MASLD (Metabolic Dysfunction–Associated Steatotic Liver Disease)

Details

MASLD (formerly NAFLD) is the most common chronic liver disease, affecting up to 38% of adults worldwide. It is defined by hepatic steatosis plus at least one metabolic syndrome trait (overweight/obesity, abdominal obesity, hypertension, dysglycaemia, or atherogenic dyslipidaemia) in the absence of significant alcohol consumption and other secondary causes. MASH (formerly NASH) is the inflammatory form affecting ~30% of MASLD patients and is the primary driver of progressive fibrosis, cirrhosis, and hepatocellular carcinoma. For cardiologists, MASLD is critical: cardiovascular disease is the leading cause of death, and MASLD independently increases CV events, AF, and heart failure risk.

Epidemiology

• Up to 38% of the adult population worldwide; 65% prevalence in type 2 diabetes (meta-analysis, ~1.8 million persons). (sources/masld-nejm-2025, rating: high)
• Global DALYs: 1.69 million (1990) → 3.67 million (2021) — ×2.2 increase over three decades; largest increases in China and India. (sources/masld-nejm-2025, rating: high)
• HCC incidence: 1.25/1000 person-years in MASLD; ~20/1000 in MASLD-related cirrhosis. (sources/masld-nejm-2025, rating: high)

Pathophysiology

• Central driver: accumulation of intrahepatic lipid droplets — both inert lipids and toxic lipids that activate cellular stress pathways. (sources/masld-nejm-2025, rating: high)
• Three main hepatic fatty acid sources: (1) free fatty acid flux from insulin-resistant adipose tissue; (2) de novo hepatic lipogenesis; (3) dietary chylomicron lipid uptake. Impaired VLDL secretion and mitochondrial oxidation accelerate progression. (sources/masld-nejm-2025, rating: high)
• Genetics (heritability ~50%): PNPLA3 I148M polymorphism = most common variant; increases risk of hepatic fat accumulation, MASH, fibrosis, cirrhosis, and HCC. TM6SF2 variant increases liver-specific risk but paradoxically attenuates cardiovascular risk by retaining lipoproteins in liver — MASLD subtypes may have divergent hepatic vs. CV trajectories. (sources/masld-nejm-2025, rating: high)
• Key progression drivers: visceral adiposity, insulin resistance, type 2 diabetes (predominant), obesity, hypertension, hypothyroidism. Oestrogens are protective. Fructose, saturated/trans fats, and alcohol worsen disease; Mediterranean diet is protective. (sources/masld-nejm-2025, rating: high)

Natural History and Fibrosis Staging

• Spectrum: isolated steatosis → MASH (lipotoxic hepatocellular damage + lobular inflammation, ~30%) → progressive fibrosis → cirrhosis → HCC.
• Fibrosis staging: F0 (none), F1 (perisinusoidal/portal), F2 (perisinusoidal + portal/periportal), F3 (septal/bridging), F4 (cirrhosis). (sources/masld-nejm-2025, rating: high)
• Clinically significant fibrosis ≥F2 = strong predictor of all-cause death and liver-related complications. Time to cirrhosis: ~30–35 years from F0/F1; ~19–20 years from F2; 5–6 years from F3. (sources/masld-nejm-2025, rating: high)
• At-risk MASH = MASH + ≥F2 fibrosis = key indication for liver-directed pharmacotherapy (regulatory endpoint for conditional drug approval). (sources/masld-nejm-2025, rating: high)

Cardiovascular and Extrahepatic Risks

• CVD is the leading cause of death in MASLD, exceeding liver-related mortality in most cohorts. (sources/masld-nejm-2025, rating: high)
• MASLD increases fatal/nonfatal CV events ×1.5 independent of traditional risk factors; ×2.5 with higher fibrosis stages. (sources/masld-nejm-2025, rating: high)
• Atrial fibrillation: MASLD associated with ×1.2–1.5 increased long-term AF risk (meta-analysis, Liver Int 2025). (sources/masld-nejm-2025, rating: high)
• New-onset heart failure: MASLD associated with ×1.2–1.5 increased risk (meta-analysis, ~11 million individuals). (sources/masld-nejm-2025, rating: high)
• New-onset type 2 diabetes: ×2.2 risk increase; ×3.4 with advanced liver disease. (sources/masld-nejm-2025, rating: high)
• CKD and extrahepatic cancers (especially colorectal, other GI, breast): ×1.2–1.5 each. (sources/masld-nejm-2025, rating: high)
• Note: TM6SF2 genetic variant dissociates hepatic from CV risk — patients with this variant have higher liver risk but lower cardiovascular risk, suggesting MASLD is not a uniform CV risk entity. (sources/masld-nejm-2025, rating: high)

