A loss-of-function variant in SUV39H2 identified in autism-spectrum disorder causes altered H3K9 trimethylation and dysregulation of protocadherin ß-cluster genes in the developing brain.

Recent evidence has documented the potential roles of histone-modifying enzymes in autism-spectrum disorder (ASD). Aberrant histone H3 lysine 9 (H3K9) dimethylation resulting from genetic variants in histone methyltransferases is known for neurodevelopmental and behavioral anomalies. However, a systematic examination of H3K9 methylation dynamics in ASD is lacking. Here we resequenced nine genes for histone methyltransferases and demethylases involved in H3K9 methylation in individuals with ASD and healthy controls using targeted next-generation sequencing. We identified a novel rare variant (A211S) in the SUV39H2, which was predicted to be deleterious. The variant showed strongly reduced histone methyltransferase activity in vitro. In silico analysis showed that the variant destabilizes the hydrophobic core and allosterically affects the enzyme activity. The Suv39h2-KO mice displayed hyperactivity and reduced behavioral flexibility in learning the tasks that required complex behavioral adaptation, which is relevant for ASD. The Suv39h2 deficit evoked an elevated expression of a subset of protocadherin ß (Pcdhb) cluster genes in the embryonic brain, which is attributable to the loss of H3K9 trimethylation (me3) at the gene promoters. Reduced H3K9me3 persisted in the cerebellum of Suv39h2-deficient mice to an adult stage. Congruently, reduced expression of SUV39H1 and SUV39H2 in the postmortem brain samples of ASD individuals was observed, underscoring the role of H3K9me3 deficiency in ASD etiology. The present study provides direct evidence for the role of SUV39H2 in ASD and suggests a molecular cascade of SUV39H2 dysfunction leading to H3K9me3 deficiency followed by an untimely, elevated expression of Pcdhb cluster genes during early neurodevelopment.

Lipid Pathology of the Corpus Callosum in Schizophrenia and the Potential Role of Abnormal Gene Regulatory Networks with Reduced Microglial Marker Expression.

Structural changes in the corpus callosum have been reported in schizophrenia; however, the underlying molecular mechanism remains unclear. As the corpus callosum is high in lipid content, we analyzed the lipid contents of the corpora callosa from 15 patients with schizophrenia and 15 age- and sex-matched controls using liquid chromatography coupled to tandem mass spectrometry and identified lipid combinations associated with schizophrenia. Real-time quantitative polymerase chain reaction analyses using extended samples (schizophrenia, n = 95; control, n = 91) showed low expression levels of lipid metabolism-related genes and their potential upstream transcription factors in schizophrenia. Subsequent pathway analysis identified a gene regulatory network where nuclear factor of activated T cells 2 (NFATC2) is placed most upstream. We also observed low gene expression levels of microglial markers, inflammatory cytokines, and colony-stimulating factor 1 receptor (CSF1R), which is known to regulate the density of microglia, in the corpus callosum in schizophrenia. The interactions between CSF1R and several genes in the presently identified gene network originating from NFATC2 have been reported. Collectively, this study provides evidence regarding lipid abnormalities in the corpora callosa of patients with schizophrenia and proposes the potential role of impaired "NFATC2-relevant gene network-microglial axis" as its underlying mechanism.

Thiosulfate promotes hair growth in mouse model.

The present study describes the hair growth-promoting effects of sodium thiosulfate (STS), a widely used compound, in mice. STS accelerated hair growth in the "telogen model", suggesting that it stimulates telogen hair follicles to reenter the anagen phase of hair growth. In the same model, STS potentiated hair growth in an additive manner with minoxidil (MXD), a drug used for the treatment of androgenic alopecia. Furthermore, in the "anagen model", STS promoted hair growth, probably by promoting hair follicle proliferation. Since STS elevated the skin surface temperature, its hair growth-promoting activity may be partly due to vasorelaxation, similar to MXD. In addition, STS is known to generate a gaseous mediator, H2S, which has vasorelaxation and anti-inflammatory/anti-oxidative stress activities. Therefore, STS and/or provisionally its metabolite, H2S, may aid the hair growth process. Collectively, these results suggest that salts of thiosulfate may represent a novel and beneficial remedy for hair loss.

