Schizophrenia is one of the most common mental disorders, affecting around 3 million Americans, and when most people think of "mentally ill," the picture that typically comes to mind is of schizophrenia. The word refers to the patient’s split from reality; the disease is one of emotional impairment and disordered perception of reality. It’s not entirely clear what causes schizophrenia. People who use amphetamines or drink to excess are prone to the disease, but more benign environmental factors also play a role. People who live in urban areas as children or young adults, people who experience social isolation, and people born in the winter or spring are more likely to develop schizophrenia.
In addition, there seems to be a genetic component to the disease—in particular, environmental factors that cause schizophrenia do so in people who have a prior vulnerability, often though not always due to genetic predisposition. An example of a non-genetic predisposition is hypoxia; infants who had low oxygen at birth are more prone to the disease. Another example is maternal prenatal malnourishment. Genetic vulnerability is more common, however. People with a parent or sibling with schizophrenia are ten times as likely to develop the illness themselves as the general population; the children of two schizophrenic parents have a 50 percent chance of being schizophrenic.
According to a recent study, however, five percent of people with schizophrenia have new mutations, that don’t affect the genes of their parents. It turns out that it is not merely a handful of genetic mutations that are responsible for schizophrenia, but a large number of rare mutations, meaning that overlapping but different sets if mutations could be responsible for the disease in different people. However, these mutations seem to occur in groups, affecting the genes responsible for building and managing synapses in the brain and for communication between neurons. Researchers also found that schizophrenic patients have less of a protein in the brain’s learning and memory center that is part of a process that protects cells. The unprotected cells die more often, leading to the symptoms of the disease.