Confirmation of association between autism and the mitochondrial aspartate/glutamate carrier SLC25A12 gene on chromosome 2q31

OBJECTIVE: Autism is a neurodevelopmental disorder with childhood onset and a known major genetic component. A recent study identified a highly significant association between autism and a two-single-nucleotide-polymorphism haplotype in the SLC25A12 gene, with a homozygote genotype relative risk between 2.4 and 4.8. The authors' goal was to investigate this association with autism in Irish affected child-parent trios because replication in an independent sample is essential in the validation of such potentially important findings. METHOD: Markers rs2056202 and rs2292813 were genotyped in a total of 158 trios (442 individuals). The Transmission Disequilibrium Test was used to examine these markers for association with autism. RESULTS: In agreement with the recent study, the authors found significant association between autism and the C alleles of both rs2056202 and rs2292813 as well as the two-marker haplotype. CONCLUSIONS: These findings provide replication of the association between autism and SLC25A12.     

Association study of polymorphisms in the mitochondrial aspartate/glutamate carrier SLC25A12 (aralar) gene with schizophrenia

Aralar is a mitochondrial calcium-regulated aspartate-glutamate carrier mainly distributed in brain and skeletal muscle, and involved in the transport of aspartate from mitochondria to the cytosol of a cell. Studies have shown that the brain N-acetyl aspartate (NAA) levels are greatly decreased in aralar-deficient mice, suggesting that aralar plays an important role in the synthesis of NAA in neuronal cells. Since magnetic resonance spectroscopy studies have revealed consistently reduced NAA levels in various brain regions of schizophrenic patients and their unaffected relatives, genes that affect aralar levels or NAA metabolism in the brain may be implicated in the pathogenesis of schizophrenia. Aralar is encoded by the SLC25A12 gene. In the past this gene has been found to be associated with susceptibility to autism; in this study we tested the hypothesis that SLC25A12 genetic variants confer susceptibility to schizophrenia. Six SLC25A12 polymorphisms were studied in a sample population of 253 people with schizophrenia and 216 normal controls. Significant linkage disequilibrium was obtained among the six polymorphisms. However, neither single marker nor haplotype analysis revealed an association between variants at the SLC25A12 locus and schizophrenia, suggesting that it is unlikely that the SLC25A12 polymorphisms investigated play a substantial role in conferring susceptibility to schizophrenia in the Chinese population. Further studies with SLC25A12 variants relating to brain NAA levels in patients with schizophrenia are suggested.     

Lack of association between autism and SLC25A12

OBJECTIVE: Autism has a strong, complex genetic component, most likely involving several genes. Multiple genomic screens have shown evidence suggesting linkage to chromosome 2q31-q33, which includes the SLC25A12 gene. Recently, an association between autism risk and two single nucleotide polymorphisms (SNPs) in SLC25A12 was reported. This study aimed to test for association in SLC25A12 in an independent data set of 327 families with autistic offspring. METHOD: The authors analyzed two SNPs that were significant in the previous study group, as well as seven additional SNPs within the gene. Association analyses for individual SNPs as well as haplotypes were performed. RESULTS: There was no evidence of an association between SLC25A12 and autism. CONCLUSIONS: These results suggest that SLC25A12 is not a major contributor to autism risk in these families.     

Linkage and association of the glutamate receptor 6 gene with autism

A genome scan was previously performed and pointed to chromosome 6q21 as a candidate region for autism. This region contains the glutamate receptor 6 (GluR6 or GRIK2) gene, a functional candidate for the syndrome. Glutamate is the principal excitatory neurotransmitter in the brain and is directly involved in cognitive functions such as memory and learning. We used two different approaches, the affected sib-pair (ASP) method and the transmission disequilibrium test (TDT), to investigate the linkage and association between GluR6 and autism. The ASP method, conducted with additional markers on the 51 original families and in eight new sibling pairs, showed a significant excess of allele sharing, generating an elevated multipoint maximum LOD score (ASPEX MLS = 3.28). TDT analysis, performed in the ASP families and in an independent data set of 107 parent-offspring trios, indicated a significant maternal transmission disequilibrium (TDTall P = 0.0004). Furthermore, TDT analysis (with only one affected proband per family) showed significant association between GluR6 and autism (TDT association P = 0.008). In contrast to maternal transmission, paternal transmission of GluR6 alleles was as expected in the absence of linkage, suggesting a maternal effect such as imprinting. Mutation screening was performed in 33 affected individuals, revealing several nucleotide polymorphisms (SNPs), including one amino acid change (M867I) in a highly conserved domain of the intracytoplasmic C-terminal region of the protein. This change is found in 8% of the autistic subjects and in 4% of the control population and seems to be more maternally transmitted than expected to autistic males (P = 0.007). Taken together, these data suggest that GluR6 is in linkage disequilibrium with autism.     

