About 3 million Americans suffer the mental illness that is probably most like what the phrase calls up: schizophrenia. This is a condition of disordered perceptions—the split from reality that gives the condition its name—difficulty with large tasks, and emotional impairment. People with schizophrenia frequently have difficulty with organized thinking, auditory hallucinations, and paranoia.
It’s not clear what causes schizophrenia It is most likely a combination of a biological predisposition set off by environmental triggers. There is evidence of a genetic link—immediate family members of schizophrenic people are likely to develop schizophrenia themselves, and identical twins, who share the same genes, have a 50 percent chance of exhibiting the disease—but there are also other factors at work. Socially isolated people are likely to be schizophrenic, which suggests that it may be as much a retreat as a disease, or else that contact with others is needed to help keep a person’s thoughts on track. In addition, people who grew up in urban areas are also more prone to the illness. For reasons not clearly understood, schizophrenia is more likely to strike people born in the winter or spring months.
Now researchers have found indications that there disease called schizophrenia is actually eight separate conditions, all with overlapping symptoms and causes, that have simply been lumped together. Though this is not the first study to suggest that the name "schizophrenia" has been used to refer to more than one separate disease, this is the first to find as many as eight, as well as being the strongest evidence found to date to support the existence of the distinction, The differences, the researchers say, are in the genetics; the study found that people with the same clusters of schizophrenia symptoms had similar genes sets of schizophrenia.
The genetic basis for the differences is a major part of the reason the disparate conditions have been so long aggregated under one name. The Before the science of genetics was developed, the idea of the similar conditions having different genetic bases could not be understood, and the conditions, having similar apparent causes—the same sorts of environmental triggers for the genetic tendencies—appeared to be one illness.