Risk Stratification

• FIB-4 index (age × AST / [platelet × √ALT]) — first-line noninvasive fibrosis biomarker:
  • <1.30 = low risk → manage in primary care, reassess over time
  • 1.30–2.67 = indeterminate → Enhanced Liver Fibrosis (ELF) test, vibration-controlled transient elastography, or liver histology

  • 2.67 = high risk → hepatologist referral

• Additional testing for indeterminate FIB-4: ELF test, FibroScan (vibration-controlled transient elastography), magnetic resonance elastography, liver biopsy. (sources/masld-nejm-2025, rating: high)

Management

Lifestyle

• Cornerstone of treatment. Weight loss targets: ≥5% for steatosis reduction; 7–10% for inflammation; ≥10% for fibrosis reduction. Long-term dietary adherence is the key challenge. (sources/masld-nejm-2025, rating: high)

Resmetirom (First FDA-Approved Drug, March 2024)

• Oral THR-β-selective agonist; liver-directed; approved for noncirrhotic MASH + moderate-to-advanced fibrosis (F2–F3).
• MAESTRO-NASH phase 3 (n=966; 52 weeks): MASH resolution 62.9% vs 34.3%; fibrosis reduction 36.8% vs 22.4%; neutral weight and insulin; reduces LDL-C, TG, Lp(a); free T4 reduced ~15–20% (TSH/T3 unaffected); nausea/diarrhea common.
• No validated predictors of response. Long-term outcomes (cirrhosis, liver death) pending. Thyroid, gonadal, and bone surveillance warranted. (sources/masld-nejm-2025, rating: high)

Incretin-Based Therapies

• Semaglutide 2.4mg/week (ESSENCE phase 3, part 1, n=800; F2–F3; 72 weeks): Superior on both histologic co-primary endpoints; 32.7% vs 16.1% MASH resolution with fibrosis reduction. Fails to reduce fibrosis in MASH-related cirrhosis (phase 2b). Real-world: lower risk of cirrhosis, hepatic decompensation, HCC vs. other glucose-lowering drugs. (sources/masld-nejm-2025, rating: high) — see entities/Semaglutide
• Tirzepatide (SYNERGY-NASH phase 2b, n=190; F2–F3; 52 weeks): MASH resolution 56–62% vs 44%; fibrosis reduction 51–55% vs 30%; ~15% weight loss. (sources/masld-nejm-2025, rating: high) — see entities/Tirzepatide
• Survodutide (GLP-1/glucagon dual agonist, phase 2b): MASH improvement 47–62% vs 14%; fibrosis reduction 32%(6mg) vs 18%; 10–15% weight loss; notable: increased heart rate; 20% discontinuation rate due to AEs.
• Retatrutide (GIP/GLP-1/glucagon triple agonist, phase 2a): ~80% liver fat reduction at highest doses; >85% hepatic steatosis resolution — most potent liver fat reduction reported to date.
• No head-to-head comparisons between any incretin agents in MASLD yet. (sources/masld-nejm-2025, rating: high)

PPAR Agonists

• Pioglitazone (PPAR-γ; meta-analysis, ~500 patients): reduces fibrosis and MASH regardless of T2DM; weight gain +2.7%.
• Lanifibranor (pan-PPAR; NATIVE phase 2b, n=247; 24 weeks): MASH resolution and fibrosis vs placebo; weight gain ~2.5%; phase 3 (72 weeks, F2–F3) ongoing. (sources/masld-nejm-2025, rating: high)

