Autosomal Recessive Hypercholesterolemia

Mendelian MONDO:0011374 Pathograph 28 Show in embeddings browser Familial Hypercholesterolemia

Autosomal recessive hypercholesterolemia (ARH) is caused by biallelic pathogenic LDLRAP1 variants. The encoded ARH adaptor couples the LDL receptor to clathrin-dependent internalization. Impaired hepatic LDL uptake produces marked LDL-cholesterol elevation, childhood xanthomas and risk of premature coronary disease and aortic valve stenosis. The defect is cell-type and ligand dependent: fibroblast LDL uptake can remain normal, whereas lymphocyte uptake is impaired; LDLR-dependent VLDL-remnant clearance is largely preserved in knockout mice and was increased in a human kinetic study. Receptors present at the cell surface are not equivalent to normal clearance, but the defect does not imply uniform absence of receptor activity or treatment response. Statins and combination therapies can substantially reduce LDL-C, with variable target attainment. LDLR-independent agents and apheresis provide additional options. Sardinian founder alleles are prominent in reported cohorts, which do not represent worldwide population frequencies.

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Inheritance

Autosomal Recessive HP:0000007

Biallelic pathogenic LDLRAP1 variants cause autosomal recessive disease; both homozygous and compound-heterozygous genotypes occur. Carriers are usually asymptomatic and may have normal lipid profiles. After confirming that both parents carry a familial pathogenic variant, each pregnancy has a 25% affected, 50% carrier and 25% noncarrier probability. A disease-wide penetrance estimate is not established by the cited cohorts.

Autosomal recessive inheritance

Show evidence (3 references)

PMID:24404629 SUPPORT REVIEW SYNTHESIS Other

"LDLRAP1-related FH is caused by biallelic pathogenic variants and is inherited in an autosomal recessive manner."

GeneReviews states the recessive mode of inheritance and the requirement for biallelic variants.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf SUPPORT REVIEW SYNTHESIS Other

"If both parents are known to be heterozygous for an LDLRAP1 pathogenic variant, each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being a carrier, and a 25% chance of inheriting neither of the familial pathogenic variants."

Recurrence probabilities are conditional on confirmed parental carrier status.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf SUPPORT REVIEW SYNTHESIS Other

"Individuals who are heterozygous for an LDLRAP1 pathogenic variant (i.e., carriers) are typically asymptomatic."

Normal lipids do not exclude carrier status.

Discussions and Knowledge Gaps

What permits fibroblast LDL uptake when LDLRAP1 is absent?

KNOWLEDGE GAP OPEN arh_dab2_cell_context

Attached to

pathophysiology#Impaired Clathrin-Mediated Endocytosis of the Hepatocyte LDL Receptor experimental_models#Patient skin fibroblasts with DAB2 depletion

DAB2 abundance differs between fibroblasts and lymphocytes. However, DAB2 depletion in patient fibroblasts reduced receptor protein itself, so the experiment cannot isolate redundant endocytosis. A translation-related role was proposed; altered degradation outside the tested pathways remains possible. HeLa double-depletion results cannot substitute for patient-fibroblast behavior.

Show evidence (1 reference)

url:https://oup.silverchair-cdn.com/article-minimal/582819 SUPPORT PRIMARY RESULT In Vitro

"Clearly, our original intention to determine whether or not Dab2 facilitates LDL-receptor internalization in ARH fibroblasts was not possible from our data."

The authors explicitly limit the mechanistic inference.

Which machinery supports ARH-independent VLDL-remnant uptake and how much does it modify human disease?

KNOWLEDGE GAP OPEN arh_remnant_entry

Attached to

pathophysiology#Preserved Hepatic VLDL Remnant Uptake

Mouse and isolated-hepatocyte experiments establish retained LDLR-dependent remnant uptake. Simple ligand affinity or clustering and the tested LRP/heparan-sulfate alternatives do not explain it. One human kinetic study supports increased direct remnant removal, but cannot establish its contribution across LDLRAP1 genotypes or treatment responses.

Show evidence (1 reference)

PMID:22157599 SUPPORT PRIMARY RESULT Human Clinical

"In contrast, the direct removal of very-low-density lipoprotein remnant was significantly greater in ARH than those in control subjects (47.5 versus 2±2%)."

One patient versus seven controls; does not define a population-wide fraction.

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Pathophysiology

Biallelic LDLRAP1 Loss-of-Function

Homozygous or compound-heterozygous pathogenic LDLRAP1 variants impair the ARH adaptor. The current locus is 1p36.11; 1p35 was the historical discovery mapping. Truncating, splice, initiation-codon and larger rearrangement alleles are described. Some alleles retain detectable shorter protein and residual uptake, so loss of function does not mean every genotype is a complete null. The two Sardinian founder alleles are enriched in that population rather than defining all worldwide disease.

LDLRAP1 hgnc:18640

Genetic context LDLRAP1 hgnc:18640 variant_origin: GERMLINE functional_impact_category: LOSS_OF_FUNCTION

Biallelic germline pathogenic variants, either homozygous or compound heterozygous. Heterozygous carriers typically have normal lipid profiles.

Downstream

Loss of ARH Adaptor Bridging of the LDL Receptor to Clathrin Biallelic variants impair the adaptor needed for effective LDL-receptor coupling to the internalization machinery; the degree and molecular consequence vary by allele.

Show evidence (3 references)

PMID:11326085 SUPPORT Human Clinical

"Here we map the ARH locus to an approximately 1-centimorgan interval on chromosome 1p35 and identify six mutations in a gene encoding a putative adaptor protein (ARH)."

The founding paper that maps ARH to 1p35 and identifies causative mutations in the adaptor gene.

PMID:32011344 SUPPORT REVIEW SYNTHESIS Other

"It is inherited as a recessive trait and causative mutations, though heterogeneous, are all predicted to be loss-of-function."

States that the heterogeneous causative alleles are uniformly loss-of-function.

PMID:30777337 SUPPORT PRIMARY RESULT In Vitro

"The patient had undetectable full-length ARH protein by Western blotting, but expressed a lower-than-normal molecular weight peptide."

Patient-derived lymphocyte protein analysis of the homozygous initiation-codon variant; supports partial functional heterogeneity rather than a complete-null rule.

Loss of ARH Adaptor Bridging of the LDL Receptor to Clathrin

The ARH phosphotyrosine-binding domain interacts with the LDLR cytoplasmic tail, while clathrin- and AP-2-binding regions connect it to coated-pit machinery. Domain-rescue experiments require the PTB domain plus either clathrin or AP-2 binding for effective clustering and LDL uptake. LDLRAP1 disease primarily affects this adaptor function rather than the LDLR coding sequence; receptor abundance and residual activity nevertheless depend on cell and allele context.

hepatocyte CL:0000182

clathrin-cargo adaptor activity GO:0035615 ⇓ LOSS OF FUNCTION low-density lipoprotein particle receptor binding GO:0050750 ↓ DECREASED

Downstream

Impaired Clathrin-Mediated Endocytosis of the Hepatocyte LDL Receptor Impaired adaptor coupling reduces receptor clustering and internalization of LDL cargo in the tested hepatocyte systems.

Show evidence (2 references)

PMID:16179341 SUPPORT In Vitro

"The disease is caused by mutations in ARH, which encodes a putative adaptor protein that interacts with the cytoplasmic tail of the LDLR, phospholipids, and two components of the clathrin endocytic machinery, clathrin and adaptor protein-2 (AP-2) in vitro."

Establishes the adaptor's three binding partners - the receptor tail, clathrin, and AP-2 - whose bridging is lost in ARH.

PMID:16179341 SUPPORT In Vitro

"The phosphotyrosine binding domain of ARH plus either the clathrin box or the AP-2 binding region were required for both clustering and internalization of the LDLR."

Defines the domain requirements for the bridging function, the LOSS_OF_FUNCTION captured by this node.

Impaired Clathrin-Mediated Endocytosis of the Hepatocyte LDL Receptor

LDL-bound receptor internalization is strongly impaired in hepatocytes lacking ARH. The defect is cargo and cell dependent rather than a global failure of clathrin endocytosis. Patient lymphocytes also show reduced LDL uptake, while cultured skin fibroblasts can retain normal LDL-receptor function. In mouse hepatocytes, LDLR-dependent VLDL-remnant uptake persists despite failure to internalize LDL. Fibroblast DAB2-dependent maintenance of receptor protein complicates a simple redundant-adaptor explanation.

hepatocyte CL:0000182

clathrin-dependent endocytosis GO:0072583 ↓ DECREASED receptor-mediated endocytosis GO:0006898 ↓ DECREASED

liver UBERON:0002107

Experimental models

Patient-derived primary lymphocytes PRIMARY CELL CULTURE Reduced cellular LDL uptake reproduces an ARH endocytic defect in lymphocytes.

Polarized WIF-B hepatocytes CELL LINE ARH PTB integrity and at least one clathrin/AP-2 interaction are required for clustering and internalization.

Animal models

Arh(-/-) mouse Mouse recapitulates Loss of ARH in mouse liver reproduces the hepatocyte LDL-receptor endocytosis defect that defines this node, generalizing the WIF-B cell-culture result to an intact liver.

Downstream

Impaired Hepatic Clearance of Plasma LDL Reduced hepatic LDL uptake contributes to slow plasma LDL-apoB removal; human kinetic data establish the clearance defect without measuring every cellular intermediary.

Show evidence (4 references)

PMID:16179341 SUPPORT In Vitro

"Autosomal recessive hypercholesterolemia is characterized by a cell type-specific defect in low density lipoprotein receptor (LDLR) endocytosis."

States that the endocytic defect itself is the cellular lesion of ARH.

PMID:11326085 SUPPORT BACKGROUND Other

"ARH appears to have a tissue-specific role in LDLR function, as it is required in liver but not in fibroblasts."

The founding abstract summarizes a liver-versus-fibroblast contrast; it does not establish that liver is the only affected cell type.

PMID:27079874 SUPPORT PRIMARY RESULT In Vitro

"Fluorescent LDL cellular uptake, also measured by flow cytometry, was reduced in ARH lymphocytes compared with control lymphocytes."

Patient lymphocyte experiments demonstrate that the uptake defect is not liver-exclusive.

+ 1 more reference

Impaired Hepatic Clearance of Plasma LDL

Plasma LDL-apoB removal is reduced. In one ARH patient, a stable-isotope study estimated LDL-apoB fractional catabolism of 0.109/day versus 0.450 ± 0.122/day in seven controls. Atorvastatin increased this patient's rate to 0.464/day. This demonstrates substantial reversibility in that individual and does not establish a universal value for all LDLRAP1 genotypes.

low-density lipoprotein particle clearance GO:0034383 ↓ DECREASED

liver UBERON:0002107

Downstream

Lifelong Elevation of Plasma LDL Cholesterol Reduced LDL removal raises circulating LDL-C. The balance also depends on precursor clearance and production; unchanged LDL production is not assumed.

Show evidence (1 reference)

PMID:22157599 SUPPORT PRIMARY RESULT Human Clinical

"FCR of low-density lipoprotein (LDL) apoB of ARH was significantly lower than those of control subjects (0.109 versus 0.450±0.122 1/day)."

Stable-isotope kinetic modeling in one ARH patient compared with seven controls; a human metabolic measurement, not an in-vitro uptake assay.

Lifelong Elevation of Plasma LDL Cholesterol

Marked LDL-C elevation is the central biochemical manifestation, but its magnitude and response to treatment vary. In a retrospective 52-patient cohort, baseline LDL-C averaged 571.9 mg/dL and the best recorded on-treatment level averaged 164.0 mg/dL. Baseline was not uniformly untreated, and nadir is not long-term average exposure. Failure to reach targets does not mean lack of response.

Downstream

Premature Atherosclerotic Cardiovascular Disease Sustained LDL burden contributes to atherosclerotic disease; the ARH cohort records substantial residual cardiovascular risk despite treatment.

Extravascular Cholesterol Deposition Chronic cholesterol excess produces tissue deposits; the individual clinical lesions require their own evidence.

Aortic Valve Stenosis Valvular disease is a recognized severe-hypercholesterolemia complication; it is distinct from coronary plaque rupture.

Increased LDL Cholesterol The elevated plasma LDL-C state is the directly measured biochemical phenotype.

Hypercholesterolemia The markedly elevated LDL fraction contributes to increased total cholesterol.

Show evidence (1 reference)

PMID:29348020 SUPPORT PRIMARY RESULT Human Clinical

"Mean LDL-C achieved at nadir was 164.0 ± 85.1 mg/dl (-69.6% from baseline), with a better response in patients taking lomitapide (-88.3%)."

Retrospective treatment combinations in 52 ARH patients. The lomitapide figure is a subgroup change from the original baseline, not a randomized or isolated add-on drug effect.

Premature Atherosclerotic Cardiovascular Disease

Premature arterial disease, especially coronary disease, produces myocardial infarction and need for coronary revascularization. A 52-patient retrospective ARH series recorded 14 incident ASCVD cases during mean 14.1-year follow-up, including five myocardial infarctions. Residual risk can be substantial despite LDL lowering. Comparisons with historical HoFH cohorts do not prove identical risk for every genotype or exclude differences from receptor-negative LDLR disease. Aortic valve stenosis is modeled separately from this arterial outcome.

artery UBERON:0001637

Downstream

Premature Coronary Artery Atherosclerosis Coronary disease is the major reported arterial manifestation.

Myocardial Infarction Coronary disease can produce myocardial infarction; five events were recorded in the 52-patient longitudinal cohort.

Show evidence (1 reference)

PMID:29348020 SUPPORT PRIMARY RESULT Human Clinical

"During follow-up, 26.9% of patients had incident ASCVD, and 11.5% had a new diagnosis of aortic valve stenosis (absolute risk per year of 1.9% and 0.8%, respectively)."

Direct retrospective clinical outcomes; no universal age of onset follows from the cohort.

Extravascular Cholesterol Deposition

Cholesterol accumulates in skin, tendons and the corneal periphery, producing distinct clinical stigmata. The 52-patient cohort recorded xanthomas in 47 patients; this generic endpoint does not provide a tendon-specific frequency. Lesion type and regression under treatment vary.

Downstream

Tendon Xanthoma Tendon cholesterol deposits are one xanthoma subtype; no generic-cohort percentage is assigned specifically to tendons.

Xanthelasma Eyelid cholesterol deposition produces xanthelasma.

Corneal Arcus Peripheral corneal lipid deposition produces an arcus.

Xanthoma Cholesterol deposition produces xanthomas of different morphologies.

Show evidence (1 reference)

url:https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf SUPPORT PRIMARY RESULT Human Clinical

"Age at ﬁrst visit was 31.3 /C6 17.1 years, 46.2% of patients were men, and 90% showed xan- thomas."

The selected ARH cohort reports generic xanthomas, not a 90% frequency for each anatomical subtype.

Preserved Hepatic VLDL Remnant Uptake

LDLR-dependent uptake of VLDL remnants is largely preserved in Arh-knockout mice despite impaired LDL uptake. Hepatocyte LDLR deletion abolishes this uptake, whereas additional LRP deletion does not. A human kinetic study in one patient found increased direct remnant removal. This retained pathway may limit LDL-precursor availability and contribute to statin responsiveness, but the precise ARH-independent internalization machinery is unresolved.

hepatocyte CL:0000182

liver UBERON:0002107

Experimental models

Primary Arh-knockout mouse hepatocytes PRIMARY CELL CULTURE ARH-deficient hepatocytes internalize beta-VLDL whereas LDLR-deficient cells do not.

Animal models

Arh(-/-) mouse Mouse recapitulates VLDL clearance is greater in Arh-knockout than Ldlr-knockout mice despite impaired LDL clearance.

Show evidence (2 references)

PMID:17200716 SUPPORT PRIMARY RESULT Model Organism

"The rate of VLDL clearance was significantly higher in Arh(-/-) mice than in Ldlr(-/-) mice, suggesting that LDLR-dependent uptake of VLDL is maintained in the absence of ARH."

Whole-mouse comparison; preserved remnant clearance is distinct from the LDL clearance defect.

PMID:22157599 SUPPORT PRIMARY RESULT Human Clinical

"In contrast, the direct removal of very-low-density lipoprotein remnant was significantly greater in ARH than those in control subjects (47.5 versus 2±2%)."

One patient versus seven controls; does not define a population-wide fraction.

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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

Cardiovascular 3

Premature Coronary Artery Atherosclerosis HP:0001677

Course: PROGRESSIVE

Show evidence (2 references)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf SUPPORT REVIEW SYNTHESIS Other

"Presentation similar to LDLR-related HoFH incl LDL-C >500 mg/dL, early-onset CAD, & aortic valve stenosis."

Gene-specific clinical association.

url:https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf SUPPORT PRIMARY RESULT Human Clinical

"ASCVD 14 (26.9) 7 (29.2) 7 (25.0)"

Table 3 whole-cohort, male and female incident ASCVD counts; ASCVD is broader than coronary disease.

Myocardial Infarction HP:0001658

Show evidence (1 reference)

url:https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf SUPPORT PRIMARY RESULT Human Clinical

"MI 5 (9.6) 2 (8.3) 3 (10.7)"

Table 3 whole-cohort, male and female myocardial-infarction counts.

Aortic Valve Stenosis HP:0001650

Show evidence (2 references)

PMID:32011344 SUPPORT REVIEW SYNTHESIS Other

"ARH is also associated with increased risk of developing aortic valve stenosis."

Directly attributes increased aortic valve stenosis risk to ARH.

url:https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf SUPPORT PRIMARY RESULT Human Clinical

"Eleven patients (21.1%) showed aortic valve stenosis, which was reported to be severe in 5.8%."

Baseline valve findings in the retrospective cohort.

Eye 1

Corneal Arcus HP:0001084

Show evidence (1 reference)

PMID:24404629 SUPPORT REVIEW SYNTHESIS Other

"Individuals with FH may develop corneal arcus (white, gray, or blue opaque ring in the corneal margin as a result of cholesterol deposition) at a younger age than those without FH."

GeneReviews documents premature corneal arcus in FH; cited at class level for the shared hypercholesterolemia phenotype.

Head and Neck 1

Xanthelasma HP:0001114

Show evidence (1 reference)

PMID:24404629 SUPPORT REVIEW SYNTHESIS Other

"Xanthelasmas (yellowish, waxy deposits) can occur around the eyelids."

GeneReviews documents xanthelasma as a cholesterol-deposition sign of FH; cited at class level for the hypercholesterolemia ARH shares.

Integument 2

Xanthoma Xanthomatosis HP:0000991

Show evidence (2 references)

url:https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf SUPPORT PRIMARY RESULT Human Clinical

"Number of xanthomas 47 (90.4) 22 (91.7) 25 (89.3)"

Table 1 gives whole-cohort, male and female counts, respectively.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf SUPPORT REVIEW SYNTHESIS Other

"Planar, tuberous, or tendon xanthomas have also been reported to develop in childhood."

LDLRAP1-specific GeneReviews table; does not provide separate frequencies for the three morphologies.

Tendon Xanthoma Tendon xanthomatosis HP:0010874

Course: PROGRESSIVE

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf SUPPORT REVIEW SYNTHESIS Other

"Planar, tuberous, or tendon xanthomas have also been reported to develop in childhood."

LDLRAP1-specific GeneReviews table; does not provide separate frequencies for the three morphologies.

Metabolism 2

Hypercholesterolemia VERY_FREQUENT HP:0003124

Temporal: CHRONIC

Show evidence (1 reference)

PMID:42730734 SUPPORT PRIMARY RESULT Human Clinical

"Total cholesterol was 516 mg/dL, low-density lipoprotein cholesterol (LDL-C) 499 mg/dL, triglycerides 47 mg/dL, and high-density lipoprotein cholesterol 35 mg/dL."

Biochemical values in one molecularly confirmed adolescent, not population averages.

Increased LDL Cholesterol VERY_FREQUENT Increased LDL cholesterol concentration HP:0003141

Temporal: CHRONIC

Show evidence (2 references)

url:https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf SUPPORT PRIMARY RESULT Human Clinical

"We collected data for 52 patients (28 females, 24 males; 31.1 /C6 17.1 years of age; baseline LDL-C: 571.9 /C6 171.7 mg/dl)."

