS:C0000744.
synonyms:
- Bassen-Kornzweig disease
- Homozygous familial hypobetalipoproteinemia
- ABL
- MTP deficiency
parents:
- Hypobetalipoproteinemia
- Intestinal Disorder
- Hereditary Peripheral Neuropathy
inheritance:
- name: Autosomal Recessive
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Autosomal recessive"
    explanation: Orphanet classifies Abetalipoproteinemia inheritance as autosomal recessive.
  - reference: PMID:30358967
    reference_title: "Abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "inherited in an autosomal recessive"
    explanation: GeneReviews states that abetalipoproteinemia is inherited in an autosomal recessive manner.
prevalence:
- population: Worldwide
  percentage: <1 per 1,000,000
  notes: >-
    Orphanet records Abetalipoproteinemia as an ultra-rare disorder with
    worldwide point prevalence below 1 per 1,000,000.
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "<1 / 1 000 000 | Worldwide | Point prevalence | PMID:30358967"
    explanation: Orphanet provides a worldwide point-prevalence estimate below 1 per 1,000,000.
progression:
- phase: Onset
  age_range: Infancy to childhood
  notes: >-
    Orphanet lists infancy and childhood onset categories, while GeneReviews
    describes typical presentation in infancy with gastrointestinal
    malabsorption and growth failure.
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Age of onset: Infancy"
    explanation: Orphanet records infancy as an onset category for Abetalipoproteinemia.
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Age of onset: Childhood"
    explanation: Orphanet records childhood as an onset category for Abetalipoproteinemia.
  - reference: PMID:30358967
    reference_title: "Abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "with failure to thrive, diarrhea, vomiting, and malabsorption of fat."
    explanation: GeneReviews supports the typical early presentation with failure to thrive and fat malabsorption.
mechanistic_hypotheses:
- hypothesis_group_id: canonical_mttp_lipoprotein_assembly_model
  hypothesis_label: Canonical MTTP ApoB-Lipoprotein Assembly Model
  status: CANONICAL
  description: >
    Biallelic MTTP pathogenic variants impair MTP function, preventing assembly
    and secretion of apoB-containing chylomicrons and VLDL particles. This
    produces absent circulating apoB lipoproteins, intestinal fat malabsorption,
    and fat-soluble vitamin deficiency that drives retinal, neurologic,
    hematologic, and coagulation manifestations.
  notes: >-
    Retained as CANONICAL. The 2026 openscientist hypothesis-search report
    (kb/hypotheses/Abetalipoproteinemia/canonical_mttp_lipoprotein_assembly_model)
    reviewed 82 papers and found zero refutations of the MTP loss-of-function
    pathway. Three qualifications refine the canonical model: (1) MTP operates
    as an obligate heterodimer with PDI and disease-causing truncations
    selectively disrupt this interaction; (2) local MTP expression in retinal
    pigment epithelium and ganglion cells suggests a tissue-autonomous
    component to ABL retinopathy beyond systemic vitamin E deficiency; and
    (3) hypomorphic MTTP alleles retain partial function and produce
    attenuated phenotypes with detectable apoB48 secretion, demonstrating a
    genotype-phenotype gradient. Pharmacological MTP inhibition with
    lomitapide and viral inhibition by HCV core protein independently
    recapitulate the canonical pathway.
  evidence:
  - reference: PMID:24288038
    reference_title: "Abetalipoproteinemia and homozygous hypobetalipoproteinemia: a framework for diagnosis and management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "improper packaging and secretion of apolipoprotein (apo)"
    explanation: This review identifies defective apoB-lipoprotein packaging and secretion as the root mechanism.
  - reference: PMID:30522860
    reference_title: "Postprandial lipid absorption in seven heterozygous carriers of deleterious variants of MTTP in two abetalipoproteinemic families."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "export apolipoprotein B-containing lipoproteins from both the intestine and the"
    explanation: This clinical lipid-absorption study supports defective intestinal and hepatic apoB-lipoprotein export.
  - reference: PMID:1439810
    reference_title: "Absence of microsomal triglyceride transfer protein in individuals with abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "MTP activity and the 88-kilodalton component of MTP were present in intestinal biopsy samples from eight control individuals but were absent in four abetalipoproteinemic subjects."
    explanation: >
      Foundational 1992 discovery directly measured absent MTP protein and
      enzymatic activity in human intestinal biopsies from ABL patients,
      establishing MTP loss as the molecular basis of the disease.
  - reference: PMID:7782284
    reference_title: "A 30 amino acid truncation of the microsomal triglyceride transfer protein large subunit disrupts its interaction with protein disulfide-isomerase and causes abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "only the normal subunit was able to form a stable, soluble complex with protein disulfide-isomerase"
    explanation: >
      Biochemical reconstitution shows that a patient-derived MTP C-terminal
      truncation fails to form the obligate stable complex with PDI,
      explaining absent MTP in the Wetterau 1992 patient and supporting the
      MTP-PDI heterodimer requirement.
  - reference: PMID:10856714
    reference_title: "Progress towards understanding the role of microsomal triglyceride transfer protein in apolipoprotein-B lipoprotein assembly."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "initiation of lipidation of the nascent apolipoprotein B polypeptide may occur through a direct association with MTP"
    explanation: >
      Review of biochemical studies supporting a two-step MTP-dependent
      assembly model: cotranslational lipidation of nascent apoB followed by
      formation of ER-lumenal triglyceride droplets that mature into
      apoB-lipoproteins.
  - reference: PMID:24842304
    reference_title: "Hepatic abnormalities in abetalipoproteinemia and homozygous familial hypobetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "liver steatosis was observed in both groups with a high prevalence of severe fibrosis"
    explanation: >
      Clinical comparison of 7 new ABL and 7 new Ho-FHBL cases plus the
      published literature shows hepatic steatosis and severe fibrosis in
      both diseases, consistent with blocked VLDL-mediated triglyceride
      export as the cause of liver disease.
  - reference: PMID:25488886
    reference_title: "Pregnancy in a 23-year-old with abetalipoproteinaemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These neurological complications stem from demyelination secondary to vitamin E deficiency."
    explanation: >
      Clinical review attributes the neurological manifestations of ABL
      (ataxia, peripheral neuropathy, hyporeflexia) to demyelination caused
      by fat-soluble vitamin (especially vitamin E) deficiency downstream of
      absent chylomicron secretion.
  - reference: PMID:28598687
    reference_title: "Lomitapide for the treatment of hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Lomitapide is an inhibitor of microsomal triglyceride transfer protein (MTP) that blocks the assembly of metabolic precursors of LDL particles."
    explanation: >
      Pharmacological MTP inhibition in HoFH patients recapitulates the ABL
      lipoprotein assembly block, providing prospective interventional
      validation of MTP as the rate-limiting step. The side-effect profile
      (GI symptoms, hepatic steatosis) mirrors ABL manifestations.
  - reference: PMID:11818366
    reference_title: "Hepatitis C virus core protein inhibits microsomal triglyceride transfer protein activity and very low density lipoprotein secretion: a model of viral-related steatosis."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Core expression led to reduction in microsomal triglyceride transfer protein (MTP) activity"
    explanation: >
      Transgenic mouse model of HCV core protein expression independently
      reproduces the MTP-VLDL-steatosis causal chain, validating MTP
      inhibition as sufficient to cause hepatic steatosis through blocked
      VLDL secretion.
  - reference: PMID:15654125
    reference_title: "Apolipoprotein B-containing lipoproteins in retinal aging and age-related macular degeneration."
    supports: PARTIAL
    evidence_source: IN_VITRO
    snippet: "MTP is expressed in RPE, the ARPE-19 cell line, and, unexpectedly, retinal ganglion cells"
    explanation: >
      Qualifies the canonical model by demonstrating local MTP expression in
      retinal pigment epithelium and ganglion cells, suggesting a
      tissue-autonomous mechanism for ABL retinopathy in addition to
      systemic vitamin E deficiency.
  - reference: PMID:30875496
    reference_title: "A novel splice site mutation in the microsomal triglyceride transfer protein gene results in abetalipoproteinemia with a milder phenotype."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "normal serum apolipoprotein B48 (apoB48) and red blood cell vitamin E concentrations"
    explanation: >
      Qualifies the canonical model by reporting a compound-heterozygous ABL
      patient with a hypomorphic MTTP allele that retains 65% of normal MTP
      activity, producing detectable apoB48 secretion and an attenuated
      phenotype. Supports a genotype-phenotype gradient within ABL.
