Schizoaffective disorder 'familial link to schizophrenia and bipolar disorder'
August 16, 2005

Schizoaffective disorder appears to be not simply a subgroup of either bipolar disorder or schizophrenia but also genetically linked to both conditions, study findings show.

In the literature, schizoaffective disorder has been considered in a number of different ways, with no clear consensus reached about its definition.

The findings from the current study, carried out by Thomas Munk Laursen (University of Aarhus, Denmark) and colleagues, suggest that schizoaffective disorder is likely to be a subtype of either schizophrenia or bipolar disorder, or a genetic intermediate form.

For their study, the team studied data from Danish registers for all people born after 1952 along with their parents and siblings. The participants were followed-up for more than 30 years, resulting in almost 38 million person-years and 1925 individuals with schizoaffective disorder, 3721 with bipolar disorder, and 12,501 with schizophrenia.

The results, published in the Archives of General Psychiatry, showed that the risk of developing schizoaffective disorder increased 2.76-fold for individuals who had a first-degree relative with a history of mental illness, compared with those who had no first-degree relatives with mental illness.

Moreover, there was an additional risk of schizoaffective disorder if the first-degree relative had schizophrenia, bipolar disorder, or schizoaffective disorder, at 2.57, 3.23, and 1.92, respectively, compared with those whose first-degree relative had other types of psychiatric disorders.

The researchers note that there was no significant difference in the risk of schizoaffective disorder between individuals who had parents and siblings with schizophrenia and those whose parents and siblings had bipolar disorder.

Therefore, "in the discussion of whether schizoaffective disorder is a subgroup of schizophrenia or a subgroup of bipolar disorder, our findings suggest that schizoaffective disorder is equally related to both disorders," Munk Laursen and team report.

"Schizoaffective disorder seems to coexist as an intermediate disorder sharing family risk factors with both schizophrenia and bipolar disorder."

Noting that the risk of developing bipolar disorder or schizophrenia was greatest among individuals whose first-degree relatives had the respective psychiatric condition, the researchers add that their results give little support to schizoaffective disorder as being a distinct condition.

Arch Gen Psychiatry 2005; 62: 841-848