hallucinations consist of a voice keeping up a running com
mentary on the person's behavior or thoughts, or two or
more voices conversingwith each other.)
For a significant portion of the time since the onset of the
disturbance, one or more major areas of functioning such
as work, interpersonal relations, or self-care aremarkedly
below the level achieved prior to the onset (or when the on
set is in childhood or adolescence, failure to achieve expect
ed level of interpersonal, academic, or occupational achiev
ement).Schizoaffective Disorder and Mood Disorder With
Psychotic Features have been considered as alternative
explanations for the symptoms and have been ruled out.
The disturbance must also not be due tothe direct physio
logical effects of use or abuse of a substance (e.g., alcohol,
drugs, medications) or a general medical condition.
There is no known single cause of schizophrenia. Manydiseases, such as heart disease, result from an interplay
of genetic, behavioral and other factors, and this may be
the case for schizophrenia as well. Scientists do not yet
understand all of thefactors necessary to produce schizo
phrenia, but all the tools of modern biomedical research
are being used to search for genes, critical moments in
brain development, and other factors that may leadto
Can It Be Inherited?
It has long been known that schizophrenia runs in fami
lies. People who have a close relative with schizophrenia
are more likely to develop the disorderthan are people
who have no relatives with the illness. For example, a
monozygotic (identical) twin of a person with schizoph
renia has the highest risk 40 to 50 percent of developing
theillness. A child whose parent has schizophrenia has
about a 10 percent chance. By comparison, the risk of
schizophrenia in the general population is about 1 percent.