In retrospective, and taking into account that the existence of leptin was postulated long before its discovery, the relevant physiological role of leptin in liver function was known even before leptin was discovered, since some of the cardinal features of both the ob/ob and the db/db mice exhibited marked alterations in liver function including impaired lipid tolerance, dyslipidemias and steatosis [38]. The gene discussed is LEP; the disease is steatosis.