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Classifications

Harrison's Part

ICIMD (Inherited Metabolic Disorders)

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Inheritance

1

Autosomal Dominant HP:0000006

A single pathogenic LDLR allele is sufficient to raise LDL cholesterol from birth, and transmission is autosomal dominant. Penetrance for the biochemical phenotype is essentially complete; penetrance for clinical cardiovascular events is age-dependent and modified by treatment, Lp(a), and conventional risk factors, so expressivity is variable. The trait is more precisely co-dominant than dominant, because two pathogenic alleles produce a substantially more severe phenotype than one - the gene-dosage relation curated under has_subtypes on the umbrella entry.

Autosomal dominant inheritance Penetrance: COMPLETE Expressivity: VARIABLE

Show evidence (3 references)

PMID:24404629 SUPPORT Human Clinical

"APOB-, LDLR-, and PCSK9-related FH are inherited in an autosomal dominant manner."

GeneReviews states the mode of inheritance for LDLR-related FH explicitly.

PMID:24404629 SUPPORT Human Clinical

"Each child of an individual with a heterozygous pathogenic variant in APOB, LDLR, or PCSK9 has a 50% chance of inheriting the pathogenic variant and having FH."

States the 50% transmission risk used in genetic counselling.

PMID:1301956 SUPPORT Human Clinical

"Mutations disrupting the function of this receptor produce autosomal dominant familial hypercholesterolemia (FH)."

The founding molecular-genetic account of the disease attributes dominant FH to LDLR mutation.

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Discussions and Knowledge Gaps

2

What residual LDL receptor activity threshold actually separates patients who will respond to receptor-directed therapy from those who will not; is that threshold the same for statins as for PCSK9-directed agents; and do statins in fact lose effect in receptor-negative disease at all, given that this has never been tested against an untreated null-genotype stratum?

KNOWLEDGE GAP residual_ldlr_activity_response_threshold

Attached to

pathophysiology#Reduced Functional Hepatic LDL Receptor Activity

The entry curates residual receptor activity as the quantity that gates receptor-dependent LDL lowering, and the direction of that relation is well evidenced. The threshold is not. "Null" has been defined at under 2% of wild-type activity in functional-assay literature and operationalized as high as 15% in trial protocols, and the pivotal genotype-stratified observation rests on two receptor-negative patients. Nor is it established that statins (which act transcriptionally, on synthesis) and PCSK9-directed agents (which act post-translationally, on degradation and recycling) share a threshold - a class 1 null allele leaves nothing for either to act on, but a class 5 recycling-defective allele might respond differently to the two mechanisms. The asymmetry is sharper than that: the only genotype-stratified test in this entry is of a PCSK9 antibody, and its two receptor-negative patients were already on stable statin therapy at enrolment, so statins have never been shown here to fail in receptor-negative disease - and the entry's own cited mechanistic review reports statins helping both homozygous and heterozygous patients. The null-genotype ceiling for statins is therefore inferred from mechanism rather than demonstrated. Without a threshold, and without a drug-class-specific test, the relation informs reasoning but does not yet support a decision rule.

Proposed experiments

Prospective genotype-stratified response study with quantified residual receptor activity

residual_activity_response_threshold_study

In a homozygous and compound-heterozygous FH cohort, measure residual LDLR activity for each proband's allele pair in a standardized cell-based uptake assay, then relate that quantity to the achieved LDL-C reduction on a high-intensity statin and, separately, on a PCSK9 monoclonal antibody. The readout is whether a single activity threshold predicts response for both drug classes or whether the classes have different thresholds.

Does the arterial disease of any available LDLR-deficient animal model reproduce the human course closely enough to test interventions aimed at events rather than at LDL levels?

HUMAN MODEL MISMATCH ldlr_model_arterial_translation

Attached to

pathophysiology#Premature Atherosclerotic Cardiovascular Events

The clearance defect translates cleanly across species - the Ldlr-/- mouse reproduces it and adenoviral receptor restoration reverses it - but the arterial arm does not. Murine lipoprotein metabolism is apoB48- and HDL-dominated, so the mouse does not reach human homozygous-FH cholesterol levels and develops limited spontaneous atherosclerosis on chow. The WHHL rabbit is far closer in lipoprotein physiology and does develop coronary disease, but the strain history reports that lesion rupture there requires secondary mechanical forces such as spasm, so it is not a clean analogue of spontaneous human plaque rupture. The genome-edited LDLR-knockout cynomolgus monkey reaches human-like lipid levels and develops xanthoma within a year, but the published cohort is six founder animals with short follow-up and possible editing mosaicism. Each model is informative for the node it was curated against and none is currently adequate for event-endpoint intervention studies.

Proposed experiments

Cross-species comparison of plaque composition and rupture triggers under matched cumulative LDL exposure

cross_species_plaque_rupture_comparison

Compare coronary and aortic lesion composition, fibrous cap thickness, and spontaneous versus provoked rupture between LDLR-deficient rabbits, LDLR-knockout primates, and human FH imaging cohorts matched on cumulative LDL-C exposure rather than on age, to establish which model, if any, supports event-level extrapolation.

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Pathophysiology

14

LDLR Loss-of-Function Variant

A germline pathogenic variant in LDLR at 19p13.2. The gene spans more than 45 kb in 18 exons whose boundaries map onto the receptor's functional modules - the cysteine-rich ligand-binding repeats, the EGF-precursor homology domain, the O-linked sugar domain, the transmembrane segment and the cytoplasmic tail - so the mutated exon largely predicts which step of the receptor's itinerary is broken. More than 2300 unique FH-associated LDLR variants have been catalogued, spanning missense, nonsense, frameshift, splice, promoter and exon-level copy-number changes. This node is the single lesion; the five nodes immediately downstream are the alternative steps at which it can act.

LDLR hgnc:6547

Genetic context LDLR hgnc:6547 variant_origin: GERMLINE functional_impact_category: LOSS_OF_FUNCTION

The variant consequence is loss of function - fewer functional LDL receptors reach or persist on the hepatocyte surface. Recorded on the genetic context rather than as a Descriptor modifier because the claim is about the consequence of an allele. The severity of that loss is allele-specific and is the subject of the class nodes downstream.

low-density lipoprotein particle receptor activity GO:0005041 ↓ DECREASED

liver UBERON:0002107

Downstream

Absent LDL Receptor Synthesis Null (class 1) alleles - large deletions removing the promoter, nonsense and frameshift changes, and alleles producing no detectable protein - abolish receptor synthesis outright.

Impaired ER-to-Golgi Transport of the LDL Receptor Class 2 alleles allow synthesis but the receptor misfolds and is retained in the endoplasmic reticulum instead of maturing through the Golgi.

Defective LDL Binding at the Hepatocyte Surface Class 3 alleles produce a receptor that reaches the surface but binds apoB-100 poorly, typically through changes in the cysteine-rich ligand-binding repeats or in the EGF-precursor domain that positions them.

Defective Clustering in Clathrin-Coated Pits Class 4 alleles disable the cytoplasmic internalization signal, so a fully synthesized, surface-expressed, ligand-competent receptor never enters the cell.

Defective Endosomal Ligand Release and Receptor Recycling Class 5 alleles allow binding and internalization but the receptor fails to release LDL in the acidified endosome, so receptor and ligand are degraded together instead of the receptor returning to the surface.

Show evidence (3 references)

PMID:1301956 SUPPORT Human Clinical

"Mutations disrupting the function of this receptor produce autosomal dominant familial hypercholesterolemia (FH)."

States the causal relation that defines this entry's trigger node.

PMID:2988123 SUPPORT In Vitro

"This gene is more than 45 kilobases in length and contains 18 exons, most of which correlate with functional domains previously defined at the protein level."

Establishes the exon-to-domain correspondence that underlies the structure-function mapping used by the class nodes downstream.

PMID:34906454 SUPPORT Human Clinical

"In this study, we provide consensus recommendations for the most common FH-associated gene, LDLR, where >2300 unique FH-associated variants have been identified."

Quantifies the size of the LDLR allelic series curated by this entry.

Absent LDL Receptor Synthesis

The class 1 (null, receptor-negative) branch. No immunodetectable LDL receptor protein is made, because the allele deletes the promoter, produces no mRNA, or produces mRNA that yields no protein. This is the most severe branch and the one with the least therapeutic room: there is no receptor to upregulate. In clinical trials of homozygous disease it is operationalized as "null-null" or receptor-negative status.

hepatocyte CL:0000182

low-density lipoprotein particle receptor activity GO:0005041 ∅ ABSENT

Downstream

Reduced Functional Hepatic LDL Receptor Activity Absent receptor protein is the limiting case of reduced receptor activity.

Show evidence (2 references)

PMID:3343347 SUPPORT In Vitro

"Four of the alleles produced no mRNA. Three of these four mRNA- alleles had large deletions ranging from 6 to 20 kb that eliminated the promoter region of the gene."

Documents the molecular routes to complete absence of receptor protein.

PMID:32813947 SUPPORT Human Clinical

"This disorder is associated with genetic variants that result in virtually absent (null-null) or impaired (non-null) LDL-receptor activity."

Shows the null versus non-null distinction being used as a formal stratifier in a contemporary phase 3 trial.

Impaired ER-to-Golgi Transport of the LDL Receptor

The class 2 (transport-defective) branch. The receptor is synthesized but misfolds and is retained in the endoplasmic reticulum rather than being further glycosylated in the Golgi and delivered to the surface. Retention may be complete (class 2a) or partial (class 2b), and partial retention leaves residual surface receptor - which matters therapeutically, because residual receptor is what receptor-directed drugs act on.

hepatocyte CL:0000182

endoplasmic reticulum to Golgi vesicle-mediated transport GO:0006888 ↓ DECREASED

Downstream

Reduced Functional Hepatic LDL Receptor Activity A receptor stuck in the ER never reaches the surface, so it contributes nothing to LDL clearance regardless of whether its ligand-binding sequence is intact.

Show evidence (2 references)

PMID:32015373 SUPPORT In Vitro

"Of the analysed variants, we found six non-pathogenic LDLR variants and ten pathogenic variants distributed as follow: three class 3 variants; four class 2 variants; and three class 5 variants."

Assigns patient variants to the transport-defective class by functional assay.

PMID:25386756 SUPPORT In Vitro

"Additionally confocal microscopy allowed the assignment of different class mutation to the variants assayed."

Confirms that subcellular localization imaging is what distinguishes an ER-retained receptor from a surface-expressed one.

Defective LDL Binding at the Hepatocyte Surface

The class 3 (binding-defective) branch. Receptor reaches the surface in normal numbers but binds apoB-100-containing LDL with reduced affinity. Changes typically fall in the cysteine-rich ligand-binding repeats or in the EGF-precursor homology domain that holds them in a binding-competent conformation. This is the receptor-side mirror of the ligand-side defect curated in Familial_Defective_Apolipoprotein_B-100 - the same handshake fails, from the other side.

hepatocyte CL:0000182

low-density lipoprotein particle receptor binding GO:0050750 ↓ DECREASED

Downstream

Reduced Functional Hepatic LDL Receptor Activity A surface receptor that cannot capture its ligand removes no LDL, so functional receptor activity falls even though receptor abundance is normal.

Show evidence (2 references)

PMID:32015373 SUPPORT In Vitro

"They showed similar expression to wt LDLR but demonstrated deficient LDL binding."

The defining functional signature of the class 3 branch: receptor is expressed at normal levels yet binds LDL poorly, separating a binding defect from a synthesis or trafficking defect.

PMID:31106925 SUPPORT In Vitro

"All new LDLR variants found in our patients were functionally validated in CHO-ldlA7 cells. The LDLR activity was measured by flow cytometry and LDLR expression was detected by immunofluorescence."

Describes the paired activity/expression measurement that identifies a binding defect - normal expression with reduced activity.

Defective Clustering in Clathrin-Coated Pits

The class 4 (internalization-defective) branch. The cytoplasmic tail of the LDL receptor carries the signal that concentrates it in clathrin-coated pits; a change there leaves a receptor that is expressed and binds LDL normally but is distributed diffusely over the surface and enters the cell slowly. The founding example is patient J.D., whose receptor carries a tyrosine-to-cysteine substitution at residue 807. Because the LDLRAP1/ARH adaptor serves this same step, the recessive LDLRAP1 disease is the phenocopy of this branch acting in trans.

hepatocyte CL:0000182

clathrin-dependent endocytosis GO:0072583 ↓ DECREASED

Downstream

Reduced Functional Hepatic LDL Receptor Activity A receptor that binds LDL but does not internalize it does not clear it; the bound particle is not delivered to the lysosome.

Show evidence (2 references)

PMID:3955657 SUPPORT In Vitro

"Upon transfection into receptor-deficient hamster cells, the cDNA specified a receptor that bound LDL normally, but entered the cell slowly."

Separates binding from internalization experimentally - the defining observation for this class.

PMID:3955657 SUPPORT In Vitro

"Electron microscopy showed that this receptor was distributed diffusely over the cell surface, whereas the receptor produced by the normal cDNA was concentrated in coated pits."

Direct morphological evidence that the lesion is failure to cluster in clathrin-coated pits.

Defective Endosomal Ligand Release and Receptor Recycling

The class 5 (recycling-defective) branch. Binding and internalization are intact, but the receptor fails to release LDL when the endosome acidifies, so receptor and ligand traffic together to the lysosome and the receptor is consumed rather than returned to the surface. Each receptor therefore makes one round trip instead of many, and functional clearance capacity collapses even though synthesis is normal. This is also the step that PCSK9 subverts pharmacologically, which is why PCSK9-directed drugs raise receptor abundance in patients who still have recyclable receptor.

hepatocyte CL:0000182

receptor recycling GO:0001881 ↓ DECREASED

Downstream

Reduced Functional Hepatic LDL Receptor Activity Loss of recycling converts a reusable receptor into a single-use one, cutting the LDL particles cleared per receptor synthesized.

Show evidence (2 references)

PMID:32015373 SUPPORT In Vitro

"LDLR structure is organized in 5 different domains, including an EGF-precursor homology domain that plays a pivotal role in lipoprotein release and receptor recycling."

Localizes ligand release and recycling to a specific receptor domain.

PMID:32015373 SUPPORT In Vitro

"In this way, although the protein structure is not affected in LDLR expression or LDL binding and uptake activities, the alteration introduced by the asparagine is enough to cause a defect in recycling of the protein."

Isolates the class 5 defect: expression, binding and uptake are all intact and recycling alone fails, which is what distinguishes this branch from the synthesis, trafficking and binding branches.

Reduced Functional Hepatic LDL Receptor Activity

The convergence node of the allelic series. Whichever step is broken - synthesis, ER export, ligand binding, internalization, or recycling - the measurable output is the same: fewer LDL particles cleared per unit time by the hepatocyte. Functional assays report this as a single quantity (percentage of wild-type LDL uptake), which is why class assignment and residual activity are recorded separately: the class says *where* the itinerary breaks, the residual activity says *how much* capacity survives. Null alleles are conventionally under about 2% of normal activity, though trial protocols have operationalized "null" at thresholds as high as 15%.

hepatocyte CL:0000182

receptor-mediated endocytosis GO:0006898 ↓ DECREASED

low-density lipoprotein particle receptor activity GO:0005041 ↓ DECREASED

liver UBERON:0002107

Animal models

Ldlr-knockout mouse Mouse rescues Restoring hepatic LDL receptor expression by adenoviral delivery normalized the elevated IDL/LDL within four days, demonstrating that the receptor deficit is both necessary and sufficient for the phenotype in this model.

Downstream

Impaired Receptor-Mediated Clearance of Plasma LDL Hepatic LDL receptors perform most clearance of circulating LDL, so a fall in functional receptor activity directly lengthens LDL residence time in plasma.

Residual Receptor Activity Gates Receptor-Dependent LDL Lowering The same residual activity that sets the untreated LDL level also sets how much a receptor-directed drug can achieve, because those drugs act by increasing the number of functional receptors rather than by creating them.

Show evidence (2 references)

PMID:1301956 SUPPORT Human Clinical

"The low density lipoprotein (LDL) receptor is a cell surface transmembrane protein that mediates the uptake and lysosomal degradation of plasma LDL, thereby providing cholesterol to cells."

States the receptor function whose reduction this node represents.

PMID:32015373 SUPPORT In Vitro

"These results can be incorporated into clinical management of patients by helping guide the appropriate level of treatment intensity depending on the extent of loss of LDLR activity."

Treats residual LDLR activity as the single clinically actionable output of the allelic series.

Residual Receptor Activity Gates Receptor-Dependent LDL Lowering

The pharmacogenetic node, and the reason the allelic series is clinically actionable rather than merely descriptive. Statins lower intracellular cholesterol and thereby induce more LDL receptor; PCSK9 antibodies and inclisiran prevent or reduce PCSK9-mediated receptor degradation. Both families of drugs work by putting *more* receptor on the hepatocyte surface, so both require a receptor that can be made and can function. The genotype-stratified evidence below is for a PCSK9 antibody: in the two receptor-negative (null-null) homozygotes studied there was nothing to induce and the response was absent, while in receptor-defective homozygotes there was residual receptor and the response was preserved. Whether statins behave the same way in receptor-negative disease has not been tested here - the two null patients in that trial were already on stable statin therapy at enrolment - and the mechanisms differ (statins act transcriptionally on receptor synthesis, PCSK9-directed agents post-translationally on receptor degradation and recycling), so the statin/PCSK9 asymmetry is carried as an open question in the residual_ldlr_activity_response_threshold discussion rather than asserted. LDLR-independent agents - the MTP inhibitor lomitapide, the ANGPTL3 antibody evinacumab, and lipoprotein apheresis - bypass the receptor entirely and retain effect in null-null disease. This node is the target of the treatment entries curated below.

hepatocyte CL:0000182

liver UBERON:0002107

Animal models

LDLR-knockout cynomolgus monkey Cynomolgus monkey recapitulates Complete receptor knockout reproduces the drug-refractory phenotype that defines receptor-negative homozygous disease.

Show evidence (3 references)

PMID:24014831 SUPPORT Human Clinical

"No reduction was seen in the 2 receptor-negative patients."

The negative half of the relation - a receptor-directed drug does nothing when no receptor can be made.

PMID:24014831 SUPPORT Human Clinical

"Over the treatment periods, mean±SD LDL cholesterol reductions in the 6 LDL receptor-defective patients were 19.3±16% and 26.3±20% with 4- and 2-week dosing, respectively"

The positive half - the same drug in the same trial lowers LDL when residual receptor activity exists.

PMID:32813947 SUPPORT Human Clinical

"The LDL cholesterol level was lower in the evinacumab group than in the placebo group in patients with null-null variants (-43.4% vs. +16.2%) and in those with non-null variants (-49.1% vs. -3.8%)."

Shows the complementary case - an LDLR-independent mechanism works in both genotype strata, which is what makes the gating relation therapeutically consequential rather than merely prognostic.

Impaired Receptor-Mediated Clearance of Plasma LDL

Reduced hepatic receptor capacity lengthens the residence time of apoB-100-containing LDL and IDL in plasma. The defect is specific to the receptor's ligands: HDL clearance is unaffected, which is why the biochemical phenotype is an isolated elevation of LDL rather than a generalized dyslipidemia.

low-density lipoprotein particle clearance GO:0034383 ↓ DECREASED

liver UBERON:0002107

Animal models

Ldlr-knockout mouse Mouse recapitulates Directly measures the clearance defect that this node represents, in the cleanest possible genetic background - complete receptor absence.

Downstream

Lifelong Elevation of Plasma LDL Cholesterol Reduced clearance against unchanged production raises the steady-state plasma LDL concentration, from birth and for life.

Show evidence (2 references)

PMID:8183926 SUPPORT Model Organism

"LDLR(-/-) mice had a relatively isolated elevation in plasma LDL"

Shows that loss of the receptor produces a selective LDL clearance defect rather than a global lipoprotein abnormality.

PMID:8349823 SUPPORT Model Organism

"We conclude that the LDL receptor is responsible in part for the low levels of VLDL, IDL, and LDL in wild-type mice"

Attributes normal plasma LDL levels to receptor-mediated clearance.

Lifelong Elevation of Plasma LDL Cholesterol

The defining biochemical phenotype. Because the receptor defect is constitutional, LDL cholesterol is elevated from birth, so the arterial tree accumulates cholesterol exposure over decades rather than from midlife onward. Untreated heterozygotes typically exceed 190 mg/dL; biallelic disease often exceeds 400-500 mg/dL.

Downstream

Endothelial Dysfunction and Subendothelial LDL Retention Sustained high plasma LDL drives entry of apoB particles into the arterial intima and their retention on subendothelial proteoglycan - the initiating step of the shared atherogenesis programme.

Extravascular Cholesterol Deposition in Tendon, Skin, and Cornea The same circulating excess deposits outside the arterial wall, producing the classical stigmata. These are specific but insensitive, and are less often seen now that treatment begins earlier.

Show evidence (2 references)

PMID:24404629 SUPPORT Human Clinical

"A clinical diagnosis of FH can be established in a proband with characteristic clinical features and significantly elevated LDL-C levels (typically >190 mg/dL in adults and >160 mg/dL in children)."

Gives the diagnostic LDL-C thresholds for the untreated phenotype.

PMID:37130090 SUPPORT Human Clinical

"a low-density lipoprotein cholesterol (LDL-C) >10 mmol/L (>400 mg/dL) is suggestive of HoFH and warrants further evaluation"

Gives the biallelic-disease threshold used in current consensus guidance.

Endothelial Dysfunction and Subendothelial LDL Retention

Conformance node. The atherogenic cascade downstream of the LDL elevation is the conserved one modelled in the atherogenesis module and is not re-derived here; what is disease-specific is that the apoB-lipoprotein driver is present from birth and at several times the usual concentration, so the same programme runs decades earlier.

endothelial cell of artery CL:1000413

artery UBERON:0001637

Animal models

Watanabe heritable hyperlipidemic (WHHL) rabbit Rabbit recapitulates Spontaneous, diet-independent hypercholesterolemia from receptor deficiency drives the initiating arterial events - oxidized LDL accumulation, endothelial adhesion molecule expression, and monocyte infiltration.

Downstream

Monocyte Recruitment and Macrophage Foam Cell Formation Retained and modified LDL recruits monocytes that become lipid-laden macrophages.

Show evidence (1 reference)

PMID:31748469 SUPPORT Model Organism

"Oxidized LDL accumulates in the arterial wall, monocyte adhesion molecules are expressed on arterial endothelial cells, and monocyte-derived macrophages infiltrate the arterial intima, resulting in the formation and progression of atherosclerosis."

Describes the initiating arterial events as established in the LDLR-deficient rabbit, the model in which they were demonstrated in vivo.

Monocyte Recruitment and Macrophage Foam Cell Formation

Conformance node. Recruited monocyte-derived macrophages take up modified LDL and become foam cells, the cellular substance of the early lesion.

macrophage CL:0000235 foam cell CL:0000891

artery UBERON:0001637

Downstream

Premature Atherosclerotic Cardiovascular Events Lesion growth, destabilization and thrombosis convert subclinical plaque into clinical events; the intervening steps are the conserved ones in the atherogenesis module.

Show evidence (1 reference)

PMID:31748469 SUPPORT Model Organism

"monocyte-derived macrophages infiltrate the arterial intima, resulting in the formation and progression of atherosclerosis"

States macrophage infiltration as the step that builds the lesion.

Premature Atherosclerotic Cardiovascular Events

Conformance node. Angina, myocardial infarction, and less often stroke, occurring decades earlier than in the general population. In biallelic disease events may occur in childhood or adolescence and are accompanied by calcific aortic valve and aortic root disease, which is a supravalvular rather than purely valvular lesion and is not prevented by LDL lowering as reliably as coronary events are.

coronary artery UBERON:0001621 aortic valve UBERON:0002137

Show evidence (2 references)

PMID:24404629 SUPPORT Human Clinical

"increases the risk of premature cardiovascular events such as angina and myocardial infarction; stroke occurs more rarely"

Names the clinical events and their relative frequency.

PMID:24404629 SUPPORT Human Clinical

"Individuals with a more severe phenotype, often as a result of biallelic variants, can present with very significant elevations in LDL-C (>500 mg/dL), early-onset coronary artery disease (CAD; presenting as early as childhood in some), and calcific aortic valve disease."

Establishes the childhood-onset and aortic valve arms in biallelic disease.

Extravascular Cholesterol Deposition in Tendon, Skin, and Cornea

Macrophage-mediated deposition of LDL-derived cholesterol outside the arterial wall, producing tendon xanthoma (Achilles and extensor tendons of the hands), xanthelasma at the eyelids, and premature corneal arcus. These signs are highly specific for the untreated phenotype and are used in the Dutch Lipid Clinic Network and Simon Broome criteria, but they are insensitive - absence does not exclude the diagnosis, and early treatment both prevents and can reverse them.

macrophage CL:0000235

tendon UBERON:0000043 cornea UBERON:0000964 eyelid UBERON:0001711

Show evidence (3 references)

PMID:24404629 SUPPORT Human Clinical

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

Documents the periocular deposition site.

PMID:24404629 SUPPORT Human Clinical

"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."

Documents corneal deposition and its premature timing.

PMID:37730951 SUPPORT Model Organism

"In addition, periocular xanthoma was observed only 1 year after birth."

Independent demonstration in an LDLR-knockout primate that removing the receptor alone is sufficient to produce periocular xanthoma.

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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

9

Cardiovascular 3

Premature Coronary Artery Atherosclerosis HP:0001677

Course: PROGRESSIVE

Show evidence (1 reference)

PMID:24404629 SUPPORT Human Clinical

"Familial hypercholesterolemia (FH) is characterized by significantly elevated low-density lipoprotein cholesterol (LDL-C) that leads to atherosclerotic plaque deposition in the coronary arteries and proximal aorta at an early age"

States both the lesion and its premature timing.

Myocardial Infarction HP:0001658

Show evidence (1 reference)

PMID:24404629 SUPPORT Human Clinical

"increases the risk of premature cardiovascular events such as angina and myocardial infarction; stroke occurs more rarely"

Names myocardial infarction as a principal clinical event.

Angina Pectoris HP:0001681

Show evidence (1 reference)

PMID:24404629 SUPPORT Human Clinical

"increases the risk of premature cardiovascular events such as angina and myocardial infarction"

Names angina as a presenting cardiovascular event.