  - reference: PMID:30640893
    reference_title: "Recent advances in the pathophysiology of chylomicron retention disease."
    supports: PARTIAL
    evidence_source: OTHER
    snippet: "CRD patients present with SAR1B mutations, which disable the formation of coat protein complex II and thus blocks the transport of chylomicron cargo from the endoplasmic reticulum to the Golgi"
    explanation: >
      Competing differential diagnosis: chylomicron retention disease (CRD)
      caused by SAR1B mutations phenocopies the intestinal component of ABL
      but spares hepatic VLDL secretion. This refines the canonical model by
      localizing the MTP defect to the lipoprotein-assembly step, distinct
      from ER-to-Golgi transport defects downstream.
pathophysiology:
- name: MTTP Loss of Function
  description: >
    Pathogenic variants in MTTP reduce or abolish microsomal triglyceride
    transfer protein function. MTP normally forms a lipid-transfer complex with
    protein disulfide isomerase; loss of the functional 97-kDa subunit or
    missense variants that disrupt the complex prevent normal apoB particle
    biogenesis.
  gene:
    preferred_term: MTTP
    term:
      id: hgnc:7467
      label: MTTP
  molecular_functions:
  - preferred_term: lipid transfer activity
    term:
      id: GO:0120013
      label: lipid transfer activity
  - preferred_term: apolipoprotein binding
    term:
      id: GO:0034185
      label: apolipoprotein binding
  biological_processes:
  - preferred_term: triglyceride transport
    term:
      id: GO:0034197
      label: triglyceride transport
  - preferred_term: lipoprotein metabolic process
    term:
      id: GO:0042157
      label: lipoprotein metabolic process
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "MTTP | microsomal triglyceride transfer protein | hgnc:7467 | Disease-causing germline mutation(s) in"
    explanation: Orphanet records MTTP as a disease-causing gene for Abetalipoproteinemia.
  - reference: PMID:10946006
    reference_title: "Novel mutations in the microsomal triglyceride transfer protein gene causing abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "mutations of the MTP gene have been screened in 4"
    explanation: Patient mutation screening supports MTTP variants as the human genetic cause of ABL.
  - reference: PMID:10946006
    reference_title: "Novel mutations in the microsomal triglyceride transfer protein gene causing abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "displayed negligible MTP activity."
    explanation: COS-1 expression testing supports loss of MTP activity for a disease-associated MTTP missense variant.
  - reference: PMID:8939939
    reference_title: "A novel abetalipoproteinemia genotype. Identification of a missense mutation in the 97-kDa subunit of the microsomal triglyceride transfer protein that prevents complex formation with protein disulfide isomerase."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "forming an active MTP complex while the mutant was not."
    explanation: Functional expression data show that an abetalipoproteinemia-associated MTTP mutant fails to form active MTP complex.
  downstream:
  - target: Impaired ApoB Lipoprotein Assembly and Secretion
    description: MTTP loss prevents the lipid-transfer activity required to assemble and secrete apoB-containing lipoproteins.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:24288038
      reference_title: "Abetalipoproteinemia and homozygous hypobetalipoproteinemia: a framework for diagnosis and management."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "improper packaging and secretion of apolipoprotein (apo)"
      explanation: The review identifies defective apoB-lipoprotein packaging and secretion as the root consequence of MTTP loss.
- name: Impaired ApoB Lipoprotein Assembly and Secretion
  description: >
    Defective MTP activity prevents assembly and secretion of apoB-containing
    particles, including intestinal chylomicrons and hepatic VLDL. The resulting
    absence of apoB-containing lipoproteins causes severe hypocholesterolemia,
    hypotriglyceridemia, and low LDL cholesterol.
  biological_processes:
  - preferred_term: chylomicron assembly
    term:
      id: GO:0034378
      label: chylomicron assembly
  - preferred_term: very-low-density lipoprotein particle assembly
    term:
      id: GO:0034379
      label: very-low-density lipoprotein particle assembly
  - preferred_term: lipid transport
    term:
      id: GO:0006869
      label: lipid transport
  cell_types:
  - preferred_term: enterocyte
    term:
      id: CL:0000584
      label: enterocyte
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  evidence:
  - reference: PMID:24288038
    reference_title: "Abetalipoproteinemia and homozygous hypobetalipoproteinemia: a framework for diagnosis and management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "chylomicrons, very low density lipoprotein and low density lipoprotein."
    explanation: The review states that apoB-containing chylomicrons, VLDL, and LDL are virtually absent.
  - reference: PMID:30522860
    reference_title: "Postprandial lipid absorption in seven heterozygous carriers of deleterious variants of MTTP in two abetalipoproteinemic families."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "undetectable concentrations of apolipoprotein B, extremely low levels of"
    explanation: This supports the characteristic apoB and LDL biochemical depletion downstream of MTTP variants.
  downstream:
  - target: Fat and Fat-Soluble Vitamin Malabsorption
    description: Loss of chylomicron export impairs intestinal absorption and transport of dietary fat and fat-soluble vitamins.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - absent intestinal chylomicron export and impaired lipid-soluble vitamin transport
    evidence:
    - reference: PMID:24288038
      reference_title: "Abetalipoproteinemia and homozygous hypobetalipoproteinemia: a framework for diagnosis and management."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "malabsorption of lipid-soluble vitamins leading to retinal degeneration,"
      explanation: The review links defective apoB-lipoprotein handling in ABL to lipid-soluble vitamin malabsorption.
  - target: Absent apoB-containing lipoproteins
    description: Failure to assemble and secrete chylomicron, VLDL, and LDL particles is observed as absent apoB-containing lipoproteins.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:24288038
      reference_title: "Abetalipoproteinemia and homozygous hypobetalipoproteinemia: a framework for diagnosis and management."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "virtually absent apo B-containing lipoproteins, including"
      explanation: The review supports absent apoB-containing lipoproteins as the direct biochemical consequence of failed apoB-particle assembly.
  - target: Abnormal circulating apolipoprotein concentration
    description: Failure to secrete apoB-containing particles causes abnormal circulating apolipoprotein concentration.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:30522860
      reference_title: "Postprandial lipid absorption in seven heterozygous carriers of deleterious variants of MTTP in two abetalipoproteinemic families."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "undetectable concentrations of apolipoprotein B, extremely low levels of"
      explanation: The clinical lipid-absorption study directly supports apoB depletion downstream of MTTP-related export failure.
  - target: Hypocholesterolemia
    description: Loss of LDL/VLDL particles causes markedly decreased circulating cholesterol.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:24288038
      reference_title: "Abetalipoproteinemia and homozygous hypobetalipoproteinemia: a framework for diagnosis and management."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "are rare diseases characterized by hypocholesterolemia and"
      explanation: The review characterizes ABL as a hypocholesterolemic disorder caused by failed apoB-lipoprotein packaging and secretion.
  - target: Decreased LDL cholesterol concentration
    description: Defective apoB-lipoprotein secretion causes absent or extremely low LDL cholesterol.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:30358967
      reference_title: "Abetalipoproteinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "proband with absent or extremely low LDL-cholesterol, triglyceride, and"
      explanation: GeneReviews supports absent or extremely low LDL cholesterol as part of the diagnostic consequence of ABL.
  - target: Decreased HDL cholesterol concentration
    description: The ABL lipid phenotype can include decreased HDL cholesterol; the intervening mechanism is not specified in the cited clinical sources.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: ORPHA:14
      reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0003233 | Decreased HDL cholesterol concentration | Frequent (79-30%)"
      explanation: Orphanet records decreased HDL cholesterol concentration as a frequent biochemical phenotype of ABL.
  - target: Hypotriglyceridemia
    description: Loss of chylomicron and VLDL secretion produces very low circulating triglycerides.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:30358967
      reference_title: "Abetalipoproteinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "proband with absent or extremely low LDL-cholesterol, triglyceride, and"
      explanation: GeneReviews supports absent or extremely low triglycerides as part of the diagnostic biochemical consequence of ABL.