Baseline cohort mean; the adjoining text and Table 1 provide dispersion and range.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf SUPPORT REVIEW SYNTHESIS Other

"Presentation similar to LDLR-related HoFH incl LDL-C >500 mg/dL, early-onset CAD, & aortic valve stenosis."

The LDLRAP1-specific GeneReviews row describes severe presentations without making the threshold obligatory.

🧬

Genetic Associations

LDLRAP1 (Pathogenic Mutations)

Gene: LDLRAP1 hgnc:18640 relationship_type: CAUSATIVE variant_origin: GERMLINE

Autosomal Recessive

Show evidence (5 references)

PMID:11326085 SUPPORT Human Clinical

"Here we map the ARH locus to an approximately 1-centimorgan interval on chromosome 1p35 and identify six mutations in a gene encoding a putative adaptor protein (ARH)."

The founding gene-discovery paper mapping and identifying LDLRAP1/ARH mutations.

url:https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf SUPPORT PRIMARY RESULT Human Clinical

"Twelve different LDLRAP1 mutations (including 2 major rearrangements) in LDLRAP1 were detected; 8 of them predict the presence of a truncated ARH protein. Thirty-nine patients were simple homozy- gotes, and 13 were compound heterozygotes."

Includes two major rearrangements and both biallelic configurations.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf SUPPORT REVIEW SYNTHESIS Other

"LDLRAP1 NM_015627.3 NP_056442.2 c.431dupA (c.432_433insA) p.His144GlnfsTer27"

Modern transcript-based founder nomenclature from GeneReviews; historical protein notations can differ.

+ 2 more references

💊

Medical Actions

Statin plus Ezetimibe (Background Lipid-Lowering Therapy)

Action: Pharmacotherapy NCIT:C15986

Agent: statin CHEBI:87631 ezetimibe CHEBI:49040

Platform: Small molecule

High-intensity or maximally tolerated statin plus ezetimibe is initial combination treatment for severe disease, with early escalation according to response and risk. ARH patients can respond substantially: in one kinetic study atorvastatin increased LDL apoB fractional catabolism from 0.109 to 0.464/day and reduced LDL-C from 8.63 to 4.22 mmol/L. Ezetimibe inhibits intestinal NPC1L1-mediated cholesterol absorption, but its downstream LDL-C effect, like statin response, partly depends on residual LDLR-mediated clearance. Neither a uniformly absent response nor universal target attainment is supported.

Mechanism Target:

INHIBITS Lifelong Elevation of Plasma LDL Cholesterol — Lowers circulating LDL-C to a variable degree; residual uptake and preserved remnant handling can contribute.

Show evidence (1 reference)

PMID:22157599 SUPPORT PRIMARY RESULT Human Clinical

"Interestingly, FCR of LDL apoB in ARH dramatically increased to 0.464 1/day, accompanying reduction of LDL cholesterol levels from 8.63 to 4.22 mmol/L after treatment with atorvastatin of 20 mg/d for 3 months."

Direct one-patient treatment/kinetic observation; not a population response estimate.

Show evidence (3 references)

PMID:37130090 SUPPORT REVIEW SYNTHESIS Other

"Patients should start on a high-intensity statin and ezetimibe rather than statin monotherapy, but most will require additional therapies to attain goal."

Consensus for the severe HoFH clinical phenotype.

PMID:22157599 SUPPORT PRIMARY RESULT Human Clinical

Direct one-patient treatment/kinetic observation; not a population response estimate.

PMID:37130090 SUPPORT REVIEW SYNTHESIS Other

"Response to statin, ezetimibe, and proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors is dependent on the degree of residual low-density lipoprotein receptor activity;"

Clarifies secondary receptor dependence despite different primary drug targets.

Lomitapide

Action: Pharmacotherapy NCIT:C15986

Agent: lomitapide CHEBI:72297

Platform: Small molecule

Microsomal triglyceride transfer protein inhibition reduces hepatic VLDL production and therefore LDL formation independently of LDLR function. In nine ARH patients receiving background statin/ezetimibe, with apheresis in three and PCSK9 inhibition in one, median LDL-C fell from 257.0 to 101.7 mg/dL (60.4%). Four patients overlapped the earlier 52-patient cohort. This uncontrolled subanalysis does not isolate comparative efficacy or prove cardiovascular-event prevention. Gastrointestinal intolerance, liver-fat accumulation and transaminase elevations require dietary support and liver monitoring; one patient stopped because of gastrointestinal effects and poor adherence. Normal stiffness in six assessed patients does not establish long-term hepatic safety.

Mechanism Target:

INHIBITS Lifelong Elevation of Plasma LDL Cholesterol — Lowers LDL production upstream of the receptor, bypassing the defective hepatic LDL-receptor internalization.

Show evidence (1 reference)

PMID:36072671 SUPPORT BACKGROUND Other

"lomitapide acts using an LDLR-independent mechanism, therefore potentially extending its efficacy in patients with an absent LDLR function, like those with ARH"

The paper summarizes the established drug mechanism; ARH is an adaptor defect, not absence of LDLR protein.

Show evidence (4 references)

PMID:36072671 SUPPORT Human Clinical

"The addition of lomitapide (mean dose, 10 mg) resulted in the achievement of a median on-treatment LDL-C of 101.7 mg/dL (IQR, 71.3-138.3; 60.4% reduction from baseline)"

Quantifies the LDL-C reduction achieved by lomitapide in the ARH subgroup.

PMID:36072671 SUPPORT PRIMARY RESULT Human Clinical

"Indeed, he stopped lomitapide after 18 months of treatment due to gastrointestinal side effects and lack of compliance."

Observed treatment discontinuation in one patient.

PMID:36072671 SUPPORT PRIMARY RESULT Human Clinical

"This patient also experienced a change in hepatic fat, from absent to moderate steatosis, at the last follow-up visit."

Documents hepatic fat accumulation; other patients also showed new or worsening fat on Table 2.

+ 1 more reference

Lipoprotein Apheresis

Action: lipoprotein apheresis Ontology label: Therapeutic Apheresis NCIT:C173286

Platform: Device

Repeated extracorporeal removal of circulating apoB-containing lipoproteins lowers LDL-C independently of receptor function. Severe childhood disease may warrant early apheresis when drug therapy does not adequately control exposure, before established coronary disease. Frequency and continuation depend on severity, venous access, response to adjunct drugs and specialist assessment. Acute postprocedure values underestimate the rebound between sessions; treatment burden and time-averaged LDL-C matter.

Mechanism Target:

INHIBITS Lifelong Elevation of Plasma LDL Cholesterol — Lowers plasma LDL cholesterol by a route independent of LDL-receptor function, so it retains efficacy despite the ARH internalization defect; current consensus treats it as foundational in severe biallelic disease.

Show evidence (2 references)

PMID:37130090 SUPPORT REVIEW SYNTHESIS Other

"for lomitapide, angiopoietin-like protein 3 (ANGPLT3)-directed therapy and lipoprotein apheresis, response is independent of low-density lipoprotein receptor function."

States that the LDL-C-lowering response to lipoprotein apheresis is independent of LDL-receptor function - the mechanism that lets it lower LDL-C in ARH despite the receptor-side (here, adaptor-side) defect.

PMID:37130090 SUPPORT REVIEW SYNTHESIS Other

"Combination LDL-C-lowering therapy-both pharmacologic intervention and lipoprotein apheresis (LA)-is foundational."

Establishes apheresis as a foundational LDL-C-lowering component of severe-disease management, the role modeled by this link.

Show evidence (2 references)

PMID:37130090 SUPPORT REVIEW SYNTHESIS Other

"Combination LDL-C-lowering therapy-both pharmacologic intervention and lipoprotein apheresis (LA)-is foundational."

Establishes apheresis as a foundational LDL-C-lowering component of severe-disease management, the role modeled by this link.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf SUPPORT REVIEW SYNTHESIS Other

"LDL apheresis (≤2x/wk) is often required from a young age."

Severe-FH class recommendation, not a requirement that coronary disease already be present.

PCSK9 Inhibitor

Action: Pharmacotherapy NCIT:C15986

Agent: PCSK9 inhibitor NCIT:C190797

Platform: Monoclonal antibody

PCSK9 monoclonal antibodies preserve LDLR abundance and can lower LDL-C in some ARH patients, but response varies with residual function. Patient lymphocyte experiments with alirocumab showed attenuated effects compared with controls; these are not clinical trials. In one patient homozygous for c.1A>G, evolocumab added to atorvastatin/ezetimibe lowered LDL-C a further 39%. A monitored trial of therapy should be judged by the individual biochemical response; poor response in one genotype does not imply universal inefficacy.

Mechanism Target:

INHIBITS Lifelong Elevation of Plasma LDL Cholesterol — May lower circulating LDL-C in responsive individuals; evidence includes a single clinical response alongside patient-cell experiments.

Show evidence (1 reference)

PMID:30777337 SUPPORT PRIMARY RESULT Human Clinical

"LDL-cholesterol levels were markedly reduced by the successive therapy with Atorvastatin and Atorvastatin plus Ezetimibe, and the addition of Evolocumab biweekly decreased LDL-cholesterol by a further 39%."

Clinical response in one initiation-codon-variant patient.

Show evidence (3 references)

PMID:27079874 SUPPORT In Vitro

"the effects of recombinant PCSK9, and hence of alirocumab, on LDL receptor expression and function were significantly less pronounced in ARH than in control cells."

Mechanistic basis for the blunted PCSK9-inhibitor response in ARH - PCSK9's effect on the LDL receptor is reduced in ARH cells.

PMID:30777337 SUPPORT PRIMARY RESULT Human Clinical

Clinical response in one initiation-codon-variant patient.

PMID:37130090 SUPPORT REVIEW SYNTHESIS Other

"If patients show >15% additional LDL-C reduction, PCSK9-directed therapy may be continued, but if response is poor, clinicians should consider stopping this therapy."

Severe-HoFH consensus threshold, not an LDLRAP1-specific trial endpoint.

Evinacumab

Action: Pharmacotherapy NCIT:C15986

Agent: Evinacumab NCIT:C169973

Platform: Monoclonal antibody

ANGPTL3-neutralizing antibody that lowers LDL-C through an LDLR-independent pathway. Two reported ARH adults achieved substantial additional lowering with monthly infusions; one continued apheresis, while the second remained below 55 mg/dL after background evolocumab and bempedoic acid were stopped. Changing co-therapy and apheresis timing preclude attributing the entire change to evinacumab. Transient first-infusion headache or abdominal colic was reported. The phase III open-label extension included two LDLRAP1 patients, but its published subgroup combines them with LDLR disease. Cardiovascular-event prevention specifically in ARH is unproven.

Mechanism Target:

INHIBITS Lifelong Elevation of Plasma LDL Cholesterol — Reduces circulating LDL-C; the evidence and limitations are specified in the treatment description.

Show evidence (1 reference)

url:https://air.unimi.it/retrieve/handle/2434/1224076/3272602/1-s2.0-S1933287426000401-main.pdf SUPPORT PRIMARY RESULT Human Clinical

"After 10 months, LDL-C levels have remained below 55 mg/dL ( Fig 2 B and Table ), with a time-averaged LDL-C decrease of 73.8%."

Second ARH case maintained low LDL-C despite discontinuation of evolocumab and bempedoic acid after three months. Background rosuvastatin/ezetimibe continued; this is not randomized or isolated drug efficacy.

Show evidence (3 references)

url:https://air.unimi.it/retrieve/handle/2434/1224076/3272602/1-s2.0-S1933287426000401-main.pdf SUPPORT PRIMARY RESULT Human Clinical

"After 10 months, LDL-C levels have remained below 55 mg/dL ( Fig 2 B and Table ), with a time-averaged LDL-C decrease of 73.8%."

PMID:41671678 SUPPORT PRIMARY RESULT Human Clinical

"At baseline, 55 (47.4%) had either identical bi-allelic variants in LDLR (n = 53) or LDLRAP1 (n = 2), and 41 (35.3%) had different bi-allelic LDLR variants."

Two LDLRAP1 patients were included in the extension; pooled LDLR/LDLRAP1 response is not a gene-specific estimate.

PMID:37130090 SUPPORT REVIEW SYNTHESIS Other

"for lomitapide, angiopoietin-like protein 3 (ANGPLT3)-directed therapy and lipoprotein apheresis, response is independent of low-density lipoprotein receptor function."

Mechanistic class rationale for ANGPTL3 blockade.

Bempedoic Acid in Combination Therapy

Action: Pharmacotherapy NCIT:C15986

Agent: Bempedoic Acid NCIT:C166494

Platform: Small molecule

A reported 15-year-old with biallelic LDLRAP1 disease received atorvastatin, ezetimibe and bempedoic acid, with LDL-C decreasing from 499 to 80 mg/dL at three months. This is case-level combination-treatment evidence, not proof of independent efficacy, routine pediatric indication or prevention of clinical events.

Mechanism Target:

INHIBITS Lifelong Elevation of Plasma LDL Cholesterol — Reduces circulating LDL-C; the evidence and limitations are specified in the treatment description.

Show evidence (1 reference)

PMID:42730734 SUPPORT PRIMARY RESULT Human Clinical

"The patient was treated with atorvastatin, ezetimibe, and bempedoic acid, resulting in a marked reduction in low-density lipoprotein cholesterol to 80 mg/dL at 3-month follow-up."

One adolescent received three agents together; the contribution of bempedoic acid cannot be separated.

Show evidence (1 reference)

PMID:42730734 SUPPORT PRIMARY RESULT Human Clinical

"The patient was treated with atorvastatin, ezetimibe, and bempedoic acid, resulting in a marked reduction in low-density lipoprotein cholesterol to 80 mg/dL at 3-month follow-up."

One adolescent received three agents together; the contribution of bempedoic acid cannot be separated.

Genetic Counseling

Category: Counseling / Informational Action: Genetic Counseling NCIT:C15240

Explain recessive inheritance and confirm parental carrier status. Discuss familial testing, partner testing and reproductive options. An affected person transmits one pathogenic allele to every child; disease risk depends on the partner genotype. Prenatal or preimplantation testing becomes possible after the familial variants are known.

Show evidence (2 references)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf SUPPORT REVIEW SYNTHESIS Other

"Genetic counseling and genetic testing can be offered to the reproductive partner to assess this risk."

LDLRAP1-specific partner evaluation.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf SUPPORT REVIEW SYNTHESIS Other

"Once the FH-causing pathogenic variant(s) have been identified in an affected family member, prenatal and preimplantation genetic testing are possible."

Family-specific reproductive testing; interpreted using the recessive LDLRAP1 inheritance model.

Lifestyle and Cardiovascular Risk Management

Category: Therapeutic

Use dietary counseling, regular physical activity, healthy weight and smoking avoidance alongside pharmacologic treatment. Address hypertension, diabetes and other modifiable risks. Lifestyle measures alone are insufficient for severe LDLRAP1 disease. Established coronary or valve disease warrants cardiovascular specialist care and indicated intervention.

Show evidence (2 references)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf SUPPORT REVIEW SYNTHESIS Other

"To prevent primary manifestations, the following are recommended: • Reduce saturated fat intake. • Increase intake of soluble fiber to 10-20 g/day. • Increase physical activity. • Do not smoke."

General FH lifestyle recommendations.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf SUPPORT REVIEW SYNTHESIS Other

"Children & adults w/clinical atherosclerotic CVD should be evaluated & treated by cardiovascular specialists."

Care of established disease is distinct from LDL-C lowering.

Pregnancy Planning and Lipid Management

Category: Therapeutic

Coordinate lipid, cardiovascular and obstetric care before conception, through pregnancy and lactation. Assess coronary and aortic-valve disease and review each medication individually. In severe disease, apheresis can limit LDL exposure during pregnancy; drug decisions require individualized maternal and fetal risk assessment.

Show evidence (2 references)

PMID:37130090 SUPPORT REVIEW SYNTHESIS Other

"HoFH women should receive integrated care from a multidisciplinary team, including cardiovascular assessment, before, during, and after pregnancy."

Class-level guidance applicable to severe ARH; no blanket medication contraindication is inferred.

PMID:37130090 SUPPORT REVIEW SYNTHESIS Other

"Thus, HoFH women should be offered weekly or fortnightly LA during pregnancy."

Severe-disease consensus, not a gene-specific pregnancy trial.

🔬

Biochemical Markers

Plasma LDL Cholesterol (Increased)

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf SUPPORT REVIEW SYNTHESIS Other

"Presentation similar to LDLR-related HoFH incl LDL-C >500 mg/dL, early-onset CAD, & aortic valve stenosis."

The LDLRAP1-specific GeneReviews row describes severe presentations without making the threshold obligatory.

🔬

Diagnosis

Molecular Genetic Testing of LDLRAP1

Identify two pathogenic or likely pathogenic LDLRAP1 variants in trans, using segregation testing when needed. An FH or broader dyslipidemia panel should include sequence and deletion/duplication analysis. A variant of uncertain significance cannot establish or exclude the diagnosis. Founder testing may be useful in Sardinian families, but a negative founder test does not exclude other alleles; one detected allele or apparent homozygosity may require copy-number analysis. Normal fibroblast LDL uptake does not exclude ARH.

Show evidence (4 references)

PMID:24404629 SUPPORT REVIEW SYNTHESIS Other

"The molecular diagnosis of FH can be established by identification of heterozygous or biallelic pathogenic variants in APOB (variants that impair binding of LDL-C to the LDL receptor), LDLR, or PCSK9 (gain of function); or rarely, identification of biallelic pathogenic variants in LDLRAP1."

GeneReviews names biallelic LDLRAP1 pathogenic variants as the molecular diagnosis of the recessive form - the ARH-specific diagnostic route.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf SUPPORT REVIEW SYNTHESIS Other

"Identification of variant(s) of uncertain significance cannot be used to confirm or rule out the diagnosis."

VUS interpretation applies to the FH molecular evaluation.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf SUPPORT REVIEW SYNTHESIS Other

"A smaller FH multigene panel that includes sequence analysis and deletion/duplication analysis of APOB, LDLR, LDLRAP1, and PCSK9 may be considered."

Panel should include copy-number analysis as well as sequencing.

+ 1 more reference

Clinical Suspicion and Lipid Evaluation

Severe LDL-C elevation, childhood xanthomas or early coronary/valve disease raise suspicion. Normal parental lipids favor recessive disease but are not diagnostic, and no single LDL-C threshold establishes LDLRAP1 disease. Measure the lipid profile, assess secondary causes and cardiovascular risk factors, and use molecular testing to distinguish phenotypically overlapping disorders.

Show evidence (2 references)

PMID:42730734 SUPPORT PRIMARY RESULT Human Clinical

"Cardiac evaluation was normal, secondary causes were excluded, and first-degree relatives had normal lipid profiles."

One molecularly confirmed case illustrates normal family lipids and absence of established cardiovascular disease.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf SUPPORT REVIEW SYNTHESIS Other

"A broader dyslipidemia multigene panel that includes APOB, LDLR, LDLRAP1, and PCSK9 as well as ABCG8, ABCG5, APOE, and LIPA (genes associated with other lipid conditions that can cause elevated LDL-C levels and early-onset CAD; see Differential Diagnosis) may also be considered."

Broader testing addresses overlapping inherited lipid disorders.

Cardiovascular Imaging Surveillance

Monitor lipids and cardiovascular risk throughout life. For severe ARH overlapping clinical HoFH, consensus supports baseline and annual echocardiography of the heart and aorta, and specialist-directed coronary CT angiography. Repeat CT depends on baseline burden, LDL-C lowering, radiation risk and clinical indication. Invasive coronary angiography is reserved for suspected ischemia or valve dysfunction. This is severity-based clinical guidance, not a requirement for routine catheterization in every LDLRAP1 patient.

Show evidence (3 references)

PMID:24404629 SUPPORT REVIEW SYNTHESIS Other

"or autosomal recessive FH (due to homozygous or compound heterozygous pathogenic variants in LDLRAP1) should be monitored with various imaging modalities (including echocardiogram, CT angiogram, and cardiac catheterization) as recommended."

