To determine whether the obesity and fatty liver in the miR-33a-deficient mice were caused by elevated SREBP-1 in vivo, miR-33a-deficient mice were bred with Srebf1 heterozygous mice, with results indicating that the level of SREBP-1 in the miR-33a−/− Srebf1+/− mice was equivalent to that in the miR-33a+/+ Srebf1+/+ mice, while the obesity (adipocyte enlargement and inflammation) and fatty liver observed in the miR-33a+/− Srebf1+/+ mice were ameliorated in the miR-33a−/−Srebf1+/− Srebf1+/+ mice. The gene discussed is SREBF1; the disease is obesity due to melanocortin 4 receptor deficiency.