Human nonsense-mediated mRNA decay factor UPF2 interacts directly with eRF3 and the SURF complex.

Nonsense-mediated mRNA decay (NMD) is an mRNA degradation pathway that regulates gene expression and mRNA quality. A complex network of macromolecular interactions regulates NMD initiation, which is only partially understood. According to prevailing models, NMD begins by the assembly of the SURF (SMG1-UPF1-eRF1-eRF3) complex at the ribosome, followed by UPF1 activation by additional factors such as UPF2 and UPF3. Elucidating the interactions between NMD factors is essential to comprehend NMD, and here we demonstrate biochemically and structurally the interaction between human UPF2 and eukaryotic release factor 3 (eRF3). In addition, we find that UPF2 associates with SURF and ribosomes in cells, in an UPF3-independent manner. Binding assays using a collection of UPF2 truncated variants reveal that eRF3 binds to the C-terminal part of UPF2. This region of UPF2 is partially coincident with the UPF3-binding site as revealed by electron microscopy of the UPF2-eRF3 complex. Accordingly, we find that the interaction of UPF2 with UPF3b interferes with the assembly of the UPF2-eRF3 complex, and that UPF2 binds UPF3b more strongly than eRF3. Together, our results highlight the role of UPF2 as a platform for the transient interactions of several NMD factors, including several components of SURF.

SMG-8 and SMG-9, two novel subunits of the SMG-1 complex, regulate remodeling of the mRNA surveillance complex during nonsense-mediated mRNA decay.

Nonsense-mediated mRNA decay (NMD) is a surveillance mechanism that detects and degrades mRNAs containing premature translation termination codons (PTCs). SMG-1 and Upf1 transiently form a surveillance complex termed "SURF" that includes eRF1 and eRF3 on post-spliced mRNAs during recognition of PTC. If an exon junction complex (EJC) exists downstream from the SURF complex, SMG-1 phosphorylates Upf1, the step that is a rate-limiting for NMD. We provide evidence of an association between the SURF complex and the ribosome in association with mRNPs, and we suggest that the SURF complex functions as a translation termination complex during NMD. We identified SMG-8 and SMG-9 as novel subunits of the SMG-1 complex. SMG-8 and SMG-9 suppress SMG-1 kinase activity in the isolated SMG-1 complex and are involved in NMD in both mammals and nematodes. SMG-8 recruits SMG-1 to the mRNA surveillance complex, and inactivation of SMG-8 induces accumulation of a ribosome:Upf1:eRF1:eRF3:EJC complex on mRNP, which physically bridges the ribosome and EJC through eRF1, eRF3, and Upf1. These results not only reveal the regulatory mechanism of SMG-1 kinase but also reveal the sequential remodeling of the ribosome:SURF complex to the predicted DECID (DECay InDucing) complex, a ribosome:SURF:EJC complex, as a mechanism of in vivo PTC discrimination.

Functional characterization of FABP3, 5 and 7 gene variants identified in schizophrenia and autism spectrum disorder and mouse behavioral studies.

