Genetic Variants of the MTMR9 Gene Are Associated with Nonspecific Intellectual Disability: A Family-Based Association Study.

Background: Mutations within the myotubularin-related protein 9 gene (MTMR9) have been identified in several families with nonsyndromic intellectual disability (NSID), a generalized neurodevelopmental disorder; however, the relationship between MTMR9 and NSID needs to be verified using a larger sample size. Aim: To explore whether genetic variants in the MTMR9 gene are linked to susceptibility of NSID among the Chinese population. Materials and Methods: Seven single nucleotide polymorphisms (SNPs) of the MTMR9 gene (rs4559208, rs3824211, rs2164272, rs2164273, rs1897951, rs6991606, and rs7815802) were analyzed using family-based association testing among 258 Han Chinese NSID families. Results: Three SNPs of MTMR9 were significantly associated with NSID (z = 2.152, p = 0.031 for rs4559208; z = 2.403, p = 0.016 for rs2164273; and z = 2.758, p = 0.006 for rs7815802). Three alleles of these SNPs were more likely to be transferred from the carrier parents to the affected offspring. Haplotypes constructed using these SNPs also showed a similar transmitting trend (z = 2.505, p = 0.012, χ2(3) = 8.835, and global p = 0.032). Carriers with the G-G-C haplotype showed a higher risk of NSID (odds ratio = 1.46, 95% confidence interval [1.01-2.09], p = 0.04) than others. In silico functional predictions supported an etiological role for these three SNPs in NSID biology. Conclusions: This study provides additional insights into the association of NSID with specific alleles, and haplotypes within the MTMR9 gene. Genotypic analyses of the MTMR9 gene should be considered for patients presenting with NSID of unknown etiology.

Mutations of ARX and non-syndromic intellectual disability in Chinese population.

Mutations of Aristaless-related homeobox (ARX) gene were looked as the third cause of non-syndromic intellectual disability (NSID), while the boundary between true disease-causing mutations and non-disease-causing variants within this gene remains elusive. To investigate the relationship between ARX mutations and NSID, a panel comprising six reported causal mutations of the ARX was detected in 369 sporadic NSID patients and 550 random participants in Chinese. Two mutations, c.428_451 dup and p.G286S, may be disease-causing mutations for NSID, while p.Q163R and p.P353L showed a great predictive value in female NSID diagnosis with significant associations (X2 = 19.60, p = 9.54e-6 for p.Q163R; X2 = 25.70, p = 4.00e-07 for p.P353L), carriers of these mutations had an increased risk of NSID of more than fourfold. Detection of this panel also predicted significant associations between genetic variants of the ARX gene and NSID (p = 3.73e-4). The present study emphasized the higher genetic burden of the ARX gene on NSID in the Chinese population, molecular analysis of this gene should be considered for patients presenting NSID of unknown etiology.

Combined metabolomic and correlation networks analyses reveal fumarase insufficiency altered amino acid metabolism.

Fumarase catalyzes the interconversion of fumarate and l-malate in the tricarboxylic acid cycle. Fumarase insufficiencies were associated with increased levels of fumarate, decreased levels of malate and exacerbated salt-induced hypertension. To gain insights into the metabolism profiles induced by fumarase insufficiency and identify key regulatory metabolites, we applied a GC-MS based metabolomics platform coupled with a network approach to analyze fumarase insufficient human umbilical vein endothelial cells (HUVEC) and negative controls. A total of 24 altered metabolites involved in seven metabolic pathways were identified as significantly altered, and enriched for the biological module of amino acids metabolism. In addition, Pearson correlation network analysis revealed that fumaric acid, l-malic acid, l-aspartic acid, glycine and l-glutamic acid were hub metabolites according to Pagerank based on their three centrality indices. Alanine aminotransferase and glutamate dehydrogenase activities increased significantly in fumarase deficiency HUVEC. These results confirmed that fumarase insufficiency altered amino acid metabolism. The combination of metabolomics and network methods would provide another perspective on expounding the molecular mechanism at metabolomics level.

