Positive symptoms include distortion in thought content (delusion), Perceptions (hallucinations), language and thought process( disorganized speech) and self monitoring or behavior (catatonic behavior). The negative symptoms criterion include restrictions in the range and intensity of emotion, in the fluency and productivity of thought and speech, and in the initiation of goal-directed behavior.
For one to be diagnosed with schizophrenia, the disturbance must persist for a continuous period of at least 6 months. During that period there must be at last one month of symptoms (or less than one month if symptoms were successfully treated) that meet the positive or negative criterion. Once schizophrenia occurs, it becomes a chronic condition that continues throughout the remainder of the patient life with varying degree of intensity.
The DSM-IV-TR divides schizophrenia in subtypes and the diagnosis of a particular subtype is based on the symptoms that occasioned the most recent evaluation or admission to clinical care and may change with time. The five subtypes are Paranoid type, Disorganized type, Catatonic type, undifferentiated type and the residual type.
Causes of schizophrenia
No one can clearly say for sure that schizophrenia is caused by a particular factor. One may be predisposed by genetic factors but that in itself, as research has shown, is not a surety that one will get it. What is known is that the development of schizophrenia can be attributed to a combination of biological dispositions (e.g. inheriting certain genes) and the environment a person is exposed to.
Brain development disruption is now known to be the result of genetic predisposition and environmental stresses early in development (e.g. during pregnancy and /or early development). This, it is suggested leads to alterations in the brain making and may lead to a person being susceptible to developing schizophrenia.
A research study by Columbia University (2004) identified approximately 14% of schizophrenia cases as having been caused by influenza during the mothers pregnancy. The study indicated that flu during the first trimester increased the risk of developing schizophrenia by the child by about 7% while flu during the third trimester increased the risk by about 3%.
Those who have immediate relatives with a History of schizophrenia or other psychiatric disease have a significantly increased risk for developing schizophrenia over that of general population. Twin studies however have shown that simple genetic transmission is not by itself resultant in developing the disease. Studies have shown that if one identical twin has schizophrenia despite the other twin having the exact genes the chances of the other developing schizophrenia is only about 50%.
A study in Finland (2004) to establish the link between genes and the environment showed that adopted children that had a high genetic biological risk of schizophrenia ( their mother had schizophrenia) had an 86 % lower rate of developing schizophrenia when brought up in a healthy family vs. dysfunctional family. Only 6% developed schizophrenia in the healthy families while 37% in dysfunctional families developed schizophrenia.
This indicates a complexity of genetic and environment which is not yet well understood. It is obvious from this research that just having multiple or single gene presence in the body does not automatically confer a certain risk for developing schizophrenia. Environmental factors in early childhood or adolescents can either damage the brain further thereby increasing the risk of developing schizophrenia or lessen the expression of genetic or neurodevelopment defects thereby decreasing the risk of developing schizophrenia
Recent research by Russell Romeo (PhD) at Rockefeller University and published in The Scientist (2007) has revealed that children and teens brains are very sensitive to stress (about 5-10 times more sensitive) than adult brains. As a result, children and teen brains can be damaged by on going stress. This stress related damage of the brain increases the risk for many types of mental illness including schizophrenia later in life.
The use of street drugs including LSD, methamphetamine, marijuana/cannabis and alcohol has been linked with significantly increased probability of developing psychosis and schizophrenia. This link has been documented in over 30 different Scientific studies done mostly in the United Kingdom, Australia, and Sweden over the past 20 years.
One such study, interviewed 50,000 members of the Swedish Army about their drug consumption and followed up with them later in life. The study established that those who were heavy consumers of cannabis at age 18 were over 6% more likely to be diagnosed with schizophrenia over the next 15 years than those who did not take it. Experts now estimate that between 8% and 13% of all schizophrenia cases are linked to marijuana /cannabis use during teen years.
Researches in New Zealand found that those who used cannabis by the age of 15 years were more than three times more likely to develop mental illness such as schizophrenia. Other similar research has backed these findings showing that cannabis use increases the risk of psychosis by up to 7 times for heavy users and that the risk increases in proportion to the amount of cannabis used.
A clinical toxicologist at Imperial College London, Professor John Henry, reports that research has shown that people with a certain genetic make up who use the drug face a ten times risk of schizophrenia. The increased risk applies to people who inherit variants of a gene named COMT ( Catechol-O-methytransferase) and who smoked cannabis as teenagers.
About a quarter of the population has this genetic make up and up to 15% of the group is likely to develop psychotic conditions if exposed to cannabis early in life. Neither the drug or the gene raises the risk by itself.