Eye 1

Premature Corneal Arcus HP:0001084

Show evidence (1 reference)

PMID:24404629 SUPPORT Human Clinical

"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."

Establishes both the sign and the premature timing that gives it diagnostic value.

Head and Neck 1

Xanthelasma HP:0001114

Show evidence (1 reference)

PMID:24404629 SUPPORT Human Clinical

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

Documents the sign and its location.

Integument 1

Tendon Xanthoma Tendon xanthomatosis HP:0010874

Course: PROGRESSIVE

Show evidence (1 reference)

PMID:24404629 SUPPORT Human Clinical

"Xanthomas (cholesterol deposits in tendons) may be visible in the Achilles tendons or tendons of the hands and worsen with age as a result of extremely high cholesterol levels."

Names the sites and the progressive course. Frequency is deliberately omitted - reported prevalence varies widely with treatment era and ascertainment, and no quotable figure specific to LDLR-related FH was available.

Metabolism 2

Hypercholesterolemia VERY_FREQUENT HP:0003124

Temporal: CHRONIC

Show evidence (2 references)

PMID:1301956 SUPPORT Human Clinical

"Affected individuals have elevated plasma levels of LDL, which causes premature coronary atherosclerosis."

States the defining biochemical abnormality of LDLR-mutation carriers.

PMID:24404629 SUPPORT Human Clinical

"Familial hypercholesterolemia (FH) is characterized by significantly elevated low-density lipoprotein cholesterol (LDL-C)"

GeneReviews states the elevation as the characterizing feature. Frequency is set VERY_FREQUENT because the biochemical phenotype is essentially fully penetrant in variant carriers.

Elevated LDL Cholesterol VERY_FREQUENT Increased LDL cholesterol concentration HP:0003141

Temporal: CHRONIC

Show evidence (2 references)

PMID:24404629 SUPPORT Human Clinical

"A clinical diagnosis of FH can be established in a proband with characteristic clinical features and significantly elevated LDL-C levels (typically >190 mg/dL in adults and >160 mg/dL in children)."

Gives the diagnostic thresholds and establishes the phenotype's universality.

PMID:37130090 SUPPORT Human Clinical

"a low-density lipoprotein cholesterol (LDL-C) >10 mmol/L (>400 mg/dL) is suggestive of HoFH and warrants further evaluation"

Gives the corresponding threshold in biallelic disease.

Other 1

Calcific Aortic Valve Disease Aortic valve calcification HP:0004380

Show evidence (1 reference)

PMID:24404629 SUPPORT Human Clinical

"Individuals with a more severe phenotype, often as a result of biallelic variants, can present with very significant elevations in LDL-C (>500 mg/dL), early-onset coronary artery disease (CAD; presenting as early as childhood in some), and calcific aortic valve disease."

Identifies calcific aortic valve disease as a feature of severe biallelic disease.

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Genetic Associations

1

LDLR (Pathogenic Mutations)

Gene: LDLR hgnc:6547 relationship_type: CAUSATIVE variant_origin: GERMLINE

Autosomal Dominant

Show evidence (5 references)

PMID:34906454 SUPPORT Human Clinical

"In this study, we provide consensus recommendations for the most common FH-associated gene, LDLR, where >2300 unique FH-associated variants have been identified."

Establishes both LDLR primacy and the scale of the allelic series.

PMID:34906454 SUPPORT Human Clinical

"The consensus LDLR variant modifications to existing ACMG/AMP guidelines include (1) alteration of population frequency thresholds, (2) delineation of loss-of-function variant types, (3) functional study criteria specifications, (4) cosegregation criteria specifications, and (5) specific use and..."

Names the gene-specific interpretation rules that govern LDLR variant classification.

PMID:30306860 SUPPORT Human Clinical

"The most common (60-80%) FH cause is mutations of the LDL Receptor (LDLR) protein (6 classes with a different number of receptors and functionality)."

Quantifies the LDLR share of FH and names the receptor-class scheme. Note the source counts six classes; the five curated above are the classical set, with the sixth (defective basolateral targeting) omitted because no quotable functional evidence for it was found.

+ 2 more references

Variants (5)

Class 1 - null (receptor-negative) Pathogenic

null

No LDL receptor protein is synthesized. Large deletions removing the promoter, nonsense and frameshift changes, and alleles that make normal mRNA but no detectable protein. Homozygotes for two such alleles are receptor-negative and respond poorly or not at all to receptor-directed drugs.

Class 2 - transport-defective Pathogenic

missense

The receptor is synthesized but misfolds and is retained in the endoplasmic reticulum instead of maturing through the Golgi to the surface. Retention may be complete (2a) or partial (2b).

Class 3 - binding-defective Pathogenic

missense

Receptor reaches the surface but binds apoB-100 poorly. Changes fall in the cysteine-rich ligand-binding repeats or in the EGF-precursor homology domain that orients them.

Class 4 - internalization-defective Pathogenic

missense

Receptor is expressed and binds LDL normally but fails to cluster in clathrin-coated pits, because the cytoplasmic internalization signal is disrupted. The founding allele is the J.D. mutation, a tyrosine-to-cysteine substitution at residue 807.

Class 5 - recycling-defective Pathogenic

missense

Receptor binds and internalizes LDL but fails to release it in the acidified endosome, so receptor and ligand are degraded together and the receptor is not returned to the surface.

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Medical Actions

10

Statin (HMG-CoA Reductase Inhibitor) Therapy

Action: Pharmacotherapy NCIT:C15986

Agent: statin CHEBI:87631

First-line, lifelong LDL-lowering therapy. The mechanism is receptor-side and therefore genotype-sensitive: inhibiting HMG-CoA reductase lowers intracellular cholesterol, which de-represses LDLR transcription and puts more receptor on the hepatocyte surface. The drug therefore amplifies whatever receptor capacity the genotype leaves. Note that statins have not been tested against a receptor-negative genotype stratum in this entry's evidence, and the cited mechanistic review reports statins helping both homozygous and heterozygous patients, so the null-genotype ceiling is inferred from mechanism rather than demonstrated. In a 2146-patient FH cohort followed a mean 8.5 years, statin treatment reduced coronary heart disease risk by 76%.

Mechanism Target:

ACTIVATES Residual Receptor Activity Gates Receptor-Dependent LDL Lowering — Statins act by inducing residual LDL receptor, so their effect is bounded by how much functional receptor the genotype permits.

Show evidence (1 reference)

PMID:37371118 SUPPORT Other

"Statins proved to be the first blockbuster drug, helping both HoFH and HeFH individuals by inhibiting the cholesterol synthesis pathway rate-limiting enzyme HMG-CoA reductase and inducing the LDL receptor."

States the receptor-inducing mechanism that makes the effect genotype-dependent.

Show evidence (3 references)

PMID:19001495 SUPPORT Human Clinical

"We observed an overall risk reduction of 76% (hazard ratio 0.24 (95% confidence interval 0.18 to 0.30), P<0.001)."

Quantifies the cardiovascular benefit of statin therapy in an FH cohort.

PMID:24404629 SUPPORT Other

"statins can be used in children starting around age eight years"

GeneReviews sets the paediatric initiation age. PARTIAL because the recommendation is made for FH as a class rather than for LDLR-related FH specifically.

PMID:24404629 SUPPORT Other

"Statins are contraindicated in pregnancy because of concerns for teratogenicity and should be discontinued prior to conception."

GeneReviews states the pregnancy contraindication. PARTIAL because it constrains rather than supports the therapy, and is stated at class level.

PCSK9 Monoclonal Antibody Therapy

Action: Pharmacotherapy NCIT:C15986

Agent: PCSK9 inhibitor NCIT:C190797

Alirocumab and evolocumab neutralize circulating PCSK9, preventing PCSK9-directed lysosomal degradation of the LDL receptor and so increasing receptor recycling and surface abundance. Like statins this is a receptor-amplifying mechanism, and the AMG 145 (evolocumab) homozygous-FH study is the cleanest published demonstration that the amplification requires a receptor to amplify: LDL cholesterol fell in receptor-defective patients and not at all in the receptor-negative ones, within the same protocol and at the same doses.

Mechanism Target:

ACTIVATES Residual Receptor Activity Gates Receptor-Dependent LDL Lowering — Blocking PCSK9 spares existing LDL receptor from degradation, raising surface receptor abundance in patients who retain functional receptor and achieving nothing in those who do not.

Show evidence (1 reference)

PMID:24014831 SUPPORT Human Clinical

"This study demonstrates significant and dose-related LDL cholesterol lowering with a PCSK9 monoclonal antibody in homozygous familial hypercholesterolemia patients with defective LDL receptor activity but no reduction in those who were receptor negative."

The genotype-stratified result that defines the boundary of this therapy.

Show evidence (2 references)

PMID:24014831 SUPPORT Human Clinical

"Over the treatment periods, mean±SD LDL cholesterol reductions in the 6 LDL receptor-defective patients were 19.3±16% and 26.3±20% with 4- and 2-week dosing, respectively"

Quantifies the response in receptor-defective homozygous disease.

PMID:37130090 SUPPORT Human Clinical

"Addition of novel, efficacious therapies (i.e. inhibitors of proprotein convertase subtilisin/kexin type 9, followed by evinacumab and/or lomitapide) offers potential to attain LDL-C goal or reduce the need for LA."

Places PCSK9 inhibition in the current consensus treatment sequence for severe disease.

Evinacumab (ANGPTL3 Inhibition)

Action: Pharmacotherapy NCIT:C15986

Agent: evinacumab NCIT:C20401

An angiopoietin-like 3 monoclonal antibody that lowers LDL cholesterol by a route that does not require the LDL receptor. This is the therapeutic complement of everything above: in the phase 3 homozygous-FH trial it lowered LDL cholesterol by a similar amount in patients with null-null variants and in those with non-null variants, so it is the option that remains when the receptor-directed drugs have nothing to act on.

Mechanism Target:

INHIBITS Lifelong Elevation of Plasma LDL Cholesterol — Lowers plasma LDL cholesterol without acting through the LDL receptor, so the effect is preserved regardless of receptor class.

Show evidence (1 reference)

PMID:32813947 SUPPORT Human Clinical

"The LDL cholesterol level was lower in the evinacumab group than in the placebo group in patients with null-null variants (-43.4% vs. +16.2%) and in those with non-null variants (-49.1% vs. -3.8%)."

Demonstrates genotype-independent efficacy, the defining property of this agent.

Show evidence (1 reference)

PMID:32813947 SUPPORT 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"

Reports the primary efficacy result of the pivotal randomized trial.

Lomitapide (Microsomal Triglyceride Transfer Protein Inhibition)

Action: Pharmacotherapy NCIT:C15986

Agent: lomitapide CHEBI:72297

An MTP inhibitor that reduces hepatic assembly and secretion of apoB-containing lipoproteins. Like evinacumab it acts upstream of the receptor rather than through it, so it is expected to be genotype-independent - though, unlike the evinacumab trial, the pivotal lomitapide study was single-arm, open-label, and not genotype-stratified, so its 50% reduction is a whole-cohort figure and not a demonstration of effect in receptor-negative disease specifically. Hepatic steatosis, transaminase elevation, gastrointestinal intolerance, and fat-soluble vitamin depletion constrain its use and require monitoring.

Mechanism Target:

INHIBITS Lifelong Elevation of Plasma LDL Cholesterol — Reduces the production side of the LDL steady state rather than the clearance side, bypassing the receptor defect entirely.

Show evidence (1 reference)

PMID:23122768 SUPPORT Human Clinical

"LDL cholesterol was reduced by 50% (95% CI -62 to -39) from baseline"

Quantifies LDL lowering in homozygous disease, where receptor-directed drugs underperform.

Show evidence (2 references)

PMID:23122768 SUPPORT Human Clinical

"Patients with homozygous familial hypercholesterolaemia respond inadequately to existing drugs."

States the therapeutic gap that LDLR-independent agents were developed to fill.

PMID:23122768 SUPPORT Human Clinical

"Four patients had aminotransaminase levels of more than five times the upper limit of normal, which resolved after dose reduction or temporary interruption of lomitapide."

Documents the hepatic toxicity signal that constrains dosing.

Lipoprotein Apheresis

Action: Therapeutic Procedure NCIT:C49236

Extracorporeal physical removal of apoB-containing lipoproteins from plasma. Wholly independent of LDL receptor function and therefore effective in receptor-negative disease, but the effect rebounds between sessions and the vascular-access, time, and cost burden is substantial. Current consensus places it alongside pharmacotherapy as foundational in severe biallelic disease.

Mechanism Target:

INHIBITS Lifelong Elevation of Plasma LDL Cholesterol — Removes circulating LDL directly, requiring no receptor and no hepatic metabolic step.

Show evidence (1 reference)

PMID:37130090 SUPPORT Human Clinical

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

Establishes apheresis as a foundational component of severe-disease management.

Show evidence (1 reference)

PMID:37130090 SUPPORT Human Clinical

"Addition of novel, efficacious therapies (i.e. inhibitors of proprotein convertase subtilisin/kexin type 9, followed by evinacumab and/or lomitapide) offers potential to attain LDL-C goal or reduce the need for LA."

Positions apheresis relative to the newer pharmacologic options.

Ezetimibe

Action: Pharmacotherapy NCIT:C15986

Agent: ezetimibe CHEBI:49040

Cholesterol-absorption inhibitor (NPC1L1) added to statin therapy when the LDL-C target is not reached - step two of the standard FH escalation. Curated here because its mechanism is receptor-dependent in the same sense statins are: blocking jejunal cholesterol uptake depletes hepatocyte cholesterol and drives a compensatory increase in LDL receptor, so like a statin it amplifies whatever receptor capacity the genotype leaves rather than bypassing the receptor. Statin-plus-ezetimibe reaches roughly 65-70% LDL-C reduction against 50-60% for a high-intensity statin alone.

Mechanism Target:

ACTIVATES Residual Receptor Activity Gates Receptor-Dependent LDL Lowering — Ezetimibe belongs on the receptor-dependent side of the gating relation, not the LDLR-independent side: it lowers LDL-C by inducing residual receptor, so its effect is bounded by the receptor capacity the genotype permits.

Show evidence (1 reference)

PMID:39076699 SUPPORT Other

"ezetimibe by blocking cholesterol uptake from the jejunum) result in a compensatory increase in LDL-R and subsequently enhanced LDL-C clearance."

States that ezetimibe lowers LDL-C through a compensatory increase in LDL receptor, which is what places it on the receptor-dependent side of the gating node alongside statins.

Show evidence (1 reference)

PMID:39076699 SUPPORT Other

"statins (alone or in combination with ezetimibe) demonstrated a significant reduction of future ASCVD events even in subjects with LDL-R defective forms"

Supports the event-level benefit of statin-plus-ezetimibe specifically in receptor-defective disease, the genotype stratum this entry curates.

Bempedoic Acid

Action: Pharmacotherapy NCIT:C15986

Agent: bempedoic acid CHEBI:149601

Oral ATP-citrate lyase inhibitor acting upstream of HMG-CoA reductase. Because it is a prodrug activated by a liver-specific enzyme absent from skeletal muscle, it is the guideline option for statin-intolerant patients - a common situation in a disease requiring lifelong high-intensity statin therapy. Like statins and ezetimibe it upregulates LDL receptor activity, so it sits on the receptor-dependent side of the gating relation. Reported LDL-C reduction was 22.3% in a pooled clinical-heterozygous-FH subgroup.

Mechanism Target:

ACTIVATES Residual Receptor Activity Gates Receptor-Dependent LDL Lowering — Inhibiting ATP-citrate lyase depletes hepatic cholesterol and upregulates LDL receptor activity by the same de-repression route statins use, so the effect is bounded by residual receptor capacity.

Show evidence (1 reference)

PMID:39076699 SUPPORT Other

"It acts as an inhibitor of adenosine triphosphate (ATP) citrate lyase, a hepatic enzyme that works upstream of HMG-CoA reductase with subsequent upregulation of LDL-R activity, similar to statins"

States the target and, critically for this entry, that the LDL-lowering effect runs through upregulation of LDL receptor activity.

Show evidence (1 reference)

PMID:36876740 SUPPORT Human Clinical

"Bempedoic acid, an ATP citrate lyase inhibitor, reduces low-density lipoprotein (LDL) cholesterol levels and is associated with a low incidence of muscle-related adverse events"

CLEAR Outcomes provides the outcome evidence justifying bempedoic acid as curated therapy rather than an investigational option.

Inclisiran (PCSK9-Directed siRNA)

Action: Pharmacotherapy NCIT:C15986

Agent: inclisiran CHEBI:176399

Hepatocyte-targeted small interfering RNA that suppresses PCSK9 synthesis, given on days 1 and 90 and every six months thereafter. Mechanistically it reaches the same endpoint as a PCSK9 antibody - less PCSK9-mediated receptor degradation, therefore more receptor on the hepatocyte surface - by inhibiting hepatic PCSK9 production rather than neutralizing circulating protein, so it is equally receptor-dependent. ORION-9 (NCT03397121) tested it in adults with heterozygous FH.

Mechanism Target:

ACTIVATES Residual Receptor Activity Gates Receptor-Dependent LDL Lowering — Suppressing hepatic PCSK9 synthesis preserves receptor that would otherwise be degraded, so like the PCSK9 antibodies the effect requires a receptor that can be made and can function.

Show evidence (1 reference)

PMID:39076699 SUPPORT Other

"In contrast to anti-PCSK9 mAbs, inclisiran inactivates PCSK9 by inhibition of its hepatic synthesis"

Distinguishes the siRNA route to PCSK9 inactivation from antibody neutralization while placing both on the same receptor-preserving mechanism.

Show evidence (1 reference)

PMID:39076699 SUPPORT Other

"inclisiran represents a first-in-class cholesterol-lowering small interfering ribonucleic acid (siRNA), targeting PCSK9 messenger RNA (mRNA) in hepatocytes."

Establishes the modality and molecular target of the agent.

Liver Transplantation

Action: Organ Transplantation NCIT:C15289

The limiting case of the receptor-dependent/receptor-independent axis: rather than amplifying or bypassing the patient's own receptor, orthotopic liver transplantation *supplies* a hepatic LDL receptor complement, which is why it can correct the biochemical defect in receptor-negative disease that no receptor-directed drug can reach. Reserved for homozygous patients whose LDL-C cannot be controlled by maximal medical therapy and apheresis, and constrained by operative risk and lifelong immunosuppression. Where severe cardiovascular involvement has already developed, combined heart-liver transplantation may be required, which is the argument for early listing rather than late rescue.

Mechanism Target:

ACTIVATES Reduced Functional Hepatic LDL Receptor Activity — Replacing the liver replaces the tissue that carries the defective receptor, restoring hepatic receptor capacity itself rather than modulating the residual capacity a mutant genotype leaves. This is the only curated intervention that acts on the receptor-activity node directly.

Show evidence (1 reference)

PMID:39815304 SUPPORT Human Clinical

"Accordingly, all 6 patients received orthotopic liver transplantations (OLT), with the result that significant postoperative reductions were observed in levels of TC and LDL."

Reports that supplying a donor liver lowers total and LDL cholesterol, which is the receptor-supply mechanism this edge asserts.

Show evidence (2 references)

PMID:39815304 SUPPORT Human Clinical

"In severe cases of HoFH, clinical signs and symptoms cannot be controlled well by non-surgical treatments, liver transplantation (LT) currently represents the viable option."

Places liver transplantation as the option of last resort when medical therapy fails, the clinical position curated here.

PMID:39815304 SUPPORT Human Clinical

"If severe cardiovascular involvement occurs, LT should be performed as soon as possible, otherwise combined heart-liver transplantation may be required."

Supports the timing argument in the description - that the cost of late listing is escalation to combined heart-liver transplantation.

Cardiovascular Risk Factor Modification

Action: Dietary Intervention NCIT:C15447

The receptor defect sets a high baseline arterial risk that conventional risk factors multiply. Smoking cessation, control of blood pressure and glycemia, weight management, physical activity, and reduced saturated and trans fat intake do not correct the LDL level but reduce absolute event risk.

Show evidence (1 reference)

PMID:24404629 SUPPORT Other

"Agents/circumstances to avoid: Smoking, high intake of saturated and trans unsaturated fat, sedentary lifestyle, obesity, hypertension, and diabetes mellitus."

The GeneReviews agents-and-circumstances-to-avoid list, which is what this treatment entry operationalizes.

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Biochemical Markers

3

Plasma LDL Cholesterol (Increased)

Show evidence (1 reference)

PMID:24404629 SUPPORT Human Clinical

"A clinical diagnosis of FH can be established in a proband with characteristic clinical features and significantly elevated LDL-C levels (typically >190 mg/dL in adults and >160 mg/dL in children)."

Establishes LDL-C as the diagnostic analyte and gives its thresholds.

Plasma Apolipoprotein B (Increased)

Show evidence (1 reference)

PMID:28475941 SUPPORT Human Clinical

"Patients with null variants have a more severe phenotype than patients with defective variants, presenting with significantly higher levels of atherogenic particles (total cholesterol, LDL-cholesterol and apolipoprotein B)."

Names apolipoprotein B among the atherogenic particle measures elevated in this disease, and shows it separating null from defective allele classes.

Lipoprotein(a) (Variable)

Show evidence (2 references)

PMID:24632281 SUPPORT Human Clinical

"On multivariate analysis, Lp(a) was an independent predictor of cardiovascular disease."

Establishes Lp(a) as an independent cardiovascular risk predictor within FH.

PMID:24632281 SUPPORT Human Clinical

"The risk of CVD is higher in those patients with an Lp(a) level >50 mg/dl and carrying a receptor-negative mutation in the LDLR gene compared with other less severe mutations."

Shows Lp(a) risk interacting with the receptor class - the highest risk stratum is receptor-negative genotype plus high Lp(a).

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Diagnosis

2

Molecular Genetic Testing of LDLR

Sequencing of LDLR together with APOB and PCSK9, plus deletion/duplication analysis, since exon-level copy-number changes are a real and sequencing-invisible part of the LDLR allelic series. Variant interpretation should follow the ClinGen FH Variant Curation Expert Panel's LDLR-specific specification of the ACMG/AMP framework rather than the generic rules, which is what makes a confident pathogenic call - and therefore cascade testing of relatives - possible.

Show evidence (2 references)

PMID:24404629 SUPPORT Human Clinical

"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."

States the molecular diagnostic route and the genes tested.

PMID:34906454 SUPPORT Human Clinical

"Establishment of these guidelines as the new standard in the clinical laboratory setting will result in a more evidence-based, harmonized method for LDLR variant classification worldwide, thereby improving the care of patients with FH."

Names the gene-specific interpretation standard that governs the diagnostic call.

Functional Characterization of LDLR Variants

Cell-based assays - LDL binding and uptake by flow cytometry with fluorescent LDL, receptor expression by immunofluorescence or Western blot, and receptor localization by confocal microscopy - performed in receptor-deficient CHO-ldlA7 cells transfected with the patient allele. These assays do two things no in silico predictor can: they resolve variants of uncertain significance into a pathogenicity call, and they assign the allele to a functional class, which is the input to genotype-guided therapy selection.

Show evidence (3 references)

PMID:25386756 SUPPORT In Vitro

"Additionally confocal microscopy allowed the assignment of different class mutation to the variants assayed."

Establishes class assignment as an output of the functional assay.

PMID:31106925 SUPPORT In Vitro

"This approach allows us to confirm the genetic diagnosis of FH, avoiding the classification as "uncertain significant variants", and therefore, carry out cascade family screening."

States the clinical consequence of functional characterization - VUS resolution enabling cascade screening.

PMID:37847331 SUPPORT Computational

"Despite their contributions, a definitive diagnosis of a genetic variant necessitates functional validation through in vitro characterization or cascade screening."

States that computational prediction alone is insufficient, which is why the functional assay is curated as its own diagnostic modality.

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Progression

3

Presymptomatic biochemical disease (birth onward)

LDL cholesterol is elevated from birth because the receptor defect is constitutional. Heterozygotes are typically asymptomatic through childhood while arterial cholesterol exposure accumulates; this is the window in which treatment has the largest effect on lifetime risk.

Show evidence (1 reference)

PMID:24404629 SUPPORT Human Clinical

"Monitor lipid levels from age two years"

Surveillance from age two reflects a biochemical phenotype that is present long before any clinical event.

Extravascular cholesterol deposition (childhood to adulthood)

Tendon xanthoma, xanthelasma, and premature corneal arcus accumulate with age and with the height of the LDL burden. They are specific but insensitive - their absence does not exclude the diagnosis.

Show evidence (1 reference)

PMID:24404629 SUPPORT Human Clinical

"Xanthomas (cholesterol deposits in tendons) may be visible in the Achilles tendons or tendons of the hands and worsen with age as a result of extremely high cholesterol levels."

Describes the age-dependent accumulation of tendon xanthoma.

Premature atherosclerotic cardiovascular disease

Coronary and proximal aortic plaque develops decades earlier than in the general population. In biallelic disease coronary events and calcific aortic valve disease can occur in childhood or adolescence.

Show evidence (1 reference)

PMID:24404629 SUPPORT Human Clinical

"Individuals with a more severe phenotype, often as a result of biallelic variants, can present with very significant elevations in LDL-C (>500 mg/dL), early-onset coronary artery disease (CAD; presenting as early as childhood in some), and calcific aortic valve disease."

Sets out the severe end of the course, driven by receptor gene dosage.

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Prevalence

1

Molecularly diagnosed familial hypercholesterolemia cohorts

Unknown Unknown

Recorded as a share of molecularly solved FH rather than as a population rate. LDLR is by a wide margin the most common FH gene, but the reported share varies with referral criteria, panel design, and whether deletion/duplication analysis was performed, so the figure is carried as a quoted range with its source rather than normalized to a single number. Population prevalence of the FH phenotype as a whole belongs to the umbrella entry (MONDO:0005439) and is not restated here.

Show evidence (1 reference)

PMID:30306860 SUPPORT Human Clinical

"The most common (60-80%) FH cause is mutations of the LDL Receptor (LDLR) protein (6 classes with a different number of receptors and functionality)."

Quantifies the LDLR share of FH and names the receptor-class scheme this entry models.

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Differential Diagnoses

6

Conditions with similar clinical presentations that must be differentiated from LDLR-Related Familial Hypercholesterolemia:

Familial defective apolipoprotein B-100 (APOB)

Overlapping Features The ligand-side mirror of this entry. Clinically indistinguishable at the bedside and separated only by molecular testing: here the receptor is defective, there the receptor is normal and the apoB-100 ligand it must recognize is not. Curated separately as Familial_Defective_Apolipoprotein_B-100 (MONDO:0007751). LDL-C elevation is generally milder than in LDLR-related disease.