Malate and Aspartate Increase L-Arginine and Nitric Oxide and Attenuate Hypertension.

Fumarase catalyzes the interconversion of fumarate and L-malate in the tricarboxylic acid cycle. The Dahl salt-sensitive (SS) rat, a model of salt-sensitive hypertension, exhibits fumarase insufficiencies. To investigate the mechanism mediating the effect of fumarase-related metabolites on hypertension, we considered the pathway in which L-malate can be converted to oxaloacetate, aspartate, argininosuccinate, and L-arginine, the substrate of nitric oxide (NO) synthase. The levels of aspartate, citrulline, L-arginine, and NO were significantly decreased in the kidneys of SS rats compared to salt-insensitive consomic SS.13BN rats. Knockdown of fumarase in human kidney cells and vascular endothelial cells resulted in decreased levels of malate, aspartate, L-arginine, and NO. Supplementation of aspartate or malate increased renal levels of L-arginine and NO and attenuated hypertension in SS rats. These findings reveal a multi-step metabolic pathway important for hypertension in which malate and aspartate may modulate blood pressure by altering levels of L-arginine and NO.

Genetic Polymorphism of GABRR2 Modulates Individuals' General Cognitive Ability in Healthy Chinese Han People.

Previous studies have indicated that the cognitive impairment or deficit is associated with GABAergic signaling in central nervous system. Inspired by the finding that receptor GABRR2 modulates concentration of GABA and phasic inhibitory GABAergic transmission in brain. This study investigated to what extent a genetic variant (c.1423C>T, rs282129) of GABRR2 gene modulates individuals' general cognitive ability in 987 Chinese Han people. Results showed a significant influence of GABRR2 gene polymorphism on individuals' Raven's Standard Progressive Matrices (RSPM) performance (F = 3.58, P = .028 by ANOVA and χ 2 = 9.35, P = .009 by K-W test, respectively), even if non-genetic factors were partialed out (gender, major, types of birthplace, and socioeconomic index) (B = -.67, SE = .26, t = 2.63, P = .009). The finding provided a strong evidence, to our knowledge, for the view that genetic variant of GABRR2 gene may contribute to the difference of individuals' general cognitive ability, independently.

Polymorphic variation in CHAT gene modulates general cognitive ability: An association study with random student cohort.

The choline O-acetyltransferase (CHAT) gene has been associated with various human disorders that involve cognitive impairment or deficiency. However, the influence of disease-associated variants of CHAT on normal individuals remains dubious. Here we demonstrated the impact of CHAT sequence variants (G-120A) on general human cognitive ability in a cohort of 750 Chinese undergraduate students. A multiple choice questionnaire was used to obtain basic demographic information, such as parents' occupations and education levels. We also administered and scored the Raven's Standard Progressive Matrices (RSPM). A one-way analysis of variance (ANOVA) and Kruskal-Wallis test (K-W) revealed a significant association between sequence polymorphisms of G-120A and individuals' Raven score (p=0.031 for ANOVA and p=0.026 for K-W tests). Moreover, further hierarchical analysis showed a similar trend in the association between G-120A variants and Raven scores only in the female subjects (p=0.008 for ANOVA and p=0.024 for K-W tests) but not in the male subjects. The results of a multiple linear regression confirmed that after we controlled gender, age, birthplace and other non-genetic factors, CHAT G-120A polymorphisms still significantly influenced individual Raven scores (B=-0.70, SE=0.28, t=-2.50, p=0.013). Our results demonstrated that sequence variants of CHAT were associated with human cognitive ability in not only patients with psychiatric disorders but also normal healthy individuals. However, some issues remained indeterminable, such as gender differences and the extent of the influence on individuals' general cognitive abilities; thus, the further research using an independent random sample was required.

A New Role for LOC101928437 in Non-Syndromic Intellectual Disability: Findings from a Family-Based Association Test.