Association study of the SLC25A12 gene and autism in Han Chinese in Taiwan

Purpose

Autism is a childhood-onset neurodevelopmental disorder with a strong genetic component in its etiology. Several studies reported that the solute carrier family 25 member A12 (SLC25A12) gene was associated with autism. This study aimed to replicate this finding in a Han Chinese sample from Taiwan using a population-based case–control approach.

Methods

We genotyped two single nucleotide polymorphisms (SNPs, rs2056202 and rs2292813) of the SLC25A12 gene that were previously reported to be associated with autism in 465 patients (402 males and 63 females) and 450 control subjects (227 males and 223 females) from Taiwan. Differences in the genotype, allele, and haplotype frequencies between the two groups were compared.

Results

We found no differences in the allele, genotype, or haplotype frequencies of these two SNPs between patients and controls.

Conclusions

Our data do not support that the SLC25A12 gene is associated with autism in our population. The discrepant results of other studies may come from the clinical heterogeneity of patients recruited for studies, or the genetic heterogeneity of autism in different populations.     

SLC25A12基因多态性与孤独性障碍的关联

目的：探讨SLC25A12基因单核苷酸多态性（SNP）与孤独性障碍的遗传关联性。方法：采用聚合酶链式反应和DNA芯片杂交技术,在124个汉族孤独性障碍患儿核心家系中,检测了SLC25A12基因的2个SNP位点（rs2056202,rs2292813）,采用传递不平衡检验（TDT）和单倍型的方法进行关联分析。结果：在124个患儿核心家系中,所测得的2个SNP位点的等位基因和基因型的频数分布均符合Hardy-Weinberg平衡检验（χ^2=0.009,P=0.92;χ^2=0.006,P=0.94）。而且这2个SNP处于一个强连锁不平衡区域（D’=0.842,r2=0.566）。对124个核心家系TDT检验,发现带有杂合子基因的父代优先传递给子代的等位基因的传递率和此传递率的置信区间差异无显著性（P〉0.05）;所有样本的2个SNP位点,未发现与孤独性障碍的显著关联。结论：SLC25A12基因可能不是这些汉族家庭儿童孤独性障碍的主要易感基因。     

Lack of evidence for association of the serotonin transporter gene SLC6A4 with autism.

BACKGROUND: The serotonin transporter (5-HTT) has long been considered likely to play a role in autism. Hyperserotonemia has been consistently found in a proportion of autistic patients, and the use of selective serotonin reuptake inhibitors (SSRIs) can have a positive effect in treating some symptoms of autism. Specific variants of the 5-HTT gene, SLC6A4, especially the insertion-deletion 5-HTTLPR promoter locus, have been found to modulate its expression and transporter function. METHODS: We examined the transmission of the short or long allele of 5-HTTLPR locus to affected individuals, using a large cohort of 352 families. In addition, we screened five single nucleotide polymorphisms (SNPs) in the 5' region of SLC6A4 previously reported to be positively associated with autism, as well as 4 additional SNPs also in the 5' region. RESULTS: No association of the 5-HTTLPR locus with autism was found. Furthermore, no evidence for association of any of the nine SNPs covering the SLC6A4 gene, or any of their haplotypes, was observed in our study. Using obsessive-compulsive behaviors (OCB), severe OCBs or rigid-compulsive subsets of our cohort gave the same negative results. CONCLUSIONS: SLC6A4 variants do not appear to be significantly involved in the liability to autism.     

Altered calcium homeostasis in autism-spectrum disorders: evidence from biochemical and genetic studies of the mitochondrial aspartate/glutamate carrier AGC1