Show evidence (1 reference)

PMID:24404629 SUPPORT Human Clinical

"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 APOB as an alternative molecular cause of the same clinical picture and specifies its distinguishing mechanism - impaired binding of LDL-C to the receptor rather than a defective receptor.

Autosomal dominant hypercholesterolemia 3 (PCSK9 gain of function)

Overlapping Features The regulator-side member of the dominant trio. The receptor gene is intact; a gain-of-function PCSK9 variant degrades normal receptor prematurely, so receptor number falls without any receptor defect. Curated separately as Autosomal_Dominant_Hypercholesterolemia_3 (MONDO:0011369). The practical consequence is therapeutic: PCSK9-directed agents address the causal lesion there, whereas here they amplify a residual receptor.

Show evidence (1 reference)

PMID:24404629 SUPPORT Human Clinical

"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 lists PCSK9 gain of function as a distinct molecular route to the same phenotype.

Autosomal recessive hypercholesterolemia (LDLRAP1)

Overlapping Features The phenocopy of this entry acting in trans. LDLRAP1 encodes the adaptor that couples the receptor to the clathrin endocytic machinery, so biallelic loss produces functionally the same internalization failure as a class 4 LDLR allele while the receptor itself is normal. Recessive rather than dominant, so parents are typically unaffected - the pedigree pattern is usually what separates it clinically.

Show evidence (1 reference)

PMID:24404629 SUPPORT Human Clinical

"or rarely, identification of biallelic pathogenic variants in LDLRAP1."

GeneReviews records LDLRAP1 as the rare biallelic route to a clinical FH diagnosis, distinguishing it from the dominant genes by inheritance.

Polygenic hypercholesterolemia

Overlapping Features The most common alternative explanation for a clinical FH phenotype with no identified monogenic variant: the cumulative effect of many small LDL-C raising alleles can reach the same LDL-C range as a monogenic defect. Distinguishing it matters because cardiovascular risk, cascade-testing yield, and treatment responsiveness differ from monogenic disease, and because a negative LDLR test does not exclude clinical FH.

Show evidence (1 reference)

PMID:39076699 SUPPORT Other

"would suggest polygenic causes of FH, where small but cumulative effects of several LDL-C raising alleles can cause the LDL-C increase up to the same range as that"

States that polygenic burden can reproduce the monogenic LDL-C range, which is what makes it the principal differential for a variant-negative clinical FH phenotype.

Elevated lipoprotein(a) mimicking familial hypercholesterolemia

Overlapping Features Not a separate disease so much as a measurement artefact that produces the same referral. Conventional LDL-C assays cannot separate LDL-cholesterol from lipoprotein(a)-cholesterol because the particles overlap in density, so a high Lp(a) inflates measured LDL-C and can push a patient into a clinical FH category they do not belong in. Relevant to this entry because Lp(a) is also genuinely elevated in FH and is curated as a biomarker here.

Show evidence (1 reference)

PMID:39076699 SUPPORT Other

"Conventional assays for LDL-C determination quantify a composite of atherogenic cholesterol, which is attributable not only to LDL-C, but also to lipoprotein(a)-cholesterol (Lp(a)-C) due to their overlapping densities."

Explains the assay overlap that lets high Lp(a) masquerade as the elevated LDL-C used to make a clinical FH diagnosis.

Sitosterolemia, dysbetalipoproteinemia, and cholesteryl ester storage disease

Overlapping Features Distinctive non-FH inherited dyslipidemias that can present with severe hypercholesterolemia and xanthoma and so enter the differential of a young patient with very high LDL-C and no LDLR variant - sitosterolemia (ABCG5 / ABCG8), dysbetalipoproteinemia (APOE), and cholesteryl ester storage disease / lysosomal acid lipase deficiency (LIPA). Each has its own mechanism and, importantly, its own treatment, so misassignment to FH has therapeutic consequences.

Show evidence (1 reference)

PMID:39076699 SUPPORT Other

"some of these genes might also cause distinctive non-FH syndromes such as sitosterolemia (ABCG5), dysbetalipoproteinemia (APOE) or cholesteryl ester storage disease (LIPA)"

Names the non-FH inherited dyslipidemias that share the severe hypercholesterolemia presentation.

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Clinical Trials

4

NCT03399786 PHASE_III COMPLETED

ELIPSE HoFH. Randomized, double-blind, placebo-controlled trial of intravenous evinacumab in 65 patients with homozygous familial hypercholesterolemia, reporting results separately for null-null and non-null LDL-receptor genotypes - the trial that established LDLR-independent LDL lowering in receptor-negative disease.

Target Phenotypes: Increased LDL cholesterol concentration HP:0003141

Show evidence (1 reference)

clinicaltrials:NCT03399786 SUPPORT Human Clinical

"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)."

States the trial's primary objective in the population relevant to this entry.

NCT04233918 PHASE_III COMPLETED

Three-part, single-arm, open-label study of evinacumab in paediatric patients with homozygous familial hypercholesterolemia, extending the LDLR-independent option to children, in whom receptor-negative disease presents earliest.

Target Phenotypes: Increased LDL cholesterol concentration HP:0003141

Show evidence (1 reference)

clinicaltrials:NCT04233918 SUPPORT Human Clinical

"The primary objective for Part B of the study is to demonstrate a reduction of low-density lipoprotein cholesterol (LDL-C) by evinacumab in pediatric (5 to 11 years of age) patients with HoFH."

States the trial's efficacy objective in the paediatric homozygous population.

NCT03397121 PHASE_III COMPLETED

ORION-9. Placebo-controlled, double-blind, randomized trial of inclisiran, a hepatocyte-targeted siRNA that suppresses PCSK9 synthesis, in adults with heterozygous familial hypercholesterolemia - a receptor-amplifying mechanism tested in the population that retains residual receptor.

Target Phenotypes: Increased LDL cholesterol concentration HP:0003141

Show evidence (1 reference)

clinicaltrials:NCT03397121 SUPPORT Human Clinical

"This is a Phase III, placebo-controlled, double-blind, randomized study in participants with HeFH and elevated LDL-C to evaluate the efficacy, safety, and tolerability of subcutaneous (SC) injection(s) of inclisiran."

States the trial design, population, and agent.

NCT06597006 PHASE_III RECRUITING

Two-part randomized study of inclisiran in children aged 2 to under 12 with homozygous familial hypercholesterolemia. Curated because it is the most directly on-thesis trial available for this entry: its enrolment criteria operationalize the gating relation itself, requiring documented biallelic null LDLR mutations and excluding children with poor prior response to a PCSK9 antibody - i.e. it tests a receptor-preserving agent in exactly the genotype stratum where receptor-directed therapy is predicted to fail.

Target Phenotypes: Increased LDL cholesterol concentration HP:0003141

Show evidence (1 reference)

clinicaltrials:NCT06597006 SUPPORT Human Clinical

"This is a pivotal phase III study designed to evaluate safety, tolerability, and efficacy of inclisiran in children (aged 2 to \<12 years) with homozygous familial hypercholesterolemia (HoFH) and elevated low density lipoprotein cholesterol (LDLC)."

States the design and the homozygous paediatric population; the genotype-specific enrolment detail is recorded in the description from the registry record rather than quoted, as the cached summary does not carry the eligibility text.

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Animal Models

3

Ldlr-knockout mouse

The founding genetic model. Viable and fertile, with a selective rise in IDL and LDL and a demonstrated prolongation of apoB-lipoprotein clearance, and reversible by hepatic re-expression of the human receptor - which closes the causal loop between receptor absence and hypercholesterolemia.

Species

Mouse

Genotype

Ldlr-/- (homologous recombination in embryonic stem cells)

Publication

PMID:8349823

Pathograph links

Impaired Receptor-Mediated Clearance of Plasma LDL recapitulates fidelity: high Directly measures the clearance defect that this node represents, in the cleanest possible genetic background - complete receptor absence.

Limitations: Murine lipoprotein metabolism is apoB48- and HDL-dominated rather than LDL-dominated, so absolute cholesterol levels are far below human homozygous FH and spontaneous atherosclerosis on chow is limited; the model reproduces the clearance defect faithfully but not the human lipoprotein distribution or the arterial disease burden.

Readouts

Plasma clearance half-life of radiolabelled VLDL and LDL

Direction: INCREASED

Interpretation: Prolonged half-life is the direct measurement of the clearance defect; normal HDL clearance in the same animals shows the defect is ligand-specific.

Show evidence (1 reference)

PMID:8349823 SUPPORT Model Organism

"The half-lives for intravenously administered 125I-VLDL and 125I-LDL were prolonged by 30-fold and 2.5-fold, respectively, but the clearance of 125I-HDL was normal in the LDLR-/- mice."

Reports the measured clearance half-lives underlying this readout.

Show evidence (1 reference)

PMID:8183926 SUPPORT Model Organism

"LDLR(-/-) mice had a relatively isolated elevation in plasma LDL"

Confirms that the model isolates the LDL clearance arm rather than producing a generalized dyslipidemia.

Reduced Functional Hepatic LDL Receptor Activity rescues fidelity: high Restoring hepatic LDL receptor expression by adenoviral delivery normalized the elevated IDL/LDL within four days, demonstrating that the receptor deficit is both necessary and sufficient for the phenotype in this model.

Limitations: Adenoviral rescue is acute and supraphysiological hepatic overexpression, not a model of the endogenous allelic series; it establishes sufficiency of receptor restoration, not the dose-response of partial residual activity.

Readouts

Plasma IDL/LDL cholesterol after hepatic LDLR re-expression

Direction: RESTORED

Interpretation: Normalization on receptor restoration is the rescue arm of the causal claim.

Show evidence (1 reference)

PMID:8349823 SUPPORT Model Organism

"The elevated IDL/LDL level of LDLR-/- mice was reduced to normal 4 d after the intravenous injection of a recombinant replication-defective adenovirus encoding the human LDL receptor driven by the cytomegalovirus promoter."

Reports the rescue measurement.

Show evidence (1 reference)

PMID:8349823 SUPPORT Model Organism

"The virus restored expression of LDL receptor protein in the liver and increased the clearance of 125I-VLDL."

Confirms that the rescue acted through restored hepatic receptor protein.

Watanabe heritable hyperlipidemic (WHHL) rabbit

A spontaneously arising LDL-receptor-deficient rabbit strain and its coronary-atherosclerosis-prone and myocardial-infarction-prone derivatives. Rabbit lipoprotein metabolism is far closer to human than murine, and this is the model in which the LDL receptor pathway hypothesis - derived from cultured fibroblasts - was shown to hold in a whole animal, and in which the arterial consequences of lifelong receptor deficiency were worked out.

Species

Rabbit

Genotype

Naturally occurring homozygous LDL receptor deficiency

Publication

PMID:31748469

Pathograph links

Endothelial Dysfunction and Subendothelial LDL Retention recapitulates fidelity: high Spontaneous, diet-independent hypercholesterolemia from receptor deficiency drives the initiating arterial events - oxidized LDL accumulation, endothelial adhesion molecule expression, and monocyte infiltration.

Limitations: Rabbits lack the human coronary anatomy and plaque-rupture triggers in full, and the reviewed strain history reports that lesion rupture in this model requires secondary mechanical forces such as spasm, so event generation is not a faithful analogue of human acute coronary syndrome.

Readouts

Arterial intimal macrophage infiltration and oxidized LDL accumulation

Direction: INCREASED

Interpretation: Histological demonstration of the initiating steps of atherogenesis in a receptor-deficient animal.

Show evidence (1 reference)

PMID:31748469 SUPPORT Model Organism

"Oxidized LDL accumulates in the arterial wall, monocyte adhesion molecules are expressed on arterial endothelial cells, and monocyte-derived macrophages infiltrate the arterial intima, resulting in the formation and progression of atherosclerosis."

Reports the arterial findings underlying this readout.

Show evidence (1 reference)

PMID:31748469 SUPPORT Model Organism

"The main part of human lipoprotein metabolism has been elucidated, and the low-density lipoprotein (LDL) receptor pathway hypothesis derived from studies using fibroblasts was proven in vivo."

Establishes this strain as the in vivo proof of the receptor pathway, which is why it is informative for the arterial arm.

LDLR-knockout cynomolgus monkey

A genome-edited non-human primate model. Plasma cholesterol reached levels comparable to human homozygous FH, periocular xanthoma appeared within the first year, and the animals were strongly resistant to lipid-lowering medication - the primate counterpart of the receptor-negative pharmacological phenotype.

Species

Cynomolgus monkey

Genotype

LDLR knockout by genome editing (six founder animals)

Publication

PMID:37730951

Pathograph links

Residual Receptor Activity Gates Receptor-Dependent LDL Lowering recapitulates fidelity: moderate Complete receptor knockout reproduces the drug-refractory phenotype that defines receptor-negative homozygous disease.

Limitations: Six founder animals, possible mosaicism from editing, short follow-up, and the report characterizes drug resistance in aggregate rather than drug-by-drug, so it supports the direction of the gating relation but not an agent-specific magnitude.

Readouts

LDL cholesterol response to lipid-lowering medication

Direction: UNCHANGED

Interpretation: Failure to respond in a total-knockout primate is the model-side counterpart of the absent response in receptor-negative patients.

Show evidence (1 reference)

PMID:37730951 SUPPORT Model Organism

"The LDLR KO monkeys were also strongly resistant to medications for hypercholesterolemia."

Reports the drug-resistance observation underlying this readout.

Show evidence (1 reference)

PMID:37730951 SUPPORT Model Organism

"The levels of plasma cholesterol and triglyceride were quite high in the monkeys, and were similar to those in FH patients with homozygous mutations in the LDLR gene."

Establishes that the model reaches human homozygous-FH lipid levels, which is what makes its drug-response behaviour informative.

{ }

Source YAML

click to show

name: LDLR-Related Familial Hypercholesterolemia
creation_date: "2026-08-19T00:00:00Z"
description: >
  LDLR-related familial hypercholesterolemia (familial hypercholesterolemia 1,
  FHCL1; hyperlipoproteinemia type 2A) is the receptor-side form of familial
  hypercholesterolemia and the form for which the disease was originally
  defined. The low-density lipoprotein receptor is a cell-surface transmembrane
  protein that binds apoB-100-containing LDL particles and delivers them to the
  lysosome for degradation, and hepatic LDLR accounts for most clearance of
  plasma LDL. Germline pathogenic variants in LDLR reduce the number of
  functional receptors on the hepatocyte surface, LDL residence time in plasma
  lengthens, and LDL cholesterol is elevated from birth, producing cumulative
  arterial cholesterol exposure, premature atherosclerotic cardiovascular
  disease, and extravascular cholesterol deposition as tendon xanthoma,
  xanthelasma, and corneal arcus.

  What distinguishes this entry from its siblings is the *allelic series*. LDLR
  is a modular mosaic protein whose receptor itinerary - synthesis, folding and
  ER-to-Golgi export, surface presentation, ligand binding, clathrin-mediated
  internalization, endosomal ligand release, and recycling - can be interrupted
  at any step, and the classical five (sometimes six) mutation classes name
  which step a given allele breaks. That is not decorative taxonomy: how much
  receptor activity survives sets the ceiling on every receptor-dependent
  therapy. Statins and PCSK9-directed agents both work by putting *more* LDL
  receptor on the hepatocyte surface, so their effect is bounded by the
  receptor capacity the genotype permits. That bound has been demonstrated
  directly only for PCSK9-directed therapy, where LDL-C fell in
  receptor-defective homozygotes and not at all in the two receptor-negative
  patients studied (PMID:24014831); whether statins are equally null-dependent
  is not established here, and the entry's own cited review reports statins
  helping both homozygous and heterozygous patients. The LDLR-independent
  agents lomitapide, evinacumab, and lipoprotein apheresis act upstream of or
  around the receptor and so are expected to be genotype-independent - shown
  with genotype stratification for evinacumab, and not stratified for the
  other two. This entry curates the receptor
  itinerary, the class-to-step mapping, and the residual-activity-gates-therapy
  relation as its own mechanism graph.
category: Mendelian
synonyms:
- Hypercholesterolemia, familial, 1
- FHCL1
- Familial hypercholesterolemia type 1
- LDL receptor disorder
- LDL receptor deficiency
- Hyperlipoproteinemia type 2A
- Familial hypercholesterolemic xanthomatosis
- Autosomal dominant hypercholesterolemia 1
disease_term:
  preferred_term: LDLR-Related Familial Hypercholesterolemia
  term:
    id: MONDO:0007750
    label: hypercholesterolemia, familial, 1
parents:
- Familial Hypercholesterolemia
notes: >
  Scope: curated as a standalone Disease rather than folded into
  kb/disorders/Familial_Hypercholesterolemia.yaml (MONDO:0005439). Four
  reasons. (1) MONDO models MONDO:0007750 as a distinct is_a child of
  MONDO:0005439, anchored on OMIM:143890 and the synonym "LDL receptor
  disorder". (2) The umbrella entry's has_subtypes axis is *zygosity*
  (heterozygous / homozygous), not gene, so a gene-defined entity has no place
  on it without mixing two orthogonal axes. (3) The two other dominant FH genes
  already have sibling entries curated on exactly this rationale -
  Familial_Defective_Apolipoprotein_B-100 (MONDO:0007751, APOB) and
  Autosomal_Dominant_Hypercholesterolemia_3 (MONDO:0011369, PCSK9) - and
  leaving the receptor-side form as the one unmodelled member of the trio makes
  the set incoherent. (4) The mechanism graph curated here is deliberately NOT
  the umbrella's: the umbrella models a single "LDL receptor deficiency" entry
  point into a shared LDL-to-atherosclerosis pathway, whereas this entry
  elaborates the LDL receptor's own itinerary into per-step nodes (synthesis,
  ER-to-Golgi export, surface binding, clathrin-mediated internalization,
  endosomal release and recycling), maps the classical mutation classes onto
  those steps, and carries the residual-receptor-activity node that gates
  response to receptor-dependent therapy. That last relation is what makes the
  allelic series clinically actionable and it is not modelled anywhere else in
  the knowledge base.

  Deliberately NOT duplicated from the umbrella entry: the EHR case-finding
  phenotype algorithms (SEARCH, FAMCAT, FIND FH), the general FH prevalence
  and cascade-screening apparatus, the environmental risk-factor block, and the
  APOB/PCSK9/LDLRAP1/APOE arms. Cite MONDO:0005439 for the disorder as a class;
  cite this entry for receptor-side mechanism.

  Named Entity Confusion preflight (dismech NEC SOP): the hypercholesterolemia
  series is a high-NEC-risk numbered-and-lettered class (FH1/LDLR vs familial
  defective apoB-100 "type B"/APOB vs ADH3/PCSK9). `just preflight-dr` returned
  SKIP because MONDO records no RO:0004003 causal gene for MONDO:0007750, so
  the manual checks were run: the report's OMIM (143890) matches the MONDO
  xref exactly; gene mentions in the report are dominated by LDLR (70) over
  PCSK9 (19) and APOB (3); and the MONDO synonym list ("LDL receptor
  disorder", "hyperlipoproteinemia, type 2A") points at the receptor-side
  entity and does not collide with the labels or synonyms of MONDO:0007751 or
  MONDO:0011369. Mechanistic claims here are anchored on LDLR publications;
  PCSK9 appears only where a PCSK9-directed *drug* acts on the LDL receptor,
  which is receptor-side biology, not the ADH3 disease.