Disturbances of lipid metabolism have been implicated in psychiatric illnesses. We previously reported an association between the gene for fatty acid binding protein 7 (FABP7) and schizophrenia. Furthermore, we identified and reported several rare non-synonymous polymorphisms of the brain-expressed genes FABP3, FABP5 and FABP7 from schizophrenia and autism spectrum disorder (ASD), diseases known to part share genetic architecture. Here, we conducted further studies to better understand the contribution these genes make to the pathogenesis of schizophrenia and ASD. In postmortem brains, we detected altered mRNA expression levels of FABP5 in schizophrenia, and of FABP7 in ASD and altered FABP5 in peripheral lymphocytes. Using a patient cohort, comprehensive mutation screening identified six missense and two frameshift variants from the three FABP genes. The two frameshift proteins, FABP3 E132fs and FABP7 N80fs, formed cellular aggregates and were unstable when expressed in cultured cells. The four missense mutants with predicted possible damaging outcomes showed no changes in intracellular localization. Examining ligand binding properties, FABP7 S86G and FABP7 V126L lost their preference for docosahexaenoic acid to linoleic acid. Finally, mice deficient in Fabp3, Fabp5 and Fabp7 were evaluated in a systematic behavioral test battery. The Fabp3 knockout (KO) mice showed decreased social memory and novelty seeking, and Fabp7 KO mice displayed hyperactive and anxiety-related phenotypes, while Fabp5 KO mice showed no apparent phenotypes. In conclusion, disturbances in brain-expressed FABPs could represent an underlying disease mechanism in a proportion of schizophrenia and ASD sufferers.

Defective craniofacial development and brain function in a mouse model for depletion of intracellular inositol synthesis.

myo-Inositol is an essential biomolecule that is synthesized by myo-inositol monophosphatase (IMPase) from inositol monophosphate species. The enzymatic activity of IMPase is inhibited by lithium, a drug used for the treatment of mood swings seen in bipolar disorder. Therefore, myo-inositol is thought to have an important role in the mechanism of bipolar disorder, although the details remain elusive. We screened an ethyl nitrosourea mutant mouse library for IMPase gene (Impa) mutations and identified an Impa1 T95K missense mutation. The mutant protein possessed undetectable enzymatic activity. Homozygotes died perinatally, and E18.5 embryos exhibited striking developmental defects, including hypoplasia of the mandible and asymmetric fusion of ribs to the sternum. Perinatal lethality and morphological defects in homozygotes were rescued by dietary myo-inositol. Rescued homozygotes raised on normal drinking water after weaning exhibited a hyper-locomotive trait and prolonged circadian periods, as reported in rodents treated with lithium. Our mice should be advantageous, compared with those generated by the conventional gene knock-out strategy, because they carry minimal genomic damage, e.g. a point mutation. In conclusion, our results reveal critical roles for intracellular myo-inositol synthesis in craniofacial development and the maintenance of proper brain function. Furthermore, this mouse model for cellular inositol depletion could be beneficial for understanding the molecular mechanisms underlying the clinical effect of lithium and myo-inositol-mediated skeletal development.

Sequencing and expression analyses of the synaptic lipid raft adapter gene PAG1 in schizophrenia.

Disruption of synaptic networks has been advocated in the pathogenesis of psychiatric diseases like schizophrenia. The majority of synaptic proteins involved in neuronal communications are localized in lipid rafts. These rafts form the platform for coordinating neuronal signal transduction, by clustering interacting partners. The PAG1 protein is a transmembrane adaptor protein in the lipid raft signaling cluster that regulates Src family kinases (SFKs), a convergent point for multiple pathways regulating N-methyl-D-aspartate (NMDA) receptors. Reports of de novo missense mutations in PAG1 and SFK mediated reductions in tyrosine phosphorylation of NMDA receptor subunit proteins in schizophrenia patients, point to a putative role in schizophrenia pathogenesis. To evaluate this, we resequenced the entire coding region of PAG1 in Japanese schizophrenia patients (n = 1,140) and controls (n = 1,140). We identified eight missense variants, of which four were previously unreported. Case-control genetic association analysis of these variants in a larger cohort (n = 4,182) showed neither a statistically significant association of the individual variants with schizophrenia, nor any increased burden of the rare alleles in the patient group. Expression levels of PAG1 in post-mortem brain samples from schizophrenia patients and controls also showed no significant differences. To assess the precise role of PAG1 in schizophrenia, future studies with larger sample sizes are needed.

