rs1064395 — NCAN

NCAN rs1064395 — A Psychiatric Risk Variant in the Brain's Scaffolding

Neurocan¹¹ Neurocan
NCAN: a chondroitin sulfate proteoglycan expressed almost exclusively in the central nervous system. It is a major component of the brain's extracellular matrix — the molecular scaffolding that supports and organises neurons and their connections (NCAN) is a structural protein in the brain's extracellular matrix that shapes how neurons grow, migrate, and form connections during development and throughout life. rs1064395 is a 3' UTR variant²² 3' UTR variant
A variant in the 3' untranslated region of the mRNA. This region controls mRNA stability, localization, and translation efficiency — making 3' UTR variants functionally important even though they don't change the protein sequence in the NCAN gene — a single-letter change in the messenger RNA that likely alters how much neurocan is produced in brain tissue. It was identified in a genome-wide association study as a significant susceptibility factor for bipolar disorder and has since been independently replicated across multiple populations and extended to schizophrenia, with neuroimaging studies showing measurable effects on hippocampal structure and memory function even in healthy individuals.

The Mechanism

Neurocan is one of the dominant chondroitin sulfate proteoglycans³³ chondroitin sulfate proteoglycans
CSPGs: a family of extracellular matrix proteins built around a protein core decorated with long chains of sulphated sugars. In the brain, CSPGs form "perineuronal nets" around inhibitory neurons and regulate synaptic plasticity by controlling which connections can form or remodel (CSPGs) in the developing and adult brain. It is highly expressed in the cortex and hippocampus — precisely the regions most relevant to memory, mood regulation, and psychiatric vulnerability. Neurocan modulates axon guidance during neural development, restricts aberrant synaptic remodelling in adults, and interacts with other extracellular matrix proteins to maintain the structural integrity of perineuronal nets⁴⁴ perineuronal nets
Dense lattices of extracellular matrix molecules that wrap around the cell bodies and proximal dendrites of certain neurons, especially fast-spiking GABAergic interneurons. Perineuronal nets consolidate synaptic connectivity and regulate critical periods of brain development.

rs1064395 falls in the 3' UTR of NCAN, which does not alter the neurocan protein sequence but likely affects mRNA stability or translational efficiency. The net functional consequence is presumed to be altered neurocan protein levels in neuronal tissue — though the exact molecular mechanism has not yet been fully characterised. Expression quantitative trait locus (eQTL) evidence from brain tissue supports a regulatory effect, consistent with the observed dose-dependent changes in hippocampal and amygdala structure with each copy of the A allele.

The Evidence

The original GWAS by Cichon and colleagues⁵⁵ original GWAS by Cichon and colleagues
Cichon S et al. Genome-wide association study identifies genetic variation in neurocan as a susceptibility factor for bipolar disorder. Am J Hum Genet, 2011 identified rs1064395 as a genome-wide significant locus for bipolar disorder in a discovery sample of 2,411 patients and 3,613 controls (OR 1.31, p = 3.02×10⁻⁸), and replicated this in 6,030 patients and 31,749 controls (OR 1.12). The meta-analysis yielded OR 1.17 and p = 2.14×10⁻⁹. A subsequent meta-analysis of 15,318 cases and 91,990 controls⁶⁶ meta-analysis of 15,318 cases and 91,990 controls
Wang L et al. Further evidence of an association between NCAN rs1064395 and bipolar disorder. Mol Neuropsychiatry, 2018 confirmed genome-wide significance (A allele OR 1.126, p = 4.92×10⁻⁹).

Mühleisen et al.⁷⁷ Mühleisen et al.
Mühleisen TW et al. Association between schizophrenia and common variation in neurocan (NCAN), a genetic risk factor for bipolar disorder. Schizophr Res, 2012 extended the association to schizophrenia across 5,061 patients and 9,655 controls (A-allele OR 1.11, p = 2.28×10⁻³), establishing rs1064395 as a shared cross-disorder psychiatric risk variant. The effect size is modest — comparable to other common psychiatric GWAS hits — consistent with the polygenic architecture of both disorders.

Neuroimaging provides the most direct window into how this variant affects the brain. Dannlowski et al.⁸⁸ Dannlowski et al.
Dannlowski U et al. NCAN cross-disorder risk variant is associated with limbic gray matter deficits in healthy subjects and major depression. Neuropsychopharmacology, 2015 found that A-allele carriers had reduced gray matter volume in the amygdala and hippocampus in both 512 healthy subjects and 171 depressed inpatients — a pattern that closely mirrors the structural changes seen in bipolar disorder. The Assmann et al.⁹⁹ Assmann et al.
Assmann A et al. Neurocan genome-wide psychiatric risk variant affects explicit memory performance and hippocampal function in healthy humans. Eur J Neurosci, 2021 functional MRI study documented reduced verbal recall and elevated false alarm rates on a recognition memory task in A-allele carriers across two independent cohorts (N=572 and N=302), with fMRI showing inefficiently increased left hippocampal activation in risk-allele carriers — a sign of compensatory over-recruitment in the face of reduced neural efficiency.

Practical Implications

The absolute risk increase from a single copy of the A allele is modest. This is a common variant with an odds ratio around 1.17 — comparable to many other GWAS-identified psychiatric risk variants. The majority of A-allele carriers never develop bipolar disorder or schizophrenia. What makes the variant notable is that it also produces measurable, subclinical effects on hippocampal structure and memory performance in the general population, suggesting a neurobiological mechanism that exists on a continuum rather than as a threshold effect.

The neuroimaging data argue for paying attention to hippocampal health: sleep quality, aerobic exercise, and omega-3 fatty acid intake are the lifestyle factors with the strongest evidence for maintaining hippocampal volume and function.

Interactions

NCAN rs1064395 has not been systematically studied in combination with other specific psychiatric risk SNPs in compound heterozygosity analyses. However, since both bipolar disorder and schizophrenia are highly polygenic, the effect of rs1064395 is best understood in the context of total polygenic risk — multiple small-effect variants accumulating to meaningful susceptibility. Individuals who carry several independently identified psychiatric risk variants (e.g. in CACNA1C, ANK3, DISC1, or other GWAS-significant loci) alongside the NCAN A-allele may have a more substantially elevated personal risk profile than any single variant implies.