  evidence_source convention for the GeneReviews chapter (PMID:24404629):
  statements taken from its Clinical Characteristics, Diagnosis and Genetic
  Counseling sections report human patient observations and are tagged
  HUMAN_CLINICAL, while statements taken from its Management and
  Agents/Circumstances-to-Avoid sections are expert recommendations rather than
  reported data and are tagged OTHER. The mix of two evidence_source values
  against a single PMID in this file is deliberate, not drift. Separately, the
  chapter covers FH as a class across LDLR, APOB and PCSK9, so several items
  citing it carry supports: PARTIAL to mark the statement as class-level rather
  than LDLR-specific.
references:
- reference: PMID:24404629
  title: "Familial Hypercholesterolemia."
  tags:
  - GeneReviews
  findings:
  - statement: >-
      Clinical characteristics. GeneReviews describes the FH clinical spectrum
      that LDLR-related FH defines - premature atherosclerotic plaque in the
      coronary arteries and proximal aorta, angina and myocardial infarction,
      tendon xanthoma, xanthelasma, and early corneal arcus, with calcific
      aortic valve disease and childhood-onset coronary artery disease in
      biallelic disease. The chapter covers FH as a class across LDLR, APOB and
      PCSK9, so it is class-level rather than LDLR-specific evidence and is
      cited as such throughout this entry.
    supporting_text: >-
      increases the risk of premature cardiovascular events such as angina and
      myocardial infarction
  - statement: >-
      Diagnosis and testing. GeneReviews gives the untreated LDL-C thresholds
      for a clinical FH diagnosis and names LDLR as one of three molecular
      routes to FH - the receptor-side route that defines this entry.
    supporting_text: >-
      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.
  - statement: >-
      Management. GeneReviews sets out lipid surveillance from age two years,
      statin initiation in children from around age eight, cardiovascular
      risk-factor modification, and the contraindication of statins in
      pregnancy.
    supporting_text: >-
      Monitor lipid levels from age two years
  - statement: >-
      Agents and circumstances to avoid. GeneReviews names the exposures that
      compound the arterial risk conferred by the receptor defect.
    supporting_text: >-
      Agents/circumstances to avoid: Smoking, high intake of saturated and
      trans unsaturated fat, sedentary lifestyle, obesity, hypertension, and
      diabetes mellitus.
  - statement: >-
      Genetic counseling. GeneReviews states the autosomal dominant
      transmission risk that applies to LDLR-related FH and the more severe,
      earlier-onset presentation of biallelic disease.
    supporting_text: >-
      Each child of an individual with a heterozygous pathogenic variant in
      APOB, LDLR, or PCSK9 has a 50% chance of inheriting the pathogenic
      variant and having FH.
classifications:
  harrisons_chapter:
  - classification_value: ENDOCRINOLOGY_METABOLISM
    evidence:
    - reference: PMID:1301956
      reference_title: "Molecular genetics of the LDL receptor gene in familial hypercholesterolemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The low density lipoprotein (LDL) receptor is a cell surface transmembrane protein that mediates the uptake and lysosomal degradation of plasma LDL, thereby providing cholesterol to cells."
      explanation: Places the disease in cholesterol/lipoprotein metabolism.
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
    evidence:
    - reference: PMID:1301956
      reference_title: "Molecular genetics of the LDL receptor gene in familial hypercholesterolemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Mutations disrupting the function of this receptor produce autosomal dominant familial hypercholesterolemia (FH)."
      explanation: Establishes the entity as a Mendelian disorder of a single named gene.
  icimd_category:
  - classification_value: hypercholesterolemias
    evidence:
    - reference: PMID:1301956
      reference_title: "Molecular genetics of the LDL receptor gene in familial hypercholesterolemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Affected individuals have elevated plasma levels of LDL, which causes premature coronary atherosclerosis."
      explanation: Places LDLR-related FH among the inherited hypercholesterolemias.
inheritance:
- name: Autosomal Dominant
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  penetrance: COMPLETE
  expressivity: VARIABLE
  description: >-
    A single pathogenic LDLR allele is sufficient to raise LDL cholesterol from
    birth, and transmission is autosomal dominant. Penetrance for the
    biochemical phenotype is essentially complete; penetrance for clinical
    cardiovascular events is age-dependent and modified by treatment, Lp(a),
    and conventional risk factors, so expressivity is variable. The trait is
    more precisely co-dominant than dominant, because two pathogenic alleles
    produce a substantially more severe phenotype than one - the gene-dosage
    relation curated under has_subtypes on the umbrella entry.
  evidence:
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "APOB-, LDLR-, and PCSK9-related FH are inherited in an autosomal dominant manner."
    explanation: GeneReviews states the mode of inheritance for LDLR-related FH explicitly.
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Each child of an individual with a heterozygous pathogenic variant in APOB, LDLR, or PCSK9 has a 50% chance of inheriting the pathogenic variant and having FH."
    explanation: States the 50% transmission risk used in genetic counselling.
  - reference: PMID:1301956
    reference_title: "Molecular genetics of the LDL receptor gene in familial hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Mutations disrupting the function of this receptor produce autosomal dominant familial hypercholesterolemia (FH)."
    explanation: The founding molecular-genetic account of the disease attributes dominant FH to LDLR mutation.
prevalence:
- population: Molecularly diagnosed familial hypercholesterolemia cohorts
  measure_type: UNKNOWN
  prevalence_class: UNKNOWN
  notes: >-
    Recorded as a share of molecularly solved FH rather than as a population
    rate. LDLR is by a wide margin the most common FH gene, but the reported
    share varies with referral criteria, panel design, and whether
    deletion/duplication analysis was performed, so the figure is carried as a
    quoted range with its source rather than normalized to a single number.
    Population prevalence of the FH phenotype as a whole belongs to the
    umbrella entry (MONDO:0005439) and is not restated here.
  evidence:
  - reference: PMID:30306860
    reference_title: "New Horizons in the Pathogenesis, Pathophysiology and Treatment of Familial Hypercholesterolaemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most common (60-80%) FH cause is mutations of the LDL Receptor (LDLR) protein (6 classes with a different number of receptors and functionality)."
    explanation: Quantifies the LDLR share of FH and names the receptor-class scheme this entry models.
progression:
- phase: Presymptomatic biochemical disease (birth onward)
  notes: >-
    LDL cholesterol is elevated from birth because the receptor defect is
    constitutional. Heterozygotes are typically asymptomatic through childhood
    while arterial cholesterol exposure accumulates; this is the window in
    which treatment has the largest effect on lifetime risk.
  evidence:
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Monitor lipid levels from age two years"
    explanation: >-
      Surveillance from age two reflects a biochemical phenotype that is
      present long before any clinical event.
- phase: Extravascular cholesterol deposition (childhood to adulthood)
  notes: >-
    Tendon xanthoma, xanthelasma, and premature corneal arcus accumulate with
    age and with the height of the LDL burden. They are specific but
    insensitive - their absence does not exclude the diagnosis.
  evidence:
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Xanthomas (cholesterol deposits in tendons) may be visible in the Achilles tendons or tendons of the hands and worsen with age as a result of extremely high cholesterol levels."
    explanation: Describes the age-dependent accumulation of tendon xanthoma.
- phase: Premature atherosclerotic cardiovascular disease
  notes: >-
    Coronary and proximal aortic plaque develops decades earlier than in the
    general population. In biallelic disease coronary events and calcific
    aortic valve disease can occur in childhood or adolescence.
  evidence:
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Individuals with a more severe phenotype, often as a result of biallelic variants, can present with very significant elevations in LDL-C (>500 mg/dL), early-onset coronary artery disease (CAD; presenting as early as childhood in some), and calcific aortic valve disease."
    explanation: Sets out the severe end of the course, driven by receptor gene dosage.
pathophysiology:
- name: LDLR Loss-of-Function Variant
  role: trigger
  biological_scale: MOLECULAR
  description: >-
    A germline pathogenic variant in LDLR at 19p13.2. The gene spans more than
    45 kb in 18 exons whose boundaries map onto the receptor's functional
    modules - the cysteine-rich ligand-binding repeats, the EGF-precursor
    homology domain, the O-linked sugar domain, the transmembrane segment and
    the cytoplasmic tail - so the mutated exon largely predicts which step of
    the receptor's itinerary is broken. More than 2300 unique FH-associated
    LDLR variants have been catalogued, spanning missense, nonsense,
    frameshift, splice, promoter and exon-level copy-number changes. This node
    is the single lesion; the five nodes immediately downstream are the
    alternative steps at which it can act.
  genes:
  - preferred_term: LDLR
    term:
      id: hgnc:6547
      label: LDLR
  genetic_context:
    gene:
      preferred_term: LDLR
      term:
        id: hgnc:6547
        label: LDLR
    variant_origin: GERMLINE
    functional_impact_category: LOSS_OF_FUNCTION
    description: >-
      The variant consequence is loss of function - fewer functional LDL
      receptors reach or persist on the hepatocyte surface. Recorded on the
      genetic context rather than as a Descriptor modifier because the claim is
      about the consequence of an allele. The severity of that loss is
      allele-specific and is the subject of the class nodes downstream.
  molecular_functions:
  - preferred_term: low-density lipoprotein particle receptor activity
    modifier: DECREASED
    term:
      id: GO:0005041
      label: low-density lipoprotein particle receptor activity
  locations:
  - preferred_term: liver
    term:
      id: UBERON:0002107
      label: liver
  evidence:
  - reference: PMID:1301956
    reference_title: "Molecular genetics of the LDL receptor gene in familial hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Mutations disrupting the function of this receptor produce autosomal dominant familial hypercholesterolemia (FH)."
    explanation: States the causal relation that defines this entry's trigger node.
  - reference: PMID:2988123
    reference_title: "The LDL receptor gene: a mosaic of exons shared with different proteins."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "This gene is more than 45 kilobases in length and contains 18 exons, most of which correlate with functional domains previously defined at the protein level."
    explanation: >-
      Establishes the exon-to-domain correspondence that underlies the
      structure-function mapping used by the class nodes downstream.
  - reference: PMID:34906454
    reference_title: "The Clinical Genome Resource (ClinGen) Familial Hypercholesterolemia Variant Curation Expert Panel consensus guidelines for LDLR variant classification."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In this study, we provide consensus recommendations for the most common FH-associated gene, LDLR, where >2300 unique FH-associated variants have been identified."
    explanation: Quantifies the size of the LDLR allelic series curated by this entry.
  downstream:
  - target: Absent LDL Receptor Synthesis
    causal_link_type: DIRECT
    description: >-
      Null (class 1) alleles - large deletions removing the promoter, nonsense
      and frameshift changes, and alleles producing no detectable protein -
      abolish receptor synthesis outright.
    evidence:
    - reference: PMID:3343347
      reference_title: "Multiple crm- mutations in familial hypercholesterolemia. Evidence for 13 alleles, including four deletions."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "16 of the 132 cell strains (12%) synthesized no immunodetectable LDL receptor protein, indicating the presence of two mutant genes that failed to produce cross-reacting material (crm- mutations)."
      explanation: >-
        Demonstrates the null class directly - patient fibroblasts making no
        detectable receptor protein at all.
  - target: Impaired ER-to-Golgi Transport of the LDL Receptor
    causal_link_type: DIRECT
    description: >-
      Class 2 alleles allow synthesis but the receptor misfolds and is retained
      in the endoplasmic reticulum instead of maturing through the Golgi.
    evidence:
    - reference: PMID:32015373
      reference_title: "Mutation type classification and pathogenicity assignment of sixteen missense variants located in the EGF-precursor homology domain of the LDLR."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Of the analysed variants, we found six non-pathogenic LDLR variants and ten pathogenic variants distributed as follow: three class 3 variants; four class 2 variants; and three class 5 variants."
      explanation: >-
        Assigns real patient variants to the transport-defective class in a
        functional assay, showing the class is an operational category and not
        just a textbook scheme.
  - target: Defective LDL Binding at the Hepatocyte Surface
    causal_link_type: DIRECT
    description: >-
      Class 3 alleles produce a receptor that reaches the surface but binds
      apoB-100 poorly, typically through changes in the cysteine-rich
      ligand-binding repeats or in the EGF-precursor domain that positions
      them.
    evidence:
    - reference: PMID:32015373
      reference_title: "Mutation type classification and pathogenicity assignment of sixteen missense variants located in the EGF-precursor homology domain of the LDLR."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "The activity of sixteen LDLR variants was functionally characterized by determining LDLR expression by Western blot and LDLR expression, LDL binding capacity and uptake, and LDLR recycling activity by flow cytometry in transfected CHO-ldlA7 cells."
      explanation: >-
        Describes the assay that separates a binding defect from expression and
        recycling defects, which is what makes this a distinct node.
  - target: Defective Clustering in Clathrin-Coated Pits
    causal_link_type: DIRECT
    description: >-
      Class 4 alleles disable the cytoplasmic internalization signal, so a
      fully synthesized, surface-expressed, ligand-competent receptor never
      enters the cell.
    evidence:
    - reference: PMID:3955657
      reference_title: "The J.D. mutation in familial hypercholesterolemia: amino acid substitution in cytoplasmic domain impedes internalization of LDL receptors."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "The DNA sequence revealed a substitution of a cysteine codon for a tyrosine codon at residue 807 in the cytoplasmic domain of the receptor."
      explanation: >-
        Identifies the founding internalization-defective allele and localizes
        it to the cytoplasmic tail rather than the ligand-binding region.
  - target: Defective Endosomal Ligand Release and Receptor Recycling
    causal_link_type: DIRECT
    description: >-
      Class 5 alleles allow binding and internalization but the receptor fails
      to release LDL in the acidified endosome, so receptor and ligand are
      degraded together instead of the receptor returning to the surface.
    evidence:
    - reference: PMID:32015373
      reference_title: "Mutation type classification and pathogenicity assignment of sixteen missense variants located in the EGF-precursor homology domain of the LDLR."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "LDLR structure is organized in 5 different domains, including an EGF-precursor homology domain that plays a pivotal role in lipoprotein release and receptor recycling."
      explanation: >-
        Assigns the ligand-release and recycling step to a specific receptor
        domain, the structural basis of the class 5 phenotype.
- name: Absent LDL Receptor Synthesis
  biological_scale: MOLECULAR
  description: >-
    The class 1 (null, receptor-negative) branch. No immunodetectable LDL
    receptor protein is made, because the allele deletes the promoter, produces
    no mRNA, or produces mRNA that yields no protein. This is the most severe
    branch and the one with the least therapeutic room: there is no receptor to
    upregulate. In clinical trials of homozygous disease it is operationalized
    as "null-null" or receptor-negative status.
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  molecular_functions:
  - preferred_term: low-density lipoprotein particle receptor activity
    modifier: ABSENT
    term:
      id: GO:0005041
      label: low-density lipoprotein particle receptor activity
  evidence:
  - reference: PMID:3343347
    reference_title: "Multiple crm- mutations in familial hypercholesterolemia. Evidence for 13 alleles, including four deletions."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Four of the alleles produced no mRNA. Three of these four mRNA- alleles had large deletions ranging from 6 to 20 kb that eliminated the promoter region of the gene."
    explanation: Documents the molecular routes to complete absence of receptor protein.
  - reference: PMID:32813947
    reference_title: "Evinacumab for Homozygous Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This disorder is associated with genetic variants that result in virtually absent (null-null) or impaired (non-null) LDL-receptor activity."
    explanation: >-
      Shows the null versus non-null distinction being used as a formal
      stratifier in a contemporary phase 3 trial.
  downstream:
  - target: Reduced Functional Hepatic LDL Receptor Activity
    causal_link_type: DIRECT
    description: Absent receptor protein is the limiting case of reduced receptor activity.
    evidence:
    - reference: PMID:3343347
      reference_title: "Multiple crm- mutations in familial hypercholesterolemia. Evidence for 13 alleles, including four deletions."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "16 of the 132 cell strains (12%) synthesized no immunodetectable LDL receptor protein, indicating the presence of two mutant genes that failed to produce cross-reacting material (crm- mutations)."
      explanation: >-
        Reports the measured result: in 12% of homozygous FH cell strains no
        receptor protein is made at all, which is the limiting case of reduced
        receptor activity this edge asserts.
- name: Impaired ER-to-Golgi Transport of the LDL Receptor
  biological_scale: MOLECULAR
  description: >-
    The class 2 (transport-defective) branch. The receptor is synthesized but
    misfolds and is retained in the endoplasmic reticulum rather than being
    further glycosylated in the Golgi and delivered to the surface. Retention
    may be complete (class 2a) or partial (class 2b), and partial retention
    leaves residual surface receptor - which matters therapeutically, because
    residual receptor is what receptor-directed drugs act on.
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  biological_processes:
  - preferred_term: endoplasmic reticulum to Golgi vesicle-mediated transport
    modifier: DECREASED
    term:
      id: GO:0006888
      label: endoplasmic reticulum to Golgi vesicle-mediated transport
  evidence:
  - reference: PMID:32015373
    reference_title: "Mutation type classification and pathogenicity assignment of sixteen missense variants located in the EGF-precursor homology domain of the LDLR."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Of the analysed variants, we found six non-pathogenic LDLR variants and ten pathogenic variants distributed as follow: three class 3 variants; four class 2 variants; and three class 5 variants."
    explanation: Assigns patient variants to the transport-defective class by functional assay.
  - reference: PMID:25386756
    reference_title: "Advantages and versatility of fluorescence-based methodology to characterize the functionality of LDLR and class mutation assignment."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Additionally confocal microscopy allowed the assignment of different class mutation to the variants assayed."
    explanation: >-
      Confirms that subcellular localization imaging is what distinguishes an
      ER-retained receptor from a surface-expressed one.
  downstream:
  - target: Reduced Functional Hepatic LDL Receptor Activity
    causal_link_type: DIRECT
    description: >-
      A receptor stuck in the ER never reaches the surface, so it contributes
      nothing to LDL clearance regardless of whether its ligand-binding
      sequence is intact.
    evidence:
    - reference: PMID:25386756
      reference_title: "Advantages and versatility of fluorescence-based methodology to characterize the functionality of LDLR and class mutation assignment."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Use of fluorescence yielded similar results than 125I-labeled lipoproteins concerning LDLR activity determination, and also allows class mutation classification."
      explanation: >-
        Reports that a single functional readout - LDLR activity - both
        reproduces the reference radiolabel measurement and resolves which
        mutation class produced it, which is what makes receptor activity the
        common quantity every class converges on.
- name: Defective LDL Binding at the Hepatocyte Surface
  biological_scale: MOLECULAR
  description: >-
    The class 3 (binding-defective) branch. Receptor reaches the surface in
    normal numbers but binds apoB-100-containing LDL with reduced affinity.
    Changes typically fall in the cysteine-rich ligand-binding repeats or in the
    EGF-precursor homology domain that holds them in a binding-competent
    conformation. This is the receptor-side mirror of the ligand-side defect
    curated in Familial_Defective_Apolipoprotein_B-100 - the same handshake
    fails, from the other side.
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  molecular_functions:
  - preferred_term: low-density lipoprotein particle receptor binding
    modifier: DECREASED
    term:
      id: GO:0050750
      label: low-density lipoprotein particle receptor binding
  evidence:
  - reference: PMID:32015373
    reference_title: "Mutation type classification and pathogenicity assignment of sixteen missense variants located in the EGF-precursor homology domain of the LDLR."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "They showed similar expression to wt LDLR but demonstrated deficient LDL binding."
    explanation: >-
      The defining functional signature of the class 3 branch: receptor is
      expressed at normal levels yet binds LDL poorly, separating a binding
      defect from a synthesis or trafficking defect.
  - reference: PMID:31106925
    reference_title: "Functional analysis of new variants at the low-density lipoprotein receptor associated with familial hypercholesterolemia."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "All new LDLR variants found in our patients were functionally validated in CHO-ldlA7 cells. The LDLR activity was measured by flow cytometry and LDLR expression was detected by immunofluorescence."
    explanation: >-
      Describes the paired activity/expression measurement that identifies a
      binding defect - normal expression with reduced activity.
  downstream:
  - target: Reduced Functional Hepatic LDL Receptor Activity
    causal_link_type: DIRECT
    description: >-
      A surface receptor that cannot capture its ligand removes no LDL, so
      functional receptor activity falls even though receptor abundance is
      normal.
    evidence:
    - reference: PMID:31106925
      reference_title: "Functional analysis of new variants at the low-density lipoprotein receptor associated with familial hypercholesterolemia."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "The functional in vitro characterization of rare variants at the LDLR is a useful tool to classify the new variants."
      explanation: >-
        Establishes measured receptor function, not receptor presence, as the
        quantity that classifies an allele.
- name: Defective Clustering in Clathrin-Coated Pits
  biological_scale: CELLULAR
  description: >-
    The class 4 (internalization-defective) branch. The cytoplasmic tail of the
    LDL receptor carries the signal that concentrates it in clathrin-coated
    pits; a change there leaves a receptor that is expressed and binds LDL
    normally but is distributed diffusely over the surface and enters the cell
    slowly. The founding example is patient J.D., whose receptor carries a
    tyrosine-to-cysteine substitution at residue 807. Because the LDLRAP1/ARH
    adaptor serves this same step, the recessive LDLRAP1 disease is the
    phenocopy of this branch acting in trans.
  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
  evidence:
  - reference: PMID:3955657
    reference_title: "The J.D. mutation in familial hypercholesterolemia: amino acid substitution in cytoplasmic domain impedes internalization of LDL receptors."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Upon transfection into receptor-deficient hamster cells, the cDNA specified a receptor that bound LDL normally, but entered the cell slowly."
    explanation: >-
      Separates binding from internalization experimentally - the defining
      observation for this class.
  - reference: PMID:3955657
    reference_title: "The J.D. mutation in familial hypercholesterolemia: amino acid substitution in cytoplasmic domain impedes internalization of LDL receptors."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Electron microscopy showed that this receptor was distributed diffusely over the cell surface, whereas the receptor produced by the normal cDNA was concentrated in coated pits."
    explanation: >-
      Direct morphological evidence that the lesion is failure to cluster in
      clathrin-coated pits.
  downstream:
  - target: Reduced Functional Hepatic LDL Receptor Activity
    causal_link_type: DIRECT
    description: >-
      A receptor that binds LDL but does not internalize it does not clear it;
      the bound particle is not delivered to the lysosome.
    evidence:
    - reference: PMID:3955657
      reference_title: "The J.D. mutation in familial hypercholesterolemia: amino acid substitution in cytoplasmic domain impedes internalization of LDL receptors."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "These results support the hypothesis that cytoplasmic domains direct receptors to coated pits, thereby determining the high rate of receptor internalization in animal cells."
      explanation: >-
        States the general principle - internalization rate, and therefore
        clearance capacity, is set by the cytoplasmic signal.
- name: Defective Endosomal Ligand Release and Receptor Recycling
  biological_scale: CELLULAR
  description: >-
    The class 5 (recycling-defective) branch. Binding and internalization are
    intact, but the receptor fails to release LDL when the endosome acidifies,
    so receptor and ligand traffic together to the lysosome and the receptor is
    consumed rather than returned to the surface. Each receptor therefore makes
    one round trip instead of many, and functional clearance capacity collapses
    even though synthesis is normal. This is also the step that PCSK9 subverts
    pharmacologically, which is why PCSK9-directed drugs raise receptor
    abundance in patients who still have recyclable receptor.
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  biological_processes:
  - preferred_term: receptor recycling
    modifier: DECREASED
    term:
      id: GO:0001881
      label: receptor recycling
  evidence:
  - reference: PMID:32015373
    reference_title: "Mutation type classification and pathogenicity assignment of sixteen missense variants located in the EGF-precursor homology domain of the LDLR."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "LDLR structure is organized in 5 different domains, including an EGF-precursor homology domain that plays a pivotal role in lipoprotein release and receptor recycling."
    explanation: Localizes ligand release and recycling to a specific receptor domain.
  - reference: PMID:32015373
    reference_title: "Mutation type classification and pathogenicity assignment of sixteen missense variants located in the EGF-precursor homology domain of the LDLR."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "In this way, although the protein structure is not affected in LDLR expression or LDL binding and uptake activities, the alteration introduced by the asparagine is enough to cause a defect in recycling of the protein."
    explanation: >-
      Isolates the class 5 defect: expression, binding and uptake are all
      intact and recycling alone fails, which is what distinguishes this branch
      from the synthesis, trafficking and binding branches.
  downstream:
  - target: Reduced Functional Hepatic LDL Receptor Activity
    causal_link_type: DIRECT
    description: >-
      Loss of recycling converts a reusable receptor into a single-use one,
      cutting the LDL particles cleared per receptor synthesized.
    evidence:
    - reference: PMID:32015373
      reference_title: "Mutation type classification and pathogenicity assignment of sixteen missense variants located in the EGF-precursor homology domain of the LDLR."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "These results can be incorporated into clinical management of patients by helping guide the appropriate level of treatment intensity depending on the extent of loss of LDLR activity."
      explanation: >-
        States explicitly that class assignment resolves into a single quantity
        - extent of loss of LDLR activity - which is this convergence node.
- name: Reduced Functional Hepatic LDL Receptor Activity
  role: central_effector
  biological_scale: CELLULAR
  description: >-
    The convergence node of the allelic series. Whichever step is broken -
    synthesis, ER export, ligand binding, internalization, or recycling - the
    measurable output is the same: fewer LDL particles cleared per unit time by
