PRKACA encodes a catalytic subunit of protein kinase A, and almost all fibrolamellar carcinomas have a heterozygous 400-kb deletion that leads to the fusion of DNAJB1 and PRKACA. The resulting DNAJB1-PRKACA fusion transcript is believed to activate protein kinase A by dysregulation of the catalytic portion of the protein. In contrast, PRKAR1A encodes one of the regulatory subunits of protein kinase A. Protein kinase A (PRKACA) has been documented as a pivotal regulator in meiosis and mitosis arrest. Somatic mutations of the catalytic subunit of the cyclic AMP-dependent protein kinase (PRKACA) gene have been identified in about 35% of cortisol-producing adenomas (CPAs), with the affected patients showing overt Cushing's syndrome.