Human myo-inositol monophosphatase 2 rescues the nematode thermotaxis mutant ttx-7 more efficiently than IMPA1: functional and evolutionary considerations of the two mammalian myo-inositol monophosphatase genes.

Mammals express two myo-inositol monophosphatase (IMPase) genes, IMPA1/Impa1 and IMPA2/Impa2. In this study, we compared the spatial expression patterns of the two IMPase gene transcripts and proteins in mouse tissues. Results indicated discrete expression of the two IMPase genes and their protein products in various organs, including the brain. In Caenorhabditis elegans, loss of the IMPase gene, ttx-7, disrupts cellular polarity in RIA neurons, eliciting abnormal thermotaxis behavior. We performed a rescue experiment in mutant nematodes using mammalian IMPases. Human IMPA2 rescued the abnormal behavioral phenotype in the ttx-7 mutants more efficiently than IMPA1. These results raise a question about the phylogenetic origin of IMPases and the biological roles of mammalian IMPase 2 in mammals. Impa2 knockout mice generated in our laboratory, exhibited neither behavioral abnormalities nor a significant reduction in myo-inositol content in the brain and other examined tissues. Given the ability of human IMPA2 to rescue the ttx-7 mutant, and its genetic association with multiple neuropsychiatric disorders, close scrutiny of IMPA2 function and the evolutionary origin of IMPase genes is warranted.

Association study of the KCNJ3 gene as a susceptibility candidate for schizophrenia in the Chinese population.

We recently reported the results of a genome-wide association study (GWAS) of schizophrenia in the Japanese population. In that study, a single nucleotide polymorphism (SNP) (rs3106653) in the KCNJ3 (potassium inwardly rectifying channel, subfamily J, member 3) gene located at 2q24.1 showed association with schizophrenia in two independent sample sets. KCNJ3, also termed GIRK1 or Kir3.1, is a member of the G protein-activated inwardly rectifying K(+) channel (GIRK) group. GIRKs are widely distributed in the brain and play an important role in regulating neural excitability through the activation of various G protein-coupled receptors. In this study, we set out to examine this association using a different population. We first performed a gene-centric association study of the KCNJ3 gene, by genotyping 38 tagSNPs in the Chinese population. We detected nine SNPs that displayed significant association with schizophrenia (lowest P = 0.0016 for rs3106658, Global significance = 0.036). The initial marker SNP (rs3106653) examined in our prior GWAS in the Japanese population also showed nominally significant association in the Chinese population (P = 0.028). Next, we analyzed transcript levels in the dorsolateral prefrontal cortex of postmortem brains from patients with schizophrenia and bipolar disorder and from healthy controls, using real-time quantitative RT-PCR. We found significantly lower KCNJ3 expression in postmortem brains from schizophrenic and bipolar patients compared with controls. These data suggest that the KCNJ3 gene is genetically associated with schizophrenia in Asian populations and add further evidence to the "channelopathy theory of psychiatric illnesses".

Role of an Atypical Cadherin Gene, Cdh23 in Prepulse Inhibition, and Implication of CDH23 in Schizophrenia.

We previously identified quantitative trait loci (QTL) for prepulse inhibition (PPI), an endophenotype of schizophrenia, on mouse chromosome 10 and reported Fabp7 as a candidate gene from an analysis of F2 mice from inbred strains with high (C57BL/6N; B6) and low (C3H/HeN; C3H) PPI levels. Here, we reanalyzed the previously reported QTLs with increased marker density. The highest logarithm of odds score (26.66) peaked at a synonymous coding and splice-site variant, c.753G>A (rs257098870), in the Cdh23 gene on chromosome 10; the c.753G (C3H) allele showed a PPI-lowering effect. Bayesian multiple QTL mapping also supported the same variant with a posterior probability of 1. Thus, we engineered the c.753G (C3H) allele into the B6 genetic background, which led to dampened PPI. We also revealed an e-QTL (expression QTL) effect imparted by the c.753G>A variant for the Cdh23 expression in the brain. In a human study, a homologous variant (c.753G>A; rs769896655) in CDH23 showed a nominally significant enrichment in individuals with schizophrenia. We also identified multiple potentially deleterious CDH23 variants in individuals with schizophrenia. Collectively, the present study reveals a PPI-regulating Cdh23 variant and a possible contribution of CDH23 to schizophrenia susceptibility.

