A genetic association study of the FXYD domain containing ion transport regulator 6 (FXYD6) gene, encoding phosphohippolin, in susceptibility to schizophrenia in a Japanese population

Sex-biased single-cell genetic landscape in mice with autism spectrum disorder

Autistic spectrum disorder (ASD) is a male-biased, heterogeneous neurodevelopmental disorder that affects approximately 1%-2% of the population. Prenatal exposure to valproic acid (VPA) is a recognized risk factor for ASD, but the cellular and molecular basis of VPA-induced ASD at the single-cell resolution is unclear. Here, we aim to compare the cellular and molecular differences in the hippocampus between male and female prenatal mice with ASD at the single-cell transcriptomic level. The transcriptomes of more than 45,000 cells are assigned to 12 major cell types, including neurons, glial cells, vascular cells, and immune cells. Cell type-specific genes with altered expression after prenatal VPA exposure are analyzed, and the largest number of differentially expressed genes (DEGs) are found in neurons, choroid plexus epithelial cells, and microglia. In microglia, several pathways related to inflammation are found in both males and females, including the tumor necrosis factor (TNF), nuclear factor kappa B (NF-κB), toll-like receptor (TLR), and mitogen-activated protein kinase (MAPK) signaling pathways, which are important for the induction of autistic-like behavior. Additionally, we note that several X-linked genes, including Bex1, Bex3, and Gria3, were among the male-specific DEGs of neurons. This pioneering study describes the landscape of the transcriptome in the hippocampus of autistic mice. The elucidation of sexual differences could provide innovative strategies for the prevention and treatment of ASD.

FXYD6 overexpression in HBV-related hepatocellular carcinoma with cirrhosis

Objective

The aim of this study was to investigate the expression of FXYD domain-containing ion transport regulator 6 (FXYD6) mRNA and protein in hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC) tissues with cirrhosis, the corresponding paracancerous tissues and the normal liver tissues, and to explore the clinical significance of FXYD6 expression in HBV-related HCC with cirrhosis.

Methods

The FXYD6 mRNA and protein were examined by semi-quantitative reverse transcription polymerase chain reaction and immunohistochemistry, respectively.

Results

The FXYD6 mRNA in HBV-related HCC tissues was significantly higher than that in the cirrhosis tissues or that in the normal liver tissues. The positive expression rate of FXYD6 protein was statistically higher in HBV-related HCC tissues than that in HBV-related cirrhosis or that in normal liver tissues. There was no significant correlation between the expression of FXYD6 protein and gender, age, histological differentiation, tumor diameter, tumor number, integrity of tumor capsule or not and alpha fetoprotein (AFP) concentration in serum, but the protein expression was associated with microvascular invasion, pathological stage, and early recurrence after operation within 1 year.

Conclusion

FXYD6 might be involved in hepatocyte carcinogenesis and tumor progression in HBV-related HCC with cirrhosis and indicated a poor prognosis.

Missense variants in ATP1A3 and FXYD gene family are associated with childhood-onset schizophrenia

Childhood-onset schizophrenia (COS) is a rare and severe form of schizophrenia defined as onset before age of 13. Here we report on two unrelated cases diagnosed with both COS and alternating hemiplegia of childhood (AHC), and for whom two distinct pathogenic de novo variants were identified in the ATP1A3 gene. ATP1A3 encodes the α-subunit of a neuron-specific ATP-dependent transmembrane sodium-potassium pump. Using whole exome sequencing data derived from a cohort of 17 unrelated COS cases, we also examined ATP1A3 and all of its interactors known to be expressed in the brain to establish if variants could be identified. This led to the identification of a third case with a possibly damaging missense mutation in ATP1A3 and three others cases with predicted pathogenic missense variants in the FXYD gene family (FXYD1, FXYD6, and FXYD6-FXYD2 readthrough). FXYD genes encode proteins that modulate the ATP-dependant pump function. This report is the first to identify variants in the same pathway for COS. Our COS study illustrates the interest of stratifying a complex condition according to the age of onset for the identification of deleterious variants. Whereas ATP1A3 is a replicated gene in rare neuropediatric diseases, this gene has previously been linked with COS in only one case report. The association with rare variants in FXYD gene family is novel and highlights the interest of exploring these genes in COS as well as in pediatric neurodevelopmental disorders.

