For most of the 20th century, the genetics of schizophrenia was studied through families and twins. Identical twins agreed on the diagnosis far more often than fraternal twins. First-degree relatives of people with schizophrenia had roughly a tenfold higher risk than the general population. The heritability of schizophrenia was estimated at around 80%. But the genes themselves stayed hidden — there was no single "schizophrenia gene" to find.
That changed with genome-wide association studies (GWAS). Over the past 15 years, GWAS has reshaped our understanding of schizophrenia genetics from a search for one missing gene to a portrait of hundreds of small-effect variants spread across the genome.
Schizophrenia GWAS has identified more than 280 genomic loci associated with the disorder, none of them individually causing it, with the strongest signal in the major histocompatibility complex (MHC) region on chromosome 6.
What a GWAS is, in plain English
A genome-wide association study compares the DNA of thousands of people with a condition to thousands of people without it. Researchers look at millions of common genetic variants — usually single-letter differences called single nucleotide polymorphisms (SNPs) — and ask, for each one, "Is this variant more common in people with the condition?" If the difference is large enough and survives correction for the millions of comparisons being made, that location in the genome is flagged.
The unit of measurement is the locus — a region of the genome where one or more SNPs are statistically associated with the condition. Each locus typically contributes a tiny fraction of risk on its own.
The Psychiatric Genomics Consortium
The driving force behind schizophrenia GWAS has been the Psychiatric Genomics Consortium (PGC), a global collaboration of researchers that pools genotyped samples to reach the enormous sample sizes GWAS requires. Early schizophrenia GWAS in the 2000s, with a few thousand cases, found almost nothing. By 2014, with around 37,000 cases and 113,000 controls, the PGC reported 108 independent genome-wide significant loci in a landmark Nature paper. By 2022, with roughly 76,755 cases and 243,649 controls, the count rose to 287 loci, implicating 120 genes prioritised by fine-mapping.
What the loci point to
The genes nearest GWAS hits are not random. They cluster in biologically meaningful systems:
- Synaptic biology — many implicated genes encode proteins involved in how neurons connect and communicate. Genes in the postsynaptic density and voltage-gated calcium channel pathways are over-represented.
- Neurodevelopment — genes regulating early brain development and synaptic pruning.
- Glutamate signalling — including subunits of the NMDA receptor.
- Dopamine signalling — including DRD2, the gene encoding the dopamine D2 receptor that is the main target of antipsychotic medications.
- Immune function — most prominently the major histocompatibility complex (MHC) on chromosome 6, the strongest single signal in schizophrenia GWAS.
The MHC and complement
The MHC region is densely packed with immune genes and is notoriously hard to fine-map. A 2016 paper from Steven McCarroll's lab traced part of the MHC signal to complement component 4 (C4), suggesting that variants increasing C4 expression may contribute to excessive synaptic pruning during adolescence. The findings were published in Nature and remain one of the most discussed mechanistic stories to come out of schizophrenia GWAS, though replication and refinement are ongoing.
What GWAS does not tell you
GWAS findings are powerful at the population level and humble at the individual level. A few things to keep in mind:
- Each locus is small. Typical odds ratios are around 1.05 to 1.20 — meaningful only when multiplied across hundreds of variants.
- The "nearest gene" is not always the causal gene. SNPs often sit in non-coding regulatory regions that affect distant genes.
- GWAS finds common variants only. Rare, high-impact variants — including copy number variants — require different methods.
- Most participants have been of European ancestry. The PGC has launched explicit efforts to expand into African, East Asian, Latin American, and South Asian samples; the picture from those studies is still emerging.
- GWAS does not diagnose. No combination of common variants identified to date is specific or strong enough to predict schizophrenia in an individual.
Shared genetics across psychiatric disorders
One of the most striking findings from cross-disorder GWAS work is the overlap between schizophrenia, bipolar disorder, depression, autism, and ADHD. The PGC Cross-Disorder Group has shown that many loci are shared, supporting a view of psychiatric conditions as overlapping rather than fully distinct. This challenges old categorical assumptions and has implications for diagnosis, drug development, and how we explain the conditions to families.
From GWAS to drugs
One of the long-term hopes of psychiatric GWAS is to point drug developers toward new biological targets. Progress is slow but real. The convergence of GWAS hits on calcium-channel and glutamate biology has reinforced interest in those pathways. The recent FDA approval of xanomeline-trospium (Cobenfy) — a muscarinic-targeted antipsychotic — was not directly driven by GWAS, but it is part of a broader push beyond dopamine that GWAS findings have helped justify.
What this means for patients and families
For patients, the practical takeaway is modest. Schizophrenia is highly heritable and polygenic. There is no single test that predicts the disorder, no genetic explanation for any one person's illness, and no genetic treatment on the immediate horizon. What GWAS has done is make schizophrenia harder to dismiss as a condition of bad parenting or weak character. It is a brain condition with deep biological roots, shaped by many small-effect variants and environmental factors. That framing alone reduces stigma and supports patients in seeking treatment.
Direct-to-consumer genetic tests do not provide clinically meaningful risk assessment for schizophrenia. Any results suggesting otherwise should be discussed with a board-certified genetic counsellor.
Where the field is going
Sample sizes continue to grow. Whole-genome sequencing is being added to the GWAS toolkit, capturing rare variants that chip-based studies miss. Functional genomics — figuring out what each implicated variant does in actual brain cells — is a major focus, often using induced pluripotent stem cells. And efforts like the PGC's ancestry expansion will, over time, make the genetic picture of schizophrenia more global.
If you want to explore further, see our companion pieces on polygenic risk scores, copy number variants, and 22q11.2 deletion syndrome.
This article is for educational purposes only and is not medical advice, diagnosis, or treatment. Always consult a qualified mental health professional. If you or someone you know is in crisis, call or text 988 in the US, or your local emergency number.