FGF21 Analogues

• Efruxifermin, pegbelfermin, pegozafermin — meta-analysis 5 phase 2 trials (~600 patients): MASH resolution and fibrosis improvement; neutral weight.
• SYMMETRY (efruxifermin in compensated cirrhosis, n=181; 96 weeks): Cirrhosis reversal 29% vs 11% — first signal of cirrhosis reversal in MASH pharmacotherapy. Phase 3 ongoing. (sources/masld-nejm-2025, rating: high)

SGLT2 Inhibitors

• Established CV and renal benefits; additional hepatoprotection.
• Dapagliflozin phase 2b (n=154; 48 weeks): MASH resolution 23% vs 8%; fibrosis reduction 45% vs 20%.
• SGLT2i associated with lower long-term liver event risk vs other glucose-lowering drugs (except GLP-1 RAs). (sources/masld-nejm-2025, rating: high)

Future: Combination Therapy

• Anticipated: semaglutide + resmetirom ± PPAR agonists/FGF21 analogues ± genetically targeted therapy.
• Genotyping (PNPLA3, TM6SF2) may define subtypes with different treatment trajectories. (sources/masld-nejm-2025, rating: high)

Contradictions / Open Questions

• Surrogate endpoint approval — hard outcome data pending: Resmetirom received conditional FDA approval based on 52-week histologic surrogate endpoints (MASH resolution, fibrosis reduction). Whether this translates to reduced cirrhosis, liver failure, or liver death is unproven; MAESTRO-NASH-OUTCOMES trial ongoing. (sources/masld-nejm-2025, rating: high)
• Semaglutide fails to reduce fibrosis in cirrhosis: Despite strong effects on MASH resolution in non-cirrhotic disease, semaglutide did not reduce liver fibrosis or resolve MASH in compensated cirrhosis (phase 2b, n=71; 48 weeks). The mechanism underlying this discordance — and whether longer treatment or combination with resmetirom would overcome it — is unknown. (sources/masld-nejm-2025, rating: high)
• No pharmacotherapy for cirrhotic MASLD: At-risk MASH (F2–F3) is the only regulatory-approved treatment target. Advanced cirrhosis (F4) has no approved liver-directed pharmacotherapy; efruxifermin (SYMMETRY) shows promise but requires phase 3 confirmation. (sources/masld-nejm-2025, rating: high)
• TM6SF2 variant — liver vs. CV risk dissociation: TM6SF2 variant increases hepatic fat retention and MASLD severity but reduces atherogenic dyslipidaemia and CV event risk. MASLD is therefore not a uniform CV risk condition — polygenic risk scores and genotyping are needed to stratify hepatic vs. CV risk in individual patients. (sources/masld-nejm-2025, rating: high)
• No head-to-head comparisons: Semaglutide, tirzepatide, retatrutide, resmetirom, lanifibranor, FGF21 analogues, and SGLT2 inhibitors have all been tested against placebo only. Optimal agent, sequencing, and combination remain entirely undefined. (sources/masld-nejm-2025, rating: high)
• No validated stoppage rules for resmetirom: Phase 3 study of 52-week resmetirom followed by noninvasive biomarker reassessment is ongoing; criteria for identifying non-responders who should discontinue are not yet validated. (sources/masld-nejm-2025, rating: high)
• Survodutide heart rate increase: Survodutide (GLP-1/glucagon dual agonist) increased heart rate and had a 20% discontinuation rate due to AEs — higher than any other MASLD agent. The cardiovascular safety of glucagon receptor agonism requires dedicated monitoring. (sources/masld-nejm-2025, rating: high)

Connections

• Related to entities/Atrial-Fibrillation — MASLD increases AF risk ×1.2–1.5; shared metabolic substrate (visceral adiposity, insulin resistance, inflammation)
• Related to entities/HFpEF — MASLD increases HF risk ×1.2–1.5; GLP-1 RA and SGLT2i benefit both conditions
• Related to entities/Semaglutide — ESSENCE phase 3 MASH data; GLP-1 class hepatoprotection
• Related to entities/Tirzepatide — SYNERGY-NASH phase 2b MASH data
• Related to entities/Obesity — overlapping risk factor; shared therapeutic pathways
• Related to concepts/Obesity-Paradox — MASLD and intentional weight loss with incretin therapy

Sources

• sources/masld-nejm-2025