GeneReviews names autosomal recessive FH (biallelic LDLRAP1) explicitly in its imaging-surveillance recommendation - the most ARH-specific management statement in the chapter.

PMID:37130090 SUPPORT REVIEW SYNTHESIS Other

"Patients with HoFH should receive echocardiographic evaluation of the heart and aorta at baseline and annually thereafter."

Class-level guidance for severe disease.

PMID:37130090 SUPPORT REVIEW SYNTHESIS Other

"Invasive coronary angiography is indicated in patients with symptoms and/or signs suggestive of ischaemia or valve malfunction."

Limits invasive investigation to a clinical indication.

Cascade and Carrier Testing

Offer targeted familial-variant testing to at-risk relatives and parents. Normal lipid levels do not reliably identify carriers. Confirm parental segregation to refine recurrence risk and investigate unexpected inheritance, including an undetected deletion or uniparental isodisomy.

Show evidence (2 references)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf SUPPORT REVIEW SYNTHESIS Other

"Carrier testing for at-risk relatives requires prior identification of the LDLRAP1 pathogenic variants in the family."

Family-specific molecular testing.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf SUPPORT REVIEW SYNTHESIS Other

"Molecular genetic testing is recommended for the parents of a proband to confirm that both parents are heterozygous for an LDLRAP1 pathogenic variant and to allow reliable recurrence risk assessment."

Parent testing confirms the presumed recessive transmission.

📈

Progression

Lifelong LDL-C Elevation from Early Life

Age: From birth

LDL cholesterol is markedly elevated from early life because hepatic LDL clearance is defective from birth. Cumulative LDL-C burden, not a discrete onset, drives the cardiovascular course.

Extravascular Deposition and Xanthomata

Age: Childhood to early adulthood

Cutaneous and tendon xanthomas may develop in childhood; the 47/52 count in the 2018 cohort covers all xanthoma morphologies. Regression depends on effective sustained LDL-C reduction and is not immediate.

Show evidence (2 references)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf SUPPORT REVIEW SYNTHESIS Other

"Planar, tuberous, or tendon xanthomas have also been reported to develop in childhood."

LDLRAP1-specific GeneReviews table; does not provide separate frequencies for the three morphologies.

url:https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf SUPPORT PRIMARY RESULT Human Clinical

"Number of xanthomas 47 (90.4) 22 (91.7) 25 (89.3)"

Table 1 gives whole-cohort, male and female counts, respectively.

Premature ASCVD Events

Age: Variable; selected adult treatment cohorts

Five of nine lomitapide-treated adults had prior ASCVD, with mean age at first event 45.2 years among those five. This is not a universal age of onset, an untreated natural history estimate or evidence excluding severe childhood disease. Four patients overlapped the earlier 52-patient cohort. Persistent lifelong LDL exposure and prior disease influence subsequent risk.

Show evidence (2 references)

PMID:36072671 SUPPORT Human Clinical

"the mean age at the first event was 45.2 ± 7.9"

Reports the mean age at first ASCVD event in the ARH cohort.

PMID:36072671 SUPPORT Human Clinical

"The age at starting lomitapide was 46 (interquartile range (IQR), 39.0-65.5) years"

Gives the age at which LDLR-independent escalation (lomitapide) was started in the cohort.

📊

Prevalence

Worldwide

Point Prevalence Ultra Rare

An ultra-rare disorder enriched in Sardinia through founder alleles. Published selected cohorts do not establish a precise worldwide prevalence.

Show evidence (1 reference)

PMID:32011344 SUPPORT REVIEW SYNTHESIS Other

"ARH is an ultrarare disorder of LDL metabolism caused by mutations in the LDLRAP1 gene."

States the ultra-rare occurrence and the causative gene.

Two free-living Sicilian populations; ARH1 allele only

Carrier Frequency

One heterozygous ARH1 carrier was identified among 2,565 participants (848 in northern and 1,717 in southern Sicily). This directly observed count concerns one allele, not all LDLRAP1 variants or Sardinia. The rounded allele frequency was 0.02%; it is not a disease-prevalence estimate.

Show evidence (1 reference)

PMID:29153781 SUPPORT PRIMARY RESULT Human Clinical

"Population-based genotyping of ARH1 in 2565 subjects allowed the identification of 1 heterozygous carrier."

Direct count, restricted to the tested allele and sampled populations.

🔀

Differential Diagnoses

Conditions with similar clinical presentations that must be differentiated from Autosomal Recessive Hypercholesterolemia:

Sitosterolemia MONDO:0008863

Overlapping Features Recessive ABCG5/ABCG8 disease can cause childhood xanthomas, high LDL-C and premature coronary disease.

Distinguishing Features

Elevated plasma plant sterols and ABCG5/ABCG8 variants distinguish it; hemolytic anemia, thrombocytopenia or stomatocytes are clues.
Treatment implications include dietary sterol restriction and ezetimibe.

Show evidence (2 references)

PMID:37130090 SUPPORT REVIEW SYNTHESIS Other

"These include sitosterolaemia (or ‘phytosterolaemia’), caused by bi-allelic rare pathogenic variants in two ATP-binding cassette transporter genes, ABCG5 and/or ABCG8 (or at least one such variant in each gene), with elevated LDL-C levels that respond well to dietary recommendations, ezetimibe..."

Consensus differential and distinct treatment response.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf SUPPORT REVIEW SYNTHESIS Other

"Hematologic abnormalities (hemolytic anemia, thrombocytopenia, stomatocytes);"

GeneReviews distinguishing features.

Lysosomal acid lipase deficiency Not Yet Curated MONDO:0800449

Overlapping Features Biallelic LIPA disease can elevate LDL-C and cause premature atherosclerosis.

Distinguishing Features

Hepatosplenomegaly, raised transaminases and triglycerides suggest the storage disorder; confirm with enzyme and molecular testing.

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf SUPPORT REVIEW SYNTHESIS Other

"In adult onset (cholesterol-ester storage disease): hepatosplenomegaly &/or ↑ liver enzymes, ↑ triglycerides"

GeneReviews hepatic/lipid clues; infantile Wolman disease is a different severity presentation.

Cerebrotendinous xanthomatosis MONDO:0008948

Overlapping Features CYP27A1 disease shares tendon xanthomas.

Distinguishing Features

Neurologic and cognitive abnormalities, cataracts and elevated cholestanol with normal or mildly elevated cholesterol favor this diagnosis.

Show evidence (1 reference)

PMID:37130090 SUPPORT REVIEW SYNTHESIS Other

"Patients with cerebrotendinous xanthomatosis may have xanthomas resembling HoFH but plasma cholesterol levels are normal to mildly elevated (with elevated cholestanol levels) associated with neurological, cognitive, and ophthalmic symptoms."

Clinical and biochemical distinction.

Secondary hypercholesterolemia

Overlapping Features Acquired disorders and medications can mimic or worsen an inherited lipid phenotype.

Distinguishing Features

Assess thyroid, renal and hepatic disease, diabetes, obesity and relevant medications alongside inherited causes.

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf SUPPORT REVIEW SYNTHESIS Other

"Hypercholesterolemia secondary to acquired conditions including obesity, diabetes mellitus, obstructive liver disease, hypothyroidism, drugs (e.g., steroids), or kidney disease can also be associated with laboratory findings similar to those of FH"

GeneReviews acquired differential; not a classification of ARH as environmental disease.

🔬

Clinical Trials

NCT00730236 PHASE_III COMPLETED

Completed single-arm phase III lomitapide study in 29 adults with clinical or functional HoFH. Stable background therapy was maintained through week 26; mean LDL-C reduction was 50%. The trial supports class-level efficacy and safety monitoring, not a separately estimated LDLRAP1 treatment effect. Eligibility allowed causative functional alleles and did not require an abnormal fibroblast assay in every participant.

Show evidence (2 references)

clinicaltrials:NCT00730236 SUPPORT PRIMARY RESULT Other

"The goal of this trial is to study the effects of AEGR-733 on LDL cholesterol, other lipids as well as measures of safety over the long-term."

Registry objective; published results are distinguished from planned endpoints.

PMID:23122768 SUPPORT PRIMARY RESULT Human Clinical

"Mean LDL-C decreased from 8·69 ± 2·95 mmol/L at baseline to 4·34 ± 2·48 mmol/L) at the end of the efficacy phase (week 26), a statistically significant percent change from baseline (−50%, 95% CI −62, −39, p<0·001) (table 1 and figure 1)."

Pooled HoFH phase III result; this is not an LDLRAP1-specific estimate.

NCT03399786 PHASE_III COMPLETED

Completed randomized placebo-controlled phase III ELIPSE trial in 65 patients aged at least 12 years with HoFH on stable therapy. At 24 weeks, evinacumab lowered LDL-C 47.1%, versus a 1.9% increase on placebo. These are pooled HoFH results, not an ARH-specific effect size.

Show evidence (2 references)

clinicaltrials:NCT03399786 SUPPORT PRIMARY RESULT Other

"The primary objective of the study is to demonstrate the reduction of low-density lipoprotein cholesterol (LDL-C) by evinacumab intravenously (IV) in comparison to placebo after 24 weeks in patients with homozygous familial hypercholesterolemia (HoFH)."

Registry objective; published results are distinguished from planned endpoints.

PMID:32813947 SUPPORT PRIMARY RESULT Human Clinical

"At week 24, patients in the evinacumab group had a relative reduction from baseline in the LDL cholesterol level of 47.1%, as compared with an increase of 1.9% in the placebo group,"

Pooled randomized HoFH result; does not isolate the ARH response.

NCT03409744 PHASE_III COMPLETED

Completed open-label phase III long-term evinacumab study, with 116 participants aged at least 12 years. The 2026 analysis identifies two LDLRAP1 participants among 55 with identical biallelic LDLR or LDLRAP1 variants. Reported week-8 and week-104 subgroup reductions combine both genes and cannot quantify the LDLRAP1-specific response.

Show evidence (2 references)

clinicaltrials:NCT03409744 SUPPORT PRIMARY RESULT Other

"To evaluate the long-term safety and tolerability of evinacumab in patients with Homozygous Familial Hypercholesterolemia (HoFH)"

Registry objective; published results are distinguished from planned endpoints.

PMID:41671678 SUPPORT PRIMARY RESULT Human Clinical

"At baseline, 55 (47.4%) had either identical bi-allelic variants in LDLR (n = 53) or LDLRAP1 (n = 2), and 41 (35.3%) had different bi-allelic LDLR variants."

Two LDLRAP1 patients were included in the extension; pooled LDLR/LDLRAP1 response is not a gene-specific estimate.

🧫

Experimental Models

Patient-derived primary lymphocytes PRIMARY_CELL_CULTURE

Mevastatin-treated lymphocytes exposed to recombinant PCSK9 with or without alirocumab. Surface receptor expression is higher but uptake lower than controls, showing why receptor abundance is not synonymous with function.

Cell source

Primary lymphocytes from 28 genetically characterized ARH patients and 11 controls

Publication

PMID:27079874

Pathograph links

Impaired Clathrin-Mediated Endocytosis of the Hepatocyte LDL Receptor recapitulates fidelity: moderate Reduced cellular LDL uptake reproduces an ARH endocytic defect in lymphocytes.

Limitations: The target names hepatocytes; this nonhepatic assay informs the shared defect but does not measure hepatic clearance or prove clinical antibody efficacy.

Readouts

Fluorescent LDL uptake

Reduced cellular LDL uptake reproduces an ARH endocytic defect in lymphocytes.

Direction: DECREASED

Show evidence (1 reference)

PMID:27079874 SUPPORT PRIMARY RESULT In Vitro

"Fluorescent LDL cellular uptake, also measured by flow cytometry, was reduced in ARH lymphocytes compared with control lymphocytes."

Patient-cell uptake measurement, distinct from plasma LDL-C response.

Show evidence (1 reference)

PMID:27079874 SUPPORT PRIMARY RESULT In Vitro

"Fluorescent LDL cellular uptake, also measured by flow cytometry, was reduced in ARH lymphocytes compared with control lymphocytes."

Patient-cell uptake measurement, distinct from plasma LDL-C response.

Polarized WIF-B hepatocytes CELL_LINE

Domain perturbation tests the receptor-binding PTB domain and clathrin/AP-2 interactions needed for LDLR clustering and internalization.

Cell source

Polarized WIF-B hepatocyte cell line with recombinant ARH domain constructs

Publication

PMID:16179341

Pathograph links

Impaired Clathrin-Mediated Endocytosis of the Hepatocyte LDL Receptor perturbs fidelity: moderate ARH PTB integrity and at least one clathrin/AP-2 interaction are required for clustering and internalization.

Limitations: Engineered cell system; abstract-only access limits detailed protocol assessment.

Show evidence (1 reference)

PMID:16179341 SUPPORT PRIMARY RESULT In Vitro

"The phosphotyrosine binding domain of ARH plus either the clathrin box or the AP-2 binding region were required for both clustering and internalization of the LDLR."

Domain perturbation in polarized cells.

Primary Arh-knockout mouse hepatocytes PRIMARY_CELL_CULTURE

Short-term culture distinguishes LDL and beta-VLDL uptake. Additional LRP deletion and heparinase experiments did not abolish preserved beta-VLDL uptake; high-affinity antibody binding or LDL aggregation alone did not reproduce it.

Cell source

Fresh primary hepatocytes from Arh- and Ldlr-knockout and control mice

Publication

PMID:17200716

Pathograph links

Preserved Hepatic VLDL Remnant Uptake recapitulates fidelity: moderate ARH-deficient hepatocytes internalize beta-VLDL whereas LDLR-deficient cells do not.

Limitations: Ligand preparation and culture duration can change assay behavior; the precise ARH-independent entry machinery remains unresolved.

Readouts

Beta-VLDL internalization relative to Ldlr knockout

ARH-deficient hepatocytes internalize beta-VLDL whereas LDLR-deficient cells do not.

Direction: INCREASED

Show evidence (1 reference)

PMID:17200716 SUPPORT PRIMARY RESULT In Vitro

"Consistent with these findings, hepatocytes from Arh(-/-) mice (but not Ldlr(-/-) mice) internalized beta-migrating VLDL (beta-VLDL)."

Isolated hepatocyte experiment, not an in-vivo uptake measurement.

Show evidence (1 reference)

PMID:17200716 SUPPORT PRIMARY RESULT In Vitro

"Consistent with these findings, hepatocytes from Arh(-/-) mice (but not Ldlr(-/-) mice) internalized beta-migrating VLDL (beta-VLDL)."

Isolated hepatocyte experiment, not an in-vivo uptake measurement.

Patient skin fibroblasts with DAB2 depletion PRIMARY_CELL_CULTURE

Baseline LDLR activity is preserved. DAB2 depletion reduces receptor protein and uptake selectively in ARH cells, without reduced LDLR mRNA; murine DAB2 rescues the phenotype. Pulse labeling favors altered protein synthesis, but unblocked degradation is not completely excluded. This does not directly demonstrate DAB2 compensation solely at endocytosis.

Cell source

Cultured skin fibroblasts from ARH patients and controls, with DAB2 siRNA and murine DAB2 rescue

Publication

PMID:17761685

Show evidence (1 reference)

PMID:17761685 SUPPORT PRIMARY RESULT In Vitro

"SiRNA-depletion of Dab2 profoundly reduced LDL-receptor activity in ARH fibroblasts as a result of profound reduction in LDL-receptor protein, but not mRNA; heterologous expression of murine Dab2 reversed this effect."

Protein loss confounds an interpretation as a pure internalization defect.

🐁

Animal Models

Arh(-/-) mouse

Arh-knockout mice and hepatic rescue constructs test LDLR internalization. Comparison with Ldlr-knockout and wild-type mice distinguishes impaired LDL clearance from preserved VLDL-remnant clearance. Similar VLDL secretion but markedly different diet-induced hypercholesterolemia argues against secretion alone explaining the phenotype.

Species

Mouse

Genotype

Arh(-/-) (LDLRAP1 knockout)

Publication

PMID:16179341

Pathograph links

Impaired Clathrin-Mediated Endocytosis of the Hepatocyte LDL Receptor recapitulates fidelity: moderate Loss of ARH in mouse liver reproduces the hepatocyte LDL-receptor endocytosis defect that defines this node, generalizing the WIF-B cell-culture result to an intact liver.

Limitations: Murine lipoprotein metabolism is apoB48- and HDL-dominated rather than LDL-dominated, so the model captures the molecular/cellular endocytic defect more faithfully than the human plasma-LDL and arterial-disease phenotype; the abstract reports in-vivo confirmation of the cell-culture findings without a separately quantified endocytosis readout.

Show evidence (1 reference)

PMID:16179341 SUPPORT Model Organism

"Parallel studies performed in vivo with the same recombinant forms of ARH in livers of Arh(-/-) mice confirmed the relevance of the cell culture findings."

Reports the Arh(-/-) mouse in-vivo confirmation that ARH is required for hepatocyte LDL-receptor clustering and internalization, supporting the use of this model for that node.

Preserved Hepatic VLDL Remnant Uptake recapitulates fidelity: moderate VLDL clearance is greater in Arh-knockout than Ldlr-knockout mice despite impaired LDL clearance.

Limitations: Mouse lipoprotein composition and diet differ from human physiology; the result does not establish the magnitude of human clinical protection.

Readouts

VLDL clearance relative to Ldlr knockout

VLDL clearance is greater in Arh-knockout than Ldlr-knockout mice despite impaired LDL clearance.

Direction: INCREASED

Show evidence (1 reference)

PMID:17200716 SUPPORT PRIMARY RESULT Model Organism

"The rate of VLDL clearance was significantly higher in Arh(-/-) mice than in Ldlr(-/-) mice, suggesting that LDLR-dependent uptake of VLDL is maintained in the absence of ARH."

Whole-animal comparison of ligand clearance.

Show evidence (1 reference)

PMID:17200716 SUPPORT PRIMARY RESULT Model Organism

"The rate of VLDL clearance was significantly higher in Arh(-/-) mice than in Ldlr(-/-) mice, suggesting that LDLR-dependent uptake of VLDL is maintained in the absence of ARH."

Whole-animal comparison of ligand clearance.

Show evidence (2 references)

PMID:17200716 SUPPORT PRIMARY RESULT Model Organism

"The rate of VLDL clearance was significantly higher in Arh(-/-) mice than in Ldlr(-/-) mice, suggesting that LDLR-dependent uptake of VLDL is maintained in the absence of ARH."

Whole-animal comparison of ligand clearance.

PMID:17200716 SUPPORT PRIMARY RESULT Model Organism

"The hyperlipidemic response to a high-sucrose diet was greatly attenuated in Arh(-/-) mice compared with Ldlr(-/-) mice despite similar rates of VLDL secretion."

Separates secretion from clearance in the whole-animal comparison.