  - target: Acanthocytic Hematologic Manifestations
    description: Severe apoB-lipoprotein depletion is clinically associated with acanthocytosis and related hematologic abnormalities.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:24288038
      reference_title: "Abetalipoproteinemia and homozygous hypobetalipoproteinemia: a framework for diagnosis and management."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Clinical diagnosis is based on signs and symptoms, acanthocytosis"
      explanation: The review places acanthocytosis in the clinical phenotype arising from defective apoB-lipoprotein packaging and secretion.
  - target: Hepatic Steatosis and Laboratory Abnormalities
    description: Failed hepatic VLDL export promotes hepatic lipid retention and downstream hepatic steatosis or liver-laboratory abnormalities.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - impaired hepatic VLDL export and hepatocyte triglyceride retention
    evidence:
    - reference: PMID:24288038
      reference_title: "Abetalipoproteinemia and homozygous hypobetalipoproteinemia: a framework for diagnosis and management."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "neuropathy and coagulopathy. Hepatic steatosis is also common."
      explanation: The review supports hepatic steatosis as a common manifestation of the apoB-lipoprotein assembly/export disorder.
- name: Fat and Fat-Soluble Vitamin Malabsorption
  description: >
    Absent intestinal chylomicron formation impairs absorption and transport of
    dietary fat and fat-soluble vitamins. This causes steatorrhea, chronic
    diarrhea, failure to thrive, and decreased circulating vitamins A, D, E, and
    K; vitamin K deficiency can prolong coagulation measures.
  biological_processes:
  - preferred_term: intestinal lipid absorption
    term:
      id: GO:0098856
      label: intestinal lipid absorption
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "A severe, familial hypobetalipoproteinemia characterized by permanently low levels (below the 5th percentile) of apolipoprotein B and LDL cholesterol, and by growth delay, malabsorption, hepatomegaly, and neurological and neuromuscular manifestations."
    explanation: Orphanet definition links hypobetalipoproteinemia with growth delay and malabsorption.
  - reference: PMID:30358967
    reference_title: "Abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Malabsorption of fat-soluble vitamins (A, D, E, and K) can"
    explanation: GeneReviews supports fat-soluble vitamin malabsorption as a consequence of the disorder.
  downstream:
  - target: Fat malabsorption
    description: Defective chylomicron export produces abnormal gastrointestinal fat absorption.
    causal_link_type: DIRECT
    evidence:
    - reference: ORPHA:14
      reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0002630 | Fat malabsorption | Very frequent (99-80%)"
      explanation: Orphanet records fat malabsorption as a very frequent ABL phenotype downstream of the lipid-absorption defect.
  - target: Steatorrhea
    description: Fat malabsorption leads to fat-rich stools.
    causal_link_type: DIRECT
    evidence:
    - reference: ORPHA:14
      reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0002570 | Steatorrhea | Very frequent (99-80%)"
      explanation: Orphanet records steatorrhea as a very frequent gastrointestinal manifestation of ABL.
  - target: Chronic diarrhea
    description: Fat malabsorption contributes to chronic diarrhea in infancy.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - unabsorbed intestinal lipid and osmotic/secretory stool losses
    evidence:
    - reference: PMID:30358967
      reference_title: "Abetalipoproteinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "with failure to thrive, diarrhea, vomiting, and malabsorption of fat."
      explanation: GeneReviews supports diarrhea and fat malabsorption as co-occurring infantile manifestations of ABL.
  - target: Failure to thrive
    description: Malabsorption and inadequate caloric utilization contribute to growth failure.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - inadequate caloric absorption from dietary fat malabsorption
    evidence:
    - reference: PMID:30358967
      reference_title: "Abetalipoproteinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "with failure to thrive, diarrhea, vomiting, and malabsorption of fat."
      explanation: GeneReviews supports failure to thrive in the infantile malabsorption presentation of ABL.
  - target: Reduced circulating vitamin A concentration
    description: Fat-soluble vitamin malabsorption lowers circulating vitamin A.
    causal_link_type: DIRECT
    evidence:
    - reference: ORPHA:14
      reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0004905 | Low levels of vitamin A | Frequent (79-30%)"
      explanation: Orphanet records low vitamin A levels as a frequent biochemical manifestation of ABL.
  - target: Decreased circulating vitamin D concentration
    description: Fat-soluble vitamin malabsorption lowers circulating vitamin D.
    causal_link_type: DIRECT
    evidence:
    - reference: ORPHA:14
      reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0100512 | Low levels of vitamin D | Frequent (79-30%)"
      explanation: Orphanet records low vitamin D levels as a frequent biochemical manifestation of ABL.
  - target: Decreased circulating vitamin E concentration
    description: Fat-soluble vitamin malabsorption lowers circulating vitamin E.
    causal_link_type: DIRECT
    evidence:
    - reference: ORPHA:14
      reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0100513 | Low levels of vitamin E | Very frequent (99-80%)"
      explanation: Orphanet records low vitamin E levels as a very frequent biochemical manifestation of ABL.
  - target: Low fat-soluble vitamin concentrations
    description: Fat-soluble vitamin malabsorption produces decreased vitamin A, D, E, and K concentrations that require surveillance.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:30358967
      reference_title: "Abetalipoproteinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Malabsorption of fat-soluble vitamins (A, D, E, and K) can"
      explanation: GeneReviews directly supports reduced fat-soluble vitamin availability as a consequence of fat-soluble vitamin malabsorption.
  - target: Vitamin E-Linked Neurologic and Retinal Injury
    description: Persistent deficiency of fat-soluble vitamins contributes to retinal degeneration and neurologic injury.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - decreased vitamin E availability to retinal, posterior-column, peripheral nerve, and muscle tissues
    evidence:
    - reference: PMID:18611256
      reference_title: "Abetalipoproteinemia: two case reports and literature review."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "deficiency of fat-soluble vitamins is associated with\ndevelopment of atypical retinitis pigmentosa, coagulopathy, posterior column\nneuropathy and myopathy."
      explanation: This clinical review links fat-soluble vitamin deficiency to retinal and neurologic complications.
  - target: Vitamin K-Related Coagulation Abnormality
    description: Fat-soluble vitamin malabsorption includes vitamin K deficiency, which can increase INR and prolong coagulation testing.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:30358967
      reference_title: "Abetalipoproteinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Malabsorption of fat-soluble vitamins (A, D, E, and K) can\nresult in an increased international normalized ratio (INR)."
      explanation: GeneReviews directly links fat-soluble vitamin malabsorption, including vitamin K, to increased INR.
- name: Vitamin E-Linked Neurologic and Retinal Injury
  description: >
    Persistent fat-soluble vitamin deficiency, especially vitamin E deficiency,
    is associated with progressive retinal degeneration and neuromuscular
    disease. Untreated individuals can develop loss of night and color vision,
    abnormal retinal pigmentation, loss of deep tendon reflexes, posterior
    column sensory dysfunction, dysarthria, ataxia, neuropathy, and myopathy.
  evidence:
  - reference: PMID:24288038
    reference_title: "Abetalipoproteinemia and homozygous hypobetalipoproteinemia: a framework for diagnosis and management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "malabsorption of lipid-soluble vitamins leading to retinal degeneration,"
    explanation: This review links lipid-soluble vitamin malabsorption to retinal degeneration.
  - reference: PMID:18611256
    reference_title: "Abetalipoproteinemia: two case reports and literature review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "development of atypical retinitis pigmentosa, coagulopathy, posterior column"
    explanation: Long-term clinical cases and review link fat-soluble vitamin deficiency to retinal, coagulation, and neurologic complications.
  downstream:
  - target: Abnormality of the nervous system
    description: Vitamin deficiency contributes to neurologic manifestations.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:18611256
      reference_title: "Abetalipoproteinemia: two case reports and literature review."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "posterior column\nneuropathy and myopathy."
      explanation: The long-term clinical review supports neurologic and neuromuscular manifestations downstream of fat-soluble vitamin deficiency.
  - target: Progressive visual loss
    description: Retinal degeneration causes progressive visual loss.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:30358967
      reference_title: "Abetalipoproteinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "with progressive loss of night vision and/or color vision in adulthood."
      explanation: GeneReviews supports progressive visual loss as a manifestation of untreated retinal involvement.
  - target: Color vision defect
    description: Retinal involvement can impair color vision.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:30358967
      reference_title: "Abetalipoproteinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "with progressive loss of night vision and/or color vision in adulthood."
      explanation: GeneReviews supports color vision loss as a retinal manifestation in untreated ABL.
