Anterior-posterior axis of hippocampal subfields across psychoses: A B-SNIP study

Abstract

Background

The hippocampus (HP) is affected across psychoses, including schizophrenia (SZ), bipolar type 1 (BDP) and schizoaffective (SAD) disorders. We examined HP subfield volumetric abnormalities along the anterior-posterior (ventral-dorsal) axis of the HP in psychosis probands, defined by traditional (DSM) diagnoses and biologically defined subtypes (biotypes, based on cognition and electrophysiology). We hypothesized that biotypes would be better discriminated by HP longitudinal axis subfields abnormalities than DSM.

Methods

The sample included 455 probands from the Bipolar Schizophrenia Network for intermediate Phenotypes (BSNIP) dataset (age 35 ± 12.0): 124 unaffected (age 40.4 ± 15.8) and 299 healthy controls (HC; 37 ± 12.0). Probands were: SZ (190), BDP (151), SAD (114). Probands according to B-SNIP defined biotypes were: biotype-1 (BT1; 120), biotype-2 (BT2; 145), biotype-3 (BT3, 190). 3 T MRI scans were processed with FreeSurfer6.0. The anterior (aHP) and posterior (pHP) HP and aHP and pHP subfields were extracted. Cognitive and clinical data were collected.

Results

All biotypes had smaller aHP subfields compared to HC. BT1 had smaller aHP than both BT2 and BT3. pHP subfields were also smaller in BT1 compared to HC and BT3, while the granule cells layer of the dentate gyrus distinguished BT2 from HC. DSM: aHP subfields were smaller in all DSM types compared to HC and did not differ among DSM categories. A few pHP subfields were affected in SAD and SZ compared to HC and distinguished SAD and SZ from BDP. Probands had smaller aHP compared to unaffected relatives.

Conclusions

Differences in subfield volumetric abnormalities along the anterior- posterior axis of the HP exist across psychoses. aHP abnormalities differ between psychosis probands and HC but do not discriminate among DSM categories. In contrast, biotypes can be differentiated from HC and from each other according to aHP-pHP subfields volumetric abnormalities. Thus, biotype typology may better reflect underlying neurobiology.