{ }

Source YAML

click to show

name: Autosomal Recessive Hypercholesterolemia
creation_date: "2026-09-03T00:00:00Z"
category: Mendelian
description: >-
  Autosomal recessive hypercholesterolemia (ARH) is caused by biallelic pathogenic LDLRAP1 variants. The encoded
  ARH adaptor couples the LDL receptor to clathrin-dependent internalization. Impaired hepatic LDL uptake produces
  marked LDL-cholesterol elevation, childhood xanthomas and risk of premature coronary disease and aortic valve
  stenosis. The defect is cell-type and ligand dependent: fibroblast LDL uptake can remain normal, whereas
  lymphocyte uptake is impaired; LDLR-dependent VLDL-remnant clearance is largely preserved in knockout mice
  and was increased in a human kinetic study. Receptors present at the cell surface are not equivalent to normal
  clearance, but the defect does not imply uniform absence of receptor activity or treatment response. Statins
  and combination therapies can substantially reduce LDL-C, with variable target attainment. LDLR-independent
  agents and apheresis provide additional options. Sardinian founder alleles are prominent in reported cohorts,
  which do not represent worldwide population frequencies.
synonyms:
- Hypercholesterolemia, familial, 4
- ARH
- LDLRAP1-related familial hypercholesterolemia
- Familial autosomal recessive hypercholesterolemia
- FHCB2
disease_term:
  preferred_term: autosomal recessive hypercholesterolemia (ARH)
  term:
    id: MONDO:0011374
    label: hypercholesterolemia, familial, 4
parents:
- Familial Hypercholesterolemia
notes: >-
  This entry is restricted to biallelic LDLRAP1 disease. LDLR-, APOB- and PCSK9-related hypercholesterolemias
  are molecular differentials. Severe ARH overlaps the clinical homozygous-FH phenotype, but results pooled
  across those genes are not LDLRAP1-specific estimates. Retrospective treatment cohorts, individual cases
  and model experiments have distinct evidential limits; overlapping published patients are not counted as
  independent cohorts. Preserved remnant clearance and variable residual uptake qualify an absolute receptor-internalization
  failure model.
references:
- reference: PMID:24404629
  title: "Familial Hypercholesterolemia."
  tags:
  - GeneReviews
- reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf
  title: "https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf"
  findings:
  - statement: Full GeneReviews Familial Hypercholesterolemia chapter, corresponding to PMID:24404629.
- reference: PMID:32011344
  title: "Autosomal recessive hypercholesterolemia: update for 2020."
- reference: PMID:29153781
  title: "Genetic epidemiology of autosomal recessive hypercholesterolemia in Sicily: Identification by next-generation sequencing of a new kindred."
- reference: PMID:11326085
  title: "Autosomal recessive hypercholesterolemia caused by mutations in a putative LDL receptor adaptor protein."
- reference: PMID:30777337
  title: "A new variant (c.1A>G) in LDLRAP1 causing autosomal recessive hypercholesterolemia: Characterization of the defect and response to PCSK9 inhibition."
- reference: PMID:16179341
  title: The modular adaptor protein autosomal recessive hypercholesterolemia (ARH) promotes low density lipoprotein receptor clustering into clathrin-coated pits.
- reference: PMID:27079874
  title: Proprotein Convertase Subtilisin Kexin Type 9 Inhibition for Autosomal Recessive Hypercholesterolemia-Brief Report.
- reference: PMID:17761685
  title: Adaptor protein disabled-2 modulates low density lipoprotein receptor synthesis in fibroblasts from patients with autosomal recessive hypercholesterolaemia.
- reference: PMID:22157599
  title: "Altered metabolism of low-density lipoprotein and very-low-density lipoprotein remnant in autosomal recessive hypercholesterolemia: results from stable isotope kinetic study in vivo."
- reference: PMID:29348020
  title: "Autosomal Recessive Hypercholesterolemia: Long-Term Cardiovascular Outcomes."
- reference: url:https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf
  title: "https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf"
  findings:
  - statement: D’Erasmo et al., 2018 JACC retrospective study of 52 ARH patients, PMID:29348020.
- reference: PMID:17200716
  title: Disruption of LDL but not VLDL clearance in autosomal recessive hypercholesterolemia.
- reference: PMID:42730734
  title: Autosomal Recessive Hypercholesterolemia Due to a Novel Homozygous LDLRAP1 Frameshift Mutation.
- reference: PMID:37130090
  title: "2023 Update on European Atherosclerosis Society Consensus Statement on Homozygous Familial Hypercholesterolaemia: new treatments and clinical guidance."
- reference: PMID:36072671
  title: "Efficacy of Long-Term Treatment of Autosomal Recessive Hypercholesterolemia With Lomitapide: A Subanalysis of the Pan-European Lomitapide Study."
- reference: url:https://air.unimi.it/retrieve/handle/2434/1224076/3272602/1-s2.0-S1933287426000401-main.pdf
  title: "https://air.unimi.it/retrieve/handle/2434/1224076/3272602/1-s2.0-S1933287426000401-main.pdf"
  findings:
  - statement: '2026 report: LDL-C target achievement after adding evinacumab in 2 patients with autosomal recessive hypercholesterolemia; DOI:10.1016/j.jacl.2026.02.007.'
- reference: PMID:41671678
  title: "Efficacy of evinacumab by genotype and low-density lipoprotein receptor function in patients with homozygous familial hypercholesterolaemia: A subanalysis from the ELIPSE open-label extension study."
- reference: url:https://oup.silverchair-cdn.com/article-minimal/582819
  title: "https://oup.silverchair-cdn.com/article-minimal/582819"
  findings:
  - statement: Full scientific text of Eden et al. 2007, corresponding to PMID:17761685.
- reference: clinicaltrials:NCT00730236
  title: A Phase III Study of Microsomal Triglyceride Transfer Protein (MTP) Inhibitor AEGR-733 in Patients With Homozygous Familial Hypercholesterolemia on Current Lipid-lowering Therapy
- reference: clinicaltrials:NCT03399786
  title: "A Randomized, Double-blind, Placebo-controlled, Parallel-group Study to Evaluate the Efficacy and Safety of Evinacumab in Patients With Homozygous Familial Hypercholesterolemia"
- reference: clinicaltrials:NCT03409744
  title: An Open-Label Study to Evaluate the Long-Term Safety and Efficacy of Evinacumab in Patients With Homozygous Familial Hypercholesterolemia
- reference: PMID:23122768
  title: "Efficacy and safety of a microsomal triglyceride transfer protein inhibitor in patients with homozygous familial hypercholesterolaemia: a single-arm, open-label, phase 3 study."
- reference: PMID:32813947
  title: Evinacumab for Homozygous Familial Hypercholesterolemia.
- reference: url:https://www.frontiersin.org/journals/genetics/articles/10.3389/fgene.2022.937750/pdf
  title: "https://www.frontiersin.org/journals/genetics/articles/10.3389/fgene.2022.937750/pdf"
  findings:
  - statement: Publisher PDF of PMID:36072671; Tables 1 and 2 supply the clinical and hepatic-fat data omitted from the XML extraction.
inheritance:
- name: Autosomal Recessive
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    Biallelic pathogenic LDLRAP1 variants cause autosomal recessive disease; both homozygous and compound-heterozygous
    genotypes occur. Carriers are usually asymptomatic and may have normal lipid profiles. After confirming
    that both parents carry a familial pathogenic variant, each pregnancy has a 25% affected, 50% carrier and
    25% noncarrier probability. A disease-wide penetrance estimate is not established by the cited cohorts.
  evidence:
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "LDLRAP1-related FH is caused by biallelic pathogenic variants and is inherited in an autosomal recessive manner."
    explanation: GeneReviews states the recessive mode of inheritance and the requirement for biallelic variants.
    quote_role: REVIEW_SYNTHESIS
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf
    reference_title: "https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      If both parents are known to be heterozygous for an LDLRAP1 pathogenic variant, each sib of an affected
      individual has at conception a 25% chance of being affected, a 50% chance of being a carrier, and a 25%
      chance of inheriting neither of the familial pathogenic variants.
    explanation: >-
      Recurrence probabilities are conditional on confirmed parental carrier status.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf
    reference_title: "https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Individuals who are heterozygous for an LDLRAP1 pathogenic variant (i.e., carriers) are typically asymptomatic.
    explanation: >-
      Normal lipids do not exclude carrier status.
prevalence:
- population: Worldwide
  measure_type: POINT_PREVALENCE
  prevalence_class: ULTRA_RARE
  notes: >-
    An ultra-rare disorder enriched in Sardinia through founder alleles. Published selected cohorts do not
    establish a precise worldwide prevalence.
  evidence:
  - reference: PMID:32011344
    reference_title: "Autosomal recessive hypercholesterolemia: update for 2020."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "ARH is an ultrarare disorder of LDL metabolism caused by mutations in the LDLRAP1 gene."
    explanation: States the ultra-rare occurrence and the causative gene.
    quote_role: REVIEW_SYNTHESIS
- population: Two free-living Sicilian populations; ARH1 allele only
  measure_type: CARRIER_FREQUENCY
  notes: >-
    One heterozygous ARH1 carrier was identified among 2,565 participants (848 in northern and 1,717 in southern
    Sicily). This directly observed count concerns one allele, not all LDLRAP1 variants or Sardinia. The rounded
    allele frequency was 0.02%; it is not a disease-prevalence estimate.
  evidence:
  - reference: PMID:29153781
    reference_title: "Genetic epidemiology of autosomal recessive hypercholesterolemia in Sicily: Identification by next-generation sequencing of a new kindred."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      Population-based genotyping of ARH1 in 2565 subjects allowed the identification of 1 heterozygous carrier.
    explanation: >-
      Direct count, restricted to the tested allele and sampled populations.
pathophysiology:
- name: Biallelic LDLRAP1 Loss-of-Function
  role: trigger
  biological_scale: MOLECULAR
  description: >-
    Homozygous or compound-heterozygous pathogenic LDLRAP1 variants impair the ARH adaptor. The current locus
    is 1p36.11; 1p35 was the historical discovery mapping. Truncating, splice, initiation-codon and larger
    rearrangement alleles are described. Some alleles retain detectable shorter protein and residual uptake,
    so loss of function does not mean every genotype is a complete null. The two Sardinian founder alleles
    are enriched in that population rather than defining all worldwide disease.
  genes:
  - preferred_term: LDLRAP1
    term:
      id: hgnc:18640
      label: LDLRAP1
  genetic_context:
    gene:
      preferred_term: LDLRAP1
      term:
        id: hgnc:18640
        label: LDLRAP1
    variant_origin: GERMLINE
    functional_impact_category: LOSS_OF_FUNCTION
    description: >-
      Biallelic germline pathogenic variants, either homozygous or compound heterozygous. Heterozygous carriers
      typically have normal lipid profiles.
  evidence:
  - reference: PMID:11326085
    reference_title: "Autosomal recessive hypercholesterolemia caused by mutations in a putative LDL receptor adaptor protein."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here we map the ARH locus to an approximately 1-centimorgan interval on chromosome 1p35 and identify six mutations in a gene encoding a putative adaptor protein (ARH)."
    explanation: The founding paper that maps ARH to 1p35 and identifies causative mutations in the adaptor gene.
  - reference: PMID:32011344
    reference_title: "Autosomal recessive hypercholesterolemia: update for 2020."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "It is inherited as a recessive trait and causative mutations, though heterogeneous, are all predicted to be loss-of-function."
    explanation: States that the heterogeneous causative alleles are uniformly loss-of-function.
    quote_role: REVIEW_SYNTHESIS
  - reference: PMID:30777337
    reference_title: "A new variant (c.1A>G) in LDLRAP1 causing autosomal recessive hypercholesterolemia: Characterization of the defect and response to PCSK9 inhibition."
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: >-
      The patient had undetectable full-length ARH protein by Western blotting, but expressed a lower-than-normal
      molecular weight peptide.
    explanation: >-
      Patient-derived lymphocyte protein analysis of the homozygous initiation-codon variant; supports partial
      functional heterogeneity rather than a complete-null rule.
  downstream:
  - target: Loss of ARH Adaptor Bridging of the LDL Receptor to Clathrin
    causal_link_type: DIRECT
    description: >-
      Biallelic variants impair the adaptor needed for effective LDL-receptor coupling to the internalization
      machinery; the degree and molecular consequence vary by allele.
- name: Loss of ARH Adaptor Bridging of the LDL Receptor to Clathrin
  biological_scale: MOLECULAR
  description: >-
    The ARH phosphotyrosine-binding domain interacts with the LDLR cytoplasmic tail, while clathrin- and AP-2-binding
    regions connect it to coated-pit machinery. Domain-rescue experiments require the PTB domain plus either
    clathrin or AP-2 binding for effective clustering and LDL uptake. LDLRAP1 disease primarily affects this
    adaptor function rather than the LDLR coding sequence; receptor abundance and residual activity nevertheless
    depend on cell and allele context.
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  molecular_functions:
  - preferred_term: clathrin-cargo adaptor activity
    modifier: LOSS_OF_FUNCTION
    term:
      id: GO:0035615
      label: clathrin-cargo adaptor activity
  - preferred_term: low-density lipoprotein particle receptor binding
    modifier: DECREASED
    term:
      id: GO:0050750
      label: low-density lipoprotein particle receptor binding
  evidence:
  - reference: PMID:16179341
    reference_title: "The modular adaptor protein autosomal recessive hypercholesterolemia (ARH) promotes low density lipoprotein receptor clustering into clathrin-coated pits."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The disease is caused by mutations in ARH, which encodes a putative adaptor protein that interacts with the cytoplasmic tail of the LDLR, phospholipids, and two components of the clathrin endocytic machinery, clathrin and adaptor protein-2 (AP-2) in vitro."
    explanation: Establishes the adaptor's three binding partners - the receptor tail, clathrin, and AP-2 - whose bridging is lost in ARH.
  - reference: PMID:16179341
    reference_title: "The modular adaptor protein autosomal recessive hypercholesterolemia (ARH) promotes low density lipoprotein receptor clustering into clathrin-coated pits."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The phosphotyrosine binding domain of ARH plus either the clathrin box or the AP-2 binding region were required for both clustering and internalization of the LDLR."
    explanation: Defines the domain requirements for the bridging function, the LOSS_OF_FUNCTION captured by this node.
  downstream:
  - target: Impaired Clathrin-Mediated Endocytosis of the Hepatocyte LDL Receptor
    causal_link_type: DIRECT
    description: >-
      Impaired adaptor coupling reduces receptor clustering and internalization of LDL cargo in the tested
      hepatocyte systems.
    evidence:
    - reference: PMID:16179341
      reference_title: "The modular adaptor protein autosomal recessive hypercholesterolemia (ARH) promotes low density lipoprotein receptor clustering into clathrin-coated pits."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "These results demonstrate that ARH must bind the LDLR tail and either clathrin or AP-2 to promote receptor clustering and internalization of LDL."
      explanation: Directly links loss of ARH bridging to failure of receptor clustering and internalization.
- name: Impaired Clathrin-Mediated Endocytosis of the Hepatocyte LDL Receptor
  biological_scale: CELLULAR
  description: >-
    LDL-bound receptor internalization is strongly impaired in hepatocytes lacking ARH. The defect is cargo
    and cell dependent rather than a global failure of clathrin endocytosis. Patient lymphocytes also show
    reduced LDL uptake, while cultured skin fibroblasts can retain normal LDL-receptor function. In mouse hepatocytes,
    LDLR-dependent VLDL-remnant uptake persists despite failure to internalize LDL. Fibroblast DAB2-dependent
    maintenance of receptor protein complicates a simple redundant-adaptor explanation.
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  biological_processes:
  - preferred_term: clathrin-dependent endocytosis
    modifier: DECREASED
    term:
      id: GO:0072583
      label: clathrin-dependent endocytosis
  - preferred_term: receptor-mediated endocytosis
    modifier: DECREASED
    term:
      id: GO:0006898
      label: receptor-mediated endocytosis
  locations:
  - preferred_term: liver
    term:
      id: UBERON:0002107
      label: liver
  evidence:
  - reference: PMID:16179341
    reference_title: "The modular adaptor protein autosomal recessive hypercholesterolemia (ARH) promotes low density lipoprotein receptor clustering into clathrin-coated pits."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Autosomal recessive hypercholesterolemia is characterized by a cell type-specific defect in low density lipoprotein receptor (LDLR) endocytosis."
    explanation: States that the endocytic defect itself is the cellular lesion of ARH.
  - reference: PMID:11326085
    reference_title: "Autosomal recessive hypercholesterolemia caused by mutations in a putative LDL receptor adaptor protein."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "ARH appears to have a tissue-specific role in LDLR function, as it is required in liver but not in fibroblasts."
    explanation: >-
      The founding abstract summarizes a liver-versus-fibroblast contrast; it does not establish that liver
      is the only affected cell type.
    quote_role: BACKGROUND
  - reference: PMID:27079874
    reference_title: Proprotein Convertase Subtilisin Kexin Type 9 Inhibition for Autosomal Recessive Hypercholesterolemia-Brief Report.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: >-
      Fluorescent LDL cellular uptake, also measured by flow cytometry, was reduced in ARH lymphocytes compared
      with control lymphocytes.
    explanation: >-
      Patient lymphocyte experiments demonstrate that the uptake defect is not liver-exclusive.
  - reference: PMID:17761685
    reference_title: Adaptor protein disabled-2 modulates low density lipoprotein receptor synthesis in fibroblasts from patients with autosomal recessive hypercholesterolaemia.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: >-
      SiRNA-depletion of Dab2 profoundly reduced LDL-receptor activity in ARH fibroblasts as a result of profound
      reduction in LDL-receptor protein, but not mRNA; heterologous expression of murine Dab2 reversed this
      effect.
    explanation: >-
      DAB2 perturbation in patient fibroblasts changes receptor abundance; these data should not be reduced
      to proof of interchangeable endocytic adaptors.
  downstream:
  - target: Impaired Hepatic Clearance of Plasma LDL
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Reduced hepatic LDL uptake contributes to slow plasma LDL-apoB removal; human kinetic data establish
      the clearance defect without measuring every cellular intermediary.
- name: Impaired Hepatic Clearance of Plasma LDL
  biological_scale: ORGANISM
  description: >-
    Plasma LDL-apoB removal is reduced. In one ARH patient, a stable-isotope study estimated LDL-apoB fractional
    catabolism of 0.109/day versus 0.450 ± 0.122/day in seven controls. Atorvastatin increased this patient's
    rate to 0.464/day. This demonstrates substantial reversibility in that individual and does not establish
    a universal value for all LDLRAP1 genotypes.
  biological_processes:
  - preferred_term: low-density lipoprotein particle clearance
    modifier: DECREASED
    term:
      id: GO:0034383
      label: low-density lipoprotein particle clearance
  locations:
  - preferred_term: liver
    term:
      id: UBERON:0002107
      label: liver
  evidence:
  - reference: PMID:22157599
    reference_title: "Altered metabolism of low-density lipoprotein and very-low-density lipoprotein remnant in autosomal recessive hypercholesterolemia: results from stable isotope kinetic study in vivo."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      FCR of low-density lipoprotein (LDL) apoB of ARH was significantly lower than those of control subjects
      (0.109 versus 0.450±0.122 1/day).
    explanation: >-
      Stable-isotope kinetic modeling in one ARH patient compared with seven controls; a human metabolic measurement,
      not an in-vitro uptake assay.
  downstream:
  - target: Lifelong Elevation of Plasma LDL Cholesterol
    causal_link_type: DIRECT
    description: >-
      Reduced LDL removal raises circulating LDL-C. The balance also depends on precursor clearance and production;
      unchanged LDL production is not assumed.
    evidence:
    - reference: PMID:22157599
      reference_title: "Altered metabolism of low-density lipoprotein and very-low-density lipoprotein remnant in autosomal recessive hypercholesterolemia: results from stable isotope kinetic study in vivo."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: PRIMARY_RESULT
      snippet: >-
        These results demonstrate that ARH exhibits decreased LDL clearance associated with decreased FCR of
        LDL apoB and increased clearance for very-low-density lipoprotein remnant.
      explanation: >-
        The measured lipoprotein pathways distinguish impaired LDL removal from preserved/increased remnant
        clearance.
- name: Lifelong Elevation of Plasma LDL Cholesterol
  biological_scale: ORGANISM
  description: >-
    Marked LDL-C elevation is the central biochemical manifestation, but its magnitude and response to treatment
    vary. In a retrospective 52-patient cohort, baseline LDL-C averaged 571.9 mg/dL and the best recorded on-treatment
    level averaged 164.0 mg/dL. Baseline was not uniformly untreated, and nadir is not long-term average exposure.
    Failure to reach targets does not mean lack of response.
  evidence:
  - reference: PMID:29348020
    reference_title: "Autosomal Recessive Hypercholesterolemia: Long-Term Cardiovascular Outcomes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      Mean LDL-C achieved at nadir was 164.0 ± 85.1 mg/dl (-69.6% from baseline), with a better response in
      patients taking lomitapide (-88.3%).
    explanation: >-
      Retrospective treatment combinations in 52 ARH patients. The lomitapide figure is a subgroup change from
      the original baseline, not a randomized or isolated add-on drug effect.
  downstream:
  - target: Premature Atherosclerotic Cardiovascular Disease
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Sustained LDL burden contributes to atherosclerotic disease; the ARH cohort records substantial residual
      cardiovascular risk despite treatment.
    evidence:
    - reference: PMID:29348020
      reference_title: "Autosomal Recessive Hypercholesterolemia: Long-Term Cardiovascular Outcomes."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: PRIMARY_RESULT
      snippet: >-
        During follow-up, 26.9% of patients had incident ASCVD, and 11.5% had a new diagnosis of aortic valve
        stenosis (absolute risk per year of 1.9% and 0.8%, respectively).
      explanation: >-
        Observed ARH outcomes over mean 14.1-year follow-up; this is not a direct experiment of the LDL-to-plaque
        mechanism.
  - target: Extravascular Cholesterol Deposition
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Chronic cholesterol excess produces tissue deposits; the individual clinical lesions require their own
      evidence.
  - target: Aortic Valve Stenosis
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Valvular disease is a recognized severe-hypercholesterolemia complication; it is distinct from coronary
      plaque rupture.
    evidence:
    - reference: PMID:32011344
      reference_title: "Autosomal recessive hypercholesterolemia: update for 2020."
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      snippet: >-
        ARH is also associated with increased risk of developing aortic valve stenosis.
      explanation: >-
        ARH-specific review association; intervening valvular mechanisms are not resolved by this sentence.
  - target: Increased LDL Cholesterol
    causal_link_type: DIRECT
    description: >-
      The elevated plasma LDL-C state is the directly measured biochemical phenotype.
  - target: Hypercholesterolemia
    causal_link_type: DIRECT
    description: >-
      The markedly elevated LDL fraction contributes to increased total cholesterol.
- name: Premature Atherosclerotic Cardiovascular Disease
