GWAS-identified bipolar disorder risk allele in the FADS1/2 gene region links mood episodes and unsaturated fatty acid metabolism in mutant mice

Molecular Psychiatry (2023)Cite this article


Large-scale genome-wide association studies (GWASs) on bipolar disorder (BD) have implicated the involvement of the fatty acid desaturase (FADS) locus. These enzymes (FADS1 and FADS2) are involved in the metabolism of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are thought to potentially benefit patients with mood disorders. To model reductions in the activity of FADS1/2 affected by the susceptibility alleles, we generated mutant mice heterozygously lacking both Fads1/2genes. We measured wheel-running activity over six months and observed bipolar swings in activity, including hyperactivity and hypoactivity. The hyperactivity episodes, in which activity was far above the norm, usually lasted half a day; mice manifested significantly shorter immobility times on the behavioral despair test performed during these episodes. The hypoactivity episodes, which lasted for several weeks, were accompanied by abnormal circadian rhythms and a marked decrease in wheel running, a spontaneous behavior associated with motivation and reward systems. We comprehensively examined lipid composition in the brain and found that levels of certain lipids were significantly altered between wild-type and the heterozygous mutant mice, but no changes were consistent with both sexes and either DHA or EPA was not altered. However, supplementation with DHA or a mixture of DHA and EPA prevented these episodic behavioral changes. Here we propose that heterozygous Fads1/2 knockout mice are a model of BD with robust constitutive, face, and predictive validity, as administration of the mood stabilizer lithium was also effective. This GWAS-based model helps to clarify how lipids and their metabolisms are involved in the pathogenesis and treatment of BD.


Bipolar disorder (BD) is a chronic mental illness characterized by recurrent manic and depressive episodes interspersed with an absence of symptoms (a euthymic state). Large-scale genome-wide association studies (GWASs) have identified dozens of loci associated with BD [1,2,3]. Among them, the FADS1/2 region was first highlighted in Japanese population [1] and replicated in the large European population [23], being the only locus with a genome-wide significant difference in multiple populations.

The FADS1 and FADS2 genes on a tight linkage disequilibrium (LD) block are located head-to-head in the GWAS-identified region (Supplementary Fig. 1a). These genes encode fatty acid desaturases, rate-limiting enzymes involved in the biosynthesis of ω3 (n-3) and ω6 (n-6) long-chain polyunsaturated fatty acids (PUFAs) (Fig. 1a). Linoleic acid (LA; 18:2n-6), which is abundant in the oils of grains such as corn, is converted to arachidonic acid (AA; 20:4n-6) by a two-step desaturating reaction catalyzed by FADS2 and FADS1. α-Linolenic acid (ALA; 18:3n-3), which is enriched in some seed oils such as linseed oil, is converted to eicosapentaenoic acid (EPA; 20:5n-3) by FADS2 and FADS1 and then to docosahexaenoic acid (DHA; 22:6n-3) by further unsaturation catalyzed by FADS2.

Fig. 1: Generation of mutant mice.
figure 1

a The PUFA biosynthesis pathways. The desaturation reactions of ω3 and ω6 PUFAs are catalyzed by FADS1 (cyan arrows) or FADS2 (yellow arrows). b A strategy for simultaneous generation of alleles using the CRISPR/Cas9 system. A CRISPR/Cas9 cocktail containing two gRNAs that targeted the Fads1/2 genes and two single-stranded DNA donor templates with the loxP sequence (Supplementary Table 3) was microinjected into mouse fertilized eggs (C57BL/6JJcl strain). Nonhomologous end joining (NHEJ) resulted in the deletion of ~124 kb (Fads(Δ)) and homology-directed repair (HDR) generated the floxed allele. c Body weight of heterozygous and homozygous Fads1/2 deficient mice. Fads(Δ/Δ) mice were significantly leaner than the Fads(Δ/+) and WT (Fads(+/+)) mice (*P < 0.05, d = 0.80 and 1.24 [large effect size (ES)], respectively, t-test with Bonferroni correction). Males, 18–33 weeks old. The box length and a horizontal bar show the interquartile range (IQR) and median, respectively. The length of the whiskers is defined as 1.5 times the upper and lower limits of the IQR. d Food intake. Daily food intake did not differ by genotype.

