GPT and attention deficit-hyperactivity disorder: ADHD: attention-deficit/hyperactivity disorder; ALT: serum alanine aminotransferase; AST: serum aspartate aminotransferase; HII: hepatic iron index, expressed as μmol Fe/g dry weight of liver/y; n.a.: not available/not applicable; PCOS: polycystic ovary syndrome; SF: serum ferritin; TS: transferrin saturation