Schizophrenia and Genetics

According to the DSM-IV schizophrenia is a disorder characterized by deteriorating ability to function in everyday life and by some combination of hallucinations, delusions, thought disorder, movement disorder, and inappropriate emotional expressions (American Psychiatric Association, 1994). The symptoms can vary; hallucinations and delusions may be the most problematic symptoms for some people while others may only have clear signs of damage to their brain yet no experience of visual or auditory delusions. What this means then is that many people suffering from schizophrenia may in fact have no commonalities in terms of specific symptoms. Typically, schizophrenia may be diagnosed according to two models: acute or chronic. Acute conditions have a sudden onset with a high probability of successful treatment. Chronic schizophrenia is characterized by a gradual onset and a long-term course of treatment that may be far more difficult to recover from. The term schizophrenia literally translated (from Greek) is "split mind," though it should not be confused with another disorder known as dissociative identity disorder/multiple personality disorder). The use of "split" in this sense means a detachment from reality as often times patients exhibit a distinction between emotional and intellectual aspects of their experiences (Kalat, 2007).

Behavioral Symptoms:

There are two types of classifications of symptoms that characterize a schizophrenic diagnosis. The first type is known as positive, and the second are negative. Positive symptoms indicate behaviors that are present that otherwise would not be; and conversely, negative symptoms indicate behaviors absent that would normally be present. Some negative symptoms of schizophrenia include poor social interaction, lacking emotional expression, troubled speech, and poor memory. Negative symptoms often times are more difficult to treat than positive symptoms.

Positive symptoms can be further broken down into two categories: psychotic or disorganized (Kalat, 2007). The psychotic symptoms include delusions and hallucinations. Delusions are defined as unfounded beliefs about experiences or oneself. Hallucinations are abnormal sensory experiences which can be auditory or visual (Kalat, 2007). Interesting information has been gathered using PET scans on patients afflicted with schizophrenia. During periods of hallucinations, researchers have found increased activity present in the thalamus, hippocampus, and certain parts of the cortex - including many parts of the brain responsible for hearing (Kalat, 2007).

Disorganized positive symptoms include inappropriate emotional displays, bizarre behaviors, and thought disorder (Kalat, 2007). Most patients exhibiting disorganized positive symptoms show difficulty understanding and applying abstract concepts. Other symptoms may include attention deficit and unusual limitations in memory. Evidence shows that the inability to understand and apply abstract concepts has led some researchers to speculate a link between schizophrenia and dysfunction in the hippocampus (Kalat, 2007).

Different patients may experience different symptoms to various degrees. Some patients suffer more, and find their lives more disabled by, disorganized thoughts rather than delusions or hallucinations. However, some cases indicate that disorganized thoughts can eventually lead to other, more serious symptoms like psychosis.

Genetics:

In the past there have been serious attempts to try and locate a gene responsible for the onset of schizophrenia. However, whereas in the past it was believed to be a genetic disorder like Huntington's disease, new evidence shows if this is the case then it's at least not one-gene responsible for schizophrenia. One way to test to find a genetic basis is through Twin Studies. It's already known that close biological relationship to someone with schizophrenia greatly increases one's chance of developing it. Studies for the genetic basis of schizophrenia take advantage of the fact that concordance rates (for schizophrenia) are much higher amongst monozygotic twins rather than dizygotic twins. This high concordance (or agreement) rate for schizophrenia has long served as the foundation for a genetic predisposition for schizophrenia. Statistics outlining the probabilities of developing schizophrenia show the highest rate between monozygotic twins (48%). Following suit are children of two schizophrenic parents (46%). Interestingly unlike many other disorders, schizophrenia does not seem to indicate a significant environmental impact. For instance, children of schizophrenic mothers who are adopted by non-schizophrenic parents still have a 17% probability of developing schizophrenia. This number is the same for dizygotic twins as well (Kalat, 2007 - statistics based on data from Gottesman, 1991).

Despite the empirical evidence suggesting a genetic basis for schizophrenia complications with the data continue to stump researchers as to potential causes. For instance, notice the probability for monozygotic twins is only 48% rather than 100%. One explanation offered is that multiple genes are needed for onset of actual symptoms, and in some cases where one twin exhibits symptoms and the other does not is that in one individual another gene is activated while suppressed in the other twin (Kalat, 2007). Other causes for this problem could be related to some environmental impact or influence on the genetic makeup of one twin over another.

Another problem to the genetic basis theory is the concordance rate and probability between dizygotic twins and regular siblings. Regular siblings have a 9% probability of developing schizophrenia while dizygotic twins have a 17% probability. However, dizygotic twins have the same genetic resemblance as normal siblings, the only difference being similar environmental factors - especially in the prenatal stage. Researchers are still investigating the possibilities of environmental factors and what role they may play in determining the outcome of whether or not an individual will develop schizophrenia and explain this difference in concordance rates.

Efforts to Locate a Gene:

As noted before there is much skepticism regarding the influence genetics play in the development of schizophrenia. One of the major causes for doubt is the fact that schizophrenics tend to die younger and have fewer children than the general population, making it less likely they will pass on their genes to potential offspring. Studies show that relatives of schizophrenics are no more likely to have more children than the general population, either. So it would seem that natural selection of passable traits would diminish the prevalence of any genes responsible for schizophrenia.

The best case scenario for linking schizophrenia to a strong genetic basis would be to discover and locate any gene(s) consistently found amongst all schizophrenic patients, similar to the genes with Huntington's or early-onset Parkinson's (Kalat, 2007). Researchers thus far have found some potential genetic link between early-onset schizophrenia; however, this is uncommon and very different than adult-onset schizophrenia (Kalat, 2007).

Attempts to replicate genes linked to adult-onset schizophrenia have produced many confusing or insignificant results. Finding genes only in those diagnosed with schizophrenia and not in the general population has proved a difficult task. One explanation for this difficulty in locating a gene responsible is that there may in fact be a combination of genes. This would mean that no individual gene plays an altogether significant role, but when all are activated and working combination with one another, the individual will develop adult-onset schizophrenia (Kalat, 2007).

Another possibility is to look at more specific genes for specific types of symptoms. For instance, researchers have made some breakthroughs in studies attempting to find genes responsible for negative symptoms of schizophrenia. Rather than try to look at the broad genetic map for schizophrenia, this has interested and encouraged researchers to concentrate more on particular symptoms and types of schizophrenia (Kalat, 2007).

Still the possibility exists that a greater role is played by environmental factors than once thought. If environmental factors are responsible instead of, or in addition to, genetics then this makes the task of discovering, isolating, and identifying genes responsible all the more difficult. Thus, researchers have attempted to come up with other hypotheses to explain why some people develop schizophrenia while others don't. Some of these alternative theories include the neurodevelopmental hypothesis. According to this theory, schizophrenia is based on abnormalities present in the prenatal environment that obstructs with the development of the fetus' nervous system. This explanation has been growing in popularity amongst researchers and offers new insight into what causes one to develop schizophrenia. New information gained from more studies may hopefully one day provide researchers with the clues they need to formulate a concrete explanation on empirical grounds.

Sources:

Kalat, James W. (2007). Biological psychology. United States: Thomson Wadsworth. American Psychiatric Association 2000. (DSM-IV-TR) Diagnostic and statistical manual of mental disorders, 4th edition, text revision. Washington, DC: American Psychiatric Press, Inc.