Table 2.
The definition and subtypes of non-alcoholic fatty liver disease
| Classification | Definition | Prevalence | Clinical implications |
|---|---|---|---|
| Traditional classification | |||
| NAFL | 5% of steatosis in hepatocytes Without any cause of fatty change | 5–30% of general populations | 30–40% of patients with NAFL seem to experience progression of fibrosis |
| NASH | NAFLD+hepatocyte ballooning degeneration and hepatic lobular inflammation | 2–30% of NAFLD | Fibrosis is a major prognostic predictor of liver-related and overall mortality |
| 3–6% of the general population | |||
| NASH-Cirrhosis | NAFLD+necroinflammatory reactions may disappear, and cirrhosis without other specific causes may be present. | 20% of patients with NASH | Cryptogenic cirrhosis is presumed to be an advanced form of NASH |
| 0.18% of the general population | |||
| Variants of NAFLD | |||
| Lean NAFLD | NAFLD in people with normal body weight (BMI <23 for Asians or <25 for Westerners) | 23.5% of the general population | Compared with non-lean NAFLD, lean NAFLD had a stronger correlation with metabolic deterioration |
| More prevalent in Asia | The risk of fibrosis is increased | ||
| Metabolically healthy | Steatosis above 5% | 6.2% of NAFLD | Diagnosed with NAFLD at a younger age |
| NAFLD | Does not meet any metabolic syndrome criteria | The disease progression from metabolically healthy to unhealthy is higher in obesity group than normal weight group | |
| MAFLD | Steatosis above 5% | 50.7% of the general population; varies across countries and regions | Paradigm shift from NAFLD to MAFLD |
| The presence of one of the following three criteria: overweight/obesity, type 2 diabetes mellitus, and evidence of metabolic dysregulation | |||
| Genetics | |||
| PNPLA3 | Common in Asians with lean NAFLD | ||
| Associated with cryptogenic cirrhosis | |||
| TM6SF2 | Increased risk for progressive NASH | ||
| HSD17B13 | Loss-of-function variant was associated with progression of NAFLD |
NAFL, non-alcoholic fatty liver; NAFLD, non-alcoholic fatty liver disease; NASH, non-alcoholic steatohepatitis; BMI, body mass index; MAFLD, metabolic (dysfunction)-associated fatty liver disease; PNPLA3, patatin-like phospholipase domain-containing protein 3; HSD17B13, hydroxysteroid 17β-dehydrogenase 13; TM6SF2, transmembrane 6 superfamily member 2.