GPT and alcoholic liver diseases: Elevated AST:ALT ratios between 1–2 are indicative of non-alcoholic fatty liver disease (NAFLD) or non-alcoholic steatohepatitis (NASH), whilst levels <2 are indicative of alcoholic liver disease [23, 24], therefore the moderate increases in the male UKB PD cohort may be indicative of NAFLD/NASH, although some individuals in the PD group have levels above 2.