  biological_scale: ORGANISM
  description: >-
    Premature arterial disease, especially coronary disease, produces myocardial infarction and need for coronary
    revascularization. A 52-patient retrospective ARH series recorded 14 incident ASCVD cases during mean 14.1-year
    follow-up, including five myocardial infarctions. Residual risk can be substantial despite LDL lowering.
    Comparisons with historical HoFH cohorts do not prove identical risk for every genotype or exclude differences
    from receptor-negative LDLR disease. Aortic valve stenosis is modeled separately from this arterial outcome.
  locations:
  - preferred_term: artery
    term:
      id: UBERON:0001637
      label: artery
  evidence:
  - reference: PMID:29348020
    reference_title: "Autosomal Recessive Hypercholesterolemia: Long-Term Cardiovascular Outcomes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      During follow-up, 26.9% of patients had incident ASCVD, and 11.5% had a new diagnosis of aortic valve
      stenosis (absolute risk per year of 1.9% and 0.8%, respectively).
    explanation: >-
      Direct retrospective clinical outcomes; no universal age of onset follows from the cohort.
  downstream:
  - target: Premature Coronary Artery Atherosclerosis
    causal_link_type: DIRECT
    description: >-
      Coronary disease is the major reported arterial manifestation.
  - target: Myocardial Infarction
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Coronary disease can produce myocardial infarction; five events were recorded in the 52-patient longitudinal
      cohort.
- name: Extravascular Cholesterol Deposition
  biological_scale: ORGANISM
  description: >-
    Cholesterol accumulates in skin, tendons and the corneal periphery, producing distinct clinical stigmata.
    The 52-patient cohort recorded xanthomas in 47 patients; this generic endpoint does not provide a tendon-specific
    frequency. Lesion type and regression under treatment vary.
  evidence:
  - reference: url:https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf
    reference_title: "https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      Age at ﬁrst visit was 31.3 /C6 17.1 years, 46.2% of patients were men, and 90% showed xan- thomas.
    explanation: >-
      The selected ARH cohort reports generic xanthomas, not a 90% frequency for each anatomical subtype.
  downstream:
  - target: Tendon Xanthoma
    causal_link_type: DIRECT
    description: >-
      Tendon cholesterol deposits are one xanthoma subtype; no generic-cohort percentage is assigned specifically
      to tendons.
  - target: Xanthelasma
    causal_link_type: DIRECT
    description: >-
      Eyelid cholesterol deposition produces xanthelasma.
  - target: Corneal Arcus
    causal_link_type: DIRECT
    description: >-
      Peripheral corneal lipid deposition produces an arcus.
  - target: Xanthoma
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Cholesterol deposition produces xanthomas of different morphologies.
    evidence:
    - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf
      reference_title: "https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf"
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      snippet: >-
        Planar, tuberous, or tendon xanthomas have also been reported to develop in childhood.
      explanation: >-
        LDLRAP1-specific GeneReviews table; does not provide separate frequencies for the three morphologies.
- name: Preserved Hepatic VLDL Remnant Uptake
  role: retained function modifying disease expression
  biological_scale: CELLULAR
  description: >-
    LDLR-dependent uptake of VLDL remnants is largely preserved in Arh-knockout mice despite impaired LDL uptake.
    Hepatocyte LDLR deletion abolishes this uptake, whereas additional LRP deletion does not. A human kinetic
    study in one patient found increased direct remnant removal. This retained pathway may limit LDL-precursor
    availability and contribute to statin responsiveness, but the precise ARH-independent internalization machinery
    is unresolved.
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  locations:
  - preferred_term: liver
    term:
      id: UBERON:0002107
      label: liver
  evidence:
  - reference: PMID:17200716
    reference_title: Disruption of LDL but not VLDL clearance in autosomal recessive hypercholesterolemia.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    quote_role: PRIMARY_RESULT
    snippet: >-
      The rate of VLDL clearance was significantly higher in Arh(-/-) mice than in Ldlr(-/-) mice, suggesting
      that LDLR-dependent uptake of VLDL is maintained in the absence of ARH.
    explanation: >-
      Whole-mouse comparison; preserved remnant clearance is distinct from the LDL clearance defect.
  - reference: PMID:22157599
    reference_title: "Altered metabolism of low-density lipoprotein and very-low-density lipoprotein remnant in autosomal recessive hypercholesterolemia: results from stable isotope kinetic study in vivo."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      In contrast, the direct removal of very-low-density lipoprotein remnant was significantly greater in
      ARH than those in control subjects (47.5 versus 2±2%).
    explanation: >-
      One patient versus seven controls; does not define a population-wide fraction.
phenotypes:
- category: Biochemical
  name: Hypercholesterolemia
  description: Elevated total plasma cholesterol driven by the LDL fraction, present from early life.
  phenotype_term:
    preferred_term: Hypercholesterolemia
    term:
      id: HP:0003124
      label: Hypercholesterolemia
    temporality: CHRONIC
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:42730734
    reference_title: Autosomal Recessive Hypercholesterolemia Due to a Novel Homozygous LDLRAP1 Frameshift Mutation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      Total cholesterol was 516 mg/dL, low-density lipoprotein cholesterol (LDL-C) 499 mg/dL, triglycerides
      47 mg/dL, and high-density lipoprotein cholesterol 35 mg/dL.
    explanation: >-
      Biochemical values in one molecularly confirmed adolescent, not population averages.
- category: Biochemical
  name: Increased LDL Cholesterol
  description: >-
    Marked LDL-C elevation with variable severity and treatment response. The 52-patient retrospective cohort
    had mean baseline LDL-C 571.9 mg/dL (range 208–1,135); baseline included treated patients. The mean nadir
    during intensified therapy was 164.0 mg/dL, a 69.6% reduction. Nadir values are not average cumulative
    exposure or guaranteed treatment response.
  phenotype_term:
    preferred_term: Increased LDL cholesterol concentration
    term:
      id: HP:0003141
      label: Increased LDL cholesterol concentration
    temporality: CHRONIC
  frequency: VERY_FREQUENT
  evidence:
  - reference: url:https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf
    reference_title: "https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      We collected data for 52 patients (28 females, 24 males; 31.1 /C6 17.1 years of age; baseline LDL-C:
      571.9 /C6 171.7 mg/dl).
    explanation: >-
      Baseline cohort mean; the adjoining text and Table 1 provide dispersion and range.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf
    reference_title: "https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Presentation similar to LDLR-related HoFH incl LDL-C >500 mg/dL, early-onset CAD, & aortic valve stenosis.
    explanation: >-
      The LDLRAP1-specific GeneReviews row describes severe presentations without making the threshold obligatory.
- name: Xanthoma
  category: Physical
  phenotype_term:
    preferred_term: Xanthomatosis
    term:
      id: HP:0000991
      label: Xanthomatosis
  description: >-
    Cutaneous or tendon cholesterol deposits, including planar and tuberous forms, often beginning in childhood.
    Any xanthoma was recorded in 47/52 patients in the 2018 retrospective cohort; this selected-cohort fraction
    is not a tendon-specific frequency or population penetrance.
  evidence:
  - reference: url:https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf
    reference_title: "https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      Number of xanthomas 47 (90.4) 22 (91.7) 25 (89.3)
    explanation: >-
      Table 1 gives whole-cohort, male and female counts, respectively.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf
    reference_title: "https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Planar, tuberous, or tendon xanthomas have also been reported to develop in childhood.
    explanation: >-
      LDLRAP1-specific GeneReviews table; does not provide separate frequencies for the three morphologies.
- category: Physical
  name: Tendon Xanthoma
  description: >-
    Tendon cholesterol deposits can develop in childhood. The frequency of tendon involvement specifically
    is not established by cohort counts of xanthomas of any morphology.
  phenotype_term:
    preferred_term: Tendon xanthomatosis
    term:
      id: HP:0010874
      label: Tendon xanthomatosis
    clinical_course: PROGRESSIVE
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf
    reference_title: "https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Planar, tuberous, or tendon xanthomas have also been reported to develop in childhood.
    explanation: >-
      LDLRAP1-specific GeneReviews table; does not provide separate frequencies for the three morphologies.
- category: Cardiovascular
  name: Premature Coronary Artery Atherosclerosis
  description: >-
    Premature coronary disease is a major complication, but its onset varies. Nine of 52 patients in the retrospective
    cohort had prior coronary disease; 14 developed ASCVD events during follow-up. These observations reflect
    treated, selected patients and do not imply inevitable childhood coronary disease.
  phenotype_term:
    preferred_term: Coronary artery atherosclerosis
    term:
      id: HP:0001677
      label: Coronary artery atherosclerosis
    clinical_course: PROGRESSIVE
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf
    reference_title: "https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Presentation similar to LDLR-related HoFH incl LDL-C >500 mg/dL, early-onset CAD, & aortic valve stenosis.
    explanation: >-
      Gene-specific clinical association.
  - reference: url:https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf
    reference_title: "https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      ASCVD 14 (26.9) 7 (29.2) 7 (25.0)
    explanation: >-
      Table 3 whole-cohort, male and female incident ASCVD counts; ASCVD is broader than coronary disease.
- category: Cardiovascular
  name: Myocardial Infarction
  description: >-
    A possible coronary complication; 5/52 patients had myocardial infarction during follow-up in the 2018
    retrospective cohort.
  phenotype_term:
    preferred_term: Myocardial infarction
    term:
      id: HP:0001658
      label: Myocardial infarction
  evidence:
  - reference: url:https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf
    reference_title: "https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      MI 5 (9.6) 2 (8.3) 3 (10.7)
    explanation: >-
      Table 3 whole-cohort, male and female myocardial-infarction counts.
- category: Cardiovascular
  name: Aortic Valve Stenosis
  description: >-
    Aortic valve disease can occur and progress despite lipid-lowering therapy. Eleven of 52 patients had stenosis
    at baseline in the 2018 cohort. Six new diagnoses were reported during follow-up, but valve follow-up was
    available in only 45 patients; the reported 11.5% uses all 52 as denominator.
  phenotype_term:
    preferred_term: Aortic valve stenosis
    term:
      id: HP:0001650
      label: Aortic valve stenosis
  evidence:
  - reference: PMID:32011344
    reference_title: "Autosomal recessive hypercholesterolemia: update for 2020."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "ARH is also associated with increased risk of developing aortic valve stenosis."
    explanation: Directly attributes increased aortic valve stenosis risk to ARH.
    quote_role: REVIEW_SYNTHESIS
  - reference: url:https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf
    reference_title: "https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      Eleven patients (21.1%) showed aortic valve stenosis, which was reported to be severe in 5.8%.
    explanation: >-
      Baseline valve findings in the retrospective cohort.
- category: Physical
  name: Xanthelasma
  description: Yellowish waxy cholesterol deposits around the eyelids.
  phenotype_term:
    preferred_term: Xanthelasma
    term:
      id: HP:0001114
      label: Xanthelasma
  evidence:
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Xanthelasmas (yellowish, waxy deposits) can occur around the eyelids."
    explanation: >-
      GeneReviews documents xanthelasma as a cholesterol-deposition sign of FH;
      cited at class level for the hypercholesterolemia ARH shares.
    quote_role: REVIEW_SYNTHESIS
- category: Physical
  name: Corneal Arcus
  description: >-
    An opaque ring at the corneal margin from cholesterol deposition, appearing
    earlier than the age-related form.
  phenotype_term:
    preferred_term: Corneal arcus
    term:
      id: HP:0001084
      label: Corneal arcus
  evidence:
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Individuals with FH may develop corneal arcus (white, gray, or blue opaque ring in the corneal margin as a result of cholesterol deposition) at a younger age than those without FH."
    explanation: >-
      GeneReviews documents premature corneal arcus in FH; cited at class level for
      the shared hypercholesterolemia phenotype.
    quote_role: REVIEW_SYNTHESIS
biochemical:
- name: Plasma LDL Cholesterol
  biomarker_term:
    preferred_term: low-density lipoprotein cholesterol
    term:
      id: CHEBI:47774
      label: low-density lipoprotein cholesterol
  presence: Increased
  notes: >-
    LDL-C is the principal diagnostic and treatment-response analyte. Values depend on genotype, treatment
    and sampling relative to apheresis. Serial values and cumulative exposure are more informative for long-term
    burden than the single best value achieved.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf
    reference_title: "https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Presentation similar to LDLR-related HoFH incl LDL-C >500 mg/dL, early-onset CAD, & aortic valve stenosis.
    explanation: >-
      The LDLRAP1-specific GeneReviews row describes severe presentations without making the threshold obligatory.
genetic:
- name: LDLRAP1
  gene_term:
    preferred_term: LDLRAP1
    term:
      id: hgnc:18640
      label: LDLRAP1
  association: Pathogenic Mutations
  presence: Positive
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  inheritance:
  - name: Autosomal Recessive
    inheritance_term:
      preferred_term: Autosomal recessive inheritance
      term:
        id: HP:0000007
        label: Autosomal recessive inheritance
  notes: >-
    LDLRAP1 at 1p36.11 encodes the cytosolic ARH adaptor. Pathogenic alleles include truncating variants, splice
    alterations, large rearrangements and initiation-codon variants. Disease requires biallelic variants, either
    homozygous or compound heterozygous. Loss of normal function need not mean complete absence of residual
    uptake: c.1A>G was associated with a shorter protein and residual lymphocyte LDLR activity. Sardinian founder
    alleles include NM_015627.3:c.431dupA (historically c.432_433insA), p.His144GlnfsTer27, and c.65G>A, p.Trp22Ter.
    Their prominence in Sardinian-enriched cohorts is not worldwide allele predominance.
  evidence:
  - reference: PMID:11326085
    reference_title: "Autosomal recessive hypercholesterolemia caused by mutations in a putative LDL receptor adaptor protein."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here we map the ARH locus to an approximately 1-centimorgan interval on chromosome 1p35 and identify six mutations in a gene encoding a putative adaptor protein (ARH)."
    explanation: The founding gene-discovery paper mapping and identifying LDLRAP1/ARH mutations.
  - reference: url:https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf
    reference_title: "https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      Twelve different LDLRAP1 mutations (including 2 major rearrangements) in LDLRAP1 were detected; 8 of
      them predict the presence of a truncated ARH protein. Thirty-nine patients were simple homozy- gotes,
      and 13 were compound heterozygotes.
    explanation: >-
      Includes two major rearrangements and both biallelic configurations.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf
    reference_title: "https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      LDLRAP1 NM_015627.3 NP_056442.2 c.431dupA (c.432_433insA) p.His144GlnfsTer27
    explanation: >-
      Modern transcript-based founder nomenclature from GeneReviews; historical protein notations can differ.
  - reference: PMID:30777337
    reference_title: "A new variant (c.1A>G) in LDLRAP1 causing autosomal recessive hypercholesterolemia: Characterization of the defect and response to PCSK9 inhibition."
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: >-
      The patient had undetectable full-length ARH protein by Western blotting, but expressed a lower-than-normal
      molecular weight peptide.
    explanation: >-
      Patient-derived lymphocyte result limits an all-null protein model.
  - reference: url:https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf
    reference_title: "https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      The most common pathogenic variants were p.(Trp22*) and p.(Ala145Serfs*26), which were present in 26.9%
      and 53.8% of patients, respectively. This is because these genetic variants are common among Sardinian
      cases of ARH (4,14) , which represented the largest subgroup in our cohort.
    explanation: >-
      The primary 2018 cohort identifies p.Trp22Ter and the historical frameshift as enriched among its Sardinian
      participants. Modern c.65G>A nomenclature is recorded in the GeneReviews molecular table; this quotation
      avoids the next table header.
diagnosis:
- name: Molecular Genetic Testing of LDLRAP1
  description: >-
    Identify two pathogenic or likely pathogenic LDLRAP1 variants in trans, using segregation testing when
    needed. An FH or broader dyslipidemia panel should include sequence and deletion/duplication analysis.
    A variant of uncertain significance cannot establish or exclude the diagnosis. Founder testing may be useful
    in Sardinian families, but a negative founder test does not exclude other alleles; one detected allele
    or apparent homozygosity may require copy-number analysis. Normal fibroblast LDL uptake does not exclude
    ARH.
  evidence:
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The molecular diagnosis of FH can be established by identification of heterozygous or biallelic pathogenic variants in APOB (variants that impair binding of LDL-C to the LDL receptor), LDLR, or PCSK9 (gain of function); or rarely, identification of biallelic pathogenic variants in LDLRAP1."
    explanation: >-
      GeneReviews names biallelic LDLRAP1 pathogenic variants as the molecular
      diagnosis of the recessive form - the ARH-specific diagnostic route.
    quote_role: REVIEW_SYNTHESIS
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf
    reference_title: "https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Identification of variant(s) of uncertain significance cannot be used to confirm or rule out the diagnosis.
    explanation: >-
      VUS interpretation applies to the FH molecular evaluation.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf
    reference_title: "https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      A smaller FH multigene panel that includes sequence analysis and deletion/duplication analysis of APOB,
      LDLR, LDLRAP1, and PCSK9 may be considered.
    explanation: >-
      Panel should include copy-number analysis as well as sequencing.
  - reference: PMID:17761685
    reference_title: Adaptor protein disabled-2 modulates low density lipoprotein receptor synthesis in fibroblasts from patients with autosomal recessive hypercholesterolaemia.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: >-
      Surprisingly, LDL-receptor function is normal in ARH patients' skin fibroblasts in culture.
    explanation: >-
      The cell-specific phenotype makes a normal fibroblast assay insufficient to rule out LDLRAP1 disease.
- name: Clinical Suspicion and Lipid Evaluation
  description: >-
    Severe LDL-C elevation, childhood xanthomas or early coronary/valve disease raise suspicion. Normal parental
    lipids favor recessive disease but are not diagnostic, and no single LDL-C threshold establishes LDLRAP1
    disease. Measure the lipid profile, assess secondary causes and cardiovascular risk factors, and use molecular
    testing to distinguish phenotypically overlapping disorders.
  evidence:
  - reference: PMID:42730734
    reference_title: Autosomal Recessive Hypercholesterolemia Due to a Novel Homozygous LDLRAP1 Frameshift Mutation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      Cardiac evaluation was normal, secondary causes were excluded, and first-degree relatives had normal
      lipid profiles.
    explanation: >-
      One molecularly confirmed case illustrates normal family lipids and absence of established cardiovascular
      disease.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf
    reference_title: "https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      A broader dyslipidemia multigene panel that includes APOB, LDLR, LDLRAP1, and PCSK9 as well as ABCG8,
      ABCG5, APOE, and LIPA (genes associated with other lipid conditions that can cause elevated LDL-C levels
      and early-onset CAD; see Differential Diagnosis) may also be considered.
    explanation: >-
      Broader testing addresses overlapping inherited lipid disorders.
- name: Cardiovascular Imaging Surveillance
  description: >-
    Monitor lipids and cardiovascular risk throughout life. For severe ARH overlapping clinical HoFH, consensus
    supports baseline and annual echocardiography of the heart and aorta, and specialist-directed coronary
    CT angiography. Repeat CT depends on baseline burden, LDL-C lowering, radiation risk and clinical indication.
    Invasive coronary angiography is reserved for suspected ischemia or valve dysfunction. This is severity-based
    clinical guidance, not a requirement for routine catheterization in every LDLRAP1 patient.
  evidence:
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "or autosomal recessive FH (due to homozygous or compound heterozygous pathogenic variants in LDLRAP1) should be monitored with various imaging modalities (including echocardiogram, CT angiogram, and cardiac catheterization) as recommended."
    explanation: >-
      GeneReviews names autosomal recessive FH (biallelic LDLRAP1) explicitly in
      its imaging-surveillance recommendation - the most ARH-specific management
      statement in the chapter.
    quote_role: REVIEW_SYNTHESIS
  - reference: PMID:37130090
    reference_title: "2023 Update on European Atherosclerosis Society Consensus Statement on Homozygous Familial Hypercholesterolaemia: new treatments and clinical guidance."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Patients with HoFH should receive echocardiographic evaluation of the heart and aorta at baseline and
      annually thereafter.
    explanation: >-
      Class-level guidance for severe disease.
  - reference: PMID:37130090
    reference_title: "2023 Update on European Atherosclerosis Society Consensus Statement on Homozygous Familial Hypercholesterolaemia: new treatments and clinical guidance."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Invasive coronary angiography is indicated in patients with symptoms and/or signs suggestive of ischaemia
      or valve malfunction.
    explanation: >-
      Limits invasive investigation to a clinical indication.
- name: Cascade and Carrier Testing
  description: >-
    Offer targeted familial-variant testing to at-risk relatives and parents. Normal lipid levels do not reliably
    identify carriers. Confirm parental segregation to refine recurrence risk and investigate unexpected inheritance,
    including an undetected deletion or uniparental isodisomy.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf
    reference_title: "https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Carrier testing for at-risk relatives requires prior identification of the LDLRAP1 pathogenic variants
      in the family.
    explanation: >-
      Family-specific molecular testing.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf
    reference_title: "https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Molecular genetic testing is recommended for the parents of a proband to confirm that both parents are
      heterozygous for an LDLRAP1 pathogenic variant and to allow reliable recurrence risk assessment.