Non-syndromic intellectual disability (NSID) is mental retardation in persons of normal physical appearance who have no recognisable features apart from obvious deficits in intellectual functioning and adaptive ability; however, its genetic etiology of most patients has remained unknown. The main purpose of this study was to fine map and identify specific causal gene(s) by genotyping a NSID family cohort using a panel of markers encompassing a target region reported in a previous work. A total of 139 families including probands, parents and relatives were included in the household survey, clinical examinations and intelligence tests, recruited from the Qinba mountain region of Shannxi province, western China. A collection of 34 tagged single nucleotide polymorphisms (tSNPs) spanning five microsatellite marker (STR) loci were genotyped using an iPLEX Gold assay. The association between tSNPs and patients was analyzed by family-based association testing (FBAT) and haplotype analysis (HBAT). Four markers (rs5974392, rs12164331, rs5929554 and rs3116911) in a block that showed strong linkage disequilibrium within the first three introns of the LOC101928437 locus were found to be significantly associated with NSID (all P<0.01) by the FBAT method for a single marker in additive, dominant and recessive models. The results of haplotype tests of this block also revealed a significant association with NSID (all P<0.05) using 2-window and larger HBAT analyses. These results suggest that LOC101928437 is a novel candidate gene for NSID in Han Chinese individuals of the Qinba region of China. Although the biological function of the gene has not been well studied, knowledge about this gene will provide insights that will increase our understanding of NSID development.

Association between ε2/3/4, promoter polymorphism (-491A/T, -427T/C, and -219T/G) at the apolipoprotein E gene, and mental retardation in children from an iodine deficiency area, China.

BACKGROUND: Several common single-nucleotide polymorphisms (SNPs) at apolipoprotein E (ApoE) have been linked with late onset sporadic Alzheimer's disease and declining normative cognitive ability in elder people, but we are unclear about their relationship with cognition in children. RESULTS: We studied -491A/T, -427T/C, and -219G/T promoter polymorphisms and ε2/ε3/ε4 at ApoE among children with mental retardation (MR, n = 130), borderline MR (n = 124), and controls (n = 334) from an iodine deficiency area in China. The allelic and genotypic distribution of individual locus did not significantly differ among three groups with Mantel-Haenszel χ (2) test (P > 0.05). However, frequencies of haplotype of -491A/-427T/-219T/ε4 were distributed as MR > borderline MR > controls (P uncorrected = 0.004), indicating that the presence of this haplotype may increase the risk of disease. CONCLUSIONS: In this large population-based study in children, we did not find any significant association between single locus of the four common ApoE polymorphisms (-491A/T, -427T/C, -219T/G, and ε2/3/4) and MR or borderline MR. However, we found that the presence of ATTε4 haplotype was associated with an increased risk of MR and borderline MR. Our present work may help enlarge our knowledge of the cognitive role of ApoE across the lifespan and the mechanisms of human cognition.

Genetic variations in COMT and DRD2 modulate attentional bias for affective facial expressions.

Studies have revealed that catechol-O-methyltransferase (COMT) and dopaminegic receptor2 (DRD2) modulate human attention bias for palatable food or tobacco. However, the existing evidence about the modulations of COMT and DRD2 on attentional bias for facial expressions was still limited. In the study, 650 college students were genotyped with regard to COMT Val158Met and DRD2 TaqI A polymorphisms, and the attentional bias for facial expressions was assessed using the spatial cueing task. The results indicated that COMT Val158Met underpinned the individual difference in attentional bias for negative emotional expressions (P = 0.03) and the Met carriers showed more engagement bias for negative expressions than the Val/Val homozygote. On the contrary, DRD2 TaqIA underpinned the individual difference in attentional bias for positive expressions (P = 0.003) and individuals with TT genotype showed much more engagement bias for positive expressions than the individuals with CC genotype. Moreover, the two genes exerted significant interactions on the engagements for negative and positive expressions (P = 0.046, P = 0.005). These findings suggest that the individual differences in the attentional bias for emotional expressions are partially underpinned by the genetic polymorphisms in COMT and DRD2.

Effect of Val66Met polymorphism in BDNF on attentional bias in an extroverted Chinese Han population.

