Although such a test remains a long way off, investigators said, the identification of the unique lipid signature is a critical first step. However, one expert noted that the lipid signature not accurately differentiating patients with schizophrenia from those with bipolar disorder (BD) and major depressive disorder (MDD) limits the findings’ applicability.
The profile includes 77 lipids identified from a large analysis of many different classes of lipid species. Lipids such as cholesterol and triglycerides made up only a small fraction of the classes assessed.
The investigators noted that some of the lipids in the profile associated with schizophrenia are involved in determining cell membrane structure and fluidity or cell-to-cell messaging, which could be important to synaptic function.
“These 77 lipids jointly constitute a lipidomic profile that discriminated between individuals with schizophrenia and individuals without a mental health diagnosis with very high accuracy,” investigator Eva C. Schulte, MD, PhD, of the Institute of Psychiatric Phenomics and Genomics (IPPG) and the department of psychiatry and psychotherapy at University Hospital of Ludwig-Maximilians-University, Munich, told this news organization.
“Of note, we did not see large profile differences between patients with a first psychotic episode who had only been treated for a few days and individuals on long-term antipsychotic therapy,” Dr. Schulte said.
The findings were published online in JAMA Psychiatry.
Lipid profiles in patients with psychiatric diagnoses have been reported previously, but those studies were small and did not identify a reliable signature independent of demographic and environmental factors.
For the current study, researchers analyzed blood plasma lipid levels from 980 individuals with severe psychiatric illness and 572 people without mental illness from three cohorts in China, Germany, Austria, and Russia.
The study sample included patients with schizophrenia (n = 478), BD (n = 184), and MDD (n = 256), as well as 104 patients with a first psychotic episode who had no long-term psychopharmacology use.
Results showed 77 lipids in 14 classes were significantly altered between participants with schizophrenia and the healthy control in all three cohorts.
The most prominent alterations at the lipid class level included increases in ceramide, triacylglyceride, and phosphatidylcholine and decreases in acylcarnitine and phosphatidylcholine plasmalogen (P < .05 for each cohort).
Schizophrenia-associated lipid differences were similar between patients with high and low symptom severity (P < .001), suggesting that the lipid alterations might represent a trait of the psychiatric disorder.
No medication effect
Most patients in the study received long-term antipsychotic medication, which has been shown previously to affect some plasma lipid compounds.
So, to assess a possible effect of medication, the investigators evaluated 13 patients with schizophrenia who were not medicated for at least 6 months prior to blood sample collection and the cohort of patients with a first psychotic episode who had been medicated for less than 1 week.
Comparison of the lipid intensity differences between the healthy controls group and either participants receiving medication or those who were not medicated revealed highly correlated alterations in both patient groups (P < .001).
“Taken together, these results indicate that the identified schizophrenia-associated alterations cannot be attributed to medication effects,” the investigators wrote.
Lipidome alterations in BPD and MDD, assessed in 184 and 256 individuals, respectively, were similar to those of schizophrenia but not identical.
Researchers isolated 97 lipids altered in the MDD cohorts and 47 in the BPD cohorts – with 30 and 28, respectively, overlapping with the schizophrenia-associated features and seven of the lipids found among all three disorders.
Although this was significantly more than expected by chance (P < .001), it was not strong enough to demonstrate a clear association, the investigators wrote.
“The profiles were very successful at differentiating individuals with severe mental health conditions from individuals without a diagnosed mental health condition, but much less so at differentiating between the different diagnostic entities,” coinvestigator Thomas G. Schulze, MD, director of IPPG, said in an interview.
“An important caveat, however, is that the available sample sizes for bipolar disorder and major depressive disorder were smaller than those for schizophrenia, which makes a direct comparison between these difficult,” added Dr. Schulze, clinical professor in psychiatry and behavioral sciences at State University of New York, Syracuse.