FAMILY-BASED RNA SEQUENCING IN BIPOLAR DISORDER FOR CANDIDATE GENE AND PATHWAY IDENTIFICATION
Authors: García-Ortiz Inés , Martínez-Jiménez Miriam , Kavanagh Tomas , Marshall Lee L , Lucas José J , Schofield Peter R , Mitchell Philip B , Cooper Antony A , Fullerton Janice M , Toma Claudio 
Published: February 2025

Importance

Genetic risk variants associated with bipolar disorder (BD) are likely to result in transcriptomic changes. RNA sequencing (RNAseq) studies in multiplex BD families are limited.

Objective

To identify candidate genes and pathways involved in BD.

Design, settings, and participants

This cohort study includes Australian families with three or more members diagnosed with BD. RNAseq was performed on total mRNA from lymphoblastoid cell lines of eight multiplex BD families. Patients were enrolled between May 1999 and October 2004. Data were analysed from June 2022 to March 2024.

Exposures

Differential gene expression changes and co-expressed gene networks in affected and unaffected relatives.

Main outcomes and measures

Quantified read counts were examined for differential gene expression and Weighted Gene Co-expression Network Analysis (WGCNA). Differentially Expressed Genes (DEGs) were validated through: i) gene-based association using BD Genome-Wide Association Study (GWAS) summary statistics; ii) Polygenic Priority Score (PoPS); and iii) replication using RNAseq data from brain tissues of 71 BD and 252 controls. DEGs and co-expressed modules were examined for enriched categories via Gene-Set Enrichment Analysis (GSEA) and Over-Representation Analysis (ORA), and were further validated through gene-set analysis using GWAS data.

Results

Sixty significant DEGs were found after comparing 16 BD (37.5% female) and 15 unaffected relatives (46.7% female), with the long non-coding RNA (lncRNA)LINC01237being the most significant. Gene expression patterns of DEGs were correlated between lymphoblastoid cell lines and brain tissues (r=0.83). After validation, five DEGs were prioritised, includingENSG00000279277, a lncRNA mapping in a GWAS locus for BD. Enrichment analyses of DEGs pointed to nervous system and gated channel activities. WGCNA identified five expression modules associated with BD. The most significant module showed enriched categories associated with ion transmembrane transport and hypoplasia oncorpus callosum,together with a protein-protein interaction network related to solute carriers at plasma membrane.

Conclusions and relevance

This study implicates a role for lncRNAs in the pathophysiology of BD. Alterations in ion homeostasis, driven by the dysregulation of gated channels, appear to be a plausible impaired process in BD. In addition, thecorpus callosumemerges as a key brain structure with a potential involvement in BD.

KEY POINTS

Question

Can transcriptomic signatures in families with multiple members affected with bipolar disorder (BD), likely due to a higher genetic load, identify genes and pathways contributing to disease risk?

Findings

In this cohort study of eight multiplex BD families, transcriptomic data implicated a pathogenic role of long non-coding RNAs, highlighting dysregulation of ion homeostasis as a key mechanism in the pathophysiologic aetiology of this condition.

Meaning

Non-coding RNA genes may play a more significant role in BD pathogenesis than previously estimated. The dysfunction of ion channels in BD indicates an endophenotype likely associated with channelopathy.