  - target: Nyctalopia
    description: Retinal involvement can cause night blindness.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:30358967
      reference_title: "Abetalipoproteinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "with progressive loss of night vision and/or color vision in adulthood."
      explanation: GeneReviews supports night vision loss as a retinal manifestation in untreated ABL.
  - target: Abnormal retinal pigmentation
    description: Untreated retinal disease produces abnormal retinal pigmentation.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:30358967
      reference_title: "Abetalipoproteinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Untreated\nindividuals may develop atypical pigmentation of the retina"
      explanation: GeneReviews directly supports abnormal retinal pigmentation in untreated ABL.
  - target: Areflexia
    description: Neuromuscular involvement includes progressive loss of reflexes.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:30358967
      reference_title: "Abetalipoproteinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "deep tendon reflexes, vibratory sense, and proprioception; muscle weakness;"
      explanation: GeneReviews supports progressive loss of deep tendon reflexes among untreated neuromuscular findings.
  - target: Ataxia
    description: Neuromuscular involvement can cause ataxia.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:30358967
      reference_title: "Abetalipoproteinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "dysarthria; and ataxia typically manifest"
      explanation: GeneReviews supports ataxia as a neuromuscular manifestation in untreated ABL.
  - target: Dysarthria
    description: Neuromuscular involvement can cause dysarthria.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:30358967
      reference_title: "Abetalipoproteinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "dysarthria; and ataxia typically manifest"
      explanation: GeneReviews supports dysarthria as a neuromuscular manifestation in untreated ABL.
  - target: Impaired vibratory sensation
    description: Posterior column and sensory involvement can impair vibratory sensation.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:30358967
      reference_title: "Abetalipoproteinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "deep tendon reflexes, vibratory sense, and proprioception; muscle weakness;"
      explanation: GeneReviews supports progressive loss of vibratory sense among untreated neuromuscular findings.
  - target: Myalgia
    description: Neuromuscular involvement can include myopathy and muscle pain.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: ORPHA:14
      reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0003326 | Myalgia | Frequent (79-30%)"
      explanation: Orphanet records myalgia as a frequent neuromuscular phenotype of ABL.
- name: Acanthocytic Hematologic Manifestations
  description: >
    ApoB-lipoprotein absence and altered lipid transport are associated with
    acanthocytosis on blood smear and hematologic manifestations including
    anemia, reticulocytosis, hemolysis, and hyperbilirubinemia.
  evidence:
  - reference: PMID:30358967
    reference_title: "Abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hematologic manifestations may include acanthocytosis (irregularly spiculated"
    explanation: GeneReviews supports acanthocytosis as part of the hematologic phenotype.
  - reference: PMID:24288038
    reference_title: "Abetalipoproteinemia and homozygous hypobetalipoproteinemia: a framework for diagnosis and management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Clinical diagnosis is based on signs and symptoms, acanthocytosis"
    explanation: This review identifies acanthocytosis as a diagnostic sign.
  downstream:
  - target: Acanthocytosis
    description: Altered red-cell membrane morphology causes acanthocytosis.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:30358967
      reference_title: "Abetalipoproteinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Hematologic manifestations may include acanthocytosis (irregularly spiculated"
      explanation: GeneReviews supports acanthocytosis as a hematologic manifestation of ABL.
  - target: Anemia
    description: Hematologic involvement can include anemia.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:30358967
      reference_title: "Abetalipoproteinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "erythrocytes), anemia, reticulocytosis, and hemolysis with resultant"
      explanation: GeneReviews supports anemia as part of the hematologic manifestation set.
  - target: Reticulocytosis
    description: Hemolysis can increase reticulocytes.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:30358967
      reference_title: "Abetalipoproteinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "erythrocytes), anemia, reticulocytosis, and hemolysis with resultant"
      explanation: GeneReviews supports reticulocytosis as part of the hematologic manifestation set.
  - target: Hyperbilirubinemia
    description: Hemolysis can increase bilirubin.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:30358967
      reference_title: "Abetalipoproteinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "hemolysis with resultant\nhyperbilirubinemia."
      explanation: GeneReviews directly links hemolysis to resultant hyperbilirubinemia.
- name: Vitamin K-Related Coagulation Abnormality
  description: >
    Fat-soluble vitamin malabsorption includes vitamin K deficiency, which can
    prolong the prothrombin time or increase the international normalized ratio.
  evidence:
  - reference: PMID:30358967
    reference_title: "Abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "result in an increased international normalized ratio (INR)."
    explanation: GeneReviews links fat-soluble vitamin malabsorption to increased INR.
  - reference: PMID:18611256
    reference_title: "Abetalipoproteinemia: two case reports and literature review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "development of atypical retinitis pigmentosa, coagulopathy, posterior column"
    explanation: Long-term case review supports coagulopathy as a later complication of fat-soluble vitamin deficiency.
  downstream:
  - target: Prolonged prothrombin time
    description: Vitamin K deficiency prolongs coagulation testing.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:30358967
      reference_title: "Abetalipoproteinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "result in an increased international normalized ratio (INR)."
      explanation: GeneReviews supports increased INR as a coagulation consequence of fat-soluble vitamin malabsorption.
- name: Hepatic Steatosis and Laboratory Abnormalities
  description: >
    Hepatic involvement can include hepatomegaly, hepatic steatosis, mild
    transaminase elevation, hypoalbuminemia, and rarely progression to fibrosis
    or cirrhosis. Hepatic steatosis is recognized in clinical reviews and is
    monitored during follow-up.
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  evidence:
  - reference: PMID:24288038
    reference_title: "Abetalipoproteinemia and homozygous hypobetalipoproteinemia: a framework for diagnosis and management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "neuropathy and coagulopathy. Hepatic steatosis is also common."
    explanation: This review supports hepatic steatosis as a common hepatic manifestation.
  - reference: PMID:30358967
    reference_title: "Abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "liver function tests (AST, ALT, GGT, total and"
    explanation: GeneReviews recommends surveillance of liver tests, supporting clinically relevant hepatic involvement.
  downstream:
  - target: Hepatomegaly
    description: Hepatic lipid handling defects can manifest as hepatomegaly.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: ORPHA:14
      reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0002240 | Hepatomegaly | Occasional (29-5%)"
      explanation: Orphanet records hepatomegaly as an occasional hepatic phenotype of ABL.
  - target: Hepatic steatosis
    description: Impaired hepatic apoB-lipoprotein export contributes to hepatic steatosis.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:24288038
      reference_title: "Abetalipoproteinemia and homozygous hypobetalipoproteinemia: a framework for diagnosis and management."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "neuropathy and coagulopathy. Hepatic steatosis is also common."
      explanation: The review directly supports hepatic steatosis as a common ABL manifestation.
  - target: Hypoalbuminemia
    description: Hepatic and malabsorptive involvement can be accompanied by hypoalbuminemia.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: ORPHA:14
      reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0003073 | Hypoalbuminemia | Frequent (79-30%)"
      explanation: Orphanet records hypoalbuminemia as a frequent biochemical/laboratory phenotype of ABL.
phenotypes:
- name: Abnormal circulating apolipoprotein concentration
  category: Biochemical
  frequency: VERY_FREQUENT
  description: Circulating apoB-containing lipoproteins are absent or extremely low.
  phenotype_term:
    preferred_term: Abnormal circulating apolipoprotein concentration
    term:
      id: HP:0025201
      label: Abnormal circulating apolipoprotein concentration
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0025201 | Abnormal circulating apolipoprotein concentration | Very frequent (99-80%)"
    explanation: Orphanet records abnormal circulating apolipoprotein concentration as very frequent.
- name: Hypocholesterolemia
  category: Biochemical
  frequency: FREQUENT
  description: Total cholesterol is markedly decreased because apoB lipoproteins are absent or extremely low.
  phenotype_term:
    preferred_term: Hypocholesterolemia
    term:
      id: HP:0003146
      label: Hypocholesterolemia
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0003146 | Hypocholesterolemia | Frequent (79-30%)"
    explanation: Orphanet records hypocholesterolemia as frequent.
  - reference: PMID:24288038
    reference_title: "Abetalipoproteinemia and homozygous hypobetalipoproteinemia: a framework for diagnosis and management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "are rare diseases characterized by hypocholesterolemia and"
    explanation: This review describes hypocholesterolemia as a core feature.
