SERPINA1 and alpha 1-antitrypsin deficiency: AATD is caused by mutations in the Serpin Family A Member 1 (SERPINA1) gene, leading to the misfolding of alpha-1 antitrypsin, which accumulates in hepatocytes and induces endoplasmic reticulum stress, while the circulating levels of alpha-1 antitrypsin decrease, ultimately resulting in liver disease.