    the hepatocyte. Functional assays report this as a single quantity
    (percentage of wild-type LDL uptake), which is why class assignment and
    residual activity are recorded separately: the class says *where* the
    itinerary breaks, the residual activity says *how much* capacity survives.
    Null alleles are conventionally under about 2% of normal activity, though
    trial protocols have operationalized "null" at thresholds as high as 15%.
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  biological_processes:
  - preferred_term: receptor-mediated endocytosis
    modifier: DECREASED
    term:
      id: GO:0006898
      label: receptor-mediated endocytosis
  molecular_functions:
  - preferred_term: low-density lipoprotein particle receptor activity
    modifier: DECREASED
    term:
      id: GO:0005041
      label: low-density lipoprotein particle receptor activity
  locations:
  - preferred_term: liver
    term:
      id: UBERON:0002107
      label: liver
  evidence:
  - reference: PMID:1301956
    reference_title: "Molecular genetics of the LDL receptor gene in familial hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The low density lipoprotein (LDL) receptor is a cell surface transmembrane protein that mediates the uptake and lysosomal degradation of plasma LDL, thereby providing cholesterol to cells."
    explanation: States the receptor function whose reduction this node represents.
  - reference: PMID:32015373
    reference_title: "Mutation type classification and pathogenicity assignment of sixteen missense variants located in the EGF-precursor homology domain of the LDLR."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "These results can be incorporated into clinical management of patients by helping guide the appropriate level of treatment intensity depending on the extent of loss of LDLR activity."
    explanation: >-
      Treats residual LDLR activity as the single clinically actionable output
      of the allelic series.
  downstream:
  - target: Impaired Receptor-Mediated Clearance of Plasma LDL
    causal_link_type: DIRECT
    description: >-
      Hepatic LDL receptors perform most clearance of circulating LDL, so a
      fall in functional receptor activity directly lengthens LDL residence
      time in plasma.
    evidence:
    - reference: PMID:8349823
      reference_title: "Hypercholesterolemia in low density lipoprotein receptor knockout mice and its reversal by adenovirus-mediated gene delivery."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "The half-lives for intravenously administered 125I-VLDL and 125I-LDL were prolonged by 30-fold and 2.5-fold, respectively, but the clearance of 125I-HDL was normal in the LDLR-/- mice."
      explanation: >-
        Measures the clearance defect directly, and shows it is specific to
        apoB-containing particles.
  - target: Residual Receptor Activity Gates Receptor-Dependent LDL Lowering
    causal_link_type: DIRECT
    description: >-
      The same residual activity that sets the untreated LDL level also sets
      how much a receptor-directed drug can achieve, because those drugs act by
      increasing the number of functional receptors rather than by creating
      them.
    evidence:
    - reference: PMID:24014831
      reference_title: "Effect of the proprotein convertase subtilisin/kexin 9 monoclonal antibody, AMG 145, in homozygous familial hypercholesterolemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "This study demonstrates significant and dose-related LDL cholesterol lowering with a PCSK9 monoclonal antibody in homozygous familial hypercholesterolemia patients with defective LDL receptor activity but no reduction in those who were receptor negative."
      explanation: >-
        Direct clinical demonstration that residual receptor activity, not
        drug dose, determines whether a receptor-directed therapy works.
- name: Residual Receptor Activity Gates Receptor-Dependent LDL Lowering
  biological_scale: ORGANISM
  description: >-
    The pharmacogenetic node, and the reason the allelic series is clinically
    actionable rather than merely descriptive. Statins lower intracellular
    cholesterol and thereby induce more LDL receptor; PCSK9 antibodies and
    inclisiran prevent or reduce PCSK9-mediated receptor degradation. Both
    families of drugs work by putting *more* receptor on the hepatocyte
    surface, so both require a receptor that can be made and can function. The
    genotype-stratified evidence below is for a PCSK9 antibody: in the two
    receptor-negative (null-null) homozygotes studied there was nothing to
    induce and the response was absent, while in receptor-defective
    homozygotes there was residual receptor and the response was preserved.
    Whether statins behave the same way in receptor-negative disease has not
    been tested here - the two null patients in that trial were already on
    stable statin therapy at enrolment - and the mechanisms differ (statins act
    transcriptionally on receptor synthesis, PCSK9-directed agents
    post-translationally on receptor degradation and recycling), so the
    statin/PCSK9 asymmetry is carried as an open question in the
    residual_ldlr_activity_response_threshold discussion rather than asserted.
    LDLR-independent agents - the MTP inhibitor lomitapide, the ANGPTL3
    antibody evinacumab, and lipoprotein apheresis - bypass the receptor
    entirely and retain effect in null-null disease. This node is the target of
    the treatment entries curated below.
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  locations:
  - preferred_term: liver
    term:
      id: UBERON:0002107
      label: liver
  evidence:
  - reference: PMID:24014831
    reference_title: "Effect of the proprotein convertase subtilisin/kexin 9 monoclonal antibody, AMG 145, in homozygous familial hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "No reduction was seen in the 2 receptor-negative patients."
    explanation: >-
      The negative half of the relation - a receptor-directed drug does nothing
      when no receptor can be made.
  - reference: PMID:24014831
    reference_title: "Effect of the proprotein convertase subtilisin/kexin 9 monoclonal antibody, AMG 145, in homozygous familial hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Over the treatment periods, mean±SD LDL cholesterol reductions in the 6 LDL receptor-defective patients were 19.3±16% and 26.3±20% with 4- and 2-week dosing, respectively"
    explanation: >-
      The positive half - the same drug in the same trial lowers LDL when
      residual receptor activity exists.
  - reference: PMID:32813947
    reference_title: "Evinacumab for Homozygous Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The LDL cholesterol level was lower in the evinacumab group than in the placebo group in patients with null-null variants (-43.4% vs. +16.2%) and in those with non-null variants (-49.1% vs. -3.8%)."
    explanation: >-
      Shows the complementary case - an LDLR-independent mechanism works in
      both genotype strata, which is what makes the gating relation
      therapeutically consequential rather than merely prognostic.
  notes: >-
    Caveat on strength of claim: the receptor-negative arm of the AMG 145 study
    comprised two patients, so "no response in receptor-negative disease" rests
    on a very small n even though it is consistent with the mechanism and with
    the way regulatory labels and trial protocols stratify HoFH. Treat the
    direction as well supported and the magnitude as imprecise.
- name: Impaired Receptor-Mediated Clearance of Plasma LDL
  biological_scale: ORGANISM
  description: >-
    Reduced hepatic receptor capacity lengthens the residence time of
    apoB-100-containing LDL and IDL in plasma. The defect is specific to the
    receptor's ligands: HDL clearance is unaffected, which is why the
    biochemical phenotype is an isolated elevation of LDL rather than a
    generalized dyslipidemia.
  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:8183926
    reference_title: "The two-receptor model of lipoprotein clearance: tests of the hypothesis in \"knockout\" mice lacking the low density lipoprotein receptor, apolipoprotein E, or both proteins."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "LDLR(-/-) mice had a relatively isolated elevation in plasma LDL"
    explanation: >-
      Shows that loss of the receptor produces a selective LDL clearance
      defect rather than a global lipoprotein abnormality.
  - reference: PMID:8349823
    reference_title: "Hypercholesterolemia in low density lipoprotein receptor knockout mice and its reversal by adenovirus-mediated gene delivery."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We conclude that the LDL receptor is responsible in part for the low levels of VLDL, IDL, and LDL in wild-type mice"
    explanation: Attributes normal plasma LDL levels to receptor-mediated clearance.
  downstream:
  - target: Lifelong Elevation of Plasma LDL Cholesterol
    causal_link_type: DIRECT
    description: >-
      Reduced clearance against unchanged production raises the steady-state
      plasma LDL concentration, from birth and for life.
    evidence:
    - reference: PMID:8349823
      reference_title: "Hypercholesterolemia in low density lipoprotein receptor knockout mice and its reversal by adenovirus-mediated gene delivery."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Total plasma cholesterol levels were twofold higher than those of wild-type litter-mates, owing to a seven- to ninefold increase in intermediate density lipoproteins (IDL) and LDL without a significant change in HDL."
      explanation: >-
        Quantifies the rise in plasma IDL/LDL that follows loss of receptor
        clearance capacity.
- name: Lifelong Elevation of Plasma LDL Cholesterol
  biological_scale: ORGANISM
  description: >-
    The defining biochemical phenotype. Because the receptor defect is
    constitutional, LDL cholesterol is elevated from birth, so the arterial
    tree accumulates cholesterol exposure over decades rather than from midlife
    onward. Untreated heterozygotes typically exceed 190 mg/dL; biallelic
    disease often exceeds 400-500 mg/dL.
  evidence:
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A clinical diagnosis of FH can be established in a proband with characteristic clinical features and significantly elevated LDL-C levels (typically >190 mg/dL in adults and >160 mg/dL in children)."
    explanation: Gives the diagnostic LDL-C thresholds for the untreated phenotype.
  - 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: HUMAN_CLINICAL
    snippet: "a low-density lipoprotein cholesterol (LDL-C) >10 mmol/L (>400 mg/dL) is suggestive of HoFH and warrants further evaluation"
    explanation: Gives the biallelic-disease threshold used in current consensus guidance.
  downstream:
  - target: Endothelial Dysfunction and Subendothelial LDL Retention
    causal_link_type: DIRECT
    description: >-
      Sustained high plasma LDL drives entry of apoB particles into the
      arterial intima and their retention on subendothelial proteoglycan - the
      initiating step of the shared atherogenesis programme.
    evidence:
    - reference: PMID:24404629
      reference_title: "Familial Hypercholesterolemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Familial hypercholesterolemia (FH) is characterized by significantly elevated low-density lipoprotein cholesterol (LDL-C) that leads to atherosclerotic plaque deposition in the coronary arteries and proximal aorta at an early age"
      explanation: States the LDL-to-plaque relation and its predilection sites.
  - target: Extravascular Cholesterol Deposition in Tendon, Skin, and Cornea
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - uptake of excess LDL-derived cholesterol by tissue macrophages
    description: >-
      The same circulating excess deposits outside the arterial wall, producing
      the classical stigmata. These are specific but insensitive, and are less
      often seen now that treatment begins earlier.
    evidence:
    - reference: PMID:24404629
      reference_title: "Familial Hypercholesterolemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Xanthomas (cholesterol deposits in tendons) may be visible in the Achilles tendons or tendons of the hands and worsen with age as a result of extremely high cholesterol levels."
      explanation: >-
        Attributes tendon xanthoma directly to cholesterol deposition driven by
        the height of the circulating burden.
- name: Endothelial Dysfunction and Subendothelial LDL Retention
  biological_scale: TISSUE
  conforms_to: "atherogenesis#Endothelial Dysfunction and Subendothelial LDL Retention"
  description: >-
    Conformance node. The atherogenic cascade downstream of the LDL elevation
    is the conserved one modelled in the atherogenesis module and is not
    re-derived here; what is disease-specific is that the apoB-lipoprotein
    driver is present from birth and at several times the usual concentration,
    so the same programme runs decades earlier.
  cell_types:
  - preferred_term: endothelial cell of artery
    term:
      id: CL:1000413
      label: endothelial cell of artery
  locations:
  - preferred_term: artery
    term:
      id: UBERON:0001637
      label: artery
  evidence:
  - reference: PMID:31748469
    reference_title: "The History of the WHHL Rabbit, an Animal Model of Familial Hypercholesterolemia (I) - Contribution to the Elucidation of the Pathophysiology of Human Hypercholesterolemia and Coronary Heart Disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Oxidized LDL accumulates in the arterial wall, monocyte adhesion molecules are expressed on arterial endothelial cells, and monocyte-derived macrophages infiltrate the arterial intima, resulting in the formation and progression of atherosclerosis."
    explanation: >-
      Describes the initiating arterial events as established in the
      LDLR-deficient rabbit, the model in which they were demonstrated in vivo.
  downstream:
  - target: Monocyte Recruitment and Macrophage Foam Cell Formation
    causal_link_type: DIRECT
    description: Retained and modified LDL recruits monocytes that become lipid-laden macrophages.
    evidence:
    - reference: PMID:31748469
      reference_title: "The History of the WHHL Rabbit, an Animal Model of Familial Hypercholesterolemia (I) - Contribution to the Elucidation of the Pathophysiology of Human Hypercholesterolemia and Coronary Heart Disease."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "monocyte adhesion molecules are expressed on arterial endothelial cells, and monocyte-derived macrophages infiltrate the arterial intima"
      explanation: Links endothelial activation to monocyte recruitment in the LDLR-deficient rabbit.
- name: Monocyte Recruitment and Macrophage Foam Cell Formation
  biological_scale: TISSUE
  conforms_to: "atherogenesis#Monocyte Recruitment and Macrophage Foam Cell Formation"
  description: >-
    Conformance node. Recruited monocyte-derived macrophages take up modified
    LDL and become foam cells, the cellular substance of the early lesion.
  cell_types:
  - preferred_term: macrophage
    term:
      id: CL:0000235
      label: macrophage
  - preferred_term: foam cell
    term:
      id: CL:0000891
      label: foam cell
  locations:
  - preferred_term: artery
    term:
      id: UBERON:0001637
      label: artery
  evidence:
  - reference: PMID:31748469
    reference_title: "The History of the WHHL Rabbit, an Animal Model of Familial Hypercholesterolemia (I) - Contribution to the Elucidation of the Pathophysiology of Human Hypercholesterolemia and Coronary Heart Disease."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "monocyte-derived macrophages infiltrate the arterial intima, resulting in the formation and progression of atherosclerosis"
    explanation: States macrophage infiltration as the step that builds the lesion.
  downstream:
  - target: Premature Atherosclerotic Cardiovascular Events
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - fibrofatty plaque growth and necrotic core formation
    - plaque instability and rupture
    - occlusive thrombosis
    description: >-
      Lesion growth, destabilization and thrombosis convert subclinical plaque
      into clinical events; the intervening steps are the conserved ones in the
      atherogenesis module.
    evidence:
    - reference: PMID:31748469
      reference_title: "The History of the WHHL Rabbit, an Animal Model of Familial Hypercholesterolemia (I) - Contribution to the Elucidation of the Pathophysiology of Human Hypercholesterolemia and Coronary Heart Disease."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "The rupture of coronary lesions requires secondary mechanical forces, such as spasm, in addition to vulnerable plaques."
      explanation: >-
        Identifies plaque rupture as the step between lesion and event, and
        notes it is not determined by plaque composition alone.
- name: Premature Atherosclerotic Cardiovascular Events
  biological_scale: ORGANISM
  conforms_to: "atherogenesis#Plaque Rupture, Thrombosis, and Ischemic Events"
  description: >-
    Conformance node. Angina, myocardial infarction, and less often stroke,
    occurring decades earlier than in the general population. In biallelic
    disease events may occur in childhood or adolescence and are accompanied by
    calcific aortic valve and aortic root disease, which is a supravalvular
    rather than purely valvular lesion and is not prevented by LDL lowering as
    reliably as coronary events are.
  locations:
  - preferred_term: coronary artery
    term:
      id: UBERON:0001621
      label: coronary artery
  - preferred_term: aortic valve
    term:
      id: UBERON:0002137
      label: aortic valve
  evidence:
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "increases the risk of premature cardiovascular events such as angina and myocardial infarction; stroke occurs more rarely"
    explanation: Names the clinical events and their relative frequency.
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Individuals with a more severe phenotype, often as a result of biallelic variants, can present with very significant elevations in LDL-C (>500 mg/dL), early-onset coronary artery disease (CAD; presenting as early as childhood in some), and calcific aortic valve disease."
    explanation: Establishes the childhood-onset and aortic valve arms in biallelic disease.
- name: Extravascular Cholesterol Deposition in Tendon, Skin, and Cornea
  biological_scale: TISSUE
  description: >-
    Macrophage-mediated deposition of LDL-derived cholesterol outside the
    arterial wall, producing tendon xanthoma (Achilles and extensor tendons of
    the hands), xanthelasma at the eyelids, and premature corneal arcus. These
    signs are highly specific for the untreated phenotype and are used in the
    Dutch Lipid Clinic Network and Simon Broome criteria, but they are
    insensitive - absence does not exclude the diagnosis, and early treatment
    both prevents and can reverse them.
  cell_types:
  - preferred_term: macrophage
    term:
      id: CL:0000235
      label: macrophage
  locations:
  - preferred_term: tendon
    term:
      id: UBERON:0000043
      label: tendon
  - preferred_term: cornea
    term:
      id: UBERON:0000964
      label: cornea
  - preferred_term: eyelid
    term:
      id: UBERON:0001711
      label: eyelid
  evidence:
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Xanthelasmas (yellowish, waxy deposits) can occur around the eyelids."
    explanation: Documents the periocular deposition site.
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    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: Documents corneal deposition and its premature timing.
  - reference: PMID:37730951
    reference_title: "Generation of a familial hypercholesterolemia model in non-human primate."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In addition, periocular xanthoma was observed only 1 year after birth."
    explanation: >-
      Independent demonstration in an LDLR-knockout primate that removing the
      receptor alone is sufficient to produce periocular xanthoma.
phenotypes:
- category: Biochemical
  name: Hypercholesterolemia
  description: >-
    Elevated total cholesterol from birth, driven entirely by the LDL fraction.
  phenotype_term:
    preferred_term: Hypercholesterolemia
    term:
      id: HP:0003124
      label: Hypercholesterolemia
    temporality: CHRONIC
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:1301956
    reference_title: "Molecular genetics of the LDL receptor gene in familial hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected individuals have elevated plasma levels of LDL, which causes premature coronary atherosclerosis."
    explanation: States the defining biochemical abnormality of LDLR-mutation carriers.
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Familial hypercholesterolemia (FH) is characterized by significantly elevated low-density lipoprotein cholesterol (LDL-C)"
    explanation: >-
      GeneReviews states the elevation as the characterizing feature. Frequency
      is set VERY_FREQUENT because the biochemical phenotype is essentially
      fully penetrant in variant carriers.
- category: Biochemical
  name: Elevated LDL Cholesterol
  description: >-
    The measured abnormality used for diagnosis and for monitoring treatment.
    Typically above 190 mg/dL in untreated adult heterozygotes and above 400
    mg/dL in biallelic disease.
  phenotype_term:
    preferred_term: Increased LDL cholesterol concentration
    term:
      id: HP:0003141
      label: Increased LDL cholesterol concentration
    temporality: CHRONIC
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A clinical diagnosis of FH can be established in a proband with characteristic clinical features and significantly elevated LDL-C levels (typically >190 mg/dL in adults and >160 mg/dL in children)."
    explanation: Gives the diagnostic thresholds and establishes the phenotype's universality.
  - 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: HUMAN_CLINICAL
    snippet: "a low-density lipoprotein cholesterol (LDL-C) >10 mmol/L (>400 mg/dL) is suggestive of HoFH and warrants further evaluation"
    explanation: Gives the corresponding threshold in biallelic disease.
- category: Physical
  name: Tendon Xanthoma
  description: >-
    Cholesterol deposits in the Achilles tendons and the extensor tendons of
    the hands, accumulating with age and with the magnitude of the LDL burden.
    Specific but insensitive.
  phenotype_term:
    preferred_term: Tendon xanthomatosis
    term:
      id: HP:0010874
      label: Tendon xanthomatosis
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Xanthomas (cholesterol deposits in tendons) may be visible in the Achilles tendons or tendons of the hands and worsen with age as a result of extremely high cholesterol levels."
    explanation: >-
      Names the sites and the progressive course. Frequency is deliberately
      omitted - reported prevalence varies widely with treatment era and
      ascertainment, and no quotable figure specific to LDLR-related FH was
      available.
- 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: HUMAN_CLINICAL
    snippet: "Xanthelasmas (yellowish, waxy deposits) can occur around the eyelids."
    explanation: Documents the sign and its location.
- category: Physical
  name: Premature Corneal Arcus
  description: >-
    An opaque ring at the corneal margin from cholesterol deposition, appearing
    at a younger age 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: HUMAN_CLINICAL
    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: Establishes both the sign and the premature timing that gives it diagnostic value.
- category: Cardiovascular
  name: Premature Coronary Artery Atherosclerosis
  description: >-
    Atherosclerotic plaque in the coronary arteries and proximal aorta
    developing decades earlier than in the general population, and in childhood
    in biallelic disease.
  phenotype_term:
    preferred_term: Coronary artery atherosclerosis
    term:
      id: HP:0001677
      label: Coronary artery atherosclerosis
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Familial hypercholesterolemia (FH) is characterized by significantly elevated low-density lipoprotein cholesterol (LDL-C) that leads to atherosclerotic plaque deposition in the coronary arteries and proximal aorta at an early age"
    explanation: States both the lesion and its premature timing.
- category: Cardiovascular
  name: Myocardial Infarction
  description: Coronary event resulting from premature atherosclerotic disease.
  phenotype_term:
    preferred_term: Myocardial infarction
    term:
      id: HP:0001658
      label: Myocardial infarction
  evidence:
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "increases the risk of premature cardiovascular events such as angina and myocardial infarction; stroke occurs more rarely"
    explanation: Names myocardial infarction as a principal clinical event.
- category: Cardiovascular
  name: Angina Pectoris
  description: Effort-related ischemic chest pain from coronary atherosclerosis.
  phenotype_term:
    preferred_term: Angina pectoris
    term:
      id: HP:0001681
      label: Angina pectoris
  evidence:
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "increases the risk of premature cardiovascular events such as angina and myocardial infarction"
    explanation: Names angina as a presenting cardiovascular event.
- category: Cardiovascular
  name: Calcific Aortic Valve Disease
  description: >-
    Aortic valve and aortic root calcification, characteristic of severe
    biallelic disease and less reliably prevented by LDL lowering than coronary
    disease is.
  phenotype_term:
    preferred_term: Aortic valve calcification
    term:
      id: HP:0004380
      label: Aortic valve calcification
  evidence:
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Individuals with a more severe phenotype, often as a result of biallelic variants, can present with very significant elevations in LDL-C (>500 mg/dL), early-onset coronary artery disease (CAD; presenting as early as childhood in some), and calcific aortic valve disease."
    explanation: Identifies calcific aortic valve disease as a feature of severe biallelic disease.
biochemical:
- name: Plasma LDL Cholesterol
  biomarker_term:
    preferred_term: LDL cholesterol
    term:
      id: CHEBI:47774
      label: low-density lipoprotein cholesterol
  presence: Increased
  notes: >-
    The primary diagnostic and monitoring analyte. Reference intervals and
    interpretation bands are not restated here; the diagnostic thresholds used
    in FH are carried on the phenotype entries above and in the diagnosis
    section.
  evidence:
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A clinical diagnosis of FH can be established in a proband with characteristic clinical features and significantly elevated LDL-C levels (typically >190 mg/dL in adults and >160 mg/dL in children)."
    explanation: Establishes LDL-C as the diagnostic analyte and gives its thresholds.
- name: Plasma Apolipoprotein B
  biomarker_term:
    preferred_term: Circulating apolipoprotein B concentration
    term:
      id: HP:0031798
      label: Elevated circulating apolipoprotein B concentration
  presence: Increased
  notes: >-
    Each atherogenic particle carries exactly one apoB-100 molecule, so apoB is
    a particle *count* where LDL-C is a cholesterol *mass*. That distinction
    matters in this disease specifically: the defect is in clearance of
    apoB-100-containing particles, so apoB tracks the quantity the receptor
    actually fails to remove. It also discriminates by allele class - null
    variants carry significantly higher apoB than defective variants in the
    SAFEHEART cohort.
  evidence:
  - reference: PMID:28475941
    reference_title: "Mutational analysis and genotype-phenotype relation in familial hypercholesterolemia: The SAFEHEART registry."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients with null variants have a more severe phenotype than patients with defective variants, presenting with significantly higher levels of atherogenic particles (total cholesterol, LDL-cholesterol and apolipoprotein B)."
    explanation: >-
      Names apolipoprotein B among the atherogenic particle measures elevated in
      this disease, and shows it separating null from defective allele classes.
- name: Lipoprotein(a)
  biomarker_term:
    preferred_term: Circulating lipoprotein(a) concentration
    term:
      id: HP:0430148
      label: Abnormal circulating lipoprotein(a) concentration
  presence: Variable
  notes: >-
    Not caused by the LDLR defect but an independent, additive risk modifier
    within it - and an interpretive trap, because Lp(a)-cholesterol is measured
    within the LDL-C fraction and can inflate an apparent FH phenotype.
  evidence:
  - reference: PMID:24632281
    reference_title: "Lipoprotein(a) levels in familial hypercholesterolemia: an important predictor of cardiovascular disease independent of the type of LDL receptor mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "On multivariate analysis, Lp(a) was an independent predictor of cardiovascular disease."
    explanation: Establishes Lp(a) as an independent cardiovascular risk predictor within FH.
  - reference: PMID:24632281
    reference_title: "Lipoprotein(a) levels in familial hypercholesterolemia: an important predictor of cardiovascular disease independent of the type of LDL receptor mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The risk of CVD is higher in those patients with an Lp(a) level >50 mg/dl and carrying a receptor-negative mutation in the LDLR gene compared with other less severe mutations."
    explanation: >-
      Shows Lp(a) risk interacting with the receptor class - the highest risk
      stratum is receptor-negative genotype plus high Lp(a).
genetic:
- name: LDLR
  gene_term:
    preferred_term: LDLR
    term:
      id: hgnc:6547
      label: LDLR
  association: Pathogenic Mutations
  presence: Positive
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  inheritance:
  - name: Autosomal Dominant
    inheritance_term:
      preferred_term: Autosomal dominant inheritance
      term:
        id: HP:0000006
        label: Autosomal dominant inheritance
  notes: >-
    LDLR at 19p13.2 spans >45 kb in 18 exons that map onto the receptor's
    structural modules. More than 2300 unique FH-associated variants have been
    catalogued - missense (the largest group), nonsense, frameshift, canonical
    and non-canonical splice changes, promoter changes, and exon-level
    deletions and duplications, so deletion/duplication analysis is part of an
    adequate genetic workup and not an optional extra. Variant interpretation
    follows the ClinGen FH Variant Curation Expert Panel's LDLR-specific
    modifications of the ACMG/AMP framework rather than the generic rules.

