New York: Identifying and treating metabolic deficiencies in individuals suffering from depression can help improve symptoms and also lead to remission in cases where antidepressant medications and therapy does not work, says a study. Depression is a mood disorder causing a persistent feeling of sadness and loss of interest. It is also one of the most common mental disorders. "Unfortunately, at least 15 per cent of patients don't find relief from conventional treatments such as antidepressant medications and psychotherapy," said lead researcher Lisa Pan, Professor at University of Pittsburgh in Pennsylvania, US. Depression is also the cause of more than two-thirds of suicides that occur annually. In some patients, medications do not work because of metabolic abnormalities interfering with brain function, the researchers said. The results indicate that there may be physiological mechanisms underlying depression that can be used to improve the quality of life in patients with this disabling illness. The study was inspired by a teenage boy with a history of suicide attempts and long-standing depression. "Over a period of years, we tried every treatment available to help this patient, and yet he still found no relief from his depression symptoms," Pan explained. The team discovered that the patient had a cerebrospinal fluid deficiency in biopterin -- a protein involved in the synthesis of several brain signalling chemicals called neurotransmitters. After receiving an analogue of biopterin to correct the deficiency, the patient's depression symptoms largely disappeared. In the new study, the team looked for metabolic abnormalities in 33 adolescents and young adults with treatment-resistant depression and 16 healthy individuals. Although the specific metabolites effect differed among patients, the researchers found that 64 per cent of the patients had a deficiency in neurotransmitter metabolism as compared to none in the healthy individuals. In almost all of these patients, treating the underlying deficiency improved their depression symptoms, and some patients even experienced complete remission. "It's really exciting that we now have another avenue to pursue for patients for whom our currently available treatments have failed. This is a potentially transformative finding for certain groups of people with depression," Pan said, in the paper published online in the American Journal of Psychiatry.