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Genetic Causes of Psychosis: A Comprehensive Review

Three tiers of genetic risk, polygenic common variants, rare high-penetrance variants, and Mendelian or metabolic disorders, and what each one means at the bedside.

Scope and framing

Psychosis is genetically heterogeneous, spanning three tiers that differ fundamentally in effect size, mechanism, and clinical relevance: (1) highly polygenic common-variant risk that accounts for most population-level liability to idiopathic schizophrenia; (2) rare high-penetrance variants, recurrent copy number variants (CNVs) and single-gene loss-of-function mutations, that individually confer large risk but explain only a minority of cases; and (3) Mendelian and metabolic disorders in which psychosis is a secondary manifestation, many of which are treatable. It focuses on schizophrenia-spectrum and related psychoses across the lifespan; affective psychoses are addressed only where genetic overlap is instructive.

Organizing principle: pleiotropy

Essentially no genetic lesion is specific to psychosis. The same variants that raise schizophrenia risk also predispose to autism, intellectual disability, ADHD, and epilepsy. This cross-diagnostic sharing shapes both the science and the clinical interpretation of any positive result. [1][2][3]

The genetic architecture in brief

Twin and family studies consistently place the heritability of schizophrenia at 60 to 80%; a nationwide Danish twin registry estimated it at 79%, with monozygotic concordance of 33% versus dizygotic concordance of 7%. [4][5] Yet the heritability captured by common SNPs on genotyping arrays is only about 24%, and current genomic approaches together explain roughly 40% of the twin-based heritability, the persistent "missing heritability" attributable to rare variants, structural variation, non-additive effects, and incomplete genomic coverage. [6][7][8] Risk distributes across a continuum from thousands of common variants of tiny effect to a handful of rare variants of very large effect, with the two ends converging on shared synaptic biology. [9][10]

60–80%

Twin-based heritability of schizophrenia

~24%

Liability captured by common SNPs on arrays

~40%

Of twin heritability explained by current genomics

Common-variant and polygenic architecture

The dominant genetic contribution to idiopathic schizophrenia is polygenic. The Psychiatric Genomics Consortium's trajectory illustrates the discovery curve: from 22 genome-wide significant loci in 2013, to 108 in 2014, culminating in the landmark PGC3 GWAS (2022), which identified 287 distinct loci in up to 76,755 cases and 243,649 controls. [9][11][12] A cross-ancestry meta-analysis (96,806 cases) added 61 further loci, including East Asian-specific signals. [13] An estimated 8,300 largely common variants collectively account for at least ~32% of liability. [5][11]

PGC3 fine-mapping prioritized 120 genes (106 protein-coding), with associations concentrated in genes expressed specifically in excitatory and inhibitory CNS neurons and enriched for synaptic organization and transmission. [9] High-confidence genes include GRIN2A (NMDA receptor GluN2A subunit) and GRIA3 (AMPA subunit), supporting glutamatergic dysfunction; DRD2, the target of all current antipsychotics; and voltage-gated calcium channel genes such as CACNA1C. [9][12][14]

The C4/MHC locus

The strongest common-variant signal lies in the MHC region on chromosome 6, and a substantial portion derives from structurally variable alleles of complement component 4 (C4). [15] Each allele associates with schizophrenia in proportion to its tendency to drive C4A expression; C4 mediates synaptic pruning during postnatal development, and C4A overexpression in mice produces excessive synapse elimination and behavioral abnormalities, a molecular link between the leading common-variant signal and the synaptic-pruning hypothesis of schizophrenia. [15][16][17] C4 alleles show sex-biased effects (1.7-fold risk variation in men versus 1.26-fold in women), potentially contributing to the male preponderance. [18]

Polygenic risk scores: real, but not yet clinically actionable

Polygenic risk scores (PRS) currently explain roughly 7.7 to 11% of liability variance. [19][20] In the UK Biobank the schizophrenia PRS carried an odds ratio of 2.04 per standard deviation, and across four health systems the highest PRS decile had up to 4.6-fold higher odds versus the lowest. [21][22]

