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The association between COL4A1 and autosomal dominant familial hematuria–retinal arteriolar tortuosity–contractures (HANAC) syndrome is best classified as Strong using ClinGen criteria. Multiple independent families with a highly characteristic multisystem phenotype (hematuria with renal cysts, retinal arteriolar tortuosity, muscle cramps/contractures, and systemic angiopathy) harbor heterozygous COL4A1 variants that segregate with disease across several generations, with cumulative linkage and segregation data in at least six pedigrees.PMID:18160688, PMID:20818663, PMID:36922284 One large ADPKD/HANAC pedigree further supports the specificity of the HANAC phenotype to COL4A1 variants distinct from PKD2.PMID:29395486 Functional work in human cells and multiple animal models shows that glycine substitutions or truncating variants within COL4A1 impair type IV collagen secretion, alter basement membrane structure, and drive a vascular small‑vessel disease mechanism that concords well with the HANAC clinical spectrum.PMID:18160688, PMID:20056676, PMID:25753534, PMID:28056338
Evidence has not yet met formal time‑ and replication‑based thresholds for a Definitive classification in this specific MONDO entity, largely because many COL4A1 reports are aggregated as a broader “COL4A1‑related small vessel disease” spectrum rather than as HANAC per se. Nonetheless, the genetic and experimental data already reach the Strong level for this defined syndrome and are sufficient to support diagnostic use, variant interpretation, and counseling in clinical and commercial settings.
Inheritance mode and severity. HANAC syndrome due to COL4A1 is predominantly autosomal dominant with high intrafamilial penetrance for ocular and muscular features and variable penetrance for renal and aneurysmal manifestations.PMID:18160688, PMID:20818663 Disease severity ranges from relatively mild, adult‑onset muscle cramps with microscopic hematuria to progressive kidney disease and systemic vascular complications; most reported HANAC families are compatible with a chronic but generally non‑fulminant course, though risk of cerebrovascular events and aneurysm rupture is clinically important.PMID:18160688, PMID:20818663
Core pedigrees and segregation. The original HANAC description identified three families with autosomal dominant transmission of a constellation of hematuria, bilateral renal cysts, muscle cramps, and intracranial aneurysms, all carrying heterozygous glycine substitutions in exons 24–25 (CB3[IV] region) of COL4A1.PMID:18160688 A subsequent study added three further families with typical HANAC manifestations and three additional glycine substitutions localised to the same CB3[IV] triple‑helical domain, confirming this region as a mutational hot spot for HANAC.PMID:20818663 Across these six families, multiple affected individuals per pedigree and absence of pathogenic variants in other collagen IV genes provide strong segregation support, with additional family‑level cosegregation data in later reports describing skeletal muscle–predominant cramps and hyperkinetic movements in a Japanese family carrying c.1538G>A (p.Gly513Asp).PMID:36922284
Case reports and series. In the large 7‑generation family evaluated for presumed ADPKD, next‑generation sequencing identified a heterozygous COL4A1 nonsense variant c.739C>T (p.Gln247Ter) in individuals whose phenotype was re‑classified as HANAC rather than PKD; at least five family members had COL4A1‑related features, with evidence of earlier end‑stage renal disease in probable PKD2/COL4A1 digenic carriers.PMID:29395486 The Japanese HANAC family contributed four affected individuals with early‑childhood onset muscle cramps and persistently elevated serum creatine kinase, all heterozygous for c.1538G>A (p.Gly513Asp). Segregation with an autosomal dominant pattern across three generations was documented.PMID:36922284 Together with the original and follow‑up multicenter HANAC families, these reports yield at least dozens of affected carriers of CB3[IV] glycine substitutions or a truncating variant fulfilling case‑level genetic criteria.PMID:18160688, PMID:20818663, PMID:29395486, PMID:36922284
Variant spectrum and recurrence. HANAC‑associated COL4A1 variants cluster in the CB3[IV] triple helical domain, which harbors critical integrin‑binding motifs. Recurrent and family‑specific missense changes involve glycine residues in the Gly‑X‑Y collagen repeat, such as:
