Schizophrenia is often found in families with high rates of psychological illness. When one member of a family has schizophrenia, the chances of other members developing psychological problems, including schizophrenia and psychosis, increase. Some of the factors that are considered when analyzing risk for illness are family history, life stressors, trauma, and IQ. Each of these had a unique relationship with risk and schizophrenia.
In a recent study, Kim W. Verweij of the Department of Psychiatry at the University Medical Centre Utrecht in the Netherlands sought to explore the influence and evidence of IQ in families with schizophrenia. Using a sample 696 individuals with schizophrenia and their siblings (766), Verweij compared IQ scores to those of 517 individuals with no history of schizophrenia or psychiatric issues. Researchers collected data from all participants without schizophrenia and scored them separately. Those with schizophrenia also completed IQ tests and their results were analyzed independently.
The results showed that siblings of those with schizophrenia only had elevated IQs if they themselves had any history of mental health issues, or if other members of their family did. Those siblings who did not have a family history, excluding the member with schizophrenia, had average IQs compared to siblings with a robust family history. Verweij also found that the individuals with schizophrenia, who also had a family member with mental health issues, had higher IQ scores than the individuals with schizophrenia and no family history.
Verweij believes that this suggests a high familial influence on psychiatric impairment in the participants with family illness, while those without may be more influenced by external and variable factors, such as trauma, premature birth, or other stressors. Not only do these factors create a ripe environment for psychological impairment, but they also increase vulnerability for intellectual and cognitive disability.
This study provides much needed insight into the unique association between IQ and genetic predisposition for schizophrenia. Verweij added, “Since the association between IQ scores and family history of psychiatric disorder in siblings is not extensively investigated, more research is needed to further address this question.”
Verweij, K.H.W., Derks, E.M., Genetic Risk and Outcome in Psychosis (GROUP) investigators (2013). The association between intelligence scores and family history of psychiatric disorder in schizophrenia patients, their siblings and healthy controls. PLoS ONE 8(10): e77215. doi:10.1371/journal.pone.0077215
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