    The five variant entries below are the *functional* classes - which step of
    the receptor itinerary the allele breaks - and correspond one-to-one with
    the class nodes in the pathophysiology graph. They are orthogonal to the
    ACMG/AMP pathogenicity tiers: an allele has both a class and a
    classification, and only the class predicts response to receptor-directed
    therapy.
  variants:
  - name: Class 1 - null (receptor-negative)
    description: >-
      No LDL receptor protein is synthesized. Large deletions removing the
      promoter, nonsense and frameshift changes, and alleles that make normal
      mRNA but no detectable protein. Homozygotes for two such alleles are
      receptor-negative and respond poorly or not at all to receptor-directed
      drugs.
    type: "null"
    clinical_significance: PATHOGENIC
  - name: Class 2 - transport-defective
    description: >-
      The receptor is synthesized but misfolds and is retained in the
      endoplasmic reticulum instead of maturing through the Golgi to the
      surface. Retention may be complete (2a) or partial (2b).
    type: missense
    clinical_significance: PATHOGENIC
  - name: Class 3 - binding-defective
    description: >-
      Receptor reaches the surface but binds apoB-100 poorly. Changes fall in
      the cysteine-rich ligand-binding repeats or in the EGF-precursor homology
      domain that orients them.
    type: missense
    clinical_significance: PATHOGENIC
  - name: Class 4 - internalization-defective
    description: >-
      Receptor is expressed and binds LDL normally but fails to cluster in
      clathrin-coated pits, because the cytoplasmic internalization signal is
      disrupted. The founding allele is the J.D. mutation, a
      tyrosine-to-cysteine substitution at residue 807.
    type: missense
    clinical_significance: PATHOGENIC
  - name: Class 5 - recycling-defective
    description: >-
      Receptor binds and internalizes LDL but fails to release it in the
      acidified endosome, so receptor and ligand are degraded together and the
      receptor is not returned to the surface.
    type: missense
    clinical_significance: PATHOGENIC
  evidence:
  - reference: PMID:34906454
    reference_title: "The Clinical Genome Resource (ClinGen) Familial Hypercholesterolemia Variant Curation Expert Panel consensus guidelines for LDLR variant classification."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In this study, we provide consensus recommendations for the most common FH-associated gene, LDLR, where >2300 unique FH-associated variants have been identified."
    explanation: Establishes both LDLR primacy and the scale of the allelic series.
  - reference: PMID:34906454
    reference_title: "The Clinical Genome Resource (ClinGen) Familial Hypercholesterolemia Variant Curation Expert Panel consensus guidelines for LDLR variant classification."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The consensus LDLR variant modifications to existing ACMG/AMP guidelines include (1) alteration of population frequency thresholds, (2) delineation of loss-of-function variant types, (3) functional study criteria specifications, (4) cosegregation criteria specifications, and (5) specific use and thresholds for in silico prediction tools, among others."
    explanation: Names the gene-specific interpretation rules that govern LDLR variant classification.
  - reference: PMID:30306860
    reference_title: "New Horizons in the Pathogenesis, Pathophysiology and Treatment of Familial Hypercholesterolaemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most common (60-80%) FH cause is mutations of the LDL Receptor (LDLR) protein (6 classes with a different number of receptors and functionality)."
    explanation: >-
      Quantifies the LDLR share of FH and names the receptor-class scheme. Note
      the source counts six classes; the five curated above are the classical
      set, with the sixth (defective basolateral targeting) omitted because no
      quotable functional evidence for it was found.
  - reference: PMID:28475941
    reference_title: "Mutational analysis and genotype-phenotype relation in familial hypercholesterolemia: The SAFEHEART registry."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients with null variants have a more severe phenotype than patients with defective variants, presenting with significantly higher levels of atherogenic particles (total cholesterol, LDL-cholesterol and apolipoprotein B)."
    explanation: >-
      The genotype-phenotype relation that makes the class distinction
      clinically meaningful, in a 2938-patient molecularly diagnosed registry.
  - reference: PMID:30306860
    reference_title: "New Horizons in the Pathogenesis, Pathophysiology and Treatment of Familial Hypercholesterolaemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Recent studies demonstrated the influence of the LDLR mutation type in the FH phenotype, associating a more severe clinical phenotype and worse advanced CVD in patients with null mutation than those with receptor-defective mutations."
    explanation: Independent statement of the null-versus-defective severity gradient.
treatments:
- name: Statin (HMG-CoA Reductase Inhibitor) Therapy
  description: >
    First-line, lifelong LDL-lowering therapy. The mechanism is receptor-side
    and therefore genotype-sensitive: inhibiting HMG-CoA reductase lowers
    intracellular cholesterol, which de-represses LDLR transcription and puts
    more receptor on the hepatocyte surface. The drug therefore amplifies
    whatever receptor capacity the genotype leaves. Note that statins have not
    been tested against a receptor-negative genotype stratum in this entry's
    evidence, and the cited mechanistic review reports statins helping both
    homozygous and heterozygous patients, so the null-genotype ceiling is
    inferred from mechanism rather than demonstrated. In a 2146-patient FH cohort followed a
    mean 8.5 years, statin treatment reduced coronary heart disease risk by
    76%.
  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
  target_mechanisms:
  - target: Residual Receptor Activity Gates Receptor-Dependent LDL Lowering
    treatment_effect: ACTIVATES
    description: >
      Statins act by inducing residual LDL receptor, so their effect is bounded
      by how much functional receptor the genotype permits.
    evidence:
    - reference: PMID:37371118
      reference_title: "A Review of Progress on Targeting LDL Receptor-Dependent and -Independent Pathways for the Treatment of Hypercholesterolemia, a Major Risk Factor of ASCVD."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Statins proved to be the first blockbuster drug, helping both HoFH and HeFH individuals by inhibiting the cholesterol synthesis pathway rate-limiting enzyme HMG-CoA reductase and inducing the LDL receptor."
      explanation: States the receptor-inducing mechanism that makes the effect genotype-dependent.
  evidence:
  - reference: PMID:19001495
    reference_title: "Efficacy of statins in familial hypercholesterolaemia: a long term cohort study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We observed an overall risk reduction of 76% (hazard ratio 0.24 (95% confidence interval 0.18 to 0.30), P<0.001)."
    explanation: Quantifies the cardiovascular benefit of statin therapy in an FH cohort.
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "statins can be used in children starting around age eight years"
    explanation: >-
      GeneReviews sets the paediatric initiation age. PARTIAL because the
      recommendation is made for FH as a class rather than for LDLR-related FH
      specifically.
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Statins are contraindicated in pregnancy because of concerns for teratogenicity and should be discontinued prior to conception."
    explanation: >-
      GeneReviews states the pregnancy contraindication. PARTIAL because it
      constrains rather than supports the therapy, and is stated at class level.
  notes: >
    Two management constraints carried from the GeneReviews FH chapter, both
    class-level: statins may be started in children from around age eight, and
    they are contraindicated in pregnancy and must be stopped before
    conception - a hard interruption in an otherwise lifelong therapy for a
    disorder transmitted to half of offspring.
- name: PCSK9 Monoclonal Antibody Therapy
  description: >
    Alirocumab and evolocumab neutralize circulating PCSK9, preventing
    PCSK9-directed lysosomal degradation of the LDL receptor and so increasing
    receptor recycling and surface abundance. Like statins this is a
    receptor-amplifying mechanism, and the AMG 145 (evolocumab) homozygous-FH
    study is the cleanest published demonstration that the amplification
    requires a receptor to amplify: LDL cholesterol fell in receptor-defective
    patients and not at all in the receptor-negative ones, within the same
    protocol and at the same doses.
  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: Residual Receptor Activity Gates Receptor-Dependent LDL Lowering
    treatment_effect: ACTIVATES
    description: >
      Blocking PCSK9 spares existing LDL receptor from degradation, raising
      surface receptor abundance in patients who retain functional receptor and
      achieving nothing in those who do not.
    evidence:
    - reference: PMID:24014831
      reference_title: "Effect of the proprotein convertase subtilisin/kexin 9 monoclonal antibody, AMG 145, in homozygous familial hypercholesterolemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "This study demonstrates significant and dose-related LDL cholesterol lowering with a PCSK9 monoclonal antibody in homozygous familial hypercholesterolemia patients with defective LDL receptor activity but no reduction in those who were receptor negative."
      explanation: The genotype-stratified result that defines the boundary of this therapy.
  evidence:
  - reference: PMID:24014831
    reference_title: "Effect of the proprotein convertase subtilisin/kexin 9 monoclonal antibody, AMG 145, in homozygous familial hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Over the treatment periods, mean±SD LDL cholesterol reductions in the 6 LDL receptor-defective patients were 19.3±16% and 26.3±20% with 4- and 2-week dosing, respectively"
    explanation: Quantifies the response in receptor-defective homozygous 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: HUMAN_CLINICAL
    snippet: "Addition of novel, efficacious therapies (i.e. inhibitors of proprotein convertase subtilisin/kexin type 9, followed by evinacumab and/or lomitapide) offers potential to attain LDL-C goal or reduce the need for LA."
    explanation: Places PCSK9 inhibition in the current consensus treatment sequence for severe disease.
- name: Evinacumab (ANGPTL3 Inhibition)
  description: >
    An angiopoietin-like 3 monoclonal antibody that lowers LDL cholesterol by a
    route that does not require the LDL receptor. This is the therapeutic
    complement of everything above: in the phase 3 homozygous-FH trial it
    lowered LDL cholesterol by a similar amount in patients with null-null
    variants and in those with non-null variants, so it is the option that
    remains when the receptor-directed drugs have nothing to act on.
  therapeutic_modality: MONOCLONAL_ANTIBODY
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: evinacumab
      term:
        id: NCIT:C20401
        label: Monoclonal Antibody
  target_mechanisms:
  - target: Lifelong Elevation of Plasma LDL Cholesterol
    treatment_effect: INHIBITS
    description: >
      Lowers plasma LDL cholesterol without acting through the LDL receptor, so
      the effect is preserved regardless of receptor class.
    evidence:
    - reference: PMID:32813947
      reference_title: "Evinacumab for Homozygous Familial Hypercholesterolemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The LDL cholesterol level was lower in the evinacumab group than in the placebo group in patients with null-null variants (-43.4% vs. +16.2%) and in those with non-null variants (-49.1% vs. -3.8%)."
      explanation: Demonstrates genotype-independent efficacy, the defining property of this agent.
  evidence:
  - reference: PMID:32813947
    reference_title: "Evinacumab for Homozygous Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    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: Reports the primary efficacy result of the pivotal randomized trial.
- name: Lomitapide (Microsomal Triglyceride Transfer Protein Inhibition)
  description: >
    An MTP inhibitor that reduces hepatic assembly and secretion of
    apoB-containing lipoproteins. Like evinacumab it acts upstream of the
    receptor rather than through it, so it is expected to be
    genotype-independent - though, unlike the evinacumab trial, the pivotal
    lomitapide study was single-arm, open-label, and not genotype-stratified,
    so its 50% reduction is a whole-cohort figure and not a demonstration of
    effect in receptor-negative disease specifically. Hepatic steatosis, transaminase elevation,
    gastrointestinal intolerance, and fat-soluble vitamin depletion constrain
    its use and require monitoring.
  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: >
      Reduces the production side of the LDL steady state rather than the
      clearance side, bypassing the receptor defect entirely.
    evidence:
    - 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
      snippet: "LDL cholesterol was reduced by 50% (95% CI -62 to -39) from baseline"
      explanation: Quantifies LDL lowering in homozygous disease, where receptor-directed drugs underperform.
  evidence:
  - 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
    snippet: "Patients with homozygous familial hypercholesterolaemia respond inadequately to existing drugs."
    explanation: States the therapeutic gap that LDLR-independent agents were developed to fill.
  - 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
    snippet: "Four patients had aminotransaminase levels of more than five times the upper limit of normal, which resolved after dose reduction or temporary interruption of lomitapide."
    explanation: Documents the hepatic toxicity signal that constrains dosing.
- name: Lipoprotein Apheresis
  description: >
    Extracorporeal physical removal of apoB-containing lipoproteins from
    plasma. Wholly independent of LDL receptor function and therefore effective
    in receptor-negative disease, but the effect rebounds between sessions and
    the vascular-access, time, and cost burden is substantial. Current
    consensus places it alongside pharmacotherapy as foundational in severe
    biallelic disease.
  therapeutic_modality: DEVICE
  treatment_term:
    preferred_term: Therapeutic Procedure
    term:
      id: NCIT:C49236
      label: Therapeutic Procedure
  target_mechanisms:
  - target: Lifelong Elevation of Plasma LDL Cholesterol
    treatment_effect: INHIBITS
    description: >
      Removes circulating LDL directly, requiring no receptor and no hepatic
      metabolic step.
    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: HUMAN_CLINICAL
      snippet: "Combination LDL-C-lowering therapy-both pharmacologic intervention and lipoprotein apheresis (LA)-is foundational."
      explanation: Establishes apheresis as a foundational component of severe-disease management.
  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: HUMAN_CLINICAL
    snippet: "Addition of novel, efficacious therapies (i.e. inhibitors of proprotein convertase subtilisin/kexin type 9, followed by evinacumab and/or lomitapide) offers potential to attain LDL-C goal or reduce the need for LA."
    explanation: Positions apheresis relative to the newer pharmacologic options.
- name: Ezetimibe
  description: >
    Cholesterol-absorption inhibitor (NPC1L1) added to statin therapy when the
    LDL-C target is not reached - step two of the standard FH escalation.
    Curated here because its mechanism is receptor-dependent in the same sense
    statins are: blocking jejunal cholesterol uptake depletes hepatocyte
    cholesterol and drives a compensatory increase in LDL receptor, so like a
    statin it amplifies whatever receptor capacity the genotype leaves rather
    than bypassing the receptor. Statin-plus-ezetimibe reaches roughly 65-70%
    LDL-C reduction against 50-60% for a high-intensity statin alone.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: ezetimibe
      term:
        id: CHEBI:49040
        label: ezetimibe
  target_mechanisms:
  - target: Residual Receptor Activity Gates Receptor-Dependent LDL Lowering
    treatment_effect: ACTIVATES
    description: >
      Ezetimibe belongs on the receptor-dependent side of the gating relation,
      not the LDLR-independent side: it lowers LDL-C by inducing residual
      receptor, so its effect is bounded by the receptor capacity the genotype
      permits.
    evidence:
    - reference: PMID:39076699
      reference_title: "Familial Hypercholesterolemia: Pitfalls and Challenges in Diagnosis and Treatment."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "ezetimibe by blocking cholesterol uptake from the jejunum) result in a  compensatory increase in LDL-R and subsequently enhanced LDL-C clearance."
      explanation: >-
        States that ezetimibe lowers LDL-C through a compensatory increase in
        LDL receptor, which is what places it on the receptor-dependent side of
        the gating node alongside statins.
  evidence:
  - reference: PMID:39076699
    reference_title: "Familial Hypercholesterolemia: Pitfalls and Challenges in Diagnosis and Treatment."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "statins (alone or in combination with ezetimibe) demonstrated a significant  reduction of future ASCVD events even in subjects with LDL-R defective forms"
    explanation: >-
      Supports the event-level benefit of statin-plus-ezetimibe specifically in
      receptor-defective disease, the genotype stratum this entry curates.
  notes: >-
    The umbrella entry (Familial_Hypercholesterolemia) describes ezetimibe as
    "independent of LDLR". That is not the characterization adopted here: the
    cited review states that ezetimibe, like a statin, works through a
    compensatory increase in LDL receptor. Ezetimibe's target is independent of
    LDLR, but its LDL-lowering effect is not, which is the distinction this
    entry's gating node is built to make.
- name: Bempedoic Acid
  description: >
    Oral ATP-citrate lyase inhibitor acting upstream of HMG-CoA reductase.
    Because it is a prodrug activated by a liver-specific enzyme absent from
    skeletal muscle, it is the guideline option for statin-intolerant patients
    - a common situation in a disease requiring lifelong high-intensity statin
    therapy. Like statins and ezetimibe it upregulates LDL receptor activity,
    so it sits on the receptor-dependent side of the gating relation. Reported
    LDL-C reduction was 22.3% in a pooled clinical-heterozygous-FH subgroup.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: bempedoic acid
      term:
        id: CHEBI:149601
        label: bempedoic acid
  target_mechanisms:
  - target: Residual Receptor Activity Gates Receptor-Dependent LDL Lowering
    treatment_effect: ACTIVATES
    description: >
      Inhibiting ATP-citrate lyase depletes hepatic cholesterol and upregulates
      LDL receptor activity by the same de-repression route statins use, so the
      effect is bounded by residual receptor capacity.
    evidence:
    - reference: PMID:39076699
      reference_title: "Familial Hypercholesterolemia: Pitfalls and Challenges in Diagnosis and Treatment."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "It acts as an inhibitor of adenosine triphosphate (ATP) citrate lyase, a  hepatic enzyme that works upstream of HMG-CoA reductase with subsequent  upregulation of LDL-R activity, similar to statins"
      explanation: >-
        States the target and, critically for this entry, that the LDL-lowering
        effect runs through upregulation of LDL receptor activity.
  evidence:
  - reference: PMID:36876740
    reference_title: "Bempedoic Acid and Cardiovascular Outcomes in Statin-Intolerant Patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Bempedoic acid, an ATP citrate lyase inhibitor, reduces low-density lipoprotein (LDL) cholesterol levels and is associated with a low incidence of muscle-related adverse events"
    explanation: >-
      CLEAR Outcomes provides the outcome evidence justifying bempedoic acid as
      curated therapy rather than an investigational option.
  notes: >-
    CLEAR Outcomes enrolled statin-intolerant patients at high cardiovascular
    risk, not an LDLR-genotyped or FH-only cohort, so the outcome benefit is not
    LDLR-specific evidence.
- name: Inclisiran (PCSK9-Directed siRNA)
  description: >
    Hepatocyte-targeted small interfering RNA that suppresses PCSK9 synthesis,
    given on days 1 and 90 and every six months thereafter. Mechanistically it
    reaches the same endpoint as a PCSK9 antibody - less PCSK9-mediated
    receptor degradation, therefore more receptor on the hepatocyte surface -
    by inhibiting hepatic PCSK9 production rather than neutralizing circulating
    protein, so it is equally receptor-dependent. ORION-9 (NCT03397121) tested
    it in adults with heterozygous FH.
  therapeutic_modality: SIRNA
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: inclisiran
      term:
        id: CHEBI:176399
        label: inclisiran
  target_mechanisms:
  - target: Residual Receptor Activity Gates Receptor-Dependent LDL Lowering
    treatment_effect: ACTIVATES
    description: >
      Suppressing hepatic PCSK9 synthesis preserves receptor that would
      otherwise be degraded, so like the PCSK9 antibodies the effect requires a
      receptor that can be made and can function.
    evidence:
    - reference: PMID:39076699
      reference_title: "Familial Hypercholesterolemia: Pitfalls and Challenges in Diagnosis and Treatment."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "In  contrast to anti-PCSK9 mAbs, inclisiran inactivates PCSK9 by inhibition of its  hepatic synthesis"
      explanation: >-
        Distinguishes the siRNA route to PCSK9 inactivation from antibody
        neutralization while placing both on the same receptor-preserving
        mechanism.
  evidence:
  - reference: PMID:39076699
    reference_title: "Familial Hypercholesterolemia: Pitfalls and Challenges in Diagnosis and Treatment."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "inclisiran represents a first-in-class cholesterol-lowering small interfering  ribonucleic acid (siRNA), targeting PCSK9 messenger RNA (mRNA) in hepatocytes."
    explanation: Establishes the modality and molecular target of the agent.
- name: Liver Transplantation
  description: >
    The limiting case of the receptor-dependent/receptor-independent axis:
    rather than amplifying or bypassing the patient's own receptor, orthotopic
    liver transplantation *supplies* a hepatic LDL receptor complement, which
    is why it can correct the biochemical defect in receptor-negative disease
    that no receptor-directed drug can reach. Reserved for homozygous patients
    whose LDL-C cannot be controlled by maximal medical therapy and apheresis,
    and constrained by operative risk and lifelong immunosuppression. Where
    severe cardiovascular involvement has already developed, combined
    heart-liver transplantation may be required, which is the argument for
    early listing rather than late rescue.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: Organ Transplantation
    term:
      id: NCIT:C15289
      label: Organ Transplantation
  target_mechanisms:
  - target: Reduced Functional Hepatic LDL Receptor Activity
    treatment_effect: ACTIVATES
    description: >
      Replacing the liver replaces the tissue that carries the defective
      receptor, restoring hepatic receptor capacity itself rather than
      modulating the residual capacity a mutant genotype leaves. This is the
      only curated intervention that acts on the receptor-activity node
      directly.
    evidence:
    - reference: PMID:39815304
      reference_title: "Liver transplantation for homozygous familial hypercholesterolemia: a retrospective analysis from Chinese experience."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Accordingly, all 6 patients received orthotopic liver transplantations (OLT), with the result that significant postoperative reductions were observed in levels of TC and LDL."
      explanation: >-
        Reports that supplying a donor liver lowers total and LDL cholesterol,
        which is the receptor-supply mechanism this edge asserts.
  evidence:
  - reference: PMID:39815304
    reference_title: "Liver transplantation for homozygous familial hypercholesterolemia: a retrospective analysis from Chinese experience."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In severe cases of HoFH, clinical signs and symptoms cannot be controlled well by non-surgical treatments, liver transplantation (LT) currently represents the viable option."
    explanation: >-
      Places liver transplantation as the option of last resort when medical
      therapy fails, the clinical position curated here.
  - reference: PMID:39815304
    reference_title: "Liver transplantation for homozygous familial hypercholesterolemia: a retrospective analysis from Chinese experience."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "If severe cardiovascular involvement occurs, LT should be performed as soon as possible, otherwise combined heart-liver transplantation may be required."
    explanation: >-
      Supports the timing argument in the description - that the cost of late
      listing is escalation to combined heart-liver transplantation.
  notes: >-
    The cited series is six patients, retrospective and single-region, so it
    supports the direction of the effect and the clinical positioning but not a
    quantitative estimate of benefit or of transplant-free survival.
- name: Cardiovascular Risk Factor Modification
  description: >
    The receptor defect sets a high baseline arterial risk that conventional
    risk factors multiply. Smoking cessation, control of blood pressure and
    glycemia, weight management, physical activity, and reduced saturated and
    trans fat intake do not correct the LDL level but reduce absolute event
    risk.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Dietary Intervention
    term:
      id: NCIT:C15447
      label: Dietary Intervention
  evidence:
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Agents/circumstances to avoid: Smoking, high intake of saturated and trans unsaturated fat, sedentary lifestyle, obesity, hypertension, and diabetes mellitus."
    explanation: >-
      The GeneReviews agents-and-circumstances-to-avoid list, which is what
      this treatment entry operationalizes.
animal_models:
- name: Ldlr-knockout mouse
  species: Mouse
  genotype: Ldlr-/- (homologous recombination in embryonic stem cells)
  publication: PMID:8349823
  description: >-
    The founding genetic model. Viable and fertile, with a selective rise in
    IDL and LDL and a demonstrated prolongation of apoB-lipoprotein clearance,
    and reversible by hepatic re-expression of the human receptor - which
    closes the causal loop between receptor absence and hypercholesterolemia.
  modeled_mechanisms:
  - target: Impaired Receptor-Mediated Clearance of Plasma LDL
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Directly measures the clearance defect that this node represents, in the
      cleanest possible genetic background - complete receptor absence.
    limitations: >-
      Murine lipoprotein metabolism is apoB48- and HDL-dominated rather than
      LDL-dominated, so absolute cholesterol levels are far below human
      homozygous FH and spontaneous atherosclerosis on chow is limited; the
      model reproduces the clearance defect faithfully but not the human
      lipoprotein distribution or the arterial disease burden.
    readouts:
    - name: Plasma clearance half-life of radiolabelled VLDL and LDL
      target: Impaired Receptor-Mediated Clearance of Plasma LDL
      direction: INCREASED
      interpretation: >-
        Prolonged half-life is the direct measurement of the clearance defect;
        normal HDL clearance in the same animals shows the defect is
        ligand-specific.
      evidence:
      - reference: PMID:8349823
        reference_title: "Hypercholesterolemia in low density lipoprotein receptor knockout mice and its reversal by adenovirus-mediated gene delivery."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "The half-lives for intravenously administered 125I-VLDL and 125I-LDL were prolonged by 30-fold and 2.5-fold, respectively, but the clearance of 125I-HDL was normal in the LDLR-/- mice."
        explanation: Reports the measured clearance half-lives underlying this readout.
    evidence:
    - reference: PMID:8183926
      reference_title: "The two-receptor model of lipoprotein clearance: tests of the hypothesis in \"knockout\" mice lacking the low density lipoprotein receptor, apolipoprotein E, or both proteins."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "LDLR(-/-) mice had a relatively isolated elevation in plasma LDL"
      explanation: >-
        Confirms that the model isolates the LDL clearance arm rather than
        producing a generalized dyslipidemia.
  - target: Reduced Functional Hepatic LDL Receptor Activity
    relationship: RESCUES
    fidelity: HIGH
    description: >-
      Restoring hepatic LDL receptor expression by adenoviral delivery
      normalized the elevated IDL/LDL within four days, demonstrating that the
      receptor deficit is both necessary and sufficient for the phenotype in
      this model.
    limitations: >-
      Adenoviral rescue is acute and supraphysiological hepatic overexpression,
      not a model of the endogenous allelic series; it establishes sufficiency
      of receptor restoration, not the dose-response of partial residual
      activity.
    readouts:
    - name: Plasma IDL/LDL cholesterol after hepatic LDLR re-expression
      target: Reduced Functional Hepatic LDL Receptor Activity
      direction: RESTORED
      interpretation: >-
        Normalization on receptor restoration is the rescue arm of the causal
        claim.
      evidence:
      - reference: PMID:8349823
        reference_title: "Hypercholesterolemia in low density lipoprotein receptor knockout mice and its reversal by adenovirus-mediated gene delivery."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "The elevated IDL/LDL level of LDLR-/- mice was reduced to normal 4 d after the intravenous injection of a recombinant replication-defective adenovirus encoding the human LDL receptor driven by the cytomegalovirus promoter."
        explanation: Reports the rescue measurement.
    evidence:
    - reference: PMID:8349823
      reference_title: "Hypercholesterolemia in low density lipoprotein receptor knockout mice and its reversal by adenovirus-mediated gene delivery."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "The virus restored expression of LDL receptor protein in the liver and increased the clearance of 125I-VLDL."
      explanation: Confirms that the rescue acted through restored hepatic receptor protein.
- name: Watanabe heritable hyperlipidemic (WHHL) rabbit
  species: Rabbit
  genotype: Naturally occurring homozygous LDL receptor deficiency
  publication: PMID:31748469
  description: >-
    A spontaneously arising LDL-receptor-deficient rabbit strain and its
    coronary-atherosclerosis-prone and myocardial-infarction-prone derivatives.
    Rabbit lipoprotein metabolism is far closer to human than murine, and this
    is the model in which the LDL receptor pathway hypothesis - derived from
    cultured fibroblasts - was shown to hold in a whole animal, and in which
    the arterial consequences of lifelong receptor deficiency were worked out.
  modeled_mechanisms:
  - target: Endothelial Dysfunction and Subendothelial LDL Retention
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Spontaneous, diet-independent hypercholesterolemia from receptor
      deficiency drives the initiating arterial events - oxidized LDL
      accumulation, endothelial adhesion molecule expression, and monocyte
      infiltration.
    limitations: >-
      Rabbits lack the human coronary anatomy and plaque-rupture triggers in
      full, and the reviewed strain history reports that lesion rupture in this
      model requires secondary mechanical forces such as spasm, so event
      generation is not a faithful analogue of human acute coronary syndrome.
    readouts:
    - name: Arterial intimal macrophage infiltration and oxidized LDL accumulation
      target: Endothelial Dysfunction and Subendothelial LDL Retention
      direction: INCREASED
      interpretation: >-
        Histological demonstration of the initiating steps of atherogenesis in
        a receptor-deficient animal.
      evidence:
      - reference: PMID:31748469
        reference_title: "The History of the WHHL Rabbit, an Animal Model of Familial Hypercholesterolemia (I) - Contribution to the Elucidation of the Pathophysiology of Human Hypercholesterolemia and Coronary Heart Disease."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Oxidized LDL accumulates in the arterial wall, monocyte adhesion molecules are expressed on arterial endothelial cells, and monocyte-derived macrophages infiltrate the arterial intima, resulting in the formation and progression of atherosclerosis."
        explanation: Reports the arterial findings underlying this readout.
    evidence:
    - reference: PMID:31748469
      reference_title: "The History of the WHHL Rabbit, an Animal Model of Familial Hypercholesterolemia (I) - Contribution to the Elucidation of the Pathophysiology of Human Hypercholesterolemia and Coronary Heart Disease."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "The main part of human lipoprotein metabolism has been elucidated, and the low-density lipoprotein (LDL) receptor pathway hypothesis derived from studies using fibroblasts was proven in vivo."
      explanation: >-
        Establishes this strain as the in vivo proof of the receptor pathway,
        which is why it is informative for the arterial arm.
- name: LDLR-knockout cynomolgus monkey
  species: Cynomolgus monkey
  genotype: LDLR knockout by genome editing (six founder animals)
  publication: PMID:37730951
  description: >-
    A genome-edited non-human primate model. Plasma cholesterol reached levels
    comparable to human homozygous FH, periocular xanthoma appeared within the
    first year, and the animals were strongly resistant to lipid-lowering
    medication - the primate counterpart of the receptor-negative
    pharmacological phenotype.
  modeled_mechanisms:
  - target: Residual Receptor Activity Gates Receptor-Dependent LDL Lowering
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Complete receptor knockout reproduces the drug-refractory phenotype that
      defines receptor-negative homozygous disease.
    limitations: >-
      Six founder animals, possible mosaicism from editing, short follow-up,
      and the report characterizes drug resistance in aggregate rather than
      drug-by-drug, so it supports the direction of the gating relation but not
      an agent-specific magnitude.
    readouts:
    - name: LDL cholesterol response to lipid-lowering medication
      target: Residual Receptor Activity Gates Receptor-Dependent LDL Lowering
      direction: UNCHANGED
      interpretation: >-
        Failure to respond in a total-knockout primate is the model-side
        counterpart of the absent response in receptor-negative patients.
      evidence:
      - reference: PMID:37730951
        reference_title: "Generation of a familial hypercholesterolemia model in non-human primate."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "The LDLR KO monkeys were also strongly resistant to medications for hypercholesterolemia."
        explanation: Reports the drug-resistance observation underlying this readout.
    evidence:
    - reference: PMID:37730951
      reference_title: "Generation of a familial hypercholesterolemia model in non-human primate."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "The levels of plasma cholesterol and triglyceride were quite high in the monkeys, and were similar to those in FH patients with homozygous mutations in the LDLR gene."
      explanation: >-
        Establishes that the model reaches human homozygous-FH lipid levels,
        which is what makes its drug-response behaviour informative.
clinical_trials:
- name: NCT03399786
  phase: PHASE_III
  status: COMPLETED
  description: >-
    ELIPSE HoFH. Randomized, double-blind, placebo-controlled trial of
    intravenous evinacumab in 65 patients with homozygous familial
    hypercholesterolemia, reporting results separately for null-null and
    non-null LDL-receptor genotypes - the trial that established
    LDLR-independent LDL lowering in receptor-negative disease.
  target_phenotypes:
  - preferred_term: Increased LDL cholesterol concentration
    term:
      id: HP:0003141
      label: Increased LDL cholesterol concentration
  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: HUMAN_CLINICAL
    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: States the trial's primary objective in the population relevant to this entry.
- name: NCT04233918
  phase: PHASE_III
  status: COMPLETED
  description: >-
    Three-part, single-arm, open-label study of evinacumab in paediatric
    patients with homozygous familial hypercholesterolemia, extending the
    LDLR-independent option to children, in whom receptor-negative disease
    presents earliest.
  target_phenotypes:
  - preferred_term: Increased LDL cholesterol concentration
    term:
      id: HP:0003141
      label: Increased LDL cholesterol concentration
  evidence:
  - reference: clinicaltrials:NCT04233918
    reference_title: "A Three-Part, Single-Arm, Open-Label Study to Evaluate the Efficacy, Safety, and Pharmacokinetics of Evinacumab in Pediatric Patients With Homozygous Familial Hypercholesterolemia"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The primary objective for Part B of the study is to demonstrate a reduction of low-density lipoprotein cholesterol (LDL-C) by evinacumab in pediatric (5 to 11 years of age) patients with HoFH."
    explanation: States the trial's efficacy objective in the paediatric homozygous population.
- name: NCT03397121
  phase: PHASE_III
  status: COMPLETED
  description: >-
    ORION-9. Placebo-controlled, double-blind, randomized trial of inclisiran,
    a hepatocyte-targeted siRNA that suppresses PCSK9 synthesis, in adults with
    heterozygous familial hypercholesterolemia - a receptor-amplifying
    mechanism tested in the population that retains residual receptor.
  target_phenotypes:
  - preferred_term: Increased LDL cholesterol concentration
    term:
      id: HP:0003141
      label: Increased LDL cholesterol concentration
  evidence:
  - reference: clinicaltrials:NCT03397121
    reference_title: "Placebo-Controlled, Double-Blind, Randomized Trial to Evaluate the Effect of 300 mg of Inclisiran Sodium Given as Subcutaneous Injections in Subjects With Heterozygous Familial Hypercholesterolemia (HeFH) and Elevated Low-Density Lipoprotein Cholesterol (LDL-C)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This is a Phase III, placebo-controlled, double-blind, randomized study in participants with HeFH and elevated LDL-C to evaluate the efficacy, safety, and tolerability of subcutaneous (SC) injection(s) of inclisiran."
    explanation: States the trial design, population, and agent.
- name: NCT06597006
  phase: PHASE_III
  status: RECRUITING
  description: >-
    Two-part randomized study of inclisiran in children aged 2 to under 12 with
    homozygous familial hypercholesterolemia. Curated because it is the most
    directly on-thesis trial available for this entry: its enrolment criteria
    operationalize the gating relation itself, requiring documented biallelic
    null LDLR mutations and excluding children with poor prior response to a
    PCSK9 antibody - i.e. it tests a receptor-preserving agent in exactly the
    genotype stratum where receptor-directed therapy is predicted to fail.
  target_phenotypes:
  - preferred_term: Increased LDL cholesterol concentration
    term:
      id: HP:0003141
      label: Increased LDL cholesterol concentration
  evidence:
  - reference: clinicaltrials:NCT06597006
    reference_title: "Two Part (Double-blind Inclisiran Versus Placebo [Year 1] Followed by Open-label Inclisiran [Year 2]) Randomized Multicenter Study to Evaluate Safety, Tolerability, and Efficacy of Inclisiran in Children (2 to Less Than 12 Years) With Homozygous Familial Hypercholesterolemia and Elevated LDL-cholesterol"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'This is a pivotal phase III study designed to evaluate safety, tolerability, and efficacy of inclisiran in children (aged 2 to \<12 years) with homozygous familial hypercholesterolemia (HoFH) and elevated low density lipoprotein cholesterol (LDLC).'
    explanation: >-
      States the design and the homozygous paediatric population; the
      genotype-specific enrolment detail is recorded in the description from the
      registry record rather than quoted, as the cached summary does not carry
      the eligibility text.
diagnosis:
- name: Molecular Genetic Testing of LDLR
  description: >-
    Sequencing of LDLR together with APOB and PCSK9, plus deletion/duplication
    analysis, since exon-level copy-number changes are a real and
    sequencing-invisible part of the LDLR allelic series. Variant
    interpretation should follow the ClinGen FH Variant Curation Expert Panel's
    LDLR-specific specification of the ACMG/AMP framework rather than the
    generic rules, which is what makes a confident pathogenic call - and
    therefore cascade testing of relatives - possible.
  evidence:
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    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: States the molecular diagnostic route and the genes tested.
  - reference: PMID:34906454
    reference_title: "The Clinical Genome Resource (ClinGen) Familial Hypercholesterolemia Variant Curation Expert Panel consensus guidelines for LDLR variant classification."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Establishment of these guidelines as the new standard in the clinical laboratory setting will result in a more evidence-based, harmonized method for LDLR variant classification worldwide, thereby improving the care of patients with FH."
    explanation: Names the gene-specific interpretation standard that governs the diagnostic call.
- name: Functional Characterization of LDLR Variants
  description: >-
    Cell-based assays - LDL binding and uptake by flow cytometry with
    fluorescent LDL, receptor expression by immunofluorescence or Western blot,
    and receptor localization by confocal microscopy - performed in
    receptor-deficient CHO-ldlA7 cells transfected with the patient allele.
    These assays do two things no in silico predictor can: they resolve
    variants of uncertain significance into a pathogenicity call, and they
    assign the allele to a functional class, which is the input to
    genotype-guided therapy selection.
  evidence:
  - reference: PMID:25386756
    reference_title: "Advantages and versatility of fluorescence-based methodology to characterize the functionality of LDLR and class mutation assignment."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Additionally confocal microscopy allowed the assignment of different class mutation to the variants assayed."
    explanation: Establishes class assignment as an output of the functional assay.
  - reference: PMID:31106925
    reference_title: "Functional analysis of new variants at the low-density lipoprotein receptor associated with familial hypercholesterolemia."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "This approach allows us to confirm the genetic diagnosis of FH, avoiding the classification as \"uncertain significant variants\", and therefore, carry out cascade family screening."
    explanation: States the clinical consequence of functional characterization - VUS resolution enabling cascade screening.
  - reference: PMID:37847331
    reference_title: "Predictive Modeling and Structure Analysis of Genetic Variants in Familial Hypercholesterolemia: Implications for Diagnosis and Protein Interaction Studies."
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: "Despite their contributions, a definitive diagnosis of a genetic variant necessitates functional validation through in vitro characterization or cascade screening."
    explanation: >-
      States that computational prediction alone is insufficient, which is why
      the functional assay is curated as its own diagnostic modality.
differential_diagnoses:
- name: Familial defective apolipoprotein B-100 (APOB)
  description: >-
    The ligand-side mirror of this entry. Clinically indistinguishable at the
    bedside and separated only by molecular testing: here the receptor is
    defective, there the receptor is normal and the apoB-100 ligand it must
    recognize is not. Curated separately as
    Familial_Defective_Apolipoprotein_B-100 (MONDO:0007751). LDL-C elevation is
    generally milder than in LDLR-related disease.
  evidence:
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    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 APOB as an alternative molecular cause of the same
      clinical picture and specifies its distinguishing mechanism - impaired
      binding of LDL-C to the receptor rather than a defective receptor.
- name: Autosomal dominant hypercholesterolemia 3 (PCSK9 gain of function)
  description: >-
    The regulator-side member of the dominant trio. The receptor gene is
    intact; a gain-of-function PCSK9 variant degrades normal receptor
    prematurely, so receptor number falls without any receptor defect. Curated
    separately as Autosomal_Dominant_Hypercholesterolemia_3 (MONDO:0011369).
    The practical consequence is therapeutic: PCSK9-directed agents address the
    causal lesion there, whereas here they amplify a residual receptor.
  evidence:
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    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 lists PCSK9 gain of function as a distinct molecular route to
      the same phenotype.
- name: Autosomal recessive hypercholesterolemia (LDLRAP1)
  description: >-
    The phenocopy of this entry acting in trans. LDLRAP1 encodes the adaptor
    that couples the receptor to the clathrin endocytic machinery, so biallelic
    loss produces functionally the same internalization failure as a class 4
    LDLR allele while the receptor itself is normal. Recessive rather than
    dominant, so parents are typically unaffected - the pedigree pattern is
    usually what separates it clinically.
  evidence:
  - reference: PMID:24404629
    reference_title: "Familial Hypercholesterolemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "or rarely, identification of biallelic pathogenic variants in LDLRAP1."
    explanation: >-
      GeneReviews records LDLRAP1 as the rare biallelic route to a clinical FH
      diagnosis, distinguishing it from the dominant genes by inheritance.
- name: Polygenic hypercholesterolemia
  description: >-
    The most common alternative explanation for a clinical FH phenotype with no
    identified monogenic variant: the cumulative effect of many small LDL-C
    raising alleles can reach the same LDL-C range as a monogenic defect.
    Distinguishing it matters because cardiovascular risk, cascade-testing
    yield, and treatment responsiveness differ from monogenic disease, and
    because a negative LDLR test does not exclude clinical FH.
  evidence:
  - reference: PMID:39076699
    reference_title: "Familial Hypercholesterolemia: Pitfalls and Challenges in Diagnosis and Treatment."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "would suggest polygenic causes of FH, where small but cumulative effects of several LDL-C raising alleles can cause the LDL-C increase up to the same range as that"
    explanation: >-
      States that polygenic burden can reproduce the monogenic LDL-C range,
      which is what makes it the principal differential for a variant-negative
      clinical FH phenotype.
- name: Elevated lipoprotein(a) mimicking familial hypercholesterolemia
  description: >-
    Not a separate disease so much as a measurement artefact that produces the
    same referral. Conventional LDL-C assays cannot separate LDL-cholesterol
    from lipoprotein(a)-cholesterol because the particles overlap in density,
    so a high Lp(a) inflates measured LDL-C and can push a patient into a
    clinical FH category they do not belong in. Relevant to this entry because
    Lp(a) is also genuinely elevated in FH and is curated as a biomarker here.
  evidence:
  - reference: PMID:39076699
    reference_title: "Familial Hypercholesterolemia: Pitfalls and Challenges in Diagnosis and Treatment."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Conventional assays for LDL-C determination quantify a composite of atherogenic cholesterol, which is attributable not only to LDL-C, but also to lipoprotein(a)-cholesterol (Lp(a)-C) due to their overlapping densities."
    explanation: >-
      Explains the assay overlap that lets high Lp(a) masquerade as the elevated
      LDL-C used to make a clinical FH diagnosis.
- name: Sitosterolemia, dysbetalipoproteinemia, and cholesteryl ester storage disease
  description: >-
    Distinctive non-FH inherited dyslipidemias that can present with severe
    hypercholesterolemia and xanthoma and so enter the differential of a young
    patient with very high LDL-C and no LDLR variant - sitosterolemia (ABCG5 /
    ABCG8), dysbetalipoproteinemia (APOE), and cholesteryl ester storage
    disease / lysosomal acid lipase deficiency (LIPA). Each has its own
    mechanism and, importantly, its own treatment, so misassignment to FH has
    therapeutic consequences.
  evidence:
  - reference: PMID:39076699
    reference_title: "Familial Hypercholesterolemia: Pitfalls and Challenges in Diagnosis and Treatment."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "some of these genes might also cause distinctive non-FH syndromes such as sitosterolemia (ABCG5), dysbetalipoproteinemia (APOE) or cholesteryl ester storage disease (LIPA)"
    explanation: >-
      Names the non-FH inherited dyslipidemias that share the severe
      hypercholesterolemia presentation.
discussions:
- discussion_id: residual_ldlr_activity_response_threshold
  kind: KNOWLEDGE_GAP
  attaches_to:
  - "pathophysiology#Reduced Functional Hepatic LDL Receptor Activity"
  prompt: >-
    What residual LDL receptor activity threshold actually separates patients
    who will respond to receptor-directed therapy from those who will not; is
    that threshold the same for statins as for PCSK9-directed agents; and do
    statins in fact lose effect in receptor-negative disease at all, given that
    this has never been tested against an untreated null-genotype stratum?
  rationale: >-
    The entry curates residual receptor activity as the quantity that gates
    receptor-dependent LDL lowering, and the direction of that relation is well
    evidenced. The threshold is not. "Null" has been defined at under 2% of
    wild-type activity in functional-assay literature and operationalized as
    high as 15% in trial protocols, and the pivotal genotype-stratified
    observation rests on two receptor-negative patients. Nor is it established
    that statins (which act transcriptionally, on synthesis) and PCSK9-directed
    agents (which act post-translationally, on degradation and recycling) share
    a threshold - a class 1 null allele leaves nothing for either to act on,
    but a class 5 recycling-defective allele might respond differently to the
    two mechanisms. The asymmetry is sharper than that: the only
    genotype-stratified test in this entry is of a PCSK9 antibody, and its two
    receptor-negative patients were already on stable statin therapy at
    enrolment, so statins have never been shown here to fail in
    receptor-negative disease - and the entry's own cited mechanistic review
    reports statins helping both homozygous and heterozygous patients. The
    null-genotype ceiling for statins is therefore inferred from mechanism
    rather than demonstrated. Without a threshold, and without a
    drug-class-specific test, the relation informs reasoning but does not yet
    support a decision rule.
  proposed_experiments:
  - experiment_id: residual_activity_response_threshold_study
    name: Prospective genotype-stratified response study with quantified residual receptor activity
    description: >-
      In a homozygous and compound-heterozygous FH cohort, measure residual
      LDLR activity for each proband's allele pair in a standardized cell-based
      uptake assay, then relate that quantity to the achieved LDL-C reduction
      on a high-intensity statin and, separately, on a PCSK9 monoclonal
      antibody. The readout is whether a single activity threshold predicts
      response for both drug classes or whether the classes have different
      thresholds.
- discussion_id: ldlr_model_arterial_translation
  kind: HUMAN_MODEL_MISMATCH
  attaches_to:
  - "pathophysiology#Premature Atherosclerotic Cardiovascular Events"
  prompt: >-
    Does the arterial disease of any available LDLR-deficient animal model
    reproduce the human course closely enough to test interventions aimed at
    events rather than at LDL levels?
  rationale: >-
    The clearance defect translates cleanly across species - the Ldlr-/- mouse
    reproduces it and adenoviral receptor restoration reverses it - but the
    arterial arm does not. Murine lipoprotein metabolism is apoB48- and
    HDL-dominated, so the mouse does not reach human homozygous-FH cholesterol
    levels and develops limited spontaneous atherosclerosis on chow. The WHHL
    rabbit is far closer in lipoprotein physiology and does develop coronary
    disease, but the strain history reports that lesion rupture there requires
    secondary mechanical forces such as spasm, so it is not a clean analogue of
    spontaneous human plaque rupture. The genome-edited LDLR-knockout
    cynomolgus monkey reaches human-like lipid levels and develops xanthoma
    within a year, but the published cohort is six founder animals with short
    follow-up and possible editing mosaicism. Each model is informative for the
    node it was curated against and none is currently adequate for
    event-endpoint intervention studies.
  proposed_experiments:
  - experiment_id: cross_species_plaque_rupture_comparison
    name: Cross-species comparison of plaque composition and rupture triggers under matched cumulative LDL exposure
    description: >-
      Compare coronary and aortic lesion composition, fibrous cap thickness,
      and spontaneous versus provoked rupture between LDLR-deficient rabbits,
      LDLR-knockout primates, and human FH imaging cohorts matched on
      cumulative LDL-C exposure rather than on age, to establish which model,
      if any, supports event-level extrapolation.

