Genetic risk between the CACNA1I gene and schizophrenia in Chinese Uygur population

Asian-European differentiation of schizophrenia-associated genes driven by admixture and natural selection

The European-centered genome-wide association studies of schizophrenia (SCZ) may not be well applied to non-European populations. We analyzed 1,592 reported SCZ-associated genes using the public genome data and found an overall higher Asian-European differentiation on the SCZ-associated variants than at the genome-wide level. Notable examples included 15 missense variants, a regulatory variant SLC5A10-rs1624825, and a damaging variant TSPAN18-rs1001292. Independent local adaptations in recent 25,000 years, after the Asian-European divergence, could have contributed to such genetic differentiation, as were identified at a missense mutation LTN1-rs57646126-A in Asians, and a non-risk allele ZSWIM6-rs72761442-G in Europeans. Altai-Neanderthal-derived alleles may have opposite effects on SCZ susceptibility between ancestries. Furthermore, adaptive introgression was detected on the non-risk haplotype at 1q21.2 in Europeans, while in Asians it was observed on the SCZ risk haplotype at 3p21.31 which is also potentially ultra-violet protective. This study emphasizes the importance of including more representative Asian samples in future SCZ studies.

Shared genetic loci and causal relations between schizophrenia and obsessive-compulsive disorder

Based on the clinical overlap between schizophrenia (SCZ) and obsessive-compulsive disorder (OCD), both disorders may share neurobiological substrates. In this study, we first analyzed recent large genome-wide associations studies (GWAS) on SCZ (n = 53,386, Psychiatric Genomics Consortium Wave 3) and OCD (n = 2688, the International Obsessive-Compulsive Disorder Foundation Genetics Collaborative (IOCDF-GC) and the OCD Collaborative Genetics Association Study (OCGAS)) using a conjunctional false discovery rate (FDR) approach to evaluate overlap in common genetic variants of European descent. Using a variety of biological resources, we functionally characterized the identified genomic loci. Then we used two-sample Mendelian randomization (MR) to estimate the bidirectional causal association between SCZ and OCD. Results showed that there is a positive genetic correlation between SCZ and OCD (r_g = 0.36, P = 0.02). We identified that one genetic locus (lead SNP rs5757717 in an intergenic region at CACNA1I) was jointly associated with SCZ and OCD (conjFDR = 2.12 × 10^-2). Mendelian randomization results showed that variants associated with increased risk for SCZ also increased the risk of OCD. This study broadens our understanding of the genetic architectures underpinning SCZ and OCD and suggests that the same molecular genetic processes may be responsible for shared pathophysiological and clinical characteristics between the two disorders.

CaV3.3 Channelopathies

CaV3.3 is the third member of the low-voltage-activated calcium channel family and the last to be recognized as disease gene. Previously, CACNA1I, the gene encoding CaV3.3, had been described as schizophrenia risk gene. More recently, de novo missense mutations in CACNA1I were identified in patients with variable degrees of neurodevelopmental disease with and without epilepsy. Their functional characterization indicated gain-of-function effects resulting in increased calcium load and hyperexcitability of neurons expressing CaV3.3. The amino acids mutated in the CaV3.3 disease variants are located in the vicinity of the channel's activation gate and thus are classified as gate-modifying channelopathy mutations. A persistent calcium leak during rest and prolonged calcium spikes due to increased voltage sensitivity of activation and slowed kinetics of channel inactivation, respectively, may be causal for the neurodevelopmental defects. The prominent expression of CaV3.3 in thalamic reticular nucleus neurons and its essential role in generating the rhythmic thalamocortical network activity are consistent with a role of the mutated channels in the etiology of epileptic seizures and thus suggest T-type channel blockers as a viable treatment option.

