The clinic said Jackson's diagnosis came after an extensive evaluation, the Chicago Tribune reported.
Jackson's condition is a treatable condition that affects parts of the brain controlling emotion, thought and drive and "most likely caused by a complex set of genetic and environmental factors," the clinic said.
The clinic noted Jackson underwent gastric-bypass surgery in 2004 and that can change how the body absorbs food, liquids, vitamins, nutrients and medications.
"Congressman Jackson has asked Mayo Clinic to distribute this information on his behalf," the Mayo Clinic said. "He and his family remain grateful for support and prayers offered and received on his behalf."
Jackson began a medical leave from Congress June 10.