Rare coding variation in OCD implicates shared genes with other psychiatric disorders

Obsessive-compulsive disorder (OCD) affects 2-3% of the population with often disabling obsessions and compulsions. Despite its high heritability, genetic studies of OCD have lagged other psychiatric disorders, particularly in understanding the role of rare genetic variants.

To identify rare coding genetic variants contributing to OCD risk and examine genetic overlap with chronic tic disorders (CTD) and other psychiatric conditions.

Family-based and case-control whole-exome sequencing (WES) study.

WES data were aggregated from 11 independent cohorts across Sweden, the United States, and the United Kingdom.

A total of 47,194 individuals were available, and 44,089 passed quality control for analysis. The final sample included 6,071 individuals with OCD, comprising 1,202 probands from family-based trios and 4,869 cases, and 38,018 controls.

Rare damaging coding variants identified by WES.

Identification of OCD risk genes through rare variant analyses, meta-analysis with CTD data, gene-set enrichment analyses, and evaluation of cross-disorder genetic overlap using curated gene sets.

The analysis provided an estimate of approximately 470 autosomal genes contributing to OCD risk through rare genetic variation. CHD8 reached genome-wide significance (q < 0.05). Meta-analysis with CTD data revealed additional risk genes, including CELSR3 (q < 0.05), QRICH1, and WWC1 (q < 0.1). We observed significant genetic overlap between OCD, autism spectrum disorder (ASD), and developmental delay: 33% of ASD genes with FDR < 0.1 showed association with OCD (p < 0.001), and 36% showed possible associations in the shared OCD-CTD genetic architecture (p < 0.001), but minimal rare-variant overlap with bipolar disorder and schizophrenia risk genes. We also found that CHD8-regulated genes were enriched for both rare and common variant associations with OCD.

In this largest study to date of rare coding variation in OCD, we confirm CHD8 as the first genome-wide significant rare-variant risk gene, show that genes that are targets of CHD8 can carry rare and common variant risk for OCD, and identify multiple additional genes and pathways contributing to risk. Taken together, the findings show that OCD shares substantially greater genetic overlap with neurodevelopmental conditions than with adult-onset psychiatric disorders, refining the developmental framework of OCD and informing future mechanistic and clinical research.