This phenotypic feature, combined with the fact that male C57BL/6J mice are generally more prone to develop diet-induced obesity when compared to female mice (98, 99), actually makes male APOE*3-Leiden.CETP mice on their C57BL/6J background a very suitable model for studying lipid-modulating interventions in metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as nonalcoholic fatty liver disease (NAFLD). The gene discussed is APOE; the disease is obesity due to melanocortin 4 receptor deficiency.