    explanation: >-
      Parent testing confirms the presumed recessive transmission.
treatments:
- name: Statin plus Ezetimibe (Background Lipid-Lowering Therapy)
  description: >-
    High-intensity or maximally tolerated statin plus ezetimibe is initial combination treatment for severe
    disease, with early escalation according to response and risk. ARH patients can respond substantially:
    in one kinetic study atorvastatin increased LDL apoB fractional catabolism from 0.109 to 0.464/day and
    reduced LDL-C from 8.63 to 4.22 mmol/L. Ezetimibe inhibits intestinal NPC1L1-mediated cholesterol absorption,
    but its downstream LDL-C effect, like statin response, partly depends on residual LDLR-mediated clearance.
    Neither a uniformly absent response nor universal target attainment is supported.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: statin
      term:
        id: CHEBI:87631
        label: statin
    - preferred_term: ezetimibe
      term:
        id: CHEBI:49040
        label: ezetimibe
  target_mechanisms:
  - target: Lifelong Elevation of Plasma LDL Cholesterol
    treatment_effect: INHIBITS
    description: >-
      Lowers circulating LDL-C to a variable degree; residual uptake and preserved remnant handling can contribute.
    evidence:
    - reference: PMID:22157599
      reference_title: "Altered metabolism of low-density lipoprotein and very-low-density lipoprotein remnant in autosomal recessive hypercholesterolemia: results from stable isotope kinetic study in vivo."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: PRIMARY_RESULT
      snippet: >-
        Interestingly, FCR of LDL apoB in ARH dramatically increased to 0.464 1/day, accompanying reduction
        of LDL cholesterol levels from 8.63 to 4.22 mmol/L after treatment with atorvastatin of 20 mg/d for
        3 months.
      explanation: >-
        Direct one-patient treatment/kinetic observation; not a population response estimate.
  evidence:
  - reference: PMID:37130090
    reference_title: "2023 Update on European Atherosclerosis Society Consensus Statement on Homozygous Familial Hypercholesterolaemia: new treatments and clinical guidance."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Patients should start on a high-intensity statin and ezetimibe rather than statin monotherapy, but most
      will require additional therapies to attain goal.
    explanation: >-
      Consensus for the severe HoFH clinical phenotype.
  - reference: PMID:22157599
    reference_title: "Altered metabolism of low-density lipoprotein and very-low-density lipoprotein remnant in autosomal recessive hypercholesterolemia: results from stable isotope kinetic study in vivo."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      Interestingly, FCR of LDL apoB in ARH dramatically increased to 0.464 1/day, accompanying reduction of
      LDL cholesterol levels from 8.63 to 4.22 mmol/L after treatment with atorvastatin of 20 mg/d for 3 months.
    explanation: >-
      Direct one-patient treatment/kinetic observation; not a population response estimate.
  - reference: PMID:37130090
    reference_title: "2023 Update on European Atherosclerosis Society Consensus Statement on Homozygous Familial Hypercholesterolaemia: new treatments and clinical guidance."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Response to statin, ezetimibe, and proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors is
      dependent on the degree of residual low-density lipoprotein receptor activity;
    explanation: >-
      Clarifies secondary receptor dependence despite different primary drug targets.
- name: Lomitapide
  description: >-
    Microsomal triglyceride transfer protein inhibition reduces hepatic VLDL production and therefore LDL formation
    independently of LDLR function. In nine ARH patients receiving background statin/ezetimibe, with apheresis
    in three and PCSK9 inhibition in one, median LDL-C fell from 257.0 to 101.7 mg/dL (60.4%). Four patients
    overlapped the earlier 52-patient cohort. This uncontrolled subanalysis does not isolate comparative efficacy
    or prove cardiovascular-event prevention. Gastrointestinal intolerance, liver-fat accumulation and transaminase
    elevations require dietary support and liver monitoring; one patient stopped because of gastrointestinal
    effects and poor adherence. Normal stiffness in six assessed patients does not establish long-term hepatic
    safety.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: lomitapide
      term:
        id: CHEBI:72297
        label: lomitapide
  target_mechanisms:
  - target: Lifelong Elevation of Plasma LDL Cholesterol
    treatment_effect: INHIBITS
    description: >
      Lowers LDL production upstream of the receptor, bypassing the defective
      hepatic LDL-receptor internalization.
    evidence:
    - reference: PMID:36072671
      reference_title: "Efficacy of Long-Term Treatment of Autosomal Recessive Hypercholesterolemia With Lomitapide: A Subanalysis of the Pan-European Lomitapide Study."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "lomitapide acts using an LDLR-independent mechanism, therefore potentially extending its efficacy in patients with an absent LDLR function, like those with ARH"
      explanation: >-
        The paper summarizes the established drug mechanism; ARH is an adaptor defect, not absence of LDLR
        protein.
      quote_role: BACKGROUND
  evidence:
  - reference: PMID:36072671
    reference_title: "Efficacy of Long-Term Treatment of Autosomal Recessive Hypercholesterolemia With Lomitapide: A Subanalysis of the Pan-European Lomitapide Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The addition of lomitapide (mean dose, 10 mg) resulted in the achievement of a median on-treatment LDL-C of 101.7 mg/dL (IQR, 71.3-138.3; 60.4% reduction from baseline)"
    explanation: Quantifies the LDL-C reduction achieved by lomitapide in the ARH subgroup.
  - reference: PMID:36072671
    reference_title: "Efficacy of Long-Term Treatment of Autosomal Recessive Hypercholesterolemia With Lomitapide: A Subanalysis of the Pan-European Lomitapide Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      Indeed, he stopped lomitapide after 18 months of treatment due to gastrointestinal side effects and lack
      of compliance.
    explanation: >-
      Observed treatment discontinuation in one patient.
  - reference: PMID:36072671
    reference_title: "Efficacy of Long-Term Treatment of Autosomal Recessive Hypercholesterolemia With Lomitapide: A Subanalysis of the Pan-European Lomitapide Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      This patient also experienced a change in hepatic fat, from absent to moderate steatosis, at the last
      follow-up visit.
    explanation: >-
      Documents hepatic fat accumulation; other patients also showed new or worsening fat on Table 2.
  - reference: PMID:36072671
    reference_title: "Efficacy of Long-Term Treatment of Autosomal Recessive Hypercholesterolemia With Lomitapide: A Subanalysis of the Pan-European Lomitapide Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      However, the small sample size and the relatively short period of observation prevent giving any definite
      conclusion.
    explanation: >-
      Authors qualify the long-term safety interpretation.
- name: Lipoprotein Apheresis
  description: >-
    Repeated extracorporeal removal of circulating apoB-containing lipoproteins lowers LDL-C independently
    of receptor function. Severe childhood disease may warrant early apheresis when drug therapy does not adequately
    control exposure, before established coronary disease. Frequency and continuation depend on severity, venous
    access, response to adjunct drugs and specialist assessment. Acute postprocedure values underestimate the
    rebound between sessions; treatment burden and time-averaged LDL-C matter.
  therapeutic_modality: DEVICE
  treatment_term:
    preferred_term: lipoprotein apheresis
    term:
      id: NCIT:C173286
      label: Therapeutic Apheresis
  target_mechanisms:
  - target: Lifelong Elevation of Plasma LDL Cholesterol
    treatment_effect: INHIBITS
    description: >
      Lowers plasma LDL cholesterol by a route independent of LDL-receptor
      function, so it retains efficacy despite the ARH internalization defect;
      current consensus treats it as foundational in severe biallelic disease.
    evidence:
    - reference: PMID:37130090
      reference_title: "2023 Update on European Atherosclerosis Society Consensus Statement on Homozygous Familial Hypercholesterolaemia: new treatments and clinical guidance."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "for lomitapide, angiopoietin-like protein 3 (ANGPLT3)-directed therapy and lipoprotein apheresis, response is independent of low-density lipoprotein receptor function."
      explanation: >-
        States that the LDL-C-lowering response to lipoprotein apheresis is
        independent of LDL-receptor function - the mechanism that lets it lower
        LDL-C in ARH despite the receptor-side (here, adaptor-side) defect.
      quote_role: REVIEW_SYNTHESIS
    - reference: PMID:37130090
      reference_title: "2023 Update on European Atherosclerosis Society Consensus Statement on Homozygous Familial Hypercholesterolaemia: new treatments and clinical guidance."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Combination LDL-C-lowering therapy-both pharmacologic intervention and lipoprotein apheresis (LA)-is foundational."
      explanation: >-
        Establishes apheresis as a foundational LDL-C-lowering component of
        severe-disease management, the role modeled by this link.
      quote_role: REVIEW_SYNTHESIS
  evidence:
  - reference: PMID:37130090
    reference_title: "2023 Update on European Atherosclerosis Society Consensus Statement on Homozygous Familial Hypercholesterolaemia: new treatments and clinical guidance."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Combination LDL-C-lowering therapy-both pharmacologic intervention and lipoprotein apheresis (LA)-is foundational."
    explanation: >-
      Establishes apheresis as a foundational LDL-C-lowering component of
      severe-disease management, the role modeled by this link.
    quote_role: REVIEW_SYNTHESIS
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf
    reference_title: "https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      LDL apheresis (≤2x/wk) is often required from a young age.
    explanation: >-
      Severe-FH class recommendation, not a requirement that coronary disease already be present.
- name: PCSK9 Inhibitor
  description: >-
    PCSK9 monoclonal antibodies preserve LDLR abundance and can lower LDL-C in some ARH patients, but response
    varies with residual function. Patient lymphocyte experiments with alirocumab showed attenuated effects
    compared with controls; these are not clinical trials. In one patient homozygous for c.1A>G, evolocumab
    added to atorvastatin/ezetimibe lowered LDL-C a further 39%. A monitored trial of therapy should be judged
    by the individual biochemical response; poor response in one genotype does not imply universal inefficacy.
  therapeutic_modality: MONOCLONAL_ANTIBODY
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: PCSK9 inhibitor
      term:
        id: NCIT:C190797
        label: PCSK9 Inhibitor
  target_mechanisms:
  - target: Lifelong Elevation of Plasma LDL Cholesterol
    treatment_effect: INHIBITS
    description: >-
      May lower circulating LDL-C in responsive individuals; evidence includes a single clinical response alongside
      patient-cell experiments.
    evidence:
    - reference: PMID:30777337
      reference_title: "A new variant (c.1A>G) in LDLRAP1 causing autosomal recessive hypercholesterolemia: Characterization of the defect and response to PCSK9 inhibition."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: PRIMARY_RESULT
      snippet: >-
        LDL-cholesterol levels were markedly reduced by the successive therapy with Atorvastatin and Atorvastatin
        plus Ezetimibe, and the addition of Evolocumab biweekly decreased LDL-cholesterol by a further 39%.
      explanation: >-
        Clinical response in one initiation-codon-variant patient.
  evidence:
  - reference: PMID:27079874
    reference_title: "Proprotein Convertase Subtilisin Kexin Type 9 Inhibition for Autosomal Recessive Hypercholesterolemia-Brief Report."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "the effects of recombinant PCSK9, and hence of alirocumab, on LDL receptor expression and function were significantly less pronounced in ARH than in control cells."
    explanation: >-
      Mechanistic basis for the blunted PCSK9-inhibitor response in ARH - PCSK9's
      effect on the LDL receptor is reduced in ARH cells.
  - reference: PMID:30777337
    reference_title: "A new variant (c.1A>G) in LDLRAP1 causing autosomal recessive hypercholesterolemia: Characterization of the defect and response to PCSK9 inhibition."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      LDL-cholesterol levels were markedly reduced by the successive therapy with Atorvastatin and Atorvastatin
      plus Ezetimibe, and the addition of Evolocumab biweekly decreased LDL-cholesterol by a further 39%.
    explanation: >-
      Clinical response in one initiation-codon-variant patient.
  - reference: PMID:37130090
    reference_title: "2023 Update on European Atherosclerosis Society Consensus Statement on Homozygous Familial Hypercholesterolaemia: new treatments and clinical guidance."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      If patients show >15% additional LDL-C reduction, PCSK9-directed therapy may be continued, but if response
      is poor, clinicians should consider stopping this therapy.
    explanation: >-
      Severe-HoFH consensus threshold, not an LDLRAP1-specific trial endpoint.
- name: Evinacumab
  description: >-
    ANGPTL3-neutralizing antibody that lowers LDL-C through an LDLR-independent pathway. Two reported ARH adults
    achieved substantial additional lowering with monthly infusions; one continued apheresis, while the second
    remained below 55 mg/dL after background evolocumab and bempedoic acid were stopped. Changing co-therapy
    and apheresis timing preclude attributing the entire change to evinacumab. Transient first-infusion headache
    or abdominal colic was reported. The phase III open-label extension included two LDLRAP1 patients, but
    its published subgroup combines them with LDLR disease. Cardiovascular-event prevention specifically in
    ARH is unproven.
  therapeutic_modality: MONOCLONAL_ANTIBODY
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: Evinacumab
      term:
        id: NCIT:C169973
        label: Evinacumab
  target_mechanisms:
  - target: Lifelong Elevation of Plasma LDL Cholesterol
    treatment_effect: INHIBITS
    description: >-
      Reduces circulating LDL-C; the evidence and limitations are specified in the treatment description.
    evidence:
    - reference: url:https://air.unimi.it/retrieve/handle/2434/1224076/3272602/1-s2.0-S1933287426000401-main.pdf
      reference_title: "https://air.unimi.it/retrieve/handle/2434/1224076/3272602/1-s2.0-S1933287426000401-main.pdf"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: PRIMARY_RESULT
      snippet: >-
        After 10 months, LDL-C levels have remained below 55 mg/dL ( Fig 2 B and Table ), with a time-averaged
        LDL-C decrease of 73.8%.
      explanation: >-
        Second ARH case maintained low LDL-C despite discontinuation of evolocumab and bempedoic acid after
        three months. Background rosuvastatin/ezetimibe continued; this is not randomized or isolated drug
        efficacy.
  evidence:
  - reference: url:https://air.unimi.it/retrieve/handle/2434/1224076/3272602/1-s2.0-S1933287426000401-main.pdf
    reference_title: "https://air.unimi.it/retrieve/handle/2434/1224076/3272602/1-s2.0-S1933287426000401-main.pdf"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      After 10 months, LDL-C levels have remained below 55 mg/dL ( Fig 2 B and Table ), with a time-averaged
      LDL-C decrease of 73.8%.
    explanation: >-
      Second ARH case maintained low LDL-C despite discontinuation of evolocumab and bempedoic acid after three
      months. Background rosuvastatin/ezetimibe continued; this is not randomized or isolated drug efficacy.
  - reference: PMID:41671678
    reference_title: "Efficacy of evinacumab by genotype and low-density lipoprotein receptor function in patients with homozygous familial hypercholesterolaemia: A subanalysis from the ELIPSE open-label extension study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      At baseline, 55 (47.4%) had either identical bi-allelic variants in LDLR (n = 53) or LDLRAP1 (n = 2),
      and 41 (35.3%) had different bi-allelic LDLR variants.
    explanation: >-
      Two LDLRAP1 patients were included in the extension; pooled LDLR/LDLRAP1 response is not a gene-specific
      estimate.
  - reference: PMID:37130090
    reference_title: "2023 Update on European Atherosclerosis Society Consensus Statement on Homozygous Familial Hypercholesterolaemia: new treatments and clinical guidance."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      for lomitapide, angiopoietin-like protein 3 (ANGPLT3)-directed therapy and lipoprotein apheresis, response
      is independent of low-density lipoprotein receptor function.
    explanation: >-
      Mechanistic class rationale for ANGPTL3 blockade.
- name: Bempedoic Acid in Combination Therapy
  description: >-
    A reported 15-year-old with biallelic LDLRAP1 disease received atorvastatin, ezetimibe and bempedoic acid,
    with LDL-C decreasing from 499 to 80 mg/dL at three months. This is case-level combination-treatment evidence,
    not proof of independent efficacy, routine pediatric indication or prevention of clinical events.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: Bempedoic Acid
      term:
        id: NCIT:C166494
        label: Bempedoic Acid
  target_mechanisms:
  - target: Lifelong Elevation of Plasma LDL Cholesterol
    treatment_effect: INHIBITS
    description: >-
      Reduces circulating LDL-C; the evidence and limitations are specified in the treatment description.
    evidence:
    - reference: PMID:42730734
      reference_title: Autosomal Recessive Hypercholesterolemia Due to a Novel Homozygous LDLRAP1 Frameshift Mutation.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: PRIMARY_RESULT
      snippet: >-
        The patient was treated with atorvastatin, ezetimibe, and bempedoic acid, resulting in a marked reduction
        in low-density lipoprotein cholesterol to 80 mg/dL at 3-month follow-up.
      explanation: >-
        One adolescent received three agents together; the contribution of bempedoic acid cannot be separated.
  evidence:
  - reference: PMID:42730734
    reference_title: Autosomal Recessive Hypercholesterolemia Due to a Novel Homozygous LDLRAP1 Frameshift Mutation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      The patient was treated with atorvastatin, ezetimibe, and bempedoic acid, resulting in a marked reduction
      in low-density lipoprotein cholesterol to 80 mg/dL at 3-month follow-up.
    explanation: >-
      One adolescent received three agents together; the contribution of bempedoic acid cannot be separated.
- name: Genetic Counseling
  action_category: COUNSELING_INFORMATIONAL
  description: >-
    Explain recessive inheritance and confirm parental carrier status. Discuss familial testing, partner testing
    and reproductive options. An affected person transmits one pathogenic allele to every child; disease risk
    depends on the partner genotype. Prenatal or preimplantation testing becomes possible after the familial
    variants are known.
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf
    reference_title: "https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Genetic counseling and genetic testing can be offered to the reproductive partner to assess this risk.
    explanation: >-
      LDLRAP1-specific partner evaluation.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf
    reference_title: "https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Once the FH-causing pathogenic variant(s) have been identified in an affected family member, prenatal
      and preimplantation genetic testing are possible.
    explanation: >-
      Family-specific reproductive testing; interpreted using the recessive LDLRAP1 inheritance model.
- name: Lifestyle and Cardiovascular Risk Management
  action_category: THERAPEUTIC
  description: >-
    Use dietary counseling, regular physical activity, healthy weight and smoking avoidance alongside pharmacologic
    treatment. Address hypertension, diabetes and other modifiable risks. Lifestyle measures alone are insufficient
    for severe LDLRAP1 disease. Established coronary or valve disease warrants cardiovascular specialist care
    and indicated intervention.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf
    reference_title: "https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      To prevent primary manifestations, the following are recommended: • Reduce saturated fat intake. • Increase
      intake of soluble fiber to 10-20 g/day. • Increase physical activity. • Do not smoke.
    explanation: >-
      General FH lifestyle recommendations.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf
    reference_title: "https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Children & adults w/clinical atherosclerotic CVD should be evaluated & treated by cardiovascular specialists.
    explanation: >-
      Care of established disease is distinct from LDL-C lowering.
- name: Pregnancy Planning and Lipid Management
  action_category: THERAPEUTIC
  description: >-
    Coordinate lipid, cardiovascular and obstetric care before conception, through pregnancy and lactation.
    Assess coronary and aortic-valve disease and review each medication individually. In severe disease, apheresis
    can limit LDL exposure during pregnancy; drug decisions require individualized maternal and fetal risk
    assessment.
  evidence:
  - reference: PMID:37130090
    reference_title: "2023 Update on European Atherosclerosis Society Consensus Statement on Homozygous Familial Hypercholesterolaemia: new treatments and clinical guidance."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      HoFH women should receive integrated care from a multidisciplinary team, including cardiovascular assessment,
      before, during, and after pregnancy.
    explanation: >-
      Class-level guidance applicable to severe ARH; no blanket medication contraindication is inferred.
  - reference: PMID:37130090
    reference_title: "2023 Update on European Atherosclerosis Society Consensus Statement on Homozygous Familial Hypercholesterolaemia: new treatments and clinical guidance."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Thus, HoFH women should be offered weekly or fortnightly LA during pregnancy.
    explanation: >-
      Severe-disease consensus, not a gene-specific pregnancy trial.
progression:
- phase: Lifelong LDL-C Elevation from Early Life
  age_range: From birth
  notes: >-
    LDL cholesterol is markedly elevated from early life because hepatic LDL
    clearance is defective from birth. Cumulative LDL-C burden, not a discrete
    onset, drives the cardiovascular course.
- phase: Extravascular Deposition and Xanthomata
  age_range: Childhood to early adulthood
  notes: >-
    Cutaneous and tendon xanthomas may develop in childhood; the 47/52 count in the 2018 cohort covers all
    xanthoma morphologies. Regression depends on effective sustained LDL-C reduction and is not immediate.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf
    reference_title: "https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Planar, tuberous, or tendon xanthomas have also been reported to develop in childhood.
    explanation: >-
      LDLRAP1-specific GeneReviews table; does not provide separate frequencies for the three morphologies.
  - reference: url:https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf
    reference_title: "https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      Number of xanthomas 47 (90.4) 22 (91.7) 25 (89.3)
    explanation: >-
      Table 1 gives whole-cohort, male and female counts, respectively.
- phase: Premature ASCVD Events
  age_range: Variable; selected adult treatment cohorts
  notes: >-
    Five of nine lomitapide-treated adults had prior ASCVD, with mean age at first event 45.2 years among those
    five. This is not a universal age of onset, an untreated natural history estimate or evidence excluding
    severe childhood disease. Four patients overlapped the earlier 52-patient cohort. Persistent lifelong LDL
    exposure and prior disease influence subsequent risk.
  evidence:
  - reference: PMID:36072671
    reference_title: "Efficacy of Long-Term Treatment of Autosomal Recessive Hypercholesterolemia With Lomitapide: A Subanalysis of the Pan-European Lomitapide Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the mean age at the first event was 45.2 ± 7.9"