Absolute risk stratification nonetheless remains weak: even at the top 1% of the PRS distribution, only about 6% of individuals are expected to develop schizophrenia, and the AUC (~0.74) is insufficient for individual prediction or differential diagnosis. [20] PRS also cannot distinguish among psychiatric diagnoses because genetic risks are highly correlated; the genetic correlation between schizophrenia and bipolar disorder is about 0.68 to 0.73. [20][21][23]

Practice point

Large relative risks still translate into modest absolute risk at the individual level. A PRS should not be used to confirm, exclude, or differentiate a psychotic disorder in clinical care.

Rare coding variants and de novo mutations

The SCHEMA consortium meta-analyzed exomes from 24,248 cases and 97,322 controls and identified 10 genes at exome-wide significance, with odds ratios spanning 3 to roughly 50. [10] De novo mutations contribute a comparatively modest ~7% of cases (versus ~38% for intellectual disability and ~34% for epileptic encephalopathy) and concentrate in constrained, brain-expressed genes overlapping neurodevelopmental disorder genes. [31][32]

SETD1A

Histone methyltransferase; first rare-variant schizophrenia gene; carriers often have learning difficulties.

GRIN2A

NMDA receptor GluN2A subunit; convergence of rare and common variants; L-serine a candidate precision therapy.

GRIA3

AMPA receptor subunit; supports glutamatergic dysfunction.

XPO7

Protein-truncating variants confer an OR of roughly 28.

CUL1

Ubiquitin ligase scaffold; synaptic protein turnover.

TRIO

Rho-GEF regulating dendritic spine and synapse development.

SP4

Transcription factor with neuronal activity-dependent regulation.

HERC1

Large E3 ligase; neurodevelopmental phenotypes.

RB1CC1

Autophagy initiation; neuronal maintenance.

CACNA1G

T-type voltage-gated calcium channel.

AKAP11

Definitive shared bipolar/schizophrenia gene (OR ~7); interacts with GSK3B, the presumed lithium target.

SRRM2, STAG1, ZNF136, SLC6A1

Added by subsequent exome and targeted sequencing studies.

Common-rare convergence

Genes prioritized from common-variant GWAS are enriched for rare disruptive variants, indicating both tiers act on shared synaptic pathways (ARC and NMDAR complexes, chromatin remodeling). [9][10][33]

Recurrent copy number variants

Approximately 2 to 3% of schizophrenia cases carry a known pathogenic CNV, versus 0.5 to 0.9% of controls. [1][2][34] The largest PGC CNV study identified eight genome-wide significant loci: deletions at 1q21.1, 2p16.3 (NRXN1), 3q29, 15q13.3, and 22q11.2, and duplications at 7q11.23 and proximal/distal 16p11.2. [35] A critical methodological caveat: population-based studies (iPSYCH) have revised effect sizes substantially downward relative to case-control designs, because case-control controls underrepresent unaffected carriers. [36][37] The 22q11.2 deletion, for example, carried a case-control OR above 20 to 60 but a population-based hazard ratio of only about 3.3. [37]

CNV locusTypeCase-control ORApprox. SCZ penetranceReferences
22q11.2Deletion>20–60~25% (clinical cohorts)[2], [35], [38]
3q29Deletion~17–40+~20%[39], [40], [41]
15q13.3Deletion~7.5–12~6–9%[36], [42]
NRXN1 (2p16.3)Deletion~7.5–14~2–3%[35], [42]
1q21.1DeletionElevated; estimates vary widely by study designLow in population-based samples[35], [36], [37]

Penetrance estimates are cohort-dependent. Ascertainment in clinical samples inflates apparent risk; population-based cohorts give substantially lower figures.

References

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This page was medically reviewed by Eric Wexler M.D., Ph.D. on August 14, 2026.