Cooperation of LIM domain-binding 2 (LDB2) with EGR in the pathogenesis of schizophrenia.

Genomic defects with large effect size can help elucidate unknown pathologic architecture of mental disorders. We previously reported on a patient with schizophrenia and a balanced translocation between chromosomes 4 and 13 and found that the breakpoint within chromosome 4 is located near the LDB2 gene. We show here that Ldb2 knockout (KO) mice displayed multiple deficits relevant to mental disorders. In particular, Ldb2 KO mice exhibited deficits in the fear-conditioning paradigm. Analysis of the amygdala suggested that dysregulation of synaptic activities controlled by the immediate early gene Arc is involved in the phenotypes. We show that LDB2 forms protein complexes with known transcription factors. Consistently, ChIP-seq analyses indicated that LDB2 binds to > 10,000 genomic sites in human neurospheres. We found that many of those sites, including the promoter region of ARC, are occupied by EGR transcription factors. Our previous study showed an association of the EGR family genes with schizophrenia. Collectively, the findings suggest that dysregulation in the gene expression controlled by the LDB2-EGR axis underlies a pathogenesis of subset of mental disorders.

Analysis of strain-dependent prepulse inhibition points to a role for Shmt1 (SHMT1) in mice and in schizophrenia.

Deficits in prepulse inhibition (PPI) are known in mental illnesses, including schizophrenia. NMDA receptor function affects PPI integrity and D-serine and glycine are endogenous co-agonists for the receptor. Our previous quantitative trait loci analysis using C57BL/6 (B6) mice with better PPI performance and C3H/He (C3) with lower PPI score, shows that genes for both D-serine synthesizing enzyme and enzyme for reversible conversion between glycine and L-serine (Srr and Shmt1, respectively) are located in the same PPI-quantitative trait loci peak. Therefore, we set out to determine which gene is likely to explain the PPI difference and whether the gene is potentially relevant to schizophrenia. We first examined brain interstitial fluid levels of the two amino acids using microdialysis. Recovery of D-serine and glycine from the dialysate was higher in B6, compared to C3. Next, we analyzed expression levels and genetic polymorphisms of the two genes. There were promoter polymorphisms in Shmt1, which elicit lower transcriptional activity in B6 compared to C3 conforming to the results of brain expression levels, but no functional genetic variants in Srr. Finally, we evaluated expression levels of the two genes in the postmortem brains of schizophrenia and genetic associations with the disease. The SHMT1 levels were higher in schizophrenic brains compared to controls, but no changes in SRR levels. We detected a nominal association between SHMT1 and schizophrenia. These results suggest that Shmt1 (SHMT1), but not Srr, is likely to be one of the genetic components regulating PPI in mice and possibly relevant to schizophrenia.

Excessive ingestion of long-chain polyunsaturated fatty acids during developmental stage causes strain- and sex-dependent eye abnormalities in mice.

The eyes are rich in long-chain polyunsaturated fatty acids (LC-PUFAs) such as arachidonic acid [ARA; 20:4 (n-6)] and docosahexaenoic acid [DHA; 22:6 (n-3)]. Despite their abundance in the eyes, ARA and DHA cannot be sufficiently synthesized de novo in mammals. During gestation, eye development is exceptionally rapid, and substantial amounts of LC-PUFAs are needed to ensure proper eye development. Here, we studied the influences of dietary LC-PUFAs in dams (C57BL/6 and C3H/He) on the eye morphogenesis and organogenesis of their pups. Intriguingly, fetuses and newborn mice from C57BL/6 dams fed an LC-PUFA (particularly ARA)-enriched diet displayed a much higher incidence of eye abnormalities such as microphthalmia (small eye) and corneal opacity than those from dams fed an LC-PUFA-poor diet. The effects of LC-PUFAs on eye anomalies were evident only in the female pups of C57BL/6 inbred mice, not in those of C3H/He mice or male C57BL/6 mice. These results demonstrate a gene-by-environment (GxE) interaction in eye development in mice. Furthermore, our molecular analysis suggested the potential roles of Pitx3 and Pax6 in the above interaction involving ARA.