Autism is a severe developmental disorder, whose pathogenetic underpinnings are still largely unknown. Temporocortical gray matter from six matched patient-control pairs was used to perform post-mortem biochemical and genetic studies of the mitochondrial aspartate/glutamate carrier (AGC), which participates in the aspartate/malate reduced nicotinamide adenine dinucleotide shuttle and is physiologically activated by calcium (Ca(2+)). AGC transport rates were significantly higher in tissue homogenates from all six patients, including those with no history of seizures and with normal electroencephalograms prior to death. This increase was consistently blunted by the Ca(2+) chelator ethylene glycol tetraacetic acid; neocortical Ca(2+) levels were significantly higher in all six patients; no difference in AGC transport rates was found in isolated mitochondria from patients and controls following removal of the Ca(2+)-containing postmitochondrial supernatant. Expression of AGC1, the predominant AGC isoform in brain, and cytochrome c oxidase activity were both increased in autistic patients, indicating an activation of mitochondrial metabolism. Furthermore, oxidized mitochondrial proteins were markedly increased in four of the six patients. Variants of the AGC1-encoding SLC25A12 gene were neither correlated with AGC activation nor associated with autism-spectrum disorders in 309 simplex and 17 multiplex families, whereas some unaffected siblings may carry a protective gene variant. Therefore, excessive Ca(2+) levels are responsible for boosting AGC activity, mitochondrial metabolism and, to a more variable degree, oxidative stress in autistic brains. AGC and altered Ca(2+) homeostasis play a key interactive role in the cascade of signaling events leading to autism: their modulation could provide new preventive and therapeutic strategies.     

No association of the norepinephrine transporter gene (SLC6A2) and cognitive and behavioural phenotypes of patients with autism spectrum disorder

We examined the association between the norepinephrine transporter (SLC6A2) gene and autism spectrum disorder (ASD) in a Korean population. In addition, we investigated which phenotypes of ASD are best attributed to the genotype of SLC6A2. A total of 184 subjects with ASD, their 156 unaffected siblings and both biological parents were recruited through university hospitals. We used the Autism Diagnostic Interview-Revised, the Aberrant Behaviour Checklist (ABC), the Child Behaviour Checklist (CBCL), the Stroop Colour-Word Interference Test and the Wisconsin Card Sorting Test (WCST) as quantitative measures of the ASD phenotypes. The associations between the quantitative measures and specific single-nucleotide polymorphisms (SNPs) were tested with linear regression analyses. We did not find any evidence of the over-transmission of either allele of the 10SLC6A2 SNPs in the DFAM test. At an empirical p value <0.05, findings that were consistent between the linear regression analyses and the QFAM tests were the positive associations between the A allele of rs36020 and attention problems on the CBCL and stereotypical behaviours on the ABC and between the C allele of rs1814270 and the number of trials required to complete the first WCST category. However, these associations did not remain after correction for multiple testing. The study results of this study do not support the association between the SLC6A2 and the diagnosis or phenotype of ASD. However, the study must be replicated in larger populations and with using more genetic markers.     

谷氨酸受体6基因多态与孤独症的关联分析

目的 在中国上海地区汉族孤独症家系中探讨谷氨酸受体6（GluR6或GRIK2）基因多态与孤独症是否关联。方法 采用PCR—RFLP法对入组的38个孤独症核心家系成员的GRIK2基因的两个单核苷酸多态性（rs6922753和rs2227283）分型,并进行传递不平衡检验。结果 rs6922753多态的C和T等位基因未发现显著性的偏移传递方式,rs2227283多态在母系传递中出现显著性的偏移,A等位基因较G等位基因传递明显增加。结论 GRIK2基因与孤独症存在传递的连锁不平衡,可能为孤独症的易感基因。     

金刚烷胺对帕金森病患者线粒体谷氨酸载体活性的影响

目的 探讨谷氨酸及符氨酸载体在帕金森病（PD）发病机制中的作用。方法 首先提取PD患者的血小板线粒体，然后分别先后用谷氨酸和草酰乙酸进一步装载这些线粒体，加入^14C-谷氨酸后启动谷氨酸载体的转运，同时测定该载体的活性，并观察多巴胺等药物对该载体活性的影响。结果 PD患者的血小板计数无明显变化，但谷氨酸载体的活性明显降低，与对照组相比差异有显著性意义（P〈0．05）。金刚烷胺（Ama）可明显提高该载体的活性（与加药前相比，P〈0．05），而多巴胺、左旋多巴和安坦对其活性无明显影响（与加药前相比，P〉0．05）。结论 谷氨酸以及谷氨酸载体参与了PD的发病机制，Ama可能通过影响谷氨酸载体的活性发挥治疗作用。     

Follow-up of genetic linkage findings on chromosome 16p13: evidence of association of N-methyl-D aspartate glutamate receptor 2A gene polymorphism with ADHD

Attention deficit hyperactivity disorder (ADHD) is a childhood onset disorder, for which there is good evidence that genetic factors contribute to the aetiology. Recently reported linkage findings suggested evidence of a susceptibility locus on chromosome 16p13 (maximum LOD score of 4.2, P=5 x 10(-6)). The GRIN2A (glutamate receptor, ionotropic, N-methyl D-aspartate 2A) gene that encodes the N-methyl D-aspartate receptor subunit 2A (NMDA2A) maps to this region of linkage. As this is also a good functional candidate gene for ADHD, we undertook family-based association analysis in a sample of 238 families. We found significant evidence of association with a GRIN2A exon 5 polymorphism (chi(2)=5.7, P=0.01). Our data suggest that genetic variation in GRIN2A may confer increased risk for ADHD and that this, at least in part, might be responsible for the linkage result on 16p reported by Smalley et al. We conclude that replication is required and that further work examining for association of GRIN2A polymorphisms with ADHD is warranted.     