CACNA1I gain-of-function mutations differentially affect channel gating and cause neurodevelopmental disorders

T-type calcium channels (Cav3.1 to Cav3.3) regulate low-threshold calcium spikes, burst firing and rhythmic oscillations of neurons and are involved in sensory processing, sleep, and hormone and neurotransmitter release. Here, we examined four heterozygous missense variants in CACNA1I, encoding the Cav3.3 channel, in patients with variable neurodevelopmental phenotypes. The p.(Ile860Met) variant, affecting a residue in the putative channel gate at the cytoplasmic end of the IIS6 segment, was identified in three family members with variable cognitive impairment. The de novo p.(Ile860Asn) variant, changing the same amino acid residue, was detected in a patient with severe developmental delay and seizures. In two additional individuals with global developmental delay, hypotonia, and epilepsy, the variants p.(Ile1306Thr) and p.(Met1425Ile), substituting residues at the cytoplasmic ends of IIIS5 and IIIS6, respectively, were found. Because structure modelling indicated that the amino acid substitutions differentially affect the mobility of the channel gate, we analysed possible effects on Cav3.3 channel function using patch-clamp analysis in HEK293T cells. The mutations resulted in slowed kinetics of current activation, inactivation, and deactivation, and in hyperpolarizing shifts of the voltage-dependence of activation and inactivation, with Cav3.3-I860N showing the strongest and Cav3.3-I860M the weakest effect. Structure modelling suggests that by introducing stabilizing hydrogen bonds the mutations slow the kinetics of the channel gate and cause the gain-of-function effect in Cav3.3 channels. The gating defects left-shifted and increased the window currents, resulting in increased calcium influx during repetitive action potentials and even at resting membrane potentials. Thus, calcium toxicity in neurons expressing the Cav3.3 variants is one likely cause of the neurodevelopmental phenotype. Computer modelling of thalamic reticular nuclei neurons indicated that the altered gating properties of the Cav3.3 disease variants lower the threshold and increase the duration and frequency of action potential firing. Expressing the Cav3.3-I860N/M mutants in mouse chromaffin cells shifted the mode of firing from low-threshold spikes and rebound burst firing with wild-type Cav3.3 to slow oscillations with Cav3.3-I860N and an intermediate firing mode with Cav3.3-I860M, respectively. Such neuronal hyper-excitability could explain seizures in the patient with the p.(Ile860Asn) mutation. Thus, our study implicates CACNA1I gain-of-function mutations in neurodevelopmental disorders, with a phenotypic spectrum ranging from borderline intellectual functioning to a severe neurodevelopmental disorder with epilepsy.

Neuronal Cav3 channelopathies: recent progress and perspectives

T-type, low-voltage activated, calcium channels, now designated Cav3 channels, are involved in a wide variety of physiological functions, especially in nervous systems. Their unique electrophysiological properties allow them to finely regulate neuronal excitability and to contribute to sensory processing, sleep, and hormone and neurotransmitter release. In the last two decades, genetic studies, including exploration of knock-out mouse models, have greatly contributed to elucidate the role of Cav3 channels in normal physiology, their regulation, and their implication in diseases. Mutations in genes encoding Cav3 channels (CACNA1G, CACNA1H, and CACNA1I) have been linked to a variety of neurodevelopmental, neurological, and psychiatric diseases designated here as neuronal Cav3 channelopathies. In this review, we describe and discuss the clinical findings and supporting in vitro and in vivo studies of the mutant channels, with a focus on de novo, gain-of-function missense mutations recently discovered in CACNA1G and CACNA1H. Overall, the studies of the Cav3 channelopathies help deciphering the pathogenic mechanisms of corresponding diseases and better delineate the properties and physiological roles Cav3 channels.

Genetic Associations between Voltage-Gated Calcium Channels and Psychiatric Disorders

Psychiatric disorders are mental, behavioral or emotional disorders. These conditions are prevalent, one in four adults suffer from any type of psychiatric disorders world-wide. It has always been observed that psychiatric disorders have a genetic component, however, new methods to sequence full genomes of large cohorts have identified with high precision genetic risk loci for these conditions. Psychiatric disorders include, but are not limited to, bipolar disorder, schizophrenia, autism spectrum disorder, anxiety disorders, major depressive disorder, and attention-deficit and hyperactivity disorder. Several risk loci for psychiatric disorders fall within genes that encode for voltage-gated calcium channels (CaVs). Calcium entering through CaVs is crucial for multiple neuronal processes. In this review, we will summarize recent findings that link CaVs and their auxiliary subunits to psychiatric disorders. First, we will provide a general overview of CaVs structure, classification, function, expression and pharmacology. Next, we will summarize tools to study risk loci associated with psychiatric disorders. We will examine functional studies of risk variations in CaV genes when available. Finally, we will review pharmacological evidence of the use of CaV modulators to treat psychiatric disorders. Our review will be of interest for those studying pathophysiological aspects of CaVs.

