Schizophrenia tends to run in families, according to WebMD. Only 1 percent of the total population has schizophrenia, but the occurrence rate is 10 percent for people who have a first-degree relative with the disorder. An identical twin has a 40 to 65 percent risk of developing the disorder.
Numerous genes are believed to be associated with a heightened chance of developing schizophrenia, and people with the disorder seem to have an elevated number of rare genetic mutations, according to WebMD. Scientists are not yet able to predict schizophrenia in certain people using genetic research.
Schizophrenia symptoms typically start appearing in men in their early- to mid-20s and in the late 20s in women, according to Mayo Clinic. Some symptoms may include hallucinations, delusions, disordered thinking and behavior and an overall decreased ability to function and display emotion normally.