It is thought that changes in the activity of prolidase enzyme may play a role in the development of many diseases such as nasal polyps, schizophrenia, anxiety, bipolar disorder, major depression, Type2 diabetes mellitus, chronic hepatitisC, osteoporosis, bronchial asthma and liver fibrosis.5, 6, 7, 8, 9, 10, 11. Here, PEPD is linked to bipolar disorder.