Association of SYNE1 locus with bipolar disorder in Chinese population

Objectives

Genome-wide association studies (GWAS) suggest that rs9371601 in the SYNE1 gene is a risk SNP for bipolar disorder (BPD) in populations of European ancestry, but further replication analyses across distinct populations are needed.

Methods

We analyzed the association between rs9371601 and BPD in a Han Chinese sample of 1315 BPD cases and 1956 controls.

Results

We observed a significant association between rs9371601 and BPD in Han Chinese (p = 0.0121, OR = 0.859). However, further examinations revealed that the Europeans and Chinese subjects had different BPD risk alleles at the locus. We then found that rs9371601 had different “minor alleles” and distinct linkage disequilibrium (LD) patterns surrounding itself in Europeans and Han Chinese, which might be the explanation of the observed inconsistent association signals for this locus in different populations. Our explorative analyses of the biological impact of rs9371601 suggested that this SNP was significantly associated with the methylation of a CpG site (cg01844274, p = 5.05⨯10^− 6) within SYNE1 in human dorsal lateral prefrontal cortex (DLPFC) tissues.

Conclusions

Our data confirms the association between rs9371601 and BPD, but the underlying biological mechanism remains to be fully elucidated in further studies.

Electronic supplementary material

The online version of this article (10.1186/s41065-019-0095-7) contains supplementary material, which is available to authorized users.

Common variants in SATB2 are associated with schizophrenia in Uygur Chinese population

OBJECTIVE

Schizophrenia is one of the most severe mental disorders and its etiology is supposed to be an interaction between genes and environmental factors. Previous genome-wide association studies of schizophrenia have reported multiple susceptibility loci including rs6704641 in the SATB2 gene. Recently, this locus was further confirmed as a genome-wide significant locus for association with schizophrenia by trans-ancestry meta-analysis of Han Chinese and Caucasian samples. However, there is no report of genetic analysis in Uygur Chinese population, which is considered to have a combined genetic background between eastern Asia and Caucasian. This study is aimed to explore whether SATB2 gene is significantly associated with schizophrenia in Uygur Chinese population, thus providing additional evidence for elucidating the role of SATB2 gene in schizophrenia.

PARTICIPANTS AND METHODS

In this study, we performed a case-control analysis focusing on seven tag single nucleotide polymorphisms located in SATB2 gene among 985 patients with schizophrenia and 1218 healthy controls recruited from the Xinjiang Province of China.

RESULTS

We found that rs6704641 was significantly associated with schizophrenia in both allelic and genotypic distributions (Pallele = 0.008, Pgenotype = 0.028 after correction). In addition, rs16831466 is significantly associated with schizophrenia in allelic distributions (corrected Pallele = 0.041). Besides, several haplotypes of single nucleotide polymorphism are significantly associated with schizophrenia too.

CONCLUSION

Our results suggest that SATB2 is also a susceptibility gene for schizophrenia in Uygur Chinese population, and subsequent functional experiments are necessary to reveal its role in the pathogenesis.

Further evidence for the genetic association between CACNA1I and schizophrenia

Background

Recent large-scale genome-wide association studies (GWAS) have showed that the neuronal calcium signaling has pivotal roles in schizophrenia (SCZ) in populations of European of ancestry. However, it is not known if calcium signaling pathway genes are also associated with SCZ in Han Chinese population.

Methods

Here we investigated the association between genetic variants in three calcium signaling pathway genes (CACNB2, CACNA1C and CACNA1I) and SCZ in 1615 SCZ cases and 1597 controls.

Results

A single nucleotide polymorphism (SNP) (rs4522708) in CACNA1I is significantly associated with SCZ in our Chinese sample (OR_{A allele} = 1.19, corrected P = 0.042), suggesting that CACNA1I may also be a risk gene for SCZ in Chinese population. Of note, the risk allele (A allele) of SNP rs4522708 is same in European and Chinese populations. Meta-analysis of Chinese and European samples further strengthened the association of rs4522708 with SCZ (OR_{A allele} = 1.074, P = 6.26 × 10⁻¹¹). Expression analysis showed that CACNA1I was significantly up-regulated in hippocampus of SCZ cases compared with controls, implying that dysregulation of CACNA1I may have a role in schizophrenia pathogenesis.

Conclusions

Our study suggests that CACNA1I is a risk gene for SCZ in Chinese population and provides further evidence that supports the potential role of neuronal calcium signaling in schizophrenia.