- name: Decreased LDL cholesterol concentration
  category: Biochemical
  frequency: FREQUENT
  description: LDL cholesterol is absent or extremely low.
  phenotype_term:
    preferred_term: Decreased LDL cholesterol concentration
    term:
      id: HP:0003563
      label: Decreased LDL cholesterol concentration
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0003563 | Decreased LDL cholesterol concentration | Frequent (79-30%)"
    explanation: Orphanet records decreased LDL cholesterol concentration as frequent.
  - reference: PMID:30358967
    reference_title: "Abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "proband with absent or extremely low LDL-cholesterol, triglyceride, and"
    explanation: GeneReviews describes absent or extremely low LDL cholesterol as a diagnostic biochemical feature.
- name: Decreased HDL cholesterol concentration
  category: Biochemical
  frequency: FREQUENT
  description: HDL cholesterol can be decreased in Abetalipoproteinemia.
  phenotype_term:
    preferred_term: Decreased HDL cholesterol concentration
    term:
      id: HP:0003233
      label: Decreased HDL cholesterol concentration
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0003233 | Decreased HDL cholesterol concentration | Frequent (79-30%)"
    explanation: Orphanet records decreased HDL cholesterol concentration as frequent.
- name: Hypotriglyceridemia
  category: Biochemical
  frequency: FREQUENT
  description: Plasma triglycerides are very low due to loss of chylomicron and VLDL export.
  phenotype_term:
    preferred_term: Hypotriglyceridemia
    term:
      id: HP:0012153
      label: Hypotriglyceridemia
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0012153 | Hypotriglyceridemia | Frequent (79-30%)"
    explanation: Orphanet records hypotriglyceridemia as frequent.
- name: Fat malabsorption
  category: Gastrointestinal
  frequency: VERY_FREQUENT
  description: Intestinal lipid absorption is impaired.
  phenotype_term:
    preferred_term: Fat malabsorption
    term:
      id: HP:0002630
      label: Fat malabsorption
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0002630 | Fat malabsorption | Very frequent (99-80%)"
    explanation: Orphanet records fat malabsorption as very frequent.
- name: Steatorrhea
  category: Gastrointestinal
  frequency: VERY_FREQUENT
  description: Fat malabsorption causes fatty stools.
  phenotype_term:
    preferred_term: Steatorrhea
    term:
      id: HP:0002570
      label: Steatorrhea
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0002570 | Steatorrhea | Very frequent (99-80%)"
    explanation: Orphanet records steatorrhea as very frequent.
- name: Chronic diarrhea
  category: Gastrointestinal
  frequency: FREQUENT
  description: Chronic diarrhea is a common early manifestation.
  phenotype_term:
    preferred_term: Chronic diarrhea
    term:
      id: HP:0002028
      label: Chronic diarrhea
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0002028 | Chronic diarrhea | Frequent (79-30%)"
    explanation: Orphanet records chronic diarrhea as frequent.
  - reference: PMID:30358967
    reference_title: "Abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "with failure to thrive, diarrhea, vomiting, and malabsorption of fat."
    explanation: GeneReviews supports diarrhea as part of the typical infant presentation.
- name: Failure to thrive
  category: Growth
  frequency: FREQUENT
  description: Infants may have poor weight gain and growth failure.
  phenotype_term:
    preferred_term: Failure to thrive
    term:
      id: HP:0001508
      label: Failure to thrive
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0001508 | Failure to thrive | Frequent (79-30%)"
    explanation: Orphanet records failure to thrive as frequent.
- name: Reduced circulating vitamin A concentration
  category: Biochemical
  frequency: FREQUENT
  description: Vitamin A is reduced due to fat-soluble vitamin malabsorption.
  phenotype_term:
    preferred_term: Reduced circulating vitamin A concentration
    term:
      id: HP:0004905
      label: Reduced circulating vitamin A concentration
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0004905 | Low levels of vitamin A | Frequent (79-30%)"
    explanation: Orphanet records low vitamin A levels as frequent.
- name: Decreased circulating vitamin D concentration
  category: Biochemical
  frequency: FREQUENT
  description: Vitamin D is reduced due to fat-soluble vitamin malabsorption.
  phenotype_term:
    preferred_term: Decreased circulating vitamin D concentration
    term:
      id: HP:0100512
      label: Decreased circulating vitamin D concentration
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0100512 | Low levels of vitamin D | Frequent (79-30%)"
    explanation: Orphanet records low vitamin D levels as frequent.
- name: Decreased circulating vitamin E concentration
  category: Biochemical
  frequency: VERY_FREQUENT
  description: Vitamin E is reduced and contributes to retinal and neurologic complications when untreated.
  phenotype_term:
    preferred_term: Decreased circulating vitamin E concentration
    term:
      id: HP:0100513
      label: Decreased circulating vitamin E concentration
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0100513 | Low levels of vitamin E | Very frequent (99-80%)"
    explanation: Orphanet records low vitamin E levels as very frequent.
- name: Acanthocytosis
  category: Hematologic
  frequency: VERY_FREQUENT
  description: Blood smears show acanthocytes.
  phenotype_term:
    preferred_term: Acanthocytosis
    term:
      id: HP:0001927
      label: Acanthocytosis
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0001927 | Acanthocytosis | Very frequent (99-80%)"
    explanation: Orphanet records acanthocytosis as very frequent.
  - reference: PMID:30358967
    reference_title: "Abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hematologic manifestations may include acanthocytosis (irregularly spiculated"
    explanation: GeneReviews supports acanthocytosis as a hematologic manifestation.
- name: Anemia
  category: Hematologic
  frequency: FREQUENT
  description: Anemia can occur as part of hematologic involvement.
  phenotype_term:
    preferred_term: Anemia
    term:
      id: HP:0001903
      label: Anemia
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0001903 | Anemia | Frequent (79-30%)"
    explanation: Orphanet records anemia as frequent.
- name: Reticulocytosis
  category: Hematologic
  frequency: FREQUENT
  description: Reticulocytosis can accompany hemolysis.
  phenotype_term:
    preferred_term: Reticulocytosis
    term:
      id: HP:0001923
      label: Reticulocytosis
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0001923 | Reticulocytosis | Frequent (79-30%)"
    explanation: Orphanet records reticulocytosis as frequent.
- name: Hyperbilirubinemia
  category: Biochemical
  frequency: FREQUENT
  description: Hyperbilirubinemia may result from hemolysis.
  phenotype_term:
    preferred_term: Hyperbilirubinemia
    term:
      id: HP:0002904
      label: Hyperbilirubinemia
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0002904 | Hyperbilirubinemia | Frequent (79-30%)"
    explanation: Orphanet records hyperbilirubinemia as frequent.
- name: Hypoalbuminemia
  category: Biochemical
  frequency: FREQUENT
  description: Low serum albumin is recorded among frequent Orphanet phenotypes.
  phenotype_term:
    preferred_term: Hypoalbuminemia
    term:
      id: HP:0003073
      label: Hypoalbuminemia
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0003073 | Hypoalbuminemia | Frequent (79-30%)"
    explanation: Orphanet records hypoalbuminemia as frequent.
- name: Abnormality of the nervous system
  category: Neurologic
  frequency: VERY_FREQUENT
  description: Neurologic abnormalities include reflex, sensory, coordination, and neuromuscular deficits when untreated.
  phenotype_term:
    preferred_term: Abnormality of the nervous system
    term:
      id: HP:0000707
      label: Abnormality of the nervous system
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0000707 | Abnormality of the nervous system | Very frequent (99-80%)"
    explanation: Orphanet records nervous-system abnormality as very frequent.
- name: Areflexia
  category: Neurologic
  frequency: FREQUENT
  description: Deep tendon reflexes can be reduced or absent.
  phenotype_term:
    preferred_term: Areflexia
    term:
      id: HP:0001284
      label: Areflexia
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0001284 | Areflexia | Frequent (79-30%)"
    explanation: Orphanet records areflexia as frequent.
  - reference: PMID:30358967
    reference_title: "Abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "deep tendon reflexes, vibratory sense, and proprioception; muscle weakness;"
    explanation: GeneReviews describes progressive loss of deep tendon reflexes in untreated individuals.
