The most common side effects in patients treated with 4 mg/day baricitinib include risk of pneumonia, herpes zoster, and infections of the urogenital tract, as well as deterioration of biochemical parameters, neutropenia, lymphopenia, anemia, thrombocytosis, and elevation of liver enzymes (ALT, AST), lipids, and creatine phosphokinase. The gene discussed is GPT; the disease is anemia (phenotype).