Phenotypic overlap across schizophrenia spectrum
medwireNews: The Bipolar-Schizophrenia Network on Intermediate Phenotypes (B-SNIP) consortium has found “scant” evidence that phenotypes cluster around the traditional schizophrenia-spectrum diagnoses.
Carol Tamminga (University of Texas Southwestern Medical School, Dallas, USA) and team studied 933 patients with schizophrenia, schizoaffective disorder, or psychotic bipolar disorder; 1055 of their first-degree relatives; and 459 mentally healthy controls.
They undertook the study “with the expectation that some phenotypes would segregate by categorical diagnosis and others would be expressed across the target psychotic disorders.”
However, they found a large amount of overlap for symptoms, psychosocial functioning, and family lineage.
Although scores on the Positive and Negative Syndrome Scale were higher in patients with schizophrenia and schizoaffective disorder than those with bipolar disorder, around 99% of patients with schizoaffective disorder and bipolar disorder had scores that were within 2 standard deviations of the schizophrenia patients’ scores.
The same was true for over 90% of patients on the Birchwood Social Functioning Scale, although bipolar disorder patients had the highest scores overall and all groups had lower scores than the controls.
The same overlaps were apparent in the patients’ families, with 27.0% of schizophrenia patients having a “pure” schizophrenia lineage (no bipolar diagnoses in the family), but 17.3% having a mixed lineage, and 11.5% only having bipolar disorder among their relatives. Among the bipolar disorder patients, 39.8% had a pure bipolar lineage, 9.9% only had relatives with schizophrenia, and 25.4% had a mixture.
“These rates support the existence of genetic overlap between these serious mental illnesses and implicate common genetic mechanisms,” write the researchers in The American Journal of Psychiatry.
Past suicide attempts were most frequent among schizoaffective disorder patients, at 51.1%, but were also common among schizophrenia and bipolar disorder patients, at 31.9% and 42.4%, respectively.
“The frequency of reported lifetime suicide attempts was disturbingly high in all groups of probands in this B-SNIP cohort, underscoring the immense public health importance of psychosis and its high medical need,” say Tamminga et al.
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By Eleanor McDermid, Senior medwireNews Reporter