- name: Ataxia
  category: Neurologic
  frequency: OCCASIONAL
  description: Ataxia can occur as part of untreated neurologic involvement.
  phenotype_term:
    preferred_term: Ataxia
    term:
      id: HP:0001251
      label: Ataxia
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0001251 | Ataxia | Occasional (29-5%)"
    explanation: Orphanet records ataxia as an occasional phenotype.
  - reference: PMID:30358967
    reference_title: "Abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "dysarthria; and ataxia typically manifest"
    explanation: GeneReviews describes ataxia among neuromuscular findings in untreated individuals.
- name: Dysarthria
  category: Neurologic
  frequency: OCCASIONAL
  description: Dysarthria can occur as part of neurologic involvement.
  phenotype_term:
    preferred_term: Dysarthria
    term:
      id: HP:0001260
      label: Dysarthria
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0001260 | Dysarthria | Occasional (29-5%)"
    explanation: Orphanet records dysarthria as an occasional phenotype.
  - reference: PMID:30358967
    reference_title: "Abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "dysarthria; and ataxia typically manifest"
    explanation: GeneReviews describes dysarthria among neuromuscular findings in untreated individuals.
- name: Impaired vibratory sensation
  category: Neurologic
  frequency: OCCASIONAL
  description: Posterior column involvement can reduce vibration sense.
  phenotype_term:
    preferred_term: Impaired vibratory sensation
    term:
      id: HP:0002495
      label: Impaired vibratory sensation
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0002495 | Impaired vibratory sensation | Occasional (29-5%)"
    explanation: Orphanet records impaired vibratory sensation as an occasional phenotype.
  - reference: PMID:30358967
    reference_title: "Abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "deep tendon reflexes, vibratory sense, and proprioception; muscle weakness;"
    explanation: GeneReviews describes progressive loss of vibratory sense in untreated individuals.
- name: Myalgia
  category: Neuromuscular
  frequency: FREQUENT
  description: Muscle pain can accompany the neuromuscular phenotype.
  phenotype_term:
    preferred_term: Myalgia
    term:
      id: HP:0003326
      label: Myalgia
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0003326 | Myalgia | Frequent (79-30%)"
    explanation: Orphanet records myalgia as frequent.
- name: Progressive visual loss
  category: Ophthalmologic
  frequency: FREQUENT
  description: Progressive retinal involvement can impair vision.
  phenotype_term:
    preferred_term: Progressive visual loss
    term:
      id: HP:0000529
      label: Progressive visual loss
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0000529 | Progressive visual loss | Frequent (79-30%)"
    explanation: Orphanet records progressive visual loss as frequent.
- name: Color vision defect
  category: Ophthalmologic
  frequency: FREQUENT
  description: Retinal disease can affect color vision.
  phenotype_term:
    preferred_term: Color vision defect
    term:
      id: HP:0000551
      label: Color vision defect
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0000551 | Color vision defect | Frequent (79-30%)"
    explanation: Orphanet records color vision defect as frequent.
  - reference: PMID:30358967
    reference_title: "Abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "with progressive loss of night vision and/or color vision in adulthood."
    explanation: GeneReviews supports acquired loss of color vision as a retinal manifestation.
- name: Nyctalopia
  category: Ophthalmologic
  frequency: FREQUENT
  description: Night blindness can occur with retinal involvement.
  phenotype_term:
    preferred_term: Nyctalopia
    term:
      id: HP:0000662
      label: Nyctalopia
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0000662 | Nyctalopia | Frequent (79-30%)"
    explanation: Orphanet records nyctalopia as frequent.
  - reference: PMID:30358967
    reference_title: "Abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "with progressive loss of night vision and/or color vision in adulthood."
    explanation: GeneReviews supports night vision loss as a retinal manifestation.
- name: Abnormal retinal pigmentation
  category: Ophthalmologic
  frequency: FREQUENT
  description: Retinal pigmentation abnormalities develop in untreated retinal disease.
  phenotype_term:
    preferred_term: Abnormal retinal pigmentation
    term:
      id: HP:0007703
      label: Abnormal retinal pigmentation
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0007703 | Abnormality of retinal pigmentation | Frequent (79-30%)"
    explanation: Orphanet records abnormal retinal pigmentation as frequent.
- name: Prolonged prothrombin time
  category: Hematologic
  frequency: OCCASIONAL
  description: Vitamin K malabsorption can increase INR or prolong prothrombin time.
  phenotype_term:
    preferred_term: Prolonged prothrombin time
    term:
      id: HP:0008151
      label: Prolonged prothrombin time
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0008151 | Prolonged prothrombin time | Occasional (29-5%)"
    explanation: Orphanet records prolonged prothrombin time as occasional.
  - reference: PMID:30358967
    reference_title: "Abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "result in an increased international normalized ratio (INR)."
    explanation: GeneReviews links fat-soluble vitamin malabsorption to increased INR.
- name: Hepatomegaly
  category: Hepatic
  frequency: OCCASIONAL
  description: Liver enlargement can occur.
  phenotype_term:
    preferred_term: Hepatomegaly
    term:
      id: HP:0002240
      label: Hepatomegaly
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0002240 | Hepatomegaly | Occasional (29-5%)"
    explanation: Orphanet records hepatomegaly as occasional.
- name: Hepatic steatosis
  category: Hepatic
  frequency: OCCASIONAL
  description: Hepatic steatosis is a recognized hepatic manifestation.
  phenotype_term:
    preferred_term: Hepatic steatosis
    term:
      id: HP:0001397
      label: Hepatic steatosis
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0001397 | Hepatic steatosis | Occasional (29-5%)"
    explanation: Orphanet records hepatic steatosis as occasional.
  - reference: PMID:24288038
    reference_title: "Abetalipoproteinemia and homozygous hypobetalipoproteinemia: a framework for diagnosis and management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "neuropathy and coagulopathy. Hepatic steatosis is also common."
    explanation: This review supports hepatic steatosis as a common manifestation.
biochemical:
- name: Absent apoB-containing lipoproteins
  presence: DECREASED
  context: >-
    ApoB-containing lipoproteins including chylomicrons, VLDL, and LDL are
    absent or virtually absent.
  readouts:
  - target: Impaired ApoB Lipoprotein Assembly and Secretion
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Absent or extremely low apoB-containing lipoproteins report failed apoB particle assembly and secretion.
    evidence:
    - reference: PMID:24288038
      reference_title: "Abetalipoproteinemia and homozygous hypobetalipoproteinemia: a framework for diagnosis and management."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "virtually absent apo B-containing lipoproteins, including"
      explanation: The review supports absent apoB-containing lipoproteins as the diagnostic biochemical readout of failed apoB-particle assembly.
  evidence:
  - reference: PMID:24288038
    reference_title: "Abetalipoproteinemia and homozygous hypobetalipoproteinemia: a framework for diagnosis and management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "virtually absent apo B-containing lipoproteins, including"
    explanation: The review supports absent apoB-containing lipoproteins as a diagnostic biochemical finding.
- name: Low fat-soluble vitamin concentrations
  presence: DECREASED
  context: >-
    Vitamin A, D, E, and K levels are reduced due to fat malabsorption and
    require surveillance.
  readouts:
  - target: Fat and Fat-Soluble Vitamin Malabsorption
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: MONITORING
    interpretation: Lower fat-soluble vitamin concentrations track impaired intestinal absorption and replacement needs.
    evidence:
    - reference: PMID:30358967
      reference_title: "Abetalipoproteinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "fat-soluble vitamin levels"
      explanation: GeneReviews recommends monitoring fat-soluble vitamin levels, supporting them as readouts of the malabsorption branch.
  evidence:
  - reference: PMID:30358967
    reference_title: "Abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Malabsorption of fat-soluble vitamins (A, D, E, and K) can"
    explanation: GeneReviews directly supports fat-soluble vitamin malabsorption as a biochemical consequence of the disease.
genetic:
- name: MTTP pathogenic variants
  gene_term:
    preferred_term: MTTP
    term:
      id: hgnc:7467
      label: MTTP
  association: Causative biallelic pathogenic variants
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  inheritance:
  - name: Autosomal recessive inheritance
    inheritance_term:
      preferred_term: Autosomal recessive inheritance
      term:
        id: HP:0000007
        label: Autosomal recessive inheritance
    evidence:
    - reference: PMID:30358967
      reference_title: "Abetalipoproteinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Abetalipoproteinemia is inherited in an autosomal recessive"
      explanation: GeneReviews states the autosomal recessive inheritance pattern.
  variants:
  - name: Biallelic MTTP pathogenic variants
    description: >
      Reported disease-causing MTTP variants include frameshift, splice-site,
      and missense variants; functional studies show that selected missense
      variants can impair MTP lipid-transfer activity or formation of the active
      MTP complex.
    gene:
      preferred_term: MTTP
      term:
        id: hgnc:7467
        label: MTTP
    clinical_significance: PATHOGENIC
    type: loss_of_function_variant
    functional_effects:
    - function: MTP lipid transfer activity
      description: Pathogenic variants reduce functional MTP activity or disrupt active MTP complex formation.
      type: loss-of-function
    evidence:
    - reference: PMID:30358967
      reference_title: "Abetalipoproteinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "biallelic pathogenic variants in MTTP"
      explanation: GeneReviews identifies biallelic MTTP pathogenic variants as the molecular diagnostic cause.