Studies have indicated that a functional polymorphism (Val66Met) in a brain-derived neurotrophic factor (BDNF) gene can influences human cognitive functions and mood disorders. In this study, we examined associations of BDNF Val66Met with attentional bias and personality in an unaffected population. The results showed that BDNF Val66Met was significantly associated with attentional disengagement for positive cueing words in extraverts. Moreover, there was a positive correlation between the dosages of Met allele and attentional disengagement, however, we did not observe any significant influences of BDNF Val66Met on personality traits. These preliminary results indicate that the individual differences in attentional bias for positive words are partially underpinned by BDNF.

The effects of DBH, MAOA, and MAOB on attentional biases for facial expressions.

Attentional bias is the interaction that occurs between emotion and attention. Monoamine oxidase and dopamine ß-hydroxylase are involved in the balances of neurotransmitters in the cortex. Much evidence has shown that those enzymes play important roles in human emotion and attention. To investigate the potential influences of some functional polymorphisms in DBH, MAOA, and MAOB on attentional bias, we performed a population-based study in a young Chinese Han group. The results indicated that -1021C/T in DBH was associated with index effect of the neutral facial expressions in spatial cueing task (F = 4.940, P = 0.007), and there was a positive correlation between the dosage of C allele and the index effect (r = 0.068, P = 0.040). Furthermore, we found significant interactions between 19-bp Ins/Del in DBH and VNTR of MAOA on attentional biases for negative expressions in spatial cueing task (F = 3.397, P = 0.009) and dot-probe task (F = 2.827, P = 0.024). The present study suggests that DBH and MAOA can influence human attentional biases, and there is a gene-gene interaction between the DBH and MAOA on attentional bias for negative expressions.

A family-based association study of dopamine receptor D4 and mental retardation in Qinba region of China.

Dopamine receptor D4 (DRD4) is activated by the neurotransmitter dopamine and links to many neurological and psychiatric conditions because of its close relationship with prefrontal cortex and other important brain regions. To explore the possibility that genetic variants of DRD4 gene predispose to children with mental retardation (MR), five target SNPs of DRD4 were selected and genotyped in the samples of 163 MR pedigrees from the Qinba region of China. Two SNPs (rs752306 and rs3758653) showed weak association with MR (the P values were 0.022 and 0.015 for dominant model, and 0.027 and 0.015 for recessive model, respectively). Although they did not bear the multiple testing corrections, the haplotype which contained rs3758653 exhibited a significant association with MR (global P values were 0.018 for dominant model and 0.028 for recessive model, respectively). The in silico analysis also indicated that rs752306 and rs3758653 would be biologically meaningful SNPs. Therefore, the present study suggested that the genetic variants of DRD4 gene may play an important role in human MR. Further investigations, such as confirmation with other independent samples and functional studies, may elucidate their effect on gene expression and MR susceptibility.

An association study on the polymorphisms of dopaminergic genes with working memory in a healthy Chinese Han population.

Working memory (WM) is a highly heritable cognitive trait that is involved in many higher-level cognitive functions. In the past few years, much evidence has indicated that the reduction of dopamine activity in human brain can impair the WM system of the neuropsychiatric disorders. In this study, we hypothesized that some genes in the dopamine system were involved in the individual difference of the cognitive ability in healthy population. To confirm this hypothesis, a population-based study was performed to examine the effects of COMT, DAT (1), DRD (1), DRD (2), DRD (3), and DRD (4) on WM spans. Our results indicated there were significant associations of TaqIA and TaqIB in DRD (2) with digital WM span, respectively (χ(2) = 9.460, p = 0.009; χ(2) = 6.845, p = 0.033). On the other hand, we found a significant interaction between Ser9Gly in DRD (3) and TaqIA of DRD (2) on digital WM span (F = 3.207, p = 0.013). COMT, DAT (1) , DRD (1), and DRD (4), however, had no significant effects on digital and spatial WM spans (χ(2)<3.84, p > 0.05). These preliminary results further indicated that certain functional variants in dopamine system, such as TaqIA and TaqIB of DRD (2), were possibly involved in difference of WM in a healthy population.

