Mendelian Randomization Study Using Dopaminergic Neuron-Specific eQTL Identifies Novel Risk Genes for Schizophrenia

Area of Science:

• Neurogenetics
• Psychiatric Genetics
• Molecular Psychiatry

Background:

• Schizophrenia (SCZ) risk variants are often non-coding, necessitating identification of target genes.
• Previous studies relied on bulk tissue eQTL data, overlooking cell-type-specific regulatory effects crucial for understanding SCZ.
• Dopaminergic neurons are implicated in SCZ pathophysiology, making them a key focus for genetic studies.

Purpose of the Study:

• To identify potential schizophrenia (SCZ) causal genes by integrating genome-wide association studies (GWAS) with cell type-specific expression quantitative trait loci (eQTL) data.
• To investigate the genetically regulated expression of genes in dopaminergic neurons at different developmental stages (young and mature).
• To compare findings from dopaminergic neuron eQTLs with bulk brain tissue eQTLs to prioritize high-confidence SCZ risk genes.

Main Methods:

• Mendelian randomization (MR) analysis integrating SCZ GWAS data (74,776 cases, 101,023 controls) with eQTL data from human induced pluripotent stem cell (iPSC)-derived dopaminergic neurons.
• Analysis of eQTL data from dopaminergic neurons at two time points: 30 days (D30, young post-mitotic) and 52 days (D52, more mature).
• Comparison of identified SCZ-associated genes between D30 and D52 eQTL datasets and with bulk brain tissue eQTL data.

Main Results:

• Identified 34 genes with potential causal roles in SCZ based on D30 dopaminergic neuron eQTLs, with ARL3 showing the strongest association.
• Identified 37 potential SCZ causal genes from D52 dopaminergic neuron eQTLs, with ARL3 and GNL3 being most significant.
• Found 12 overlapping genes between D30 and D52 datasets, indicating time-point-specific genetic regulation. Prioritized DDHD2 and GALNT10 by comparing with bulk brain tissue data.

Conclusions:

• This study successfully identified multiple candidate risk genes causally linked to schizophrenia (SCZ) through their genetically regulated expression in dopaminergic neurons.
• The findings underscore the importance of cell type-specific eQTL analysis, particularly in dopaminergic neurons, for dissecting the genetic architecture of SCZ.
• Further research into the identified genes, such as ARL3, GNL3, DDHD2, and GALNT10, is crucial for understanding SCZ pathogenesis and developing targeted therapies.