S1 Data -

Introduction
Schizophrenia (SCZ) is characterized by widespread cognitive impairments, such as executive functions. Most of the available research indicate that executive impairment has a certain genetic predisposition. Shared neuropathological characteristics of patients with SCZ and their siblings may reveal intermediate behavioral phenotypes that can be used to further characterize the illness.
Methods
Our study involved 32 SCZ patients, 32 unaffected siblings (US), and 33 persons as healthy controls (HCS). These three groups underwent a computerized version of the Wisconsin Card Sorting Test (WCST), and a battery of cognitive neuropsychological assessments. These tests also evaluate executive function and several cognitive domains.
Results
The performed study on SCZ patients and their unaffected siblings showed an inferior WCST performance to the HCS subjects, further indicating that unaffected siblings have a functional impairment, and they also performed poorly on the neuropsychological assessment compared with the HCS.
Conclusion
This result supports the claim that the development of functional impairment is not limited to SCZ patients and unaffected siblings may also have a certain level of abnormal brain function. Consequently. neurological abnormalities lead to the abnormal functioning in siblings and patients, suggesting that genetics plays a considerable role in such results.