TPMT and autoimmune hepatitis: However, most recent studies implied that neither Thiopurine S-methyltransferase (TPMT) heterozygosity nor 6-mercaptopurine (6-MP) metabolite levels were reliable predictors of AZA efficacy or toxicity in patients with AIH and related cirrhosis, and cytopenia is frequently encountered due to advanced fibrosis (Czaja and Carpenter, 2006; Heneghan et al., 2006; Hindorf et al., 2010).