Linkage disequilibrium in aquaporin 4 gene and association study with schizophrenia

Aquaporin 4 (AQP4) has an important role in water homeostasis of human brain and a dysfunction of AQP4 could induce pathological conditions in neuronal activity. Several genome scan studies for schizophrenia found a suggestive linkage on 18q, where human AQP4 (18q11.2-12.1) is located nearby. A case-control study was performed which comprised 261 schizophrenia subjects and 278 controls from the Japanese population with four SNP markers. We found strong linkage disequilibrium (LD) and an LD block in the AQP4 gene but found no association between AQP4 and schizophrenia, both single SNP and haplotype analyses. The present study shows that AQP4 is not directly associated with schizophrenia in these Japanese patients.     

SLC25A12 expression is associated with neurite outgrowth and is upregulated in the prefrontal cortex of autistic subjects

Autism is a neurodevelopmental disorder with a strong genetic component, probably involving several genes. Genome screens have provided evidence of linkage to chromosome 2q31-q33, which includes the SLC25A12 gene. Association between autism and single-nucleotide polymorphisms in SLC25A12 has been reported in various studies. SLC25A12 encodes the mitochondrial aspartate/glutamate carrier functionally important in neurons with high-metabolic activity. Neuropathological findings and functional abnormalities in autism have been reported for Brodmann's area (BA) 46 and the cerebellum. We found that SLC25A12 was expressed more strongly in the post-mortem brain tissues of autistic subjects than in those of controls, in the BA46 prefrontal cortex but not in cerebellar granule cells. SLC25A12 expression was not modified in brain subregions of bipolar and schizophrenic patients. SLC25A12 was expressed in developing human neuronal tissues, including neocortical regions containing excitatory neurons and neocortical progenitors and the ganglionic eminences that generate neocortical inhibitory interneurons. At mid-gestation, when gyri and sulci start to develop, SLC25A12 molecular gradients were identified in the lateral prefrontal and ventral temporal cortex. These fetal structures generate regions with abnormal activity in autism, including the dorsolateral prefrontal cortex (BA46), the pars opercularis of the inferior frontal cortex and the fusiform gyrus. SLC25A12 overexpression or silencing in mouse embryonic cortical neurons also modified dendrite length and the mobility of dendritic mitochondria. Our findings suggest that SLC25A12 overexpression may be involved in the pathophysiology of autism, modifying neuronal networks in specific subregions, such as the dorsolateral prefrontal cortex and fusiform gyrus, at both pre- and postnatal stages.     

Identification of SLC25A37 as a major depressive disorder risk gene

Major depressive disorder (MDD) is one of the most prevalent and disabling mental disorders, but the genetic etiology remains largely unknown. We performed a meta-analysis (14,543 MDD cases and 14,856 controls) through combining the GWAS data from the Major Depressive Disorder Working Group of the Psychiatric GWAS Consortium and the CONVERGE consortium and identified seven SNPs (four of them located in the downstream of SCL25A37) that showed suggestive associations (P < 5.0 × 10⁻⁷) with MDD. Systematic integration (Sherlock integrative analysis) of brain eQTL and GWAS meta-analysis identified SCL25A37 as a novel MDD risk gene (P = 2.22 × 10⁻⁶). A cis SNP (rs6983724, ∼28 kb downstream of SCL25A37) showed significant association with SCL25A37 expression (P = 1.19 × 10⁻⁹) and suggestive association with MDD (P = 1.65 × 10⁻⁷). We validated the significant association between rs6983724 and SCL25A37 expression in independent expression datasets. Finally, we found that SCL25A37 is significantly down-regulated in hippocampus and blood of MDD patients (P = 3.49 × 10⁻³ and P = 2.66 × 10⁻¹³, respectively). Our findings implicate that the SCL25A37 is a MDD susceptibility gene whose expression may influence MDD risk. The consistent down-regulation of SCL25A37 in MDD patients in three independent samples suggest that SCL25A37 may be used as a potential biomarker for MDD diagnosis. Further functional characterization of SCL25A37 may provide a potential target for future therapeutics and diagnostics.