A 31-year-old woman has experienced increasing malaise for the past 4 months. Physical examination yields no remarkable findings. Laboratory studies show total serum protein of 6.4 g/dL, albumin of 3.6 g/dL, total bilirubin of 1.4 mg/dL, AST of 67 U/L, ALT of 91 U/L, and alkaline phosphatase of 99 U/L. Results of serologic testing for HAV, HBV, and HCV are negative. Test results for ANA, anti-liver kidney microsome-1 and anti-smooth muscle antibody are positive. A liver biopsy is done; microscopically, there are minimal portal mononuclear cell infiltrates with minimal interface hepatitis and mild portal fibrosis. What is the most likely diagnosis?