As a group, the HANAC series is enriched for pathogenic or likely pathogenic missense variants affecting conserved glycine residues within the collagenous domain, plus a smaller number of truncating alleles. All reported HANAC variants are heterozygous and segregate in an autosomal dominant manner; autosomal recessive inheritance has not been reported for the HANAC phenotype, although it occurs in other COL4A1‑related encephalopathies.PMID:32042920
Phenotypic and population context. Phenotypic core features across families include microscopic hematuria, bilateral renal cortical or medullary cysts, retinal arteriolar tortuosity, and painful muscle cramps/contractures, often accompanied by laboratory evidence of chronic myopathy (elevated creatine kinase) and asymptomatic small‑vessel brain disease.PMID:18160688, PMID:20818663, PMID:36922284 Reported families are mainly of European origin in the original HANAC series and a Japanese kindred in the more recent study.PMID:18160688, PMID:20818663, PMID:36922284 Population‑level data (cystic kidney disease, porencephaly, CSVD cohorts) show that COL4A1 glycine substitutions are rare and enriched in clinically affected individuals compared with controls, further supporting pathogenicity.PMID:21527998, PMID:22522439, PMID:35401403
Mechanism of pathogenicity. The predominant mechanism for HANAC appears to be a dominant‑negative effect of mutant COL4A1 in the α1α1α2(IV) heterotrimer, leading to impaired secretion, endoplasmic reticulum (ER) retention, and basement membrane defects. In vitro studies of multiple COL4A1 missense variants—including those in CB3[IV] and other domains—demonstrate intracellular accumulation of mutant collagen IV with decreased extracellular deposition, activation of the unfolded protein response, ER stress, and cytotoxicity in vascular endothelial and other cells.PMID:20056676, PMID:22209247, PMID:23065703, PMID:28056338, PMID:24001601 For some truncating alleles, nonsense‑mediated decay and haploinsufficiency are implicated, but these have been more clearly linked to severe perinatal intracerebral hemorrhage and porencephaly rather than classical HANAC.PMID:23065703, PMID:27190376
Animal models. Mouse models carrying Col4a1 missense mutations, including ones analogous to human glycine substitutions, show a multisystem small‑vessel and muscular phenotype that overlaps significantly with HANAC: vascular basement membrane detachment, impaired vasoconstrictor responses, endothelial dysfunction, and myopathy with elevated creatine kinase.PMID:20056676 Mice engineered with the HANAC‑linked p.Gly498Val mutation (CG498V) exhibit skeletal muscle fiber atrophy, centronucleation, focal inflammatory infiltrates, fibrosis, and endothelial cell defects with intracytoplasmic collagen IV accumulation and ER stress—closely mirroring the human muscular component of HANAC.PMID:28056338 Col4a1 mutant mice also develop progressive retinal vascular pathology with neovascularization and hemorrhages, supporting the ocular manifestations of HANAC and the broader retinal tortuosity phenotype.PMID:26813606
Vascular pathophysiology. Detailed vascular physiology experiments in Col4a1 mutant mice demonstrate age‑dependent defects in vascular tone, including reduced responses to norepinephrine, hypersensitivity to acetylcholine that is nitric oxide synthase–dependent, and altered small‑artery biomechanics—all of which confirm that type IV collagen abnormalities drive a primary vascular small‑vessel disease.PMID:20056676 More recent work shows loss of myogenic constriction and impaired smooth‑muscle calcium signaling in Col4a1+/G1344D mice, and that chemical chaperone treatment (4‑phenylbutyrate) restores SR calcium handling, normalizes vascular tone, and reduces intracerebral hemorrhage burden—strong mechanistic and therapeutic proof‑of‑concept for mutant‑collagen–induced ER stress as a treatable driver of pathology.PMID:37963192 Parallel studies in Col4a1 and Col4a2 mutant mice show that reducing intracellular collagen accumulation with chemical chaperones diminishes hemorrhagic stroke frequency, again reinforcing the dominant‑negative, ER‑stress model.PMID:25753534, PMID:24001601
