Importantly, steatosis (triglycerides) and fibrosis (e.g., picrosirius red staining, hydroxyproline levels, and transcripts for TGFβ, Col1α1, and Col3α1) that increase with age were significantly higher in the livers of the old hRipk3-KI or hMlkl-KI mice compared to old control mice. The gene discussed is COL3A1; the disease is steatosis.