Further support for hippocampal volume as psychosis biomarker

By Eleanor McDermid, Senior medwireNews Reporter

Findings from the Bipolar-Schizophrenia Network on Intermediate Phenotypes (B-SNIP) provide further evidence that reduced hippocampal volume is a consistent feature of schizophrenia.

“These findings from a large psychosis family sample (B-SNIP) support structural alterations in hippocampus as a putative biomarker for the 2 major psychosis phenotypes, schizophrenia and schizoaffective disorder,” report Elena Ivleva (University of Texas Southwestern Medical Center, Dallas, USA) and team.

Reduced hippocampal volume relative to controls was present in patients with schizophrenia or schizoaffective disorder, and was not seen in their first-degree relatives.

The study included 71 patients with schizophrenia plus 74 of their first-degree relatives, and 70 with schizoaffective disorder plus 62 of their relatives. On structural magnetic resonance imaging using a manual and a semiautomated region-of-interest analysis, the patients had reduced hippocampal volumes compared with 145 mentally healthy controls.

Patients also had reduced hippocampal volumes when compared with their relatives, whereas the relatives had similar volumes to those of the controls. However, there was an overall familial effect, in that patients with hippocampal volumes below the median for the patient group tended to have relatives whose volumes were below the median for their group.

Lower bilateral hippocampal volumes correlated with more severe total and positive symptoms on the Positive and Negative Syndrome Scale, but bore no relation to treatment with antipsychotic medication.

The study also included 86 patients with psychotic bipolar I disorder and 88 of their first-degree relatives. However, the researchers did not detect reduced hippocampal volumes in these patients , in common with some, but not all previous studies.

They suggest this could indicate different disease mechanisms underlying psychosis in schizophrenia and bipolar disorder.

“Alternatively, it is possible that hippocampal volume preservation in [bipolar disorder] could be secondary to a medication effect”, they write in Schizophrenia Bulletin.

The team found that patients with bipolar disorder who were taking a mood stabiliser had higher hippocampal volumes than those not taking this medication, although this was nonsignificant for most regions. They suggest that any disease-associated reduction in hippocampal volume could be concealed by the effects of chronic mood-stabilising treatment.

However, they caution: “Disambiguating disease and medication effects is difficult, especially in a cross-sectional study such as ours.”

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