Neurobiologic causes of mental illness include all of the following, except:

A. Neurotransmitters play a central role in the development of mental illness. Imbalances in chemicals such as dopamine, serotonin, and norepinephrine are strongly associated with conditions like depression, schizophrenia, and anxiety disorders. B. Stress on the immune system has been linked to mental illness through the mind–body connection. Chronic stress and immune dysfunction can alter brain chemistry and increase vulnerability to psychiatric conditions. C. Genetics are a well-documented factor, as family and twin studies show a hereditary component in disorders such as bipolar disorder, schizophrenia, and major depression. D. Infection is not generally considered a primary neurobiologic cause of mental illness. While some infections can affect the brain and indirectly influence mental health, infection is not one of the core neurobiologic factors identified in psychiatric theory.