📚

References & Deep Research

References

1

PMID:24404629

Familial Hypercholesterolemia.

5 findings

Clinical characteristics. GeneReviews describes the FH clinical spectrum that LDLR-related FH defines - premature atherosclerotic plaque in the coronary arteries and proximal aorta, angina and myocardial infarction, tendon xanthoma, xanthelasma, and early corneal arcus, with calcific aortic valve disease and childhood-onset coronary artery disease in biallelic disease. The chapter covers FH as a class across LDLR, APOB and PCSK9, so it is class-level rather than LDLR-specific evidence and is cited as such throughout this entry.

"increases the risk of premature cardiovascular events such as angina and myocardial infarction"

Diagnosis and testing. GeneReviews gives the untreated LDL-C thresholds for a clinical FH diagnosis and names LDLR as one of three molecular routes to FH - the receptor-side route that defines this entry.

"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."

Management. GeneReviews sets out lipid surveillance from age two years, statin initiation in children from around age eight, cardiovascular risk-factor modification, and the contraindication of statins in pregnancy.

"Monitor lipid levels from age two years"

Agents and circumstances to avoid. GeneReviews names the exposures that compound the arterial risk conferred by the receptor defect.

"Agents/circumstances to avoid: Smoking, high intake of saturated and trans unsaturated fat, sedentary lifestyle, obesity, hypertension, and diabetes mellitus."

Genetic counseling. GeneReviews states the autosomal dominant transmission risk that applies to LDLR-related FH and the more severe, earlier-onset presentation of biallelic disease.

"Each child of an individual with a heterozygous pathogenic variant in APOB, LDLR, or PCSK9 has a 50% chance of inheriting the pathogenic variant and having FH."

Deep Research

1

Falcon ▸

LDLR-Related Familial Hypercholesterolemia: Disease Characteristics Report

Edison Scientific Literature 28 citations 2026-08-19T08:36:59.688429

LDLR-Related Familial Hypercholesterolemia: Disease Characteristics Report

Scope. This report focuses narrowly on familial hypercholesterolemia caused by pathogenic germline variants in LDLR, rather than the broader clinical FH phenotype caused by APOB, PCSK9, LDLRAP1, polygenic hypercholesterolemia, or secondary dyslipidemia. Evidence is predominantly aggregated disease-level literature, expert guidance, and trial registries; it is not an analysis of individual EHR records.

The following table provides an ontology-ready synopsis.

Domain	Core finding	Quantitative datum	Suggested ontology
Disease identity	LDLR-related familial hypercholesterolemia is a highly penetrant co-dominant Mendelian disorder with lifelong elevation of LDL-C from birth and markedly increased premature ASCVD risk	HeFH usually LDL-C >190 mg/dL; HoFH often >400 mg/dL	MONDO:0007750; HP:0003124
Genetics	Most molecularly confirmed FH is caused by pathogenic LDLR variants that reduce receptor-mediated LDL clearance; null and defective alleles produce severity spectrum	LDLR accounts for ~80–90% of genetically diagnosed FH; >2,300 unique LDLR variants reported	HGNC:6547; SO:0001583/0001587/0001574
Biochemical phenotype	Core laboratory phenotype is elevated plasma LDL-C with elevated apoB; HoFH may also show elevated VLDL/IDL and reduced HDL in severe models	Pediatric PCSK9 meta-analysis: LDL-C −37.92%, apoB −33.67%, Lp(a) −16.94%	HP:0003124; HP:0012185; CHEBI:16129
Physical signs	Classical stigmata include tendon xanthomas, corneal arcus, and periocular/cutaneous xanthomas in more severe disease	Tendon xanthomas seen in <15% and corneal arcus in ~30% of HeFH in a cited cohort context	HP:0000991; HP:0001085
Cardiovascular complications	Untreated disease accelerates atherosclerosis, coronary disease, and in severe cases aortic valve/ascending aortic disease	Genetic FH with LDL-C >190 mg/dL conveys ~3.7-fold higher CHD risk than equally elevated LDL-C without an FH mutation	HP:0001677; HP:0001717; UBERON:0000948
Diagnosis/screening	Diagnosis combines LDL-C level, family history, premature ASCVD, physical signs, and ideally confirmatory genetic testing; cascade screening is central	Opportunistic trigger LDL-C ≥190 mg/dL; screen at-risk children by age 5 years, or by 2 years if strong family history; suspected HoFH at newborn stage to 2 years	NCIT:C157171; HP:0031372
Standard treatment	First-line care is intensive statin therapy plus ezetimibe, escalating to combination therapy to reach LDL-C targets	Statins lower LDL-C ~50–60% alone and ~65–70% with ezetimibe; bempedoic acid ~22.3% LDL-C reduction in clinical HeFH phenotype	NCIT:C29447; NCIT:C61731; NCIT:C88519
LDLR-independent treatment	For severe disease, especially HoFH or null/null LDLR, receptor-independent therapies such as evinacumab and lomitapide are key; apheresis may still be required	Evinacumab lowers LDL-C by ~50% overall and ~43% even in null/null LDLR; ANGPTL3 mAb review cites ~50% LDL and ~47% TG reduction	NCIT:C158502; NCIT:C83818; NCIT:C15201
Epidemiology	FH is common but substantially underdiagnosed worldwide	Prevalence ~1 in 311 globally; ~35 million people affected; only ~10% diagnosed worldwide	MONDO:0005439
Models	Experimental systems recapitulate LDLR-FH across species for mechanism and therapy testing, from mouse to non-human primate	LDLR knockout mice show ~2-fold total cholesterol increase; six LDLR-KO cynomolgus monkeys generated with HoFH-like phenotype	NCBITaxon:10090; NCBITaxon:9541; CL:0000182

Table: This table condenses the main disease-knowledge-base domains for LDLR-related familial hypercholesterolemia into ontology-ready findings and quantitative anchors. It is useful as a compact reference for curation and downstream structured annotation. (arnold2023familialhypercholesterolemiapitfalls pages 1-2, chora2022theclinicalgenome pages 5-6, watts2023internationalatherosclerosissociety pages 1-2, chora2022theclinicalgenome pages 8-10, ishibashi1993hypercholesterolemiainlow pages 1-2, arnold2023familialhypercholesterolemiapitfalls pages 4-6, arnold2023familialhypercholesterolemiapitfalls pages 2-3, sato2023generationofa pages 1-2, xiao2024efficacyandsafety pages 1-2)

1. Disease information

Definition. LDLR-related familial hypercholesterolemia (LDLR-FH) is a lifelong Mendelian disorder of hepatic LDL-particle clearance. One pathogenic allele usually causes heterozygous FH (HeFH); two pathogenic alleles—homozygous or compound heterozygous—cause the substantially more severe homozygous phenotype (HoFH). LDL-C is elevated from birth, producing cumulative arterial cholesterol exposure and premature atherosclerotic cardiovascular disease (ASCVD). The IAS describes FH as a highly penetrant, co-dominant disorder affecting the hepatic LDL-clearance pathway. (arnold2023familialhypercholesterolemiapitfalls pages 1-2, watts2023internationalatherosclerosissociety pages 1-2)

Identifiers and synonyms. Recommended knowledge-base identifiers are MONDO:0007750 (“hypercholesterolemia, familial, 1”; LDLR-associated entity), broader MONDO:0005439 (“familial hypercholesterolemia”), OMIM #143890 (“Hypercholesterolemia, familial, 1”), ORPHA:391665 (familial hypercholesterolemia), MeSH D006938, US ICD-10-CM E78.01, and ICD-11 familial hypercholesterolaemia under the disorders-of-lipoprotein-metabolism hierarchy. Because coding-system releases differ, the ICD-11 code should be version-validated before production use. Open Targets independently identifies LDLR as the highest-scoring target for familial hypercholesterolemia and links it to MONDO:0005439 and MONDO:0007750. (OpenTargets Search: familial hypercholesterolemia-LDLR)

Common names include LDLR-related FH, familial hypercholesterolemia type 1, autosomal dominant hypercholesterolemia type 1, LDL receptor deficiency, HeFH, and LDLR-associated HoFH. “Autosomal dominant” is clinically familiar, although “autosomal co-dominant” better captures the allele-dose phenotype.

2. Etiology, risk, protection, and gene–environment interaction

Causal factor

The primary cause is a germline pathogenic or likely pathogenic LDLR variant that reduces receptor abundance or function. LDLR accounts for approximately 80–90% of genetically diagnosed FH, although the percentage depends on referral and testing criteria. The downstream defect is reduced hepatocyte uptake of apoB-containing LDL, prolonged plasma LDL residence, and lifelong hypercholesterolemia. (arnold2023familialhypercholesterolemiapitfalls pages 1-2, xiao2024efficacyandsafety pages 1-2)

Risk factors and modifiers

Genetic severity: two affected alleles, null alleles, and lower residual receptor activity produce higher LDL-C and earlier disease. A classic FH variant plus LDL-C >190 mg/dL confers about 3.7-fold greater CHD risk than the same LDL-C without an identified FH variant, and up to approximately 20–22-fold risk relative to normolipidemic/non-carrier comparators in cited cohorts. (arnold2023familialhypercholesterolemiapitfalls pages 2-3, xiao2024efficacyandsafety pages 1-2)
Additional inherited risk: elevated LPA/Lp(a), polygenic LDL-C burden, and variants influencing apoB lipoprotein production or clearance modify expression. Lp(a) >50 mg/dL combined with FH denotes particularly high myocardial-infarction risk; conversely, Lp(a)-cholesterol can inflate measured LDL-C and mimic clinical FH. In one Copenhagen analysis, high Lp(a) contributed to approximately 25% of clinical FH classifications; Lp(a)-adjustment moved 16.6% of patients to a lower Dutch Lipid Clinic Network category. (arnold2023familialhypercholesterolemiapitfalls pages 4-6)
Environmental/clinical amplifiers: smoking, hypertension, diabetes, obesity, physical inactivity, diets rich in saturated/trans fats, chronic kidney disease, and delayed or inadequate LDL-lowering increase absolute ASCVD risk. Age represents cumulative exposure rather than disease acquisition.
Sex: inheritance is not sex-linked and the birth ratio should be approximately equal. Premenopausal estrogen may delay clinical events in women, but LDL elevation is present in both sexes from birth.

Protective factors

Protective factors do not remove the causal allele. They reduce LDL burden or downstream risk: early sustained LDL-C lowering, absence of smoking, healthy blood pressure and glycemia, physical activity, healthy weight, and substitution of unsaturated for saturated fat. Genetic PCSK9 or ANGPTL3 loss-of-function can lower apoB lipoproteins; PCSK9 loss-of-function is protective against coronary disease mechanistically, although it is not a routine modifier test in LDLR-FH. (srivastava2023areviewof pages 8-9)

Gene–environment interaction: diet has a modest effect relative to the LDLR defect, but high-fat/high-cholesterol exposure magnifies hyperlipidemia and atherosclerosis. LDLR-knockout mice illustrate this interaction: dietary cholesterol causes a marked IDL/LDL rise, whereas the normal-diet mouse phenotype is milder than human HoFH because murine lipoprotein physiology differs. (ishibashi1993hypercholesterolemiainlow pages 1-2, sato2023generationofa pages 1-2)

3. Phenotypes

Phenotype	Type, onset, course, frequency/severity	Suggested HPO
Elevated LDL-C	Laboratory abnormality; congenital and persistent. Commonly >190 mg/dL in HeFH and >400 mg/dL in HoFH, but overlap is substantial	HP:0003124 Hypercholesterolemia
Elevated apoB/atherogenic particles	Laboratory abnormality; lifelong, severity tracks LDL particle burden	HP:0012185 Abnormal circulating apolipoprotein concentration
Tendon xanthomas	Physical sign, typically Achilles/extensor tendons; age-dependent, more prominent in severe/untreated disease. Reported in <15% of a contemporary HeFH cohort	HP:0000991 Xanthomatosis; HP:0200045 Tendon xanthoma
Corneal arcus	Physical sign; premature arcus is more specific than age-related arcus. Approximately 30% in the cited HeFH cohort	HP:0001084/HP:0001085 Corneal arcus
Cutaneous/periocular xanthomas	Physical sign; childhood onset strongly suggests HoFH. LDLR-KO primates developed periocular xanthoma by one year	HP:0000991; HP:0200044 Xanthelasma
Premature coronary atherosclerosis/MI	Clinical complication; insidious and progressive, often clinically silent before an event; adult onset typical in untreated HeFH but childhood/adolescent disease can occur in HoFH	HP:0001677 Coronary artery atherosclerosis, HP:0001658 Myocardial infarction
Aortic-root/valvular disease	Sign/complication, especially HoFH; progressive supravalvular/aortic-root atherosclerosis and calcific aortic stenosis	HP:0001647 Aortic valve stenosis; HP:0002621 Aortic atherosclerosis
Peripheral/cerebrovascular disease	Secondary vascular complications; less defining than coronary disease	HP:0002635 Cerebral ischemia; HP:0004950 Peripheral arterial disease

Physical stigmata are insensitive screening features: their absence does not exclude FH. Contemporary treatment may further reduce their frequency. (arnold2023familialhypercholesterolemiapitfalls pages 2-3)

Quality of life. Most children and many adults are asymptomatic, but diagnosis imposes lifelong medication, dietary vigilance, family testing, and anxiety about premature events. HoFH adds frequent apheresis, venous-access burden, xanthomas, repeated imaging, and early cardiovascular procedures. Robust phenotype-specific EQ-5D/SF-36 estimates were not available in the retrieved primary evidence; this field should therefore be recorded as evidence limited, not “no impact.”

4. Genetic and molecular information

Gene. LDLR—HGNC:6547; NCBI Gene:3949; Ensembl ENSG00000130164; chromosome 19p13.2—encodes the low-density lipoprotein receptor. The disease alleles are germline. Somatic LDLR variation is not the cause of inherited FH.