    explanation: Reports the mean age at first ASCVD event in the ARH cohort.
  - reference: PMID:36072671
    reference_title: "Efficacy of Long-Term Treatment of Autosomal Recessive Hypercholesterolemia With Lomitapide: A Subanalysis of the Pan-European Lomitapide Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The age at starting lomitapide was 46 (interquartile range (IQR), 39.0-65.5) years"
    explanation: Gives the age at which LDLR-independent escalation (lomitapide) was started in the cohort.
animal_models:
- name: Arh(-/-) mouse
  species: Mouse
  genotype: Arh(-/-) (LDLRAP1 knockout)
  publication: PMID:16179341
  description: >-
    Arh-knockout mice and hepatic rescue constructs test LDLR internalization. Comparison with Ldlr-knockout
    and wild-type mice distinguishes impaired LDL clearance from preserved VLDL-remnant clearance. Similar
    VLDL secretion but markedly different diet-induced hypercholesterolemia argues against secretion alone
    explaining the phenotype.
  modeled_mechanisms:
  - target: Impaired Clathrin-Mediated Endocytosis of the Hepatocyte LDL Receptor
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Loss of ARH in mouse liver reproduces the hepatocyte LDL-receptor
      endocytosis defect that defines this node, generalizing the WIF-B
      cell-culture result to an intact liver.
    limitations: >-
      Murine lipoprotein metabolism is apoB48- and HDL-dominated rather than
      LDL-dominated, so the model captures the molecular/cellular endocytic defect
      more faithfully than the human plasma-LDL and arterial-disease phenotype; the
      abstract reports in-vivo confirmation of the cell-culture findings without a
      separately quantified endocytosis readout.
    evidence:
    - reference: PMID:16179341
      reference_title: "The modular adaptor protein autosomal recessive hypercholesterolemia (ARH) promotes low density lipoprotein receptor clustering into clathrin-coated pits."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Parallel studies performed in vivo with the same recombinant forms of ARH in livers of Arh(-/-) mice confirmed the relevance of the cell culture findings."
      explanation: >-
        Reports the Arh(-/-) mouse in-vivo confirmation that ARH is required for
        hepatocyte LDL-receptor clustering and internalization, supporting the use
        of this model for that node.
  - target: Preserved Hepatic VLDL Remnant Uptake
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      VLDL clearance is greater in Arh-knockout than Ldlr-knockout mice despite impaired LDL clearance.
    limitations: >-
      Mouse lipoprotein composition and diet differ from human physiology; the result does not establish the
      magnitude of human clinical protection.
    evidence:
    - reference: PMID:17200716
      reference_title: Disruption of LDL but not VLDL clearance in autosomal recessive hypercholesterolemia.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      quote_role: PRIMARY_RESULT
      snippet: >-
        The rate of VLDL clearance was significantly higher in Arh(-/-) mice than in Ldlr(-/-) mice, suggesting
        that LDLR-dependent uptake of VLDL is maintained in the absence of ARH.
      explanation: >-
        Whole-animal comparison of ligand clearance.
    readouts:
    - name: VLDL clearance relative to Ldlr knockout
      target: Preserved Hepatic VLDL Remnant Uptake
      direction: INCREASED
      description: >-
        VLDL clearance is greater in Arh-knockout than Ldlr-knockout mice despite impaired LDL clearance.
      evidence:
      - reference: PMID:17200716
        reference_title: Disruption of LDL but not VLDL clearance in autosomal recessive hypercholesterolemia.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        quote_role: PRIMARY_RESULT
        snippet: >-
          The rate of VLDL clearance was significantly higher in Arh(-/-) mice than in Ldlr(-/-) mice, suggesting
          that LDLR-dependent uptake of VLDL is maintained in the absence of ARH.
        explanation: >-
          Whole-animal comparison of ligand clearance.
  evidence:
  - reference: PMID:17200716
    reference_title: Disruption of LDL but not VLDL clearance in autosomal recessive hypercholesterolemia.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    quote_role: PRIMARY_RESULT
    snippet: >-
      The rate of VLDL clearance was significantly higher in Arh(-/-) mice than in Ldlr(-/-) mice, suggesting
      that LDLR-dependent uptake of VLDL is maintained in the absence of ARH.
    explanation: >-
      Whole-animal comparison of ligand clearance.
  - reference: PMID:17200716
    reference_title: Disruption of LDL but not VLDL clearance in autosomal recessive hypercholesterolemia.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    quote_role: PRIMARY_RESULT
    snippet: >-
      The hyperlipidemic response to a high-sucrose diet was greatly attenuated in Arh(-/-) mice compared with
      Ldlr(-/-) mice despite similar rates of VLDL secretion.
    explanation: >-
      Separates secretion from clearance in the whole-animal comparison.
differential_diagnoses:
- name: LDLR-, APOB- or PCSK9-related familial hypercholesterolemia
  description: >-
    May produce a severe biallelic HoFH phenotype resembling ARH.
  distinguishing_features:
  - Molecular testing identifies the causal gene; a single pathogenic allele in these genes can produce dominant disease, unlike typical LDLRAP1 carrier status.
  - A normal fibroblast uptake assay does not exclude LDLRAP1 disease; genotype and cell context matter.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf
    reference_title: "https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      A heterozygous gain-of-function pathogenic (or likely pathogenic) variant in PCSK9
    explanation: >-
      Dominant PCSK9 diagnosis is mechanistically distinct.
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The molecular diagnosis of FH can be established by identification of heterozygous or biallelic pathogenic variants in APOB (variants that impair binding of LDL-C to the LDL receptor), LDLR, or PCSK9 (gain of function); or rarely, identification of biallelic pathogenic variants in LDLRAP1."
    explanation: >-
      GeneReviews names biallelic LDLRAP1 pathogenic variants as the molecular
      diagnosis of the recessive form - the ARH-specific diagnostic route.
    quote_role: REVIEW_SYNTHESIS
- name: Sitosterolemia
  disease_term:
    preferred_term: sitosterolemia
    term:
      id: MONDO:0008863
      label: sitosterolemia
  description: >-
    Recessive ABCG5/ABCG8 disease can cause childhood xanthomas, high LDL-C and premature coronary disease.
  distinguishing_features:
  - Elevated plasma plant sterols and ABCG5/ABCG8 variants distinguish it; hemolytic anemia, thrombocytopenia or stomatocytes are clues.
  - Treatment implications include dietary sterol restriction and ezetimibe.
  evidence:
  - reference: PMID:37130090
    reference_title: "2023 Update on European Atherosclerosis Society Consensus Statement on Homozygous Familial Hypercholesterolaemia: new treatments and clinical guidance."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      These include sitosterolaemia (or ‘phytosterolaemia’), caused by bi-allelic rare pathogenic variants
      in two ATP-binding cassette transporter genes, ABCG5 and/or ABCG8 (or at least one such variant in each
      gene), with elevated LDL-C levels that respond well to dietary recommendations, ezetimibe and/or resins,
    explanation: >-
      Consensus differential and distinct treatment response.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf
    reference_title: "https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Hematologic abnormalities (hemolytic anemia, thrombocytopenia, stomatocytes);
    explanation: >-
      GeneReviews distinguishing features.
- name: Lysosomal acid lipase deficiency
  disease_term:
    preferred_term: lysosomal acid lipase deficiency
    term:
      id: MONDO:0800449
      label: lysosomal acid lipase deficiency
  description: >-
    Biallelic LIPA disease can elevate LDL-C and cause premature atherosclerosis.
  distinguishing_features:
  - Hepatosplenomegaly, raised transaminases and triglycerides suggest the storage disorder; confirm with enzyme and molecular testing.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf
    reference_title: "https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      In adult onset (cholesterol-ester storage disease): hepatosplenomegaly &/or ↑ liver enzymes, ↑ triglycerides
    explanation: >-
      GeneReviews hepatic/lipid clues; infantile Wolman disease is a different severity presentation.
- name: Cerebrotendinous xanthomatosis
  disease_term:
    preferred_term: cerebrotendinous xanthomatosis
    term:
      id: MONDO:0008948
      label: cerebrotendinous xanthomatosis
  description: >-
    CYP27A1 disease shares tendon xanthomas.
  distinguishing_features:
  - Neurologic and cognitive abnormalities, cataracts and elevated cholestanol with normal or mildly elevated cholesterol favor this diagnosis.
  evidence:
  - reference: PMID:37130090
    reference_title: "2023 Update on European Atherosclerosis Society Consensus Statement on Homozygous Familial Hypercholesterolaemia: new treatments and clinical guidance."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Patients with cerebrotendinous xanthomatosis may have xanthomas resembling HoFH but plasma cholesterol
      levels are normal to mildly elevated (with elevated cholestanol levels) associated with neurological,
      cognitive, and ophthalmic symptoms.
    explanation: >-
      Clinical and biochemical distinction.
- name: Secondary hypercholesterolemia
  description: >-
    Acquired disorders and medications can mimic or worsen an inherited lipid phenotype.
  distinguishing_features:
  - Assess thyroid, renal and hepatic disease, diabetes, obesity and relevant medications alongside inherited causes.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf
    reference_title: "https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Hypercholesterolemia secondary to acquired conditions including obesity, diabetes mellitus, obstructive
      liver disease, hypothyroidism, drugs (e.g., steroids), or kidney disease can also be associated with
      laboratory findings similar to those of FH
    explanation: >-
      GeneReviews acquired differential; not a classification of ARH as environmental disease.
experimental_models:
- name: Patient-derived primary lymphocytes
  experimental_model_type: PRIMARY_CELL_CULTURE
  cell_source: Primary lymphocytes from 28 genetically characterized ARH patients and 11 controls
  publication: PMID:27079874
  description: >-
    Mevastatin-treated lymphocytes exposed to recombinant PCSK9 with or without alirocumab. Surface receptor
    expression is higher but uptake lower than controls, showing why receptor abundance is not synonymous with
    function.
  modeled_mechanisms:
  - target: Impaired Clathrin-Mediated Endocytosis of the Hepatocyte LDL Receptor
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Reduced cellular LDL uptake reproduces an ARH endocytic defect in lymphocytes.
    limitations: >-
      The target names hepatocytes; this nonhepatic assay informs the shared defect but does not measure hepatic
      clearance or prove clinical antibody efficacy.
    evidence:
    - reference: PMID:27079874
      reference_title: Proprotein Convertase Subtilisin Kexin Type 9 Inhibition for Autosomal Recessive Hypercholesterolemia-Brief Report.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: >-
        Fluorescent LDL cellular uptake, also measured by flow cytometry, was reduced in ARH lymphocytes compared
        with control lymphocytes.
      explanation: >-
        Patient-cell uptake measurement, distinct from plasma LDL-C response.
    readouts:
    - name: Fluorescent LDL uptake
      target: Impaired Clathrin-Mediated Endocytosis of the Hepatocyte LDL Receptor
      direction: DECREASED
      description: >-
        Reduced cellular LDL uptake reproduces an ARH endocytic defect in lymphocytes.
      evidence:
      - reference: PMID:27079874
        reference_title: Proprotein Convertase Subtilisin Kexin Type 9 Inhibition for Autosomal Recessive Hypercholesterolemia-Brief Report.
        supports: SUPPORT
        evidence_source: IN_VITRO
        quote_role: PRIMARY_RESULT
        snippet: >-
          Fluorescent LDL cellular uptake, also measured by flow cytometry, was reduced in ARH lymphocytes
          compared with control lymphocytes.
        explanation: >-
          Patient-cell uptake measurement, distinct from plasma LDL-C response.
- name: Polarized WIF-B hepatocytes
  experimental_model_type: CELL_LINE
  cell_source: Polarized WIF-B hepatocyte cell line with recombinant ARH domain constructs
  publication: PMID:16179341
  description: >-
    Domain perturbation tests the receptor-binding PTB domain and clathrin/AP-2 interactions needed for LDLR
    clustering and internalization.
  modeled_mechanisms:
  - target: Impaired Clathrin-Mediated Endocytosis of the Hepatocyte LDL Receptor
    relationship: PERTURBS
    fidelity: MODERATE
    description: >-
      ARH PTB integrity and at least one clathrin/AP-2 interaction are required for clustering and internalization.
    limitations: >-
      Engineered cell system; abstract-only access limits detailed protocol assessment.
    evidence:
    - reference: PMID:16179341
      reference_title: The modular adaptor protein autosomal recessive hypercholesterolemia (ARH) promotes low density lipoprotein receptor clustering into clathrin-coated pits.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: >-
        The phosphotyrosine binding domain of ARH plus either the clathrin box or the AP-2 binding region were
        required for both clustering and internalization of the LDLR.
      explanation: >-
        Domain perturbation in polarized cells.
- name: Primary Arh-knockout mouse hepatocytes
  experimental_model_type: PRIMARY_CELL_CULTURE
  cell_source: Fresh primary hepatocytes from Arh- and Ldlr-knockout and control mice
  publication: PMID:17200716
  description: >-
    Short-term culture distinguishes LDL and beta-VLDL uptake. Additional LRP deletion and heparinase experiments
    did not abolish preserved beta-VLDL uptake; high-affinity antibody binding or LDL aggregation alone did
    not reproduce it.
  modeled_mechanisms:
  - target: Preserved Hepatic VLDL Remnant Uptake
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      ARH-deficient hepatocytes internalize beta-VLDL whereas LDLR-deficient cells do not.
    limitations: >-
      Ligand preparation and culture duration can change assay behavior; the precise ARH-independent entry
      machinery remains unresolved.
    evidence:
    - reference: PMID:17200716
      reference_title: Disruption of LDL but not VLDL clearance in autosomal recessive hypercholesterolemia.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: >-
        Consistent with these findings, hepatocytes from Arh(-/-) mice (but not Ldlr(-/-) mice) internalized
        beta-migrating VLDL (beta-VLDL).
      explanation: >-
        Isolated hepatocyte experiment, not an in-vivo uptake measurement.
    readouts:
    - name: Beta-VLDL internalization relative to Ldlr knockout
      target: Preserved Hepatic VLDL Remnant Uptake
      direction: INCREASED
      description: >-
        ARH-deficient hepatocytes internalize beta-VLDL whereas LDLR-deficient cells do not.
      evidence:
      - reference: PMID:17200716
        reference_title: Disruption of LDL but not VLDL clearance in autosomal recessive hypercholesterolemia.
        supports: SUPPORT
        evidence_source: IN_VITRO
        quote_role: PRIMARY_RESULT
        snippet: >-
          Consistent with these findings, hepatocytes from Arh(-/-) mice (but not Ldlr(-/-) mice) internalized
          beta-migrating VLDL (beta-VLDL).
        explanation: >-
          Isolated hepatocyte experiment, not an in-vivo uptake measurement.
- name: Patient skin fibroblasts with DAB2 depletion
  experimental_model_type: PRIMARY_CELL_CULTURE
  cell_source: Cultured skin fibroblasts from ARH patients and controls, with DAB2 siRNA and murine DAB2 rescue
  publication: PMID:17761685
  description: >-
    Baseline LDLR activity is preserved. DAB2 depletion reduces receptor protein and uptake selectively in
    ARH cells, without reduced LDLR mRNA; murine DAB2 rescues the phenotype. Pulse labeling favors altered
    protein synthesis, but unblocked degradation is not completely excluded. This does not directly demonstrate
    DAB2 compensation solely at endocytosis.
  evidence:
  - reference: PMID:17761685
    reference_title: Adaptor protein disabled-2 modulates low density lipoprotein receptor synthesis in fibroblasts from patients with autosomal recessive hypercholesterolaemia.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: >-
      SiRNA-depletion of Dab2 profoundly reduced LDL-receptor activity in ARH fibroblasts as a result of profound
      reduction in LDL-receptor protein, but not mRNA; heterologous expression of murine Dab2 reversed this
      effect.
    explanation: >-
      Protein loss confounds an interpretation as a pure internalization defect.
discussions:
- discussion_id: arh_dab2_cell_context
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: What permits fibroblast LDL uptake when LDLRAP1 is absent?
  attaches_to:
  - pathophysiology#Impaired Clathrin-Mediated Endocytosis of the Hepatocyte LDL Receptor
  - experimental_models#Patient skin fibroblasts with DAB2 depletion
  rationale: >-
    DAB2 abundance differs between fibroblasts and lymphocytes. However, DAB2 depletion in patient fibroblasts
    reduced receptor protein itself, so the experiment cannot isolate redundant endocytosis. A translation-related
    role was proposed; altered degradation outside the tested pathways remains possible. HeLa double-depletion
    results cannot substitute for patient-fibroblast behavior.
  evidence:
  - reference: url:https://oup.silverchair-cdn.com/article-minimal/582819
    reference_title: "https://oup.silverchair-cdn.com/article-minimal/582819"
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: >-
      Clearly, our original intention to determine whether or not Dab2 facilitates LDL-receptor internalization
      in ARH fibroblasts was not possible from our data.
    explanation: >-
      The authors explicitly limit the mechanistic inference.
- discussion_id: arh_remnant_entry
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: Which machinery supports ARH-independent VLDL-remnant uptake and how much does it modify human disease?
  attaches_to:
  - pathophysiology#Preserved Hepatic VLDL Remnant Uptake
  rationale: >-
    Mouse and isolated-hepatocyte experiments establish retained LDLR-dependent remnant uptake. Simple ligand
    affinity or clustering and the tested LRP/heparan-sulfate alternatives do not explain it. One human kinetic
    study supports increased direct remnant removal, but cannot establish its contribution across LDLRAP1 genotypes
    or treatment responses.
  evidence:
  - reference: PMID:22157599
    reference_title: "Altered metabolism of low-density lipoprotein and very-low-density lipoprotein remnant in autosomal recessive hypercholesterolemia: results from stable isotope kinetic study in vivo."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      In contrast, the direct removal of very-low-density lipoprotein remnant was significantly greater in
      ARH than those in control subjects (47.5 versus 2±2%).
    explanation: >-
      One patient versus seven controls; does not define a population-wide fraction.
clinical_trials:
- name: NCT00730236
  phase: PHASE_III
  status: COMPLETED
  description: >-
    Completed single-arm phase III lomitapide study in 29 adults with clinical or functional HoFH. Stable background
    therapy was maintained through week 26; mean LDL-C reduction was 50%. The trial supports class-level efficacy
    and safety monitoring, not a separately estimated LDLRAP1 treatment effect. Eligibility allowed causative
    functional alleles and did not require an abnormal fibroblast assay in every participant.
  notes: >-
    Phase, completion status, enrollment and eligibility checked against the ClinicalTrials.gov API on 2026-09-23.
    The cached registry excerpt contains the stated objectives.
  evidence:
  - reference: clinicaltrials:NCT00730236
    reference_title: A Phase III Study of Microsomal Triglyceride Transfer Protein (MTP) Inhibitor AEGR-733 in Patients With Homozygous Familial Hypercholesterolemia on Current Lipid-lowering Therapy
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: PRIMARY_RESULT
    snippet: >-
      The goal of this trial is to study the effects of AEGR-733 on LDL cholesterol, other lipids as well as
      measures of safety over the long-term.
    explanation: >-
      Registry objective; published results are distinguished from planned endpoints.
  - reference: PMID:23122768
    reference_title: "Efficacy and safety of a microsomal triglyceride transfer protein inhibitor in patients with homozygous familial hypercholesterolaemia: a single-arm, open-label, phase 3 study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      Mean LDL-C decreased from 8·69 ± 2·95 mmol/L at baseline to 4·34 ± 2·48 mmol/L) at the end of the efficacy
      phase (week 26), a statistically significant percent change from baseline (−50%, 95% CI −62, −39, p<0·001)
      (table 1 and figure 1).
    explanation: >-
      Pooled HoFH phase III result; this is not an LDLRAP1-specific estimate.
- name: NCT03399786
  phase: PHASE_III
  status: COMPLETED
  description: >-
    Completed randomized placebo-controlled phase III ELIPSE trial in 65 patients aged at least 12 years with
    HoFH on stable therapy. At 24 weeks, evinacumab lowered LDL-C 47.1%, versus a 1.9% increase on placebo.
    These are pooled HoFH results, not an ARH-specific effect size.
  notes: >-
    Phase, completion status, enrollment and eligibility checked against the ClinicalTrials.gov API on 2026-09-23.
    The cached registry excerpt contains the stated objectives.
  evidence:
  - reference: clinicaltrials:NCT03399786
    reference_title: "A Randomized, Double-blind, Placebo-controlled, Parallel-group Study to Evaluate the Efficacy and Safety of Evinacumab in Patients With Homozygous Familial Hypercholesterolemia"
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: PRIMARY_RESULT
    snippet: >-
      The primary objective of the study is to demonstrate the reduction of low-density lipoprotein cholesterol
      (LDL-C) by evinacumab intravenously (IV) in comparison to placebo after 24 weeks in patients with homozygous
      familial hypercholesterolemia (HoFH).
    explanation: >-
      Registry objective; published results are distinguished from planned endpoints.
  - reference: PMID:32813947
    reference_title: Evinacumab for Homozygous Familial Hypercholesterolemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      At week 24, patients in the evinacumab group had a relative reduction from baseline in the LDL cholesterol
      level of 47.1%, as compared with an increase of 1.9% in the placebo group,
    explanation: >-
      Pooled randomized HoFH result; does not isolate the ARH response.
- name: NCT03409744
  phase: PHASE_III
  status: COMPLETED
  description: >-
    Completed open-label phase III long-term evinacumab study, with 116 participants aged at least 12 years.
    The 2026 analysis identifies two LDLRAP1 participants among 55 with identical biallelic LDLR or LDLRAP1
    variants. Reported week-8 and week-104 subgroup reductions combine both genes and cannot quantify the LDLRAP1-specific
    response.
  notes: >-
    Phase, completion status, enrollment and eligibility checked against the ClinicalTrials.gov API on 2026-09-23.
    The cached registry excerpt contains the stated objectives.
  evidence:
  - reference: clinicaltrials:NCT03409744
    reference_title: An Open-Label Study to Evaluate the Long-Term Safety and Efficacy of Evinacumab in Patients With Homozygous Familial Hypercholesterolemia
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: PRIMARY_RESULT
    snippet: >-
      To evaluate the long-term safety and tolerability of evinacumab in patients with Homozygous Familial
      Hypercholesterolemia (HoFH)
    explanation: >-
      Registry objective; published results are distinguished from planned endpoints.
  - reference: PMID:41671678
    reference_title: "Efficacy of evinacumab by genotype and low-density lipoprotein receptor function in patients with homozygous familial hypercholesterolaemia: A subanalysis from the ELIPSE open-label extension study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: >-
      At baseline, 55 (47.4%) had either identical bi-allelic variants in LDLR (n = 53) or LDLRAP1 (n = 2),
      and 41 (35.3%) had different bi-allelic LDLR variants.
    explanation: >-
      Two LDLRAP1 patients were included in the extension; pooled LDLR/LDLRAP1 response is not a gene-specific
      estimate.

