Although research suggests a higher risk of psychosis in siblings of people with schizophrenia, less is known about depressive symptoms in these siblings.
To investigate the family risk for psychosis and depressive symptoms, R. Klaassen of Rivierduinen Mental Health in the Netherlands conducted a study involving 822 individuals with schizophrenia, 813 siblings, and 527 participants with no family or personal history of mental illness who served as controls.
For the study, Klaassen looked at the lifetime history of depressed mood, episodes of depression, and psychosis in all three groups.
As the researchers expected, the subjects with schizophrenia had the highest levels of lifetime depressive episodes and depressed mood.
They also found that their siblings had a greater risk for depressive episodes compared to control participants.
No difference was found in the history or risk of lifetime depressed mood between the controls and their siblings.
A direct relationship was also found between the frequency and length of depressed symptoms and negative psychotic symptoms, both clinical and subclinical. Only quantity of depressed symptoms was associated with positive psychotic symptoms in siblings and individuals with schizophrenia.
And while Klaassen did find a family risk for depressed mood, there was no link discovered for episodes of depression over the lifetime.
Another finding that has clinical relevance is that the patients with schizophrenia and siblings all had increased risk for experiencing episodes of depression. These risks were statistically significant, suggesting that family members of individuals with schizophrenia should be closely watched for depression.
Furthermore, people with psychosis should be evaluated for depression as depressive symptoms can worsen psychotic symptoms and lead to a less effective treatment and health outcome.
Klaassen believes that this research adds to the existing body of evidence showing that depression has a direct effect on the symptoms of psychosis in those with schizophrenia and immediate family members.
“These findings suggest that a co-occurring genetic vulnerability for both depressive and positive and negative psychotic symptomatology exists on a clinical and also on a subclinical level,” he said.
Source: Psychological Medicine