Family Studies show a strong relationship between degree of genetic similarity and schizophrenia. Gottesman’s large scale study found someone with an aunt with schizophrenia has a 2% chance of developing it, 9% for siblings and 48% for identical twins. Though family members share environment, this still indicated support for genetics.
Candidate genes; schizophrenia is polygenic, requiring multiple genes and is aetiologically heterogeneous, risk is affected by different combinations. Ripke combined all previous data from genome-wide studies and found 108 separate genes associated with increased risk of schizophrenia.
Schizophrenia can also have a genetic origin in the absence of family history because of mutation in parental DNA. Evidence comes from correlation between paternal age (increased risk of sperm mutation) and risk of schizophrenia (Brown).
