Mitral Valve Prolapse (MVP)
Details of the Concept
Mitral valve prolapse is characterised by redundant and thickened valve leaflets with abnormal sagging of one or both leaflets into the left atrium during systole. It is the most common cause of primary mitral regurgitation in high-income countries and one of the most prevalent valve conditions overall (1 in 40 individuals). Despite its frequency, the molecular mechanisms are only partially understood and no disease-modifying medical therapy exists.
Key Facts
Epidemiology
- Prevalence: 1 in 40 individuals (~2.5% of the population); equal between sexes on community-based echocardiography (Framingham Heart Study) sources/vhd-mechanism-aha-2024 (very high)
- Most patients never develop significant MR or require intervention
- ~25% develop significant MR, sometimes requiring surgical repair
- Sex differences: Women have less posterior prolapse, less flail, more leaflet thickening; women have higher mortality and lower surgery rates for severe MR than men — partly attributed to height/weight differences affecting LV enlargement interpretation sources/vhd-mechanism-aha-2024 (very high)
Two Distinct Forms
- Barlow disease (classic myxomatous MVP): thick valves; excess connective tissue; amorphous ECM; proteoglycan-rich; fragmented elastin; poor in collagen; chordae tendineae also affected; younger patients sources/vhd-mechanism-aha-2024 (very high)
- Fibroelastic deficiency: thin leaflets; reduced proteoglycans, collagen, and elastin; older patients; more focal disease; biological mechanisms less well characterised
Molecular Pathogenesis
Syndromic forms:
- Marfan syndrome (FBN1 — fibrillin-1): ↑MMP secretion → collagen and elastin fragmentation sources/vhd-mechanism-aha-2024 (very high)
- Loeys-Dietz syndrome (TGFBR1/2/3/SMAD2/3): TGF-β pathway activation → cell proliferation and myofibroblast differentiation
- Vascular Ehlers-Danlos syndrome (COL3A1): collagen fragmentation → ↑MMPs
- MVP also occurs in BAV disease and select patients with HCM (overlap with cardiomyopathy genes)
Familial non-syndromic forms:
- FLNA (filamin-A): X-linked polyvalvulopathy; FLNA is an actin-binding protein crosslinking actin filaments to membrane glycoproteins — defect → structural cytoskeletal failure sources/vhd-mechanism-aha-2024 (very high)
- DCHS1 (dachsous cadherin-related 1): loss-of-function → altered VIC migration and cell polarity during valve development; confirmed in mice and zebrafish
- DZIP1 (DAZ interacting zinc finger protein 1): primary cilia gene; loss → altered ECM deposition during valve development + enhanced progressive myxomatous degeneration
GWAS findings (sporadic MVP):
- TNS1 (tensin-1): focal adhesion protein involved in cytoskeleton organisation — long-range regulatory element sources/vhd-mechanism-aha-2024 (very high)
- LMCD1 (LIM and cysteine-rich domains 1): repressor of GATA6 (cardiac development activator); activates calcineurin/NFAT pathway — reduced LMCD1 expression increases MVP risk; LMCD1 knockdown in zebrafish → ↑AV valve regurgitation
- TGFβ2 and LTBP2: TGF-β pathway scaffolding; β-spectrin (TGF-β scaffolding protein)
- Cardiomyopathy genes ALPK3, BAG3, RBM20 as potential MVP risk loci (mechanistic link not yet established)
TGF-β pathway (central theme):
- Central role confirmed by syndromic (Loeys-Dietz) and sporadic (GWAS) genetics
- TGF-β promotes VIC activation, ECM remodeling, and myofibroblast differentiation; amplified by mechanical stress
- Mechanosensing/mechanotransduction contributions from FLNA and TNS1
Serotonin pathway:
- Polymorphisms in SLC6A4 (serotonin transporter SERT) → earlier requirement for mitral valve surgery
- Decreased SERT activity → accelerated mitral valve remodeling and progression to MR sources/vhd-mechanism-aha-2024 (very high)
Clinical Manifestations
- Most common presentation: asymptomatic murmur discovered on examination
- Progressive MR over years; occasional acute MR from chordal rupture
- MVP-associated arrhythmias: sudden cardiac death risk in a small subset; specific genetic and anatomical factors being elucidated (research priority)
Potential Therapeutic Targets
- TGF-β pathway: most promising but highly pleiotropic (cancer, fibrosis, development) — tissue-specific targeting is essential; in clinical trials for systemic sclerosis and cancer
- Calcineurin/NFAT via LMCD1: calcineurin inhibitors (cyclosporin A, FK-506) are approved immunosuppressants; calcineurin activators not in clinical use and may be required
- Tensin-1 (TNS1) and GLIS1: possible targets but biology requires further elucidation
- The long latency between diagnosis and surgical need creates a therapeutic opportunity for disease-modifying agents, but on-target toxicity is a major safety concern sources/vhd-mechanism-aha-2024 (very high)
Animal Models
- Spontaneous MVP in Cavalier King Charles Spaniels and other small dog breeds: genetics and relevance to human MVP under investigation; represents accessible therapeutic development resource sources/vhd-mechanism-aha-2024 (very high)
- No validated animal model for sporadic MVP currently exists
Contradictions / Open Questions
- Mechanisms differentiating Barlow disease (myxomatous) from fibroelastic deficiency remain unknown — different VIC/VEC pathways, gene programs, and optimal therapeutic approaches may differ
- Whether malignant MVP (arrhythmic, high SCD risk) can be prospectively identified and how to manage it remains unresolved
- Sex-specific outcomes in MVP (higher female mortality, lower female surgery rates for severe MR) are not fully explained biologically sources/vhd-mechanism-aha-2024 (very high)
- Cardiomyopathy gene associations (ALPK3, BAG3, RBM20) at MVP GWAS loci — mechanistic link undetermined
Connections
- Related to concepts/Valvular-Heart-Disease — clinical VHD framework
- Related to concepts/Primary-Mitral-Regurgitation — surgical thresholds and TEER indications
- Related to concepts/CAVD-Mechanisms — parallel VHD molecular mechanisms
- Related to entities/Rheumatic-Heart-Disease — alternative cause of mitral disease in low-income countries
- Related to sources/vhd-mechanism-aha-2024