Genetics and Mental Illness

GENETIC FACTORS AND MENTAL ILLNESS

Introduction and Overview

In recent years, mental health professionals have become increasingly aware of the importance of genetic factors in the etiology (causes) of mental disorders. Since the Human Genome Project began its mapping of the entire sequence of human DNA in 1990, the implications of its findings for psychiatric diagnosis and treatment have accumulated rapidly. A new subspecialty known as biological psychiatry (also called physiological psychology or psychiatric genetics) has emerged from the discoveries of the last two decades. Biological psychiatry got its start in the late 1980s, when several research groups identified genes associated with manic depression and schizophrenia respectively. These studies ran into difficulties fairly quickly, however, because of the complexity of the relationship between genetic factors and mental illness.

The ongoing search for genes related to psychiatric symptoms and disorders is complicated by several factors:

• Psychiatric diagnosis relies on a doctor's human judgment and evaluation of a patient's behavior or appearance to a greater degree than diagnosis in other fields of medicine. For example, there is no blood or urine test for schizophrenia or a personality disorder. Diagnostic questionnaires for mental disorders are helpful in trimming the list of possible diagnoses but do not have the same degree of precision or objectivity as laboratory findings.

• Mental disorders almost always involve more than one gene. Studies have shown that one mental disorder can be caused by different genes on different chromosomes in different populations. For example, one study in the late 1980s found two genes on two different chromosomes among two populations that caused manic depression. Studies of schizophrenia done in the late 1980s and early 1990s revealed the same finding— different genes on different chromosomes produced schizophrenia in different populations. It now appears...