Cellular and basement membrane defects. Histologic analysis of kidney and skin biopsies from HANAC and related COL4A1 patients reveals complex basement membrane irregularities in glomerular capillaries and systemic small vessels, consistent with the angiopathy and nephropathy components of the syndrome.PMID:18160688 In HANAC mouse muscle, reduced extracellular secretion of the α1α1α2(IV) trimer, endothelial ER dilation, and unfolded protein response activation correlate with increased endothelial apoptosis, tightly linking COL4A1 dysfunction to tissue‑level vascular fragility.PMID:28056338
COL4A1 is pleiotropic. Pathogenic variants cause a spectrum of phenotypes: familial porencephaly and perinatal intracerebral hemorrhage,PMID:23225343 ischemic and hemorrhagic cerebral small vessel disease,PMID:22522439 Walker–Warburg/muscle‑eye‑brain disease,PMID:21625620 autosomal dominant kidney‑limited cystic disease,PMID:27190376 and PADMAL due to 3′UTR variants that increase COL4A1 expression.PMID:27666438 This phenotypic diversity does not conflict with the HANAC association; rather, it indicates allelic and mechanistic heterogeneity, with CB3[IV] glycine missense variants particularly enriched in HANAC. Some studies of keratoconus and other complex traits identify COL4A1 variants that do not segregate with disease or are predicted benign, arguing against a role for these specific alleles and supporting the need for stringent variant interpretation.PMID:21527998 Additionally, an autosomal recessive encephalopathy due to homozygous COL4A1 p.Gly1278Ser shows that loss of function in biallelic form can produce yet another phenotype, but this does not undermine the dominant HANAC mechanism.PMID:32042920
Cumulatively, genetic data from multiple unrelated families with segregating CB3[IV] glycine substitutions or a truncating COL4A1 variant, together with robust functional evidence from cellular assays and animal models demonstrating a consistent vascular and muscular pathomechanism, support a Strong gene–disease association between COL4A1 and autosomal dominant familial hematuria–retinal arteriolar tortuosity–contractures (HANAC) syndrome. Additional evidence from broader COL4A1 small‑vessel disease cohorts already exceeds typical ClinGen point caps for experimental support. Clinically, COL4A1 sequencing should be considered in patients and families presenting with the HANAC triad (hematuria/cystic kidney disease, retinal tortuosity, and muscle cramps/contractures) and can refine the diagnosis in individuals initially labelled as having ADPKD or other hereditary nephropathies, informing surveillance for systemic vascular complications and targeted counseling on inheritance risk and potential emerging chaperone‑based therapies.
Key take‑home: Pathogenic heterozygous COL4A1 variants—especially glycine substitutions in the CB3[IV] domain—cause a well‑defined, autosomal dominant HANAC syndrome with kidney, retinal, and muscular involvement, supported by strong genetic segregation and concordant mechanistic data that justify routine diagnostic testing and variant interpretation in appropriate clinical contexts.
Gene–Disease AssociationStrongMultiple independent families (>6) with characteristic HANAC phenotype show autosomal dominant segregation of heterozygous COL4A1 variants, primarily glycine substitutions in the CB3[IV] domain; at least several dozen affected carriers across pedigrees with consistent renal, retinal, and muscular signs, plus strong mechanistic support from mouse and cellular models of mutant collagen IV.PMID:18160688, PMID:20818663, PMID:29395486, PMID:36922284 Genetic EvidenceStrongHeterozygous COL4A1 variants (predominantly glycine missense in CB3[IV], plus a truncating allele) segregate with HANAC in at least six core families and additional case reports, with clear autosomal dominant transmission, multiple affected individuals per pedigree, and absence in controls or lack of segregation for benign variants in other cohorts.PMID:18160688, PMID:20818663, PMID:29395486, PMID:36922284, PMID:35401403 Functional EvidenceStrongCol4a1 mutant mouse models, including a HANAC-specific p.Gly498Val allele, reproduce vascular, muscular, and ocular pathology corresponding to HANAC; in vitro studies show that COL4A1 missense mutations impair heterotrimer secretion, cause ER stress and unfolded protein response, and alter vascular tone. Chemical chaperone treatment rescues collagen trafficking and reduces intracerebral hemorrhage, providing strong mechanistic concordance for a dominant-negative, small-vessel disease mechanism underpinning HANAC.PMID:20056676, PMID:28056338, PMID:25753534, PMID:37963192, PMID:18160688 |