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Guo DC, Pannu H, Tran-Fadulu V, Papke CL, Yu RK, Avidan N, Bourgeois S, Estrera AL, Safi HJ, Sparks E, et al. Mutations in smooth muscle alpha-actin (ACTA2) lead to thoracic aortic aneurysms and dissections. Nature Genetics. 2007;39(12):1488-93. PMID 17994018

One-paragraph summary

Vascular smooth muscle cell (SMC) contractile force requires cyclic interactions between SMC α-actin (encoded by ACTA2) and β-myosin heavy chain (encoded by MYH11). This study showed that missense mutations in ACTA2 are responsible for 14% of inherited ascending thoracic aortic aneurysms and dissections (TAAD) — making it, at publication, the largest single known genetic cause of non-syndromic familial TAAD. Structural analyses and immunofluorescence of actin filaments in SMCs derived from heterozygous individuals showed that the mutations interfere with actin filament assembly and are predicted to decrease SMC contraction. Aortic tissue from affected individuals showed aortic medial degeneration, focal areas of medial SMC hyperplasia and disarray, and stenotic arteries in the vasa vasorum caused by medial SMC proliferation. Combined with the previously reported MYH11 mutations causing familial TAAD (PMID 16444274), the finding established that maintaining the structural integrity of the ascending aorta depends on SMC contraction.

Key findings

  • ACTA2 missense mutations account for 14% of inherited ascending TAAD.
  • Mutations interfere with actin filament assembly in patient-derived SMCs (immunofluorescence) and are structurally predicted to decrease SMC contractile force.
  • Aortic histopathology in mutation carriers: medial degeneration; focal medial SMC hyperplasia and disarray; stenotic vasa vasorum arteries due to medial SMC proliferation — i.e. the pathology is proliferative as well as degenerative.
  • Establishes, together with MYH11, a second mechanistic class of aortopathy gene distinct from the ECM/TGF-β class: failure of the contractile unit itself.

Limitations

  • Cohort composition and ascertainment are not specified in the abstract; the 14% figure applies to inherited ascending TAAD referred to specialist centres, and should not be read as 14% of all TAAD.
  • The link from "interferes with filament assembly" to "decreases SMC contraction" is predicted from structure, not measured as contractile force in this work.
  • Cross-sectional histology from surgical/autopsy specimens cannot establish whether SMC hyperplasia and vasa vasorum stenosis are causal or secondary to established disease.
  • No natural-history data: the paper identifies the gene but not the event rates, ages, or diameters at which carriers dissect. Those came later (Regalado 2015, PMID 25759435).
  • Genotype–phenotype resolution within the gene is absent here; the codon-level risk differences (p.R179, p.R258 high risk; p.R185Q, p.R118Q low risk) were only established eight years afterwards.

Why it matters

This paper split the genetics of thoracic aortic disease into two mechanistic families and made the second one respectable. Before it, the field's organising model was extracellular matrix failure — fibrillin, collagen, TGF-β signalling. ACTA2 (with MYH11) showed that an aorta with intact matrix genes can still fail if its smooth muscle cannot contract, which reframed the aortic wall as a mechanically active tissue rather than a passive elastic tube. That reframing is what makes MYLK (PMID 21055718) and PRKG1 (PMID 23910461) interpretable as members of a coherent pathway — actin → myosin → myosin light chain kinase → PKG-mediated regulation — rather than as isolated curiosities. Clinically, ACTA2 became the most common non-syndromic TAAD gene and the best-characterised example of within-gene risk stratification, where the specific codon materially changes prognosis. The vasa vasorum finding also opened a still-underexplored line: that the aortic media may be injured by its own microvascular supply failing.

Cited by wiki pages

  • genetics of TAA