📚

References & Deep Research

References

PMID:24404629

Familial Hypercholesterolemia.

No top-level findings curated for this source.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf

https://www.ncbi.nlm.nih.gov/sites/books/NBK174884/pdf/Bookshelf_NBK174884.pdf

1 finding

Full GeneReviews Familial Hypercholesterolemia chapter, corresponding to PMID:24404629.

PMID:32011344

Autosomal recessive hypercholesterolemia: update for 2020.

No top-level findings curated for this source.

PMID:29153781

Genetic epidemiology of autosomal recessive hypercholesterolemia in Sicily: Identification by next-generation sequencing of a new kindred.

No top-level findings curated for this source.

PMID:11326085

Autosomal recessive hypercholesterolemia caused by mutations in a putative LDL receptor adaptor protein.

No top-level findings curated for this source.

PMID:30777337

A new variant (c.1A>G) in LDLRAP1 causing autosomal recessive hypercholesterolemia: Characterization of the defect and response to PCSK9 inhibition.

No top-level findings curated for this source.

PMID:16179341

The modular adaptor protein autosomal recessive hypercholesterolemia (ARH) promotes low density lipoprotein receptor clustering into clathrin-coated pits.

No top-level findings curated for this source.

PMID:27079874

Proprotein Convertase Subtilisin Kexin Type 9 Inhibition for Autosomal Recessive Hypercholesterolemia-Brief Report.

No top-level findings curated for this source.

PMID:17761685

Adaptor protein disabled-2 modulates low density lipoprotein receptor synthesis in fibroblasts from patients with autosomal recessive hypercholesterolaemia.

No top-level findings curated for this source.

PMID:22157599

Altered metabolism of low-density lipoprotein and very-low-density lipoprotein remnant in autosomal recessive hypercholesterolemia: results from stable isotope kinetic study in vivo.

No top-level findings curated for this source.

PMID:29348020

Autosomal Recessive Hypercholesterolemia: Long-Term Cardiovascular Outcomes.

No top-level findings curated for this source.

url:https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf

https://gredos.usal.es/bitstream/handle/10366/155662/1801%20Colesterol%20retrospectivo.pdf

1 finding

D’Erasmo et al., 2018 JACC retrospective study of 52 ARH patients, PMID:29348020.

PMID:17200716

Disruption of LDL but not VLDL clearance in autosomal recessive hypercholesterolemia.

No top-level findings curated for this source.

PMID:42730734

Autosomal Recessive Hypercholesterolemia Due to a Novel Homozygous LDLRAP1 Frameshift Mutation.

No top-level findings curated for this source.

PMID:37130090

2023 Update on European Atherosclerosis Society Consensus Statement on Homozygous Familial Hypercholesterolaemia: new treatments and clinical guidance.

No top-level findings curated for this source.

PMID:36072671

Efficacy of Long-Term Treatment of Autosomal Recessive Hypercholesterolemia With Lomitapide: A Subanalysis of the Pan-European Lomitapide Study.

No top-level findings curated for this source.

url:https://air.unimi.it/retrieve/handle/2434/1224076/3272602/1-s2.0-S1933287426000401-main.pdf

https://air.unimi.it/retrieve/handle/2434/1224076/3272602/1-s2.0-S1933287426000401-main.pdf

1 finding

2026 report: LDL-C target achievement after adding evinacumab in 2 patients with autosomal recessive hypercholesterolemia; DOI:10.1016/j.jacl.2026.02.007.

PMID:41671678

Efficacy of evinacumab by genotype and low-density lipoprotein receptor function in patients with homozygous familial hypercholesterolaemia: A subanalysis from the ELIPSE open-label extension study.

No top-level findings curated for this source.

url:https://oup.silverchair-cdn.com/article-minimal/582819

https://oup.silverchair-cdn.com/article-minimal/582819

1 finding

Full scientific text of Eden et al. 2007, corresponding to PMID:17761685.

clinicaltrials:NCT00730236

A Phase III Study of Microsomal Triglyceride Transfer Protein (MTP) Inhibitor AEGR-733 in Patients With Homozygous Familial Hypercholesterolemia on Current Lipid-lowering Therapy

No top-level findings curated for this source.

clinicaltrials:NCT03399786

A Randomized, Double-blind, Placebo-controlled, Parallel-group Study to Evaluate the Efficacy and Safety of Evinacumab in Patients With Homozygous Familial Hypercholesterolemia

No top-level findings curated for this source.

clinicaltrials:NCT03409744

An Open-Label Study to Evaluate the Long-Term Safety and Efficacy of Evinacumab in Patients With Homozygous Familial Hypercholesterolemia

No top-level findings curated for this source.

PMID:23122768

Efficacy and safety of a microsomal triglyceride transfer protein inhibitor in patients with homozygous familial hypercholesterolaemia: a single-arm, open-label, phase 3 study.

No top-level findings curated for this source.

PMID:32813947

Evinacumab for Homozygous Familial Hypercholesterolemia.

No top-level findings curated for this source.

url:https://www.frontiersin.org/journals/genetics/articles/10.3389/fgene.2022.937750/pdf

https://www.frontiersin.org/journals/genetics/articles/10.3389/fgene.2022.937750/pdf

1 finding

Publisher PDF of PMID:36072671; Tables 1 and 2 supply the clinical and hepatic-fat data omitted from the XML extraction.

Deep Research

Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.

Evaluations and curation notes (1)

Create: Autosomal Recessive Hypercholesterolemia · 2026-09-03T15:26:33Z · View source

Created the LDLRAP1/ARH recessive hypercholesterolemia entry (MONDO:0011374) end-to-end. entry_type DISEASE: distinct recessive gene (LDLRAP1) and mechanism (loss of the cytosolic adaptor bridging a structurally normal LDL receptor to clathrin-mediated endocytosis), kept separate from the dominant FH entries (LDLR/APOB/PCSK9). Curated a full pathophysiology chain (biallelic LDLRAP1 LOF -> loss of ARH adaptor bridging -> impaired hepatocyte LDLR clathrin-mediated endocytosis, liver-restricted -> impaired hepatic LDL clearance -> lifelong LDL-C elevation -> premature ASCVD and extravascular cholesterol deposition), 8 phenotypes (hypercholesterolemia, increased LDL-C, tendon xanthoma, premature coronary atherosclerosis, MI, aortic valve stenosis, xanthelasma, corneal arcus), LDLRAP1 genetic block with AR inheritance and Sardinian ARH1/ARH2 founder alleles, structured prevalence (ultra-rare; Sardinia/Sicily founder), LDL-C biomarker, and four treatments (statin+ezetimibe, lomitapide, lipoprotein apheresis, PCSK9 inhibitor) with target_mechanisms and therapeutic_modality. Evidence: PMID:11326085 (Garcia 2001 gene discovery), PMID:16179341 (adaptor/clathrin mechanism), PMID:32011344 (ARH 2020 review), PMID:36072671 (Pan-European lomitapide subanalysis), PMID:27079874 (PCSK9i in ARH), PMID:29153781 (Sicily/Sardinia epidemiology), PMID:24404629 (FH GeneReviews, class-level, tagged GeneReviews). Deep-research fallback: automated claude_code run produced no report (host filesystem ENOSPC, concurrent sibling run); performed a manual PubMed sweep instead, recorded in research/. Validated to green: just validate (49/49 snippets), validate-terms, validate-disorders, check-causal-targets, check-duplicate-keys, check-entity-refs, check-qualifier-terms, check-enum-values, snippet-grading/length/title/folded-hyphens all pass. Closes #10721; deletes stub.

Claude Code ▸

Autosomal Recessive Hypercholesterolemia (ARH) — manual research sweep

Summary

ARH (hypercholesterolemia, familial, 4; MONDO:0011374; OMIM:603813) is a recessively inherited monogenic hypercholesterolemia caused by biallelic loss-of-function variants in LDLRAP1 (hgnc:18640), which encodes the LDL receptor adaptor protein (ARH). ARH is a cytosolic adaptor whose phosphotyrosine binding (PTB) domain recognizes the FDNPVY/NPxY motif in the LDL receptor cytoplasmic tail and whose clathrin-box and AP-2-binding regions bridge the bound receptor to the clathrin endocytic machinery. Its function is tissue specific — required in hepatocytes but not fibroblasts (where Dab2 is redundant). Loss of ARH leaves a structurally normal LDL receptor that reaches the hepatocyte surface but cannot cluster into clathrin-coated pits and internalize LDL. Hepatic LDL clearance fails, plasma LDL-C is markedly and lifelong elevated (homozygous-FH magnitude), and patients develop tendon xanthomas, premature ASCVD, and aortic valve stenosis. ARH behaves as a phenocopy of homozygous FH. It is ultra-rare, with a Sardinian founder concentration (ARH1/ARH2 alleles). Because conventional receptor-dependent therapies (statins, PCSK9 inhibitors) act by increasing receptor number and the ARH receptor cannot internalize LDL, LDL-C stays far from target on conventional therapy; LDL-receptor-independent approaches (lomitapide, ezetimibe, lipoprotein apheresis) retain efficacy.

Mechanism chain (as curated)

Biallelic LDLRAP1 loss-of-function → loss of ARH adaptor bridging of the LDL receptor to clathrin (PTB↔NPxY, clathrin/AP-2) → impaired clathrin-mediated endocytosis of the hepatocyte LDL receptor (liver-restricted; Dab2 redundant in fibroblasts) → impaired hepatic clearance of plasma LDL → lifelong LDL-C elevation → premature ASCVD (coronary atherosclerosis, aortic valve stenosis) and extravascular cholesterol deposition (tendon xanthoma, xanthelasma, corneal arcus).

References used (all fetched and snippet-verified against the local cache)

PMID:11326085 — Garcia et al., Science 2001. Founding gene-discovery paper: maps ARH to 1p35, identifies six LDLRAP1 mutations, PTB domain binding NPxY, tissue-specific role (liver not fibroblasts). (HUMAN_CLINICAL)
PMID:16179341 — Michaely et al., J Biol Chem 2005. ARH bridges the LDLR tail to clathrin/AP-2; PTB + clathrin-box/AP-2 required for LDLR clustering and internalization; cell-type-specific endocytic defect. *(IN_VITRO / WIF-B hepatocytes
Arh−/− mouse confirmation)*
PMID:32011344 — D'Erasmo et al., Curr Opin Lipidol 2020. ARH update: ultrarare, LDLRAP1, recessive, uniformly LOF; phenocopy of HoFH; elevated ASCVD and aortic valve stenosis risk; LDL-C far from target on conventional therapy; lomitapide as a new opportunity. (HUMAN_CLINICAL review)
PMID:36072671 — D'Erasmo et al., Front Genet 2022. Pan-European Lomitapide Study ARH subanalysis (n=9): mechanism (LDLRAP1 cytosolic adaptor, hepatocyte LDL internalization), ~90% xanthomata, ASCVD comparable to HoFH, PCSK9i efficacy disputed (residual-LDLR-dependent), lomitapide LDLR-independent → median on-treatment LDL-C 101.7 mg/dL (60.4% reduction). (HUMAN_CLINICAL cohort; full text cached)
PMID:27079874 — Cameron et al./Tveten et al., ATVB 2016. PCSK9 inhibition (alirocumab) in ARH lymphocytes: surface LDLR higher in ARH than control; PCSK9's effect on LDLR expression/function less pronounced in ARH; partial potential in some patients. (IN_VITRO)
PMID:29153781 — Averna group, J Clin Lipidol 2018. Genetic epidemiology of ARH in Sicily/Sardinia: high mutated-allele frequency in Sardinia, ARH1/ARH2 founder alleles, ARH1 allele frequency 0.02% in Sicily, extremely rare outside Sardinia. (HUMAN_CLINICAL)
PMID:24404629 — GeneReviews: Familial Hypercholesterolemia (Adam et al.). Class-level FH chapter used for inheritance (biallelic LDLRAP1, autosomal recessive, obligate-carrier parents), clinical stigmata (MI, xanthelasma, corneal arcus), and management (LDL apheresis in established CAD). Tagged GeneReviews in the entry. (HUMAN_CLINICAL / OTHER for management)

Reference Validation

All seven references were fetched with just fetch-reference and every evidence snippet in the curated entry was verified as an exact substring against the local references_cache/ (49/49 snippets verified by just validate / just validate-disorders). No fabricated identifiers; PMIDs preferred throughout (no DOI-only citations).

Term Validation

All ontology CURIEs bound in the entry resolved against their ontologies and passed just validate-terms. The one term not previously in the local cache (GO:0035615, clathrin-cargo adaptor activity) was independently confirmed reachable from GO:0003674 (molecular_function) via local OAK before binding.

Named Entity Confusion preflight

The hypercholesterolemia series is a high-NEC-risk numbered/lettered class (FH1/LDLR, familial defective apoB-100/APOB, ADH3/PCSK9, ARH/LDLRAP1). Every mechanistic and clinical claim here is anchored on LDLRAP1/ARH publications; the shared distal LDL-to-plaque cascade is deliberately not re-derived from the dominant-FH entries. The MONDO term MONDO:0011374 (hypercholesterolemia, familial, 4) and OMIM:603813 both key on the LDLRAP1/ARH recessive entity.

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References & Deep Research

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Deep Research

Autosomal Recessive Hypercholesterolemia (ARH) — manual research sweep

Summary

Mechanism chain (as curated)

References used (all fetched and snippet-verified against the local cache)

Reference Validation

Term Validation

Named Entity Confusion preflight