    - reference: PMID:10946006
      reference_title: "Novel mutations in the microsomal triglyceride transfer protein gene causing abetalipoproteinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Three novel mutations have been identified: a"
      explanation: Patient variant screening identified frameshift, missense, and splice-site MTTP mutations in ABL.
    - reference: PMID:8939939
      reference_title: "A novel abetalipoproteinemia genotype. Identification of a missense mutation in the 97-kDa subunit of the microsomal triglyceride transfer protein that prevents complex formation with protein disulfide isomerase."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "interaction between the 97-kDa subunit and protein disulfide isomerase."
      explanation: Functional evidence shows one MTTP missense variant disrupts formation of the MTP complex.
  evidence:
  - reference: ORPHA:14
    reference_title: "Abetalipoproteinemia (Orphanet structured-database record)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "MTTP | microsomal triglyceride transfer protein | hgnc:7467 | Disease-causing germline mutation(s) in"
    explanation: Orphanet records MTTP as a disease-causing germline gene for Abetalipoproteinemia.
  - reference: PMID:30358967
    reference_title: "Abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "biallelic pathogenic variants in MTTP"
    explanation: GeneReviews supports biallelic MTTP pathogenic variants as diagnostic for Abetalipoproteinemia.
treatments:
- name: Low-fat diet with long-chain fatty acid avoidance
  description: >
    Prescribed dietary fat restriction reduces steatorrhea and limits the load
    of long-chain fatty acids that cannot be normally transported by
    chylomicrons.
  treatment_term:
    preferred_term: dietary intervention
    term:
      id: MAXO:0000088
      label: dietary intervention
  target_mechanisms:
  - target: Fat and Fat-Soluble Vitamin Malabsorption
    treatment_effect: MODULATES
    description: Low-fat diet reduces symptoms caused by defective intestinal chylomicron-mediated lipid transport.
    evidence:
    - reference: PMID:24288038
      reference_title: "Abetalipoproteinemia and homozygous hypobetalipoproteinemia: a framework for diagnosis and management."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Mainstays of treatment include adherence to a low-fat"
      explanation: The review identifies low-fat diet as a mainstay of treatment.
  evidence:
  - reference: PMID:30358967
    reference_title: "Abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "low-fat diet (10%-20% of total calories from fat); oral"
    explanation: GeneReviews gives the dietary fat target for treatment.
  - reference: PMID:30358967
    reference_title: "Abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "particularly those rich in long-chain fatty acids."
    explanation: GeneReviews recommends avoiding fatty foods, especially those rich in long-chain fatty acids.
- name: Fat-soluble vitamin supplementation
  description: >
    High-dose supplementation with vitamins A, D, E, and K is used to prevent
    or limit retinal, neurologic, hematologic, and coagulation complications.
  treatment_term:
    preferred_term: nutritional supplementation
    term:
      id: MAXO:0000106
      label: nutritional supplementation
  target_mechanisms:
  - target: Fat and Fat-Soluble Vitamin Malabsorption
    treatment_effect: RESTORES
    description: Supplementation replaces fat-soluble vitamins that are poorly absorbed and transported.
    evidence:
    - reference: PMID:30358967
      reference_title: "Abetalipoproteinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Most complications can be prevented through institution"
      explanation: GeneReviews states most complications can be prevented by low-fat diet plus fat-soluble vitamin supplementation.
  - target: Vitamin E-Linked Neurologic and Retinal Injury
    treatment_effect: INHIBITS
    description: Vitamin supplementation, especially vitamin E, is intended to prevent or halt neurologic and retinal complications.
    evidence:
    - reference: PMID:18611256
      reference_title: "Abetalipoproteinemia: two case reports and literature review."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Treatment appears to have been associated with arrest of the neuropathy"
      explanation: Long-term treated cases support vitamin supplementation as associated with arrest of neuropathy and other complications.
  evidence:
  - reference: PMID:30358967
    reference_title: "Abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "polyunsaturated fatty acids, as tolerated); supplementation with vitamin A"
    explanation: GeneReviews recommends supplementation with fat-soluble vitamins beginning with vitamin A.
  - reference: PMID:18611256
    reference_title: "Abetalipoproteinemia: two case reports and literature review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "high oral doses of fat soluble vitamins, including vitamin E over the last three"
    explanation: Long-term cases describe high-dose fat-soluble vitamin treatment including vitamin E.
- name: Essential fatty acid supplementation
  description: >
    Small amounts of oils rich in polyunsaturated fatty acids are used as
    tolerated to provide essential fatty acids despite overall dietary fat
    restriction.
  treatment_term:
    preferred_term: nutritional supplementation
    term:
      id: MAXO:0000106
      label: nutritional supplementation
  target_mechanisms:
  - target: Fat and Fat-Soluble Vitamin Malabsorption
    treatment_effect: MODULATES
    description: Essential fatty acid supplementation balances deficiency risk against fat intolerance.
    evidence:
    - reference: PMID:30358967
      reference_title: "Abetalipoproteinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "essential fatty acid supplementation (up to 1 teaspoon per day of oils rich in"
      explanation: GeneReviews recommends oral essential fatty acid supplementation as tolerated.
  evidence:
  - reference: PMID:24288038
    reference_title: "Abetalipoproteinemia and homozygous hypobetalipoproteinemia: a framework for diagnosis and management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "supplementation with essential fatty acids and high oral doses of fat"
    explanation: The management review lists essential fatty acid supplementation as a mainstay of treatment.
diagnosis:
- name: Lipid profile and MTTP genetic testing
  diagnosis_term:
    preferred_term: genetic testing
    term:
      id: MAXO:0000127
      label: genetic testing
  description: >
    Diagnosis is established by absent or extremely low LDL cholesterol,
    triglyceride, and apoB levels together with biallelic pathogenic MTTP
    variants.
  results: Absent or extremely low LDL cholesterol, triglyceride, and apoB with biallelic MTTP pathogenic variants supports the diagnosis.
  evidence:
  - reference: PMID:30358967
    reference_title: "Abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "proband with absent or extremely low LDL-cholesterol, triglyceride, and"
    explanation: GeneReviews describes the biochemical diagnostic pattern.
  - reference: PMID:30358967
    reference_title: "Abetalipoproteinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "biallelic pathogenic variants in MTTP"
    explanation: GeneReviews identifies biallelic MTTP pathogenic variants as part of establishing the diagnosis.
references:
- reference: ORPHA:14
  title: Abetalipoproteinemia
  found_in:
  - Abetalipoproteinemia-deep-research-fallback.md
  findings:
  - statement: ORPHA:14 provides the structured disease identity, MONDO exact mapping, inheritance, MTTP gene association, and phenotype frequencies used for this entry.
    supporting_text: ORPHA:14 structured record for disease definition, MONDO exact mapping, inheritance, prevalence, MTTP gene association, onset, and HPO phenotype frequencies.
- reference: PMID:24288038
  title: "Abetalipoproteinemia and homozygous hypobetalipoproteinemia: a framework for diagnosis and management."
  found_in:
  - Abetalipoproteinemia-deep-research-fallback.md
  findings:
  - statement: This review supports defective apoB-lipoprotein packaging and secretion as the core mechanism and describes low-fat diet plus essential fatty acid and fat-soluble vitamin supplementation as mainstays of treatment.
    supporting_text: PMID:24288038 for the canonical management framework and the mechanism that defective packaging and secretion of apoB-containing lipoproteins underlies abetalipoproteinemia.