FXYD6 is a new biomarker of cholangiocarcinoma

Members of the FXYD domain-containing ion transport regulator protein family, including FXYD3 and FXYD5, play an important role in the pathogenesis of numerous tumors. However, the correlation between the expression of FXYD6 and tumors remains poorly understood. In the current study, the expression of FXYD6 was examined immunohistochemically in 72 cholangiocarcinoma tissues and 30 distal normal bile duct tissues matched with the tumors. The results show that the positive expression rate of FXYD6 was significantly higher in cholangiocarcinoma than that in normal bile duct tissue (69 vs. 33.3%; P=0.002). Furthermore, the positive expression rate of FXYD6 in well- and moderately-differentiated cholangiocarcinoma was clearly higher than that in poorly-differentiated and mucinous cholangiocarcinoma (85.7 vs. 40%; P=0.000). However, there was no significant correlation between the expression of FXYD6 and gender (P=0.393), age (P=0.174), histological type (P=0.123), T stage (P=0.164), lymph node metastasis (P=0.343), perineural invasion (P=0.088) and tumor location (P=0.238). The results of this study indicate that FXYD6 may be a new biomarker for cholangiocarcinoma and may be associated with a favorable prognosis in this malignant disease.

A monoclonal antibody against human FXYD6

Previous research has shown that FXYD6 (FXYD domain-containing ion transport regulator 6) is highly increased in bile duct tumor. However, the biological function of FXYD6 is unclear. We aim to prepare and identify a monoclonal antibody against FXYD6, which will be used in diagnostics and as a tool in understanding the role of FXYD6 in pathogenesis of hepatobiliary cancer. In this study, hybridoma cell fusion technology is used for production of FXYD6 monoclonal antibody. BALB/c mice are immunized with FXYD6 synthetic peptide fragment. Hybridoma clones are screened using indirect enzyme-linked immunosorbent assay (ELISA). FXYD6 monoclonal antibody is produced by ascites revulsion. Protein A affinity chromatography is used for the purification of FXYD6 monoclonal antibody. Titer and specificity of monoclonal antibody are assessed by ELISA. Expression of FXYD6 in pancreatic cancer is detected by immunohistochemistry. As a result, one stable hybridoma cell clone producing FXYD6 monoclonal antibody has been established. 2.86 mg monoclonal antibody against FXYD6 with high specificity is prepared with titer of 1:5400. Immunohistochemistry shows that FXYD6 positive staining occurs in the cell membrane of pancreatic cancer, which results in an advantage in investigating the tissue distribution and biological function of FXYD6.

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.

No association between the FXYD6 gene and schizophrenia in the Chinese Han population

Choudhury et al. identified FXYD6 as a susceptible gene for schizophrenia in the London and Aberdeen populations. We genotyped D11S1998 and 8 SNPs (rs869789, rs11216567, rs10790212, rs876797, rs4938445, rs497768, rs11216598, rs11605223) in a Chinese sample consisting of 1514 schizophrenia patients and 1514 healthy controls. We also compared the expression levels of FXYD6 in lymphocytes in 86 schizophrenia patients and 94 controls. No association was detected either in D11S1998 or the 8 SNPs. No difference was found in expression level between patients and controls. Our study suggests that FXYD6 does not play a role in schizophrenia in the Chinese Han population.

Association analyses of the interaction between the ADSS and ATM genes with schizophrenia in a Chinese population

BACKGROUND

The blood-derived RNA levels of the adenylosuccinate synthase (ADSS) and ataxia telangiectasia mutated (ATM) genes were found to be down- and up-regulated, respectively, in schizophrenics compared with controls, and ADSS and ATM were among eight biomarker genes to discriminate schizophrenics from normal controls. ADSS catalyzes the first committed step of AMP synthesis, while ATM kinase serves as a key signal transducer in the DNA double-strand breaks response pathway. It remains unclear whether these changes result from mutations or polymorphisms in the two genes.

METHODS

Six SNPs in the ADSS gene and three SNPs in the ATM gene in a Chinese population of 488 schizophrenics and 516 controls were genotyped to examine their association with schizophrenia (SZ). Genotyping was performed using the Sequenom platform.

RESULTS

There was no significant difference in the genotype, allele, or haplotype distributions of the nine SNPs between cases and controls. Using the Multifactor Dimensionality Reduction (MDR) method, we found that the interactions among rs3102460 in the ADSS gene and rs227061 and rs664143 in the ATM gene revealed a significant association with SZ. This model held a maximum testing accuracy of 60.4% and a maximum cross-validation consistency of 10 out of 10.

CONCLUSION

These findings suggest that the combined effects of the polymorphisms in the ADSS and ATM genes may confer susceptibility to the development of SZ in a Chinese population.