Home / Deep Research / Autosomal Recessive Hypercholesterolemia

Autosomal Recessive Hypercholesterolemia

Autosomal Recessive Hypercholesterolemia (ARH) — manual research sweep

Claude Code MONDO:0011374

Autosomal Recessive Hypercholesterolemia (ARH) — manual research sweep

Summary

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

Mechanism chain (as curated)

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

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

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

Reference Validation

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

Term Validation

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

Named Entity Confusion preflight

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