- reference: PMID:30358967
  title: Abetalipoproteinemia.
  tags:
  - GeneReviews
  found_in:
  - Abetalipoproteinemia-deep-research-fallback.md
  findings:
  - statement: GeneReviews supports the clinical presentation, diagnostic lipid and MTTP criteria, autosomal recessive inheritance, and management recommendations used in this entry.
    supporting_text: PMID:30358967 for GeneReviews clinical characteristics, diagnosis/testing, diet and vitamin management, surveillance, and genetic counseling.
- reference: PMID:10946006
  title: Novel mutations in the microsomal triglyceride transfer protein gene causing abetalipoproteinemia.
  found_in:
  - Abetalipoproteinemia-deep-research-fallback.md
  findings:
  - statement: Patient variant screening and functional expression evidence support MTTP defects as the proximal cause of Abetalipoproteinemia.
    supporting_text: PMID:10946006 for patient MTTP variant screening and functional evidence that MTP gene defects are the proximal cause of abetalipoproteinemia.
- reference: PMID:8939939
  title: A novel abetalipoproteinemia genotype. Identification of a missense mutation in the 97-kDa subunit of the microsomal triglyceride transfer protein that prevents complex formation with protein disulfide isomerase.
  found_in:
  - Abetalipoproteinemia-deep-research-fallback.md
  findings:
  - statement: Functional evidence supports a mechanism in which an MTTP missense variant prevents formation of an active MTP complex.
    supporting_text: PMID:8939939 for functional evidence that an abetalipoproteinemia-associated MTTP missense variant disrupts formation of an active MTP complex with protein disulfide isomerase.
- reference: PMID:30522860
  title: Postprandial lipid absorption in seven heterozygous carriers of deleterious variants of MTTP in two abetalipoproteinemic families.
  found_in:
  - Abetalipoproteinemia-deep-research-fallback.md
  findings:
  - statement: This clinical lipid-absorption study supports the association between deleterious MTTP variants, undetectable apoB, extremely low LDL cholesterol, and impaired apoB-lipoprotein export.
    supporting_text: PMID:30522860 for clinical evidence that deleterious MTTP variants produce undetectable apoB, extremely low LDL cholesterol, and inability to export apoB-containing lipoproteins from intestine and liver.
- reference: PMID:18611256
  title: "Abetalipoproteinemia: two case reports and literature review."
  found_in:
  - Abetalipoproteinemia-deep-research-fallback.md
  findings:
  - statement: Long-term clinical reports support high-dose fat-soluble vitamin treatment, including vitamin E, as associated with arrest of neuropathy and other complications.
    supporting_text: PMID:18611256 for long-term human clinical reports supporting high-dose fat-soluble vitamin treatment, including vitamin E, with arrest of neuropathy and other complications.
differential_diagnoses: []
clinical_trials: []
datasets: []
📚

References & Deep Research

References

7
ORPHA:14
Abetalipoproteinemia
1 finding
ORPHA:14 provides the structured disease identity, MONDO exact mapping, inheritance, MTTP gene association, and phenotype frequencies used for this entry.
"ORPHA:14 structured record for disease definition, MONDO exact mapping, inheritance, prevalence, MTTP gene association, onset, and HPO phenotype frequencies."
PMID:24288038
Abetalipoproteinemia and homozygous hypobetalipoproteinemia: a framework for diagnosis and management.
1 finding
This review supports defective apoB-lipoprotein packaging and secretion as the core mechanism and describes low-fat diet plus essential fatty acid and fat-soluble vitamin supplementation as mainstays of treatment.
"PMID:24288038 for the canonical management framework and the mechanism that defective packaging and secretion of apoB-containing lipoproteins underlies abetalipoproteinemia."
PMID:30358967
Abetalipoproteinemia.
1 finding
GeneReviews supports the clinical presentation, diagnostic lipid and MTTP criteria, autosomal recessive inheritance, and management recommendations used in this entry.
"PMID:30358967 for GeneReviews clinical characteristics, diagnosis/testing, diet and vitamin management, surveillance, and genetic counseling."
PMID:10946006
Novel mutations in the microsomal triglyceride transfer protein gene causing abetalipoproteinemia.
1 finding
Patient variant screening and functional expression evidence support MTTP defects as the proximal cause of Abetalipoproteinemia.
"PMID:10946006 for patient MTTP variant screening and functional evidence that MTP gene defects are the proximal cause of abetalipoproteinemia."
PMID:8939939
A novel abetalipoproteinemia genotype. Identification of a missense mutation in the 97-kDa subunit of the microsomal triglyceride transfer protein that prevents complex formation with protein disulfide isomerase.
1 finding
Functional evidence supports a mechanism in which an MTTP missense variant prevents formation of an active MTP complex.
"PMID:8939939 for functional evidence that an abetalipoproteinemia-associated MTTP missense variant disrupts formation of an active MTP complex with protein disulfide isomerase."
PMID:30522860
Postprandial lipid absorption in seven heterozygous carriers of deleterious variants of MTTP in two abetalipoproteinemic families.
1 finding
This clinical lipid-absorption study supports the association between deleterious MTTP variants, undetectable apoB, extremely low LDL cholesterol, and impaired apoB-lipoprotein export.
"PMID:30522860 for clinical evidence that deleterious MTTP variants produce undetectable apoB, extremely low LDL cholesterol, and inability to export apoB-containing lipoproteins from intestine and liver."
PMID:18611256
Abetalipoproteinemia: two case reports and literature review.
1 finding
Long-term clinical reports support high-dose fat-soluble vitamin treatment, including vitamin E, as associated with arrest of neuropathy and other complications.
"PMID:18611256 for long-term human clinical reports supporting high-dose fat-soluble vitamin treatment, including vitamin E, with arrest of neuropathy and other complications."

Deep Research

1
Abetalipoproteinemia Deep Research Fallback ▸

Abetalipoproteinemia Deep Research Fallback

Provider Attempts

  • 2026-05-04T05:24Z: timeout 120 just research-disorder falcon Abetalipoproteinemia timed out with exit code 124 after the provider command was terminated by timeout.
  • 2026-05-04T05:26Z: timeout 120 just research-disorder openai Abetalipoproteinemia timed out with exit code 124 after the provider command was terminated by timeout.

No provider-generated research artifact was available to integrate. Curation therefore proceeded from generated structured Orphanet evidence and fetched PubMed caches, without hand-editing any references_cache/*.md files.

Evidence Scope Used For Curation

  • ORPHA:14 structured record for disease definition, MONDO exact mapping, inheritance, prevalence, MTTP gene association, onset, and HPO phenotype frequencies.
  • PMID:24288038 for the canonical management framework and the mechanism that defective packaging and secretion of apoB-containing lipoproteins underlies abetalipoproteinemia.
  • PMID:30358967 for GeneReviews clinical characteristics, diagnosis/testing, diet and vitamin management, surveillance, and genetic counseling.
  • PMID:10946006 for patient MTTP variant screening and functional evidence that MTP gene defects are the proximal cause of abetalipoproteinemia.
  • PMID:8939939 for functional evidence that an abetalipoproteinemia-associated MTTP missense variant disrupts formation of an active MTP complex with protein disulfide isomerase.
  • PMID:30522860 for clinical evidence that deleterious MTTP variants produce undetectable apoB, extremely low LDL cholesterol, and inability to export apoB-containing lipoproteins from intestine and liver.
  • PMID:18611256 for long-term human clinical reports supporting high-dose fat-soluble vitamin treatment, including vitamin E, with arrest of neuropathy and other complications.

Curation Conclusions

The accepted disease model is MTTP loss of function causing defective intestinal chylomicron assembly and hepatic VLDL assembly, with loss of apoB-containing lipoprotein secretion. This explains the biochemical profile of absent or extremely low apoB lipoproteins, hypocholesterolemia, hypotriglyceridemia, fat malabsorption, and secondary fat-soluble vitamin deficiency. The clinical graph links these defects to ORPHA-supported gastrointestinal, hematologic, retinal, neurologic, hepatic, and biochemical phenotypes. Treatment evidence supports low-fat diet, essential fatty acid supplementation, and high-dose fat-soluble vitamin supplementation as the main management axis.