Full size image

Even before this FADS1/2 genomic region attracted attention as a locus of BD susceptibility shared across populations, it had seized the spotlight due to the significant changes in haplotype diversity (Supplementary Fig. 1b) since humans commenced crop agriculture [4,5,6]. The increased intake of grain oils has resulted in an increase in the proportion of people carrying a haplotype associated with higher FADS1/2 activity (Haplotype D) [4]. This haplotype has a protective effect against BD [1,2,3]. GWASs of blood lipid composition have also demonstrated a pivotal role of the FADS1/2locus in the plasma levels of ω3 and ω6 PUFAs [7]. Consistent with these results, expression quantitative trait loci (eQTL) analysis suggested that the other major haplotype (Haplotype A) conferring susceptibility to BD was associated with decreased expression of FADS1/2 and likely with lower enzyme activity [8]. Although the odds ratio for the susceptible alleles is not high (at most 1.18) [1,2,3], these evolutional and functional underpinnings of the locus collectively suggest that an animal mimicking a decreased, but not completely nullified, activity of both FADS1/2 can be a valid model and contribute to a better understanding of the pathogenesis of BD. In the present study, to generate such a model, we deleted the region containing the mouse Fads1 and Fads2 genes in a heterozygous manner (referred to as Fads(Δ/+) mice).

Single knockout (KO) mice deficient in either Fads1 or Fads2 have been investigated prior to our study; [9,10,11,12,13,14,15] however, if these mice are crossed, double KO mice cannot be generated because these genes are located only approximately 100 kb apart. Additionally, since studies using single KO mice were conducted from the perspective of nutrition, they mainly analyzed homozygous KO mice fed semipurified diets [9,10,11,12,13,14,15]. Data on behavioral phenotypes were not reported so far.

The inverse relationship between seafood consumption and the prevalence of depression and BD highlights a possible nutritional or pharmacological effect of ω3 PUFAs, such as DHA and EPA [16]. Several previous studies reported the therapeutic efficacy of ω3 PUFAs for depressive episodes in BD [1718], but the results from randomized clinical trials were debatable [19]. Data on plasma PUFA levels in patients are also inconsistent; however, recent studies with the largest sample size to date have reported low levels of EPA and DHA and high levels of AA in patients with BD [20]. In addition, studies of lipids in postmortem brains are limited, with small sample sizes and inconsistent results [21,22,23]. Moreover, food and medication can be major confounding factors in human studies, requiring analysis using animal models that provide greater experimental control.

In this study, we established Fads(Δ/+) mice as a preclinical model of the GWAS-identified risk factor in BD; these mice exhibited both mania- and depression-like episodic behavioral changes. To detect these infrequent episodic behavioral changes, we monitored the wheel-running activity of Fads(Δ/+) mice continuously for six months. Unlike other locomotor activities, wheel running in mice is a strongly goal-directed behavior having a significant reward value [2425]; thus, a reduction in wheel running is associated with “markedly diminished pleasure (anhedonia)”, a core symptom of a depressive episode [26]. In addition, we provided proof of concept that long-term supplementation with DHA improved the behavioral abnormalities in the model mice.


Generation of Fads1/2 mutant mice

All animal procedures were approved by the Wako Animal Experiment Committee of RIKEN (H27-2-233, H29-2-230, W2019-2-040, W2021-2-042). We developed Fads(Δ/+) and Fads(flox/+) mice by the CRISPR/Cas9 system, which have been deposited in RIKEN BioResource Center (RBRC11813 and RBRC11814). A detailed description of the procedure and animal husbandry is provided in Supplementary Methods.

Determination of the lipid composition