Polymorphism screening of brain-expressed FABP7, 5 and 3 genes and association studies in autism and schizophrenia in Japanese subjects.

Fatty acid-binding protein (FABP) gene family encode fatty acid-binding proteins and consist of at least 12 members, of which FABP7, 5 and 3 are expressed in the brain. We previously showed that FABP7 is associated with schizophrenia and bipolar disorder. Recently, genetic overlap between autism and schizophrenia has been reported. Therefore, in this study, we set out to examine the possible roles of brain-expressed FABPs in autism, focusing primarily on potentially functional polymorphisms (that is, missense polymorphisms). First, we resequenced the three genes using 285 autism samples. We identified 13 polymorphisms, of which 7 are novel. Of the novel single-nucleotide polymorphisms (SNPs), two are missense mutations, namely, 376G>C (Val126Leu) in FABP7 and 340G>C (Gly114Arg) in FABP5. Second, we tested for the genetic association of four missense SNPs with autism and schizophrenia, but failed to detect significant results. Finally, as a web-based algorithm predicts that the 8A>G (Asp3Gly; rs17848124) in FABP3 is 'probably damaging', we estimated the possible impact of this SNP, and found that the loss of charge and salt bridge, caused by the Asp3-to-Gly3, may affect stability of the FABP3 protein. Future searches for associated phenotypes with missense SNPs using larger samples are highly warranted.

Fabp7 maps to a quantitative trait locus for a schizophrenia endophenotype.

Deficits in prepulse inhibition (PPI) are a biological marker for schizophrenia. To unravel the mechanisms that control PPI, we performed quantitative trait loci (QTL) analysis on 1,010 F2 mice derived by crossing C57BL/6 (B6) animals that show high PPI with C3H/He (C3) animals that show low PPI. We detected six major loci for PPI, six for the acoustic startle response, and four for latency to response peak, some of which were sex-dependent. A promising candidate on the Chromosome 10-QTL was Fabp7 (fatty acid binding protein 7, brain), a gene with functional links to the N-methyl-D-aspartic acid (NMDA) receptor and expression in astrocytes. Fabp7-deficient mice showed decreased PPI and a shortened startle response latency, typical of the QTL's proposed effects. A quantitative complementation test supported Fabp7 as a potential PPI-QTL gene, particularly in male mice. Disruption of Fabp7 attenuated neurogenesis in vivo. Human FABP7 showed altered expression in schizophrenic brains and genetic association with schizophrenia, which were both evident in males when samples were divided by sex. These results suggest that FABP7 plays a novel and crucial role, linking the NMDA, neurodevelopmental, and glial theories of schizophrenia pathology and the PPI endophenotype, with larger or overt effects in males. We also discuss the results from the perspective of fetal programming.

[Analysis of mouse strain-dependent prepulse inhibition points to a role for Shmt1 (SHMT1) in mice and in schizophrenia].