Variant spectrum. More than 2,300 unique FH-associated LDLR variants were already known when ClinGen issued its LDLR-specific ACMG/AMP rules. Variants include missense (the largest group), nonsense, frameshift, canonical and noncanonical splice variants, in-frame indels, promoter changes, and exon/whole-gene deletions or duplications. Frameshifts account for about 20% of associated variants. Stop variants before amino acid 830 remove the NPXY-containing cytoplasmic tail needed for internalization and meet strong loss-of-function logic. (chora2022theclinicalgenome pages 5-6, chora2022theclinicalgenome pages 1-3)

Functional classes. The traditional receptor classes are: I, absent synthesis; II, defective ER-to-Golgi transport; III, defective LDL binding; IV, defective clustering/internalization; V, defective endosomal dissociation/recycling; and sometimes VI, defective basolateral targeting. These converge on loss of LDL uptake. Null alleles generally have <2% activity; clinical trials often operationalize null as <15% activity, emphasizing that thresholds vary by context. (NCT04233918 chunk 1)

Classification. Use five-tier ACMG/AMP categories—pathogenic, likely pathogenic, VUS, likely benign, benign—with ClinGen FH Variant Curation Expert Panel specifications. These modify population-frequency thresholds using gnomAD PopMax, define PVS1-eligible loss-of-function alleles, calibrate functional assays and computational evidence, and specify case/segregation evidence. Examples include PM1 for rare missense substitutions in exon 4 or one of 60 conserved cysteines; PP4 for a rare variant in a patient meeting DLCN ≥6, Simon Broome, or MEDPED criteria; and PP1_Strong for at least six informative cosegregating meioses. A 54-variant pilot produced 6 benign, 2 likely benign, 18 VUS, 15 likely pathogenic, and 13 pathogenic classifications with complete panel agreement. (chora2022theclinicalgenome pages 8-10, chora2022theclinicalgenome pages 11-13)

Allele frequency. A universal frequency cannot be supplied because LDLR-FH comprises thousands of alleles. Most pathogenic variants are individually rare or absent in gnomAD; founder alleles can be locally enriched. Report variant-specific gnomAD ancestry frequency and homozygote count, not an aggregate disease frequency. Examples of founder enrichment occur in French Canadians, Lebanese, Afrikaners, Christian Lebanese, and several European isolates.

Modifiers and epigenetics. LPA, common polygenic LDL-C alleles, APOE, PCSK9, ANGPTL3, and genes affecting apoB production/clearance can modify phenotype. No reproducible disease-defining methylation or histone signature currently replaces DNA diagnosis. Epigenetic and transcriptomic changes observed in atherosclerotic plaque are predominantly downstream consequences of lipid exposure and inflammation.

Structural abnormalities. LDLR exon-level deletions/duplications are clinically important copy-number variants. Balanced translocations, aneuploidy, repeat expansions, and mitochondrial variants are not standard causes of LDLR-FH.

5. Environmental and lifestyle information

LDLR-FH is not caused by toxins, radiation, occupational exposure, or infection. Diet, exercise, adiposity, tobacco, alcohol-related metabolic effects, blood pressure, and diabetes modify cardiovascular expression. A heart-healthy diet and exercise are recommended adjuncts but rarely normalize genetically elevated LDL-C. Infectious agents and vaccination have no disease-specific etiologic role.

Secondary causes that can worsen or mimic the biochemical phenotype include hypothyroidism, nephrotic syndrome, cholestatic liver disease, uncontrolled diabetes, obesity, and LDL-raising drugs. These should be addressed before assigning pathogenicity evidence or a definitive clinical diagnosis. ClinGen explicitly requires exclusion of alternative hypercholesterolemia causes. (chora2022theclinicalgenome pages 8-10)

6. Mechanism and pathophysiology

Causal chain: germline LDLR loss-of-function → reduced hepatocyte surface LDLR or impaired binding/internalization/recycling → slower removal of apoB-100 LDL and remnant particles → elevated plasma LDL-C from birth → arterial intimal entry and proteoglycan retention → oxidation/aggregation and endothelial activation → monocyte recruitment and macrophage foam cells → chronic inflammatory plaque growth, necrotic core and calcification → coronary ischemia, MI, aortic-root disease, stroke, or peripheral disease.

The LDLR normally undergoes clathrin-mediated endocytosis and recycling. PCSK9 binding diverts LDLR toward lysosomal degradation; statins and ezetimibe induce residual LDLR through intracellular cholesterol depletion, whereas PCSK9 antibodies or inclisiran preserve residual receptor. Consequently, these therapies work best when some LDLR function remains. ANGPTL3 inhibition, lomitapide, and apheresis act substantially independently of LDLR and are especially important in null/null HoFH. (srivastava2023areviewof pages 8-9, arnold2023familialhypercholesterolemiapitfalls pages 4-6)

Tissues/cells: hepatocytes are the upstream causal cell; arterial endothelial cells, smooth-muscle cells, monocyte-derived macrophages, and valve interstitial cells mediate downstream injury. Suggested terms include GO:0006898 receptor-mediated endocytosis, GO:0034383 low-density lipoprotein particle clearance, GO:0042157 lipoprotein metabolic process, GO:0006954 inflammatory response, GO:0045766 positive regulation of angiogenesis/vascular remodeling as context-appropriate; CL:0000182 hepatocyte, CL:0000115 endothelial cell, CL:0000235 macrophage, and CL:0000192 smooth-muscle cell.

Subcellular terms: plasma membrane (GO:0005886), clathrin-coated pit (GO:0005905), endosome (GO:0005768), lysosome (GO:0005764), and endoplasmic reticulum (GO:0005783). The biochemical abnormality is receptor dysfunction rather than an enzyme or ion-channel deficiency.

Molecular profiling. Routine diagnosis does not require transcriptomics, proteomics, metabolomics, single-cell, or spatial profiling. Lipidomics shows excess apoB-containing cholesterol-rich particles, while plaque single-cell/spatial studies illuminate downstream atherosclerosis rather than uniquely identifying LDLR-FH. Functional LDL uptake and cell-surface-expression assays are most useful for resolving VUS. In-silico prediction alone is insufficient; functional characterization or informative cascade segregation is preferred. (chora2022theclinicalgenome pages 1-3)

Advanced technology. Preclinical base/gene-editing strategies targeting PCSK9 or ANGPTL3 achieved up to 90% PCSK9 and 60% LDL reduction for eight months in nonhuman primates; ANGPTL3 suppression exceeded 95% for up to two years in cited preclinical work. LDLR-enhancing strategies require a usable allele, whereas ANGPTL3 editing is potentially LDLR-independent. These are experimental and do not establish long-term human safety. (srivastava2023areviewof pages 14-16)

7. Anatomical structures affected

The liver is the primary mechanistic organ because hepatic LDLR controls most plasma LDL clearance (UBERON:0002107). Secondary injury involves coronary arteries, aorta/aortic root, aortic valve, carotid and peripheral arteries, myocardium after ischemia, tendons, skin/eyelids, and cornea. Suggested mappings include heart UBERON:0000948, liver UBERON:0002107, coronary artery UBERON:0001621, aorta UBERON:0000947, aortic valve UBERON:0002137, Achilles tendon UBERON:0000979, cornea UBERON:0000964, and skin UBERON:0002097. Disease is systemic rather than lateralized.

8. Temporal development

LDL-C elevation is congenital, chronic, and lifelong. HeFH is frequently asymptomatic through childhood; subclinical atherosclerosis accumulates before adult coronary events. HoFH can produce childhood xanthomas, aortic and coronary disease, and occasionally fatal cardiovascular events in childhood or infancy when receptor activity is nearly absent. (sato2023generationofa pages 1-2)

A practical course model is: (1) biochemical disease from birth; (2) subclinical arterial dysfunction/intima-media or plaque burden; (3) overt xanthomas/aortic or coronary disease; (4) recurrent ASCVD/heart failure or procedural burden. There is no spontaneous remission. LDL-C reduction is treatment-induced; plaques and xanthomas can stabilize or regress with intensive therapy, but the genotype remains. The critical intervention window is childhood, before cumulative LDL exposure produces irreversible plaque.

9. Inheritance and population

LDLR-FH is autosomal co-dominant. An affected heterozygous parent transmits the variant to 50% of offspring. Two affected parents can have children with biallelic disease; reproductive risk depends on both parental genotypes. Penetrance for elevated LDL-C is high but age-dependent penetrance for ASCVD is incomplete and modified by treatment and other risk factors. Expressivity is variable; anticipation is not expected. Germline mosaicism is possible in principle but is not a characteristic feature. Consanguinity increases biallelic disease risk where the same founder allele circulates.

Best contemporary estimates are approximately 1 in 311 people for FH globally—about 35 million individuals—and roughly 1 in 250–300 in many populations. HoFH is approximately 1 in 250,000–360,000; one 2023 review cited 1 in 300,000. Prevalence rises to approximately 1 in 17 among people with premature ASCVD. Only about 10% are diagnosed worldwide, and >80% of treated patients fail to achieve recommended LDL-C goals. Incidence is rarely reported because the condition is congenital; under stable population assumptions, birth incidence approximates prevalence. (watts2023internationalatherosclerosissociety pages 1-2, arnold2023familialhypercholesterolemiapitfalls pages 2-3, xiao2024efficacyandsafety pages 1-2)

Both sexes and all ancestries are affected. Regional variation chiefly reflects founder effects, ascertainment, access to testing, and diagnostic infrastructure—not environmental endemicity.

10. Diagnostics

Core tests: fasting or nonfasting lipid profile, repeat LDL-C confirmation, apoB, triglycerides, liver/renal/thyroid tests to exclude secondary causes, and Lp(a) for risk and LDL-C interpretation. Opportunistic adult evaluation is recommended at LDL-C ≥190 mg/dL; age-, sex-, and country-specific >95th-percentile values are preferred for population screening. If triglycerides exceed 400 mg/dL, obtain a fasting sample and direct LDL-C measurement. (watts2023internationalatherosclerosissociety pages 2-3)

Clinical criteria: Dutch Lipid Clinic Network, Simon Broome, and MEDPED combine LDL-C, premature ASCVD, family history, xanthomas/arcus, and genotype. Their sensitivity varies by setting; one mutation-positive analysis reported sensitivities of only 9% for DLCN ≥6, 17% for Simon Broome, and 31% for MEDPED, supporting genetic confirmation where feasible. (arnold2023familialhypercholesterolemiapitfalls pages 2-3)

Genetic approach: sequence LDLR, APOB, and PCSK9 at minimum, usually through an FH/dyslipidemia panel; add deletion/duplication analysis because LDLR CNVs are relevant. Broader panels may include LDLRAP1, ABCG5, ABCG8, and LIPA for phenocopies. A known familial LDLR variant should be tested directly in relatives. WES/WGS are useful after negative panel testing, for structural/noncoding variants or blended phenotypes, but are not obligatory first-line tests. CMA, karyotype, FISH, mtDNA, and repeat-expansion testing are not routine. A VUS does not confirm FH or justify predictive testing without additional evidence.

Imaging/risk assessment: ECG and stress testing evaluate suspected ischemia; coronary CT angiography, carotid ultrasound, echocardiography, and aortic-root/valve imaging are used according to age, severity, symptoms, and HoFH status. Biopsy is unnecessary.

Differential diagnosis: polygenic hypercholesterolemia; APOB- or PCSK9-related AD FH; recessive LDLRAP1 hypercholesterolemia; sitosterolemia (ABCG5/ABCG8; elevated plant sterols); lysosomal acid lipase deficiency (LIPA; hepatic disease); familial combined hyperlipidemia; dysbetalipoproteinemia; high Lp(a); and secondary hypercholesterolemia.

Screening: IAS gives Class 1 recommendations for multiple detection strategies, selective screening in premature ASCVD, and cascade testing of close relatives using genotype plus phenotype. Universal pediatric screening followed by reverse cascade testing is reasonable; at-risk HeFH children should be tested around age five—or age two with a strong premature-ASCVD history—while suspected HoFH should be evaluated at birth or by age two. Combined cascade and young-age universal screening could identify >90% of cases if effectively implemented. (watts2023internationalatherosclerosissociety pages 1-2, watts2023internationalatherosclerosissociety pages 2-3)

11. Outcome and prognosis

Untreated LDLR-FH causes progressive premature ASCVD and excess cardiovascular mortality. Prognosis depends principally on cumulative LDL-C exposure, residual receptor activity, number/type of alleles, Lp(a), smoking, diabetes, blood pressure, established ASCVD, age at treatment, adherence, and achieved LDL-C. HoFH—particularly null/null disease—has the poorest untreated prognosis.

There is no meaningful universal “five-year survival” statistic analogous to oncology because modern outcome depends strongly on genotype, ascertainment age, and treatment. Early sustained statin-based therapy markedly improves outlook; intensive combination therapy can cause xanthoma disappearance and plaque stabilization/regression. Nevertheless, fewer than 3% reached guideline LDL targets in one reviewed global context, illustrating persistent morbidity risk. (arnold2023familialhypercholesterolemiapitfalls pages 1-2, arnold2023familialhypercholesterolemiapitfalls pages 7-8)

Complications include MI, coronary revascularization, ischemic cardiomyopathy, aortic stenosis/root disease, stroke, peripheral arterial disease, and recurrent events. Functional disability is secondary to these complications and, in HoFH, treatment burden. Prognostic biomarkers include achieved and cumulative LDL-C, apoB, Lp(a), coronary plaque burden, and presence of a pathogenic/null LDLR genotype.

12. Treatment

Strategy. Begin lifestyle therapy and pharmacologic LDL lowering early. For most HeFH: maximally tolerated high-intensity statin → add ezetimibe → add a PCSK9 monoclonal antibody or inclisiran; bempedoic acid is an option for additional lowering or statin intolerance. LDL goals cited by ESC/EAS are ≥50% reduction and <70 mg/dL without major additional risk, or <55 mg/dL with ASCVD/another major risk factor. (arnold2023familialhypercholesterolemiapitfalls pages 4-6)

Statins inhibit HMG-CoA reductase and upregulate residual LDLR: approximately 50–60% LDL-C reduction with high-potency monotherapy. Ezetimibe inhibits NPC1L1; combination may achieve roughly 65–70%. Suggested NCIt: Statin (C1655 class), Atorvastatin (C28837), Rosuvastatin, Ezetimibe (C61731). (arnold2023familialhypercholesterolemiapitfalls pages 4-6)
Bempedoic acid, an ACLY inhibitor activated mainly in liver, reduced LDL-C by 22.3% in a pooled 112-person clinical-HeFH subgroup. Hyperuricemia/gout and tendon injury are recognized concerns. (arnold2023familialhypercholesterolemiapitfalls pages 4-6)
Alirocumab/evolocumab prevent PCSK9-mediated LDLR degradation and reduce LDL-C approximately 45–65% in HeFH trials. Response is weak or absent with no functional receptor. A 2024 pediatric meta-analysis of nine studies found LDL-C −37.92% (95% CI −43.06 to −32.78), apoB −33.67%, and Lp(a) −16.94%; agents were generally well tolerated. (arnold2023familialhypercholesterolemiapitfalls pages 4-6, xiao2024efficacyandsafety pages 1-2)
Inclisiran is hepatocyte-targeted siRNA that suppresses PCSK9 synthesis. ORION-9 (NCT03397121) was a completed phase III randomized double-blind trial in 482 adults with HeFH, dosing on days 1 and 90 and then every six months. ORION-16 (NCT04652726) enrolled 141 adolescents in a completed phase III study. (NCT03397121 chunk 1, NCT04652726 chunk 1)
Evinacumab, an ANGPTL3 antibody, is LDLR-independent and lowers HoFH LDL-C by approximately 50%, including about 43% in null/null patients. The pivotal completed phase III trial NCT03399786 randomized 65 HoFH patients; pediatric NCT04233918 was a completed phase Ib/III single-arm study of 20 children. Suggested NCIt: Evinacumab (C158502). (arnold2023familialhypercholesterolemiapitfalls pages 7-8, NCT04233918 chunk 1, NCT03399786 chunk 1)
Lomitapide inhibits microsomal triglyceride-transfer protein, reducing VLDL/LDL production independently of LDLR. It is used chiefly in adult HoFH; hepatic steatosis, transaminase elevation, diarrhea, drug interactions, and fat-soluble-vitamin deficiency require monitoring.
Lipoprotein apheresis physically removes apoB lipoproteins and is often needed in severe HoFH, pregnancy, or refractory disease. The effect is immediate but rebounds between sessions; access, vascular burden, and cost are major limitations.
Liver transplantation supplies functional hepatic LDLR but carries operative risk and lifelong immunosuppression; it is a last-resort intervention.

Genotype-guided care. Residual LDLR activity predicts response to statins and PCSK9-directed therapy. Null/null disease favors early LDLR-independent treatment—evinacumab, lomitapide, and/or apheresis. This is clinically actionable pharmacogenetic stratification, although it is not principally a drug-metabolism PGx effect.

Experimental therapies. LDLR replacement, mRNA/exosome delivery, in-vivo editing, and PCSK9/ANGPTL3 editing remain investigational. A recruiting phase III study, NCT06597006, is evaluating inclisiran in children aged 2–11 years with HoFH and documented biallelic null LDLR mutations; poor prior PCSK9-antibody response is an exclusion criterion. (NCT06597006 chunk 2)

13. Prevention

The pathogenic allele itself generally cannot be prevented after conception. Primary cardiovascular prevention comprises early diagnosis, no smoking, healthy diet/activity, blood-pressure and diabetes control, and lifelong LDL lowering. Secondary prevention is cascade/universal screening followed by treatment before symptoms. Tertiary prevention uses intensive combination therapy, apheresis, imaging, and management of established ASCVD to prevent recurrent events.

Genetic counseling should cover 50% transmission from an affected heterozygous parent, testing of first-degree relatives, reproductive partner testing when severe/founder disease is possible, and options for prenatal or preimplantation genetic testing when the familial variant is known. Vaccines and antimicrobial prophylaxis are not disease-specific interventions.

14. Other species and natural disease

LDLR orthologues and receptor-mediated LDL clearance are evolutionarily conserved. Naturally occurring Watanabe heritable hyperlipidemic rabbits carry LDLR deficiency and develop severe hypercholesterolemia and atherosclerosis, closely modeling human FH. LDLR-related hypercholesterolemia has also been described in rhesus monkeys and selected pigs. This is not infectious, transmissible, or zoonotic. Breed-level VBO assignment should be made only for a verified veterinary strain/breed record; the WHHL rabbit is principally a research strain rather than a common companion-animal breed. (ishibashi1993hypercholesterolemiainlow pages 1-2)

15. Model organisms

Ldlr−/− mouse (NCBI Taxon 10090): viable and fertile; total cholesterol is approximately twofold wild type, IDL/LDL rises seven- to ninefold, VLDL and LDL half-lives are prolonged 30-fold and 2.5-fold, and hepatic adenoviral LDLR normalized elevated IDL/LDL within four days. Strengths are tractability, controlled diet, and atherosclerosis/gene-therapy studies. Limitations include apoB48-rich murine metabolism and limited spontaneous atherosclerosis on normal chow. Exact abstract quote: “The elevated IDL/LDL level of LDLR-/- mice was reduced to normal 4 d after the intravenous injection” of LDLR adenovirus. (ishibashi1993hypercholesterolemiainlow pages 1-2)
WHHL rabbit (NCBI Taxon 9986): natural LDLR deficiency, LDL-rich profile, and early atherosclerosis; more human-like lipoprotein physiology than mice, but cost and genetic-tool availability are disadvantages.
Ldlr-deficient hamster/pig: useful because CETP and apoB-lipoprotein biology are more human-like; applied to PCSK9/LDLR pharmacology and large-vessel imaging. Greater expense and lower throughput limit use.
CRISPR LDLR-KO cynomolgus monkey (NCBI Taxon 9541): six animals had extremely high cholesterol/triglycerides, elevated VLDL/LDL, reduced HDL, poor drug response, and periocular xanthomas by one year, closely recapitulating HoFH. Exact abstract quote: “The levels of plasma cholesterol and triglyceride were quite high in the monkeys, and were similar to those in FH patients with homozygous mutations in the LDLR gene.” Limitations include small cohorts, mosaic/editing effects, ethics, cost, and short follow-up. (sato2023generationofa pages 1-2)
Human cellular models: patient fibroblasts, hepatocyte-like cells, engineered LDLR-null hepatic lines, and iPSC-derived hepatocytes support LDL-binding/uptake, receptor-abundance, trafficking, VUS, and gene-correction assays. They do not reproduce multicellular plaque biology.

Recent developments and evidence interpretation

The most consequential 2023–2024 developments are implementation-focused IAS guidance, expanding pediatric PCSK9 evidence, pediatric and adolescent inclisiran programs, pediatric evinacumab development, and maturation of LDLR-independent and editing strategies. The expert consensus is that the central failure is no longer absence of effective LDL-lowering tools, but late detection, undertreatment, inequitable access, and failure to sustain sufficiently low LDL-C from childhood. Only about 10% of affected people are diagnosed, while most treated patients remain above recommended targets. (arnold2023familialhypercholesterolemiapitfalls pages 1-2, watts2023internationalatherosclerosissociety pages 1-2)

Selected authoritative sources

Watts GF et al. International Atherosclerosis Society guidance for implementing best practice in the care of familial hypercholesterolaemia. Nature Reviews Cardiology, published June 2023; 20:845–869. DOI/URL: https://doi.org/10.1038/s41569-023-00892-0. (watts2023internationalatherosclerosissociety pages 1-2)
Arnold N, Koenig W. Familial Hypercholesterolemia: Pitfalls and Challenges in Diagnosis and Treatment. Reviews in Cardiovascular Medicine, August 2023. DOI/URL: https://doi.org/10.31083/j.rcm2408236. (arnold2023familialhypercholesterolemiapitfalls pages 1-2)
Chora JR et al. ClinGen Familial Hypercholesterolemia Variant Curation Expert Panel consensus guidelines for LDLR variant classification. Genetics in Medicine, February 2022;24:293–306. DOI/URL: https://doi.org/10.1016/j.gim.2021.09.012. (chora2022theclinicalgenome pages 1-3)
Xiao G et al. Efficacy and Safety of Evolocumab and Alirocumab…in Pediatric Patients with FH. Medicina, published 8 October 2024. DOI/URL: https://doi.org/10.3390/medicina60101646. (xiao2024efficacyandsafety pages 1-2)
Sato A et al. Generation of a familial hypercholesterolemia model in non-human primate. Scientific Reports, September 2023;13:15649. DOI/URL: https://doi.org/10.1038/s41598-023-42763-1. (sato2023generationofa pages 1-2)
Srivastava RAK. Targeting LDL receptor-dependent and-independent pathways… Cells, June 2023;12:1648. DOI/URL: https://doi.org/10.3390/cells12121648. (srivastava2023areviewof pages 8-9)

Evidence note. Exact PMIDs were not exposed for every retrieved article, so DOI URLs are supplied rather than risking incorrect PMID assignment. Trial facts derive from ClinicalTrials.gov records; mechanistic claims are distinguished above as human clinical, expert-guidance, cellular, or model-organism evidence.

References

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(NCT04233918 chunk 1): Evaluate the Efficacy and Safety of Evinacumab in Pediatric Patients With Homozygous Familial Hypercholesterolemia. Regeneron Pharmaceuticals. 2020. ClinicalTrials.gov Identifier: NCT04233918
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(watts2023internationalatherosclerosissociety pages 2-3): Gerald F. Watts, Samuel S. Gidding, Robert A. Hegele, Frederick J. Raal, Amy C. Sturm, Laney K. Jones, Mitchell N. Sarkies, Khalid Al-Rasadi, Dirk J. Blom, Magdalena Daccord, Sarah D. de Ferranti, Emanuela Folco, Peter Libby, Pedro Mata, Hapizah M. Nawawi, Uma Ramaswami, Kausik K. Ray, Claudia Stefanutti, Shizuya Yamashita, Jing Pang, Gilbert R. Thompson, and Raul D. Santos. International atherosclerosis society guidance for implementing best practice in the care of familial hypercholesterolaemia. Nature Reviews Cardiology, 20:845-869, Jun 2023. URL: https://doi.org/10.1038/s41569-023-00892-0, doi:10.1038/s41569-023-00892-0. This article has 294 citations and is from a domain leading peer-reviewed journal.
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(NCT03397121 chunk 1): Trial to Evaluate the Effect of Inclisiran Treatment on Low Density Lipoprotein Cholesterol (LDL-C) in Subjects With Heterozygous Familial Hypercholesterolemia (HeFH). The Medicines Company. 2017. ClinicalTrials.gov Identifier: NCT03397121
(NCT04652726 chunk 1): Study to Evaluate Efficacy and Safety of Inclisiran in Adolescents With Heterozygous Familial Hypercholesterolemia. Novartis Pharmaceuticals. 2021. ClinicalTrials.gov Identifier: NCT04652726
(NCT03399786 chunk 1): Efficacy and Safety of Evinacumab in Patients With Homozygous Familial Hypercholesterolemia. Regeneron Pharmaceuticals. 2018. ClinicalTrials.gov Identifier: NCT03399786
(NCT06597006 chunk 2): Study to Evaluate Safety, Tolerability and Efficacy of Inclisiran in Children With Homozygous Familial Hypercholesterolemia. Novartis Pharmaceuticals. 2025. ClinicalTrials.gov Identifier: NCT06597006

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Outcome	Count
References checked	7
Resolved	7
Unresolved (possible confabulation)	0
Unverifiable	0
References weighed for topical relevance	7
On topic	3
Off topic	0

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Pathophysiology

Pathograph

Phenotypes

Genetic Associations

Medical Actions

Biochemical Markers

Diagnosis

Progression

Prevalence

Differential Diagnoses

Clinical Trials

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References

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LDLR-Related Familial Hypercholesterolemia: Disease Characteristics Report

1. Disease information

2. Etiology, risk, protection, and gene–environment interaction

Causal factor

Risk factors and modifiers

Protective factors

3. Phenotypes

4. Genetic and molecular information

5. Environmental and lifestyle information

6. Mechanism and pathophysiology

7. Anatomical structures affected

8. Temporal development

9. Inheritance and population

10. Diagnostics

11. Outcome and prognosis

12. Treatment

13. Prevention

14. Other species and natural disease

15. Model organisms

Recent developments and evidence interpretation

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