Deficits in prepulse inhibition (PPI) are thought to be a biological trait of mental illnesses, including schizophrenia. It is known that the N-methyl-D-aspartate type glutamate (NMDA) receptor function affects PPI integrity and D-serine and glycine are typical endogenous co-agonists for the receptor. In parallel, we re-visited our prior quantitative trait loci (QTL) analysis study that examined C57BL/6 (B6) mice with high PPI and C3H/He (C3) with low PPI, and noticed that the genes encoding enzymes responsible for the productions of D-serine (serine racemase: Srr) and glycine (serine hydroxymethyltransferase 1: Shmt1) map to the chromosome 11 QTL. Therefore, we set out to examine whether brain interstitial fluid (ISF) levels of the two amino acids are different between the two mouse strains, using in vivo microdialysis. Recovery of D-serine and glycine from the dialysate of the frontal cortex was higher in B6 mice, which performed better in PPI, compared to C3 mice. Next, we analyzed the two genes, Srr and Shmt1. We then identified promoter polymorphisms in Shmt1 which elicit lower transcriptional activity in B6 compared to C3 mice. Human studies revealed higher expression levels of SHMT1 in the frontal cortex of postmortem brains from schizophrenics compared to controls, but no changes in SRR levels. In addition, genetic analysis detected a nominal association between SHMT1 and schizophrenia. These results suggest that Shmt1 (SHMT1) is one of the genetic components regulating PPI in mice and is relevant to schizophrenia susceptibility in humans.

Failure to confirm genetic association of the FXYD6 gene with schizophrenia: the Japanese population and meta-analysis.

The FXYD domain-containing ion transport regulator 6 (FXYD6) gene encodes phosphohippolin that regulates cellular ion transport by altering the kinetic properties of Na,K-ATPase. Phosphohippolin is highly expressed in brain regions that are relevant to schizophrenia. The FXYD6 gene is located at chromosome 11q22-24, one of the most established linkage regions for schizophrenia. Therefore, it may be possible that genetic variants in FXYD6, including the regulatory genomic elements could cause abnormal function or expression of phosphohippolin and increase the genetic risk for schizophrenia. A previous study suggested that polymorphisms in FXYD6 are associated with schizophrenia in UK samples. However, conflicting results have been reported in the Japanese population. In this study, we aimed to test the prior genetic association findings using different samples from the ethnically homogeneous Japanese population (1,060 schizophrenic patients and 1,060 age- and sex-matched controls). From the FXYD6 gene, we examined six single nucleotide polymorphisms (rs11216573, rs555577, rs1815774, rs4938445, rs4938446, and rs497768), all of which were previously analyzed for association. We did not detect any significant allelic, genotypic or haplotypic association in our Japanese samples. Meta-analysis incorporating previous and the present studies also showed that the FXYD6 gene is not associated with schizophrenia. We conclude that the FXYD6 gene does not have a major influence on susceptibility to schizophrenia across populations.

Association analyses between brain-expressed fatty-acid binding protein (FABP) genes and schizophrenia and bipolar disorder.

Deficits in prepulse inhibition (PPI) are a biological marker for psychiatric illnesses such as schizophrenia and bipolar disorder. To unravel PPI-controlling mechanisms, we previously performed quantitative trait loci (QTL) analysis in mice, and identified Fabp7, that encodes a brain-type fatty acid binding protein (Fabp), as a causative gene. In that study, human FABP7 showed genetic association with schizophrenia. FABPs constitute a gene family, of which members FABP5 and FABP3 are also expressed in the brain. These FABP proteins are molecular chaperons for polyunsaturated fatty acids (PUFAs) such as arachidonic and docosahexaenoic acids. Additionally, the involvement of PUFAs has been documented in the pathophysiology of schizophrenia and mood disorders. Therefore in this study, we examined the genetic roles of FABP5 and 3 in schizophrenia (N = 1,900 in combination with controls) and FABP7, 5, and 3 in bipolar disorder (N = 1,762 in the case-control set). Three single nucleotide polymorphisms (SNPs) from FABP7 showed nominal association with bipolar disorder, and haplotypes of the same gene showed empirical associations with bipolar disorder even after correction of multiple testing. We could not perform association studies on FABP5, due to the lack of informative SNPs. FABP3 displayed no association with either disease. Each FABP is relatively small and it is assumed that there are multiple regulatory elements that control gene expression. Therefore, future identification of unknown regulatory elements will be necessary to make a more detailed analysis of their genetic contribution to mental illnesses.