A family-based association study of DIO2 and children mental retardation in the Qinba region of China.

Deiodinase enzyme II (DIO2) has an important role in individuals' thyroid hormones' level, the development of central and peripheral nervous systems and characterized by mental retardation (MR). The DIO2 gene was genotyped by using five haplotype-tagging single-nucleotide polymorphisms (SNPs) in 157 Chinese MR high-density family pedigrees, including 452 nuclear families and >1460 persons. The single marker and haplotype analyses were performed by Family-based Association Tests (FBAT). Three SNPs had P-values <0.05 in at least one inherited model survived with the correction. Several haplotypes composed of these SNPs were also associated with MR. The in silico analyses identified that one of the SNPs, rs1388378, may be a functional SNP. However, further in vitro studies of this SNP should be considered in elucidating its effect on gene expression and the possible role in MR susceptibility.

Positive association of CC2D1A and CC2D2A gene haplotypes with mental retardation in a Han Chinese population.

The CC2D1A and CC2D2A genes are involved in Ca(2+)-regulated signaling pathways and have recently been implicated in the etiology of mental retardation (MR). The aim of this study was to investigate whether CC2D1A and CC2D2A polymorphisms are associated with susceptibility to MR in a Han Chinese population using a family based association approach. The sample included 172 trios (parents and offspring), and all subjects were genotyped for several single-nucleotide polymorphisms covering CC2D1A and CC2D2A. Linkage disequilibrium (LD) analysis revealed that the rs6511901 and rs10410239 polymorphisms of CC2D1A were in strong LD (D'=0.865), and haplotype analysis showed evidence for over-transmission from parents to MR offspring (p=0.0009). The LD analysis also revealed that CC2D2A single-nucleotide polymorphisms rs10025837, rs13116304, and rs7661102 were in strong LD (D'=0.848), and haplotype analysis showed significant transmission disequilibrium (p=0.0004). The results suggest the involvement of CC2D1A and CC2D2A in MR in the Han Chinese population, and some specific haplotypes may be susceptible or protective.

An association study of the genetic polymorphisms in 13 neural plasticity-related genes with semantic and episodic memories.

Semantic and episodic memories were two different attributes of long-term memory. In the past few years, plenty of physiological evidence has indicated that neural plasticity is involved in the formation of long-term memory. In the present study, we hypothesized that some functional variants of neural plasticity-related genes were related to episodic and semantic memories. To confirm this hypothesis, we examined the relationship of 13 plasticity-related genes with episodic and semantic memories. The results indicated that there was a statistically significant difference in semantic memory scores among the three genotype groups of T267C in 5-HT ( 6 ) (χ (2) = 16.638, p = 0.0002). However, the functional variations in BDNF, COMT, DBH, DRD ( 2 ), DRD ( 3 ), DRD ( 4 ), MAOA, TPH ( 2 ), 5-HT ( 2A ), GRM ( 1 ), and GRIN2B had no observable effects on the memories. Our preliminary results confirm the hypothesis that a small number of functional variants of the neural plasticity-related genes, such as T267C in 5-HT ( 6 ), play important roles in human specific memory.

Variants in COMT and DBH influence on response inhibition ability in Chinese Han females.

Catechol-O-methyltransferase (COMT) and dopamine-beta hydroxylase (DBH) are key enzymes to breakdown dopamine. Some previous studies have indicated that val158met in COMT and 19 bp insertion/deletion in 5' flank of DBH are related to the performance of executive function. To further investigate the associations of the two genes with executive function, we performed a population-based study in a Chinese Han population. The results indicated that val158met in COMT and the 19 bp insertion/deletion of DBH were associated with the average reaction time of response inhibition in female group (P = 0.01, P = 0.03), respectively. Furthermore, there was a significant interaction of the two genes on the reaction time (P = 0.006). This present study suggests that not only do COMT and DBH influence independently on response inhibition in females, but also exert a significant interaction on response inhibition.

Association analysis of TPH2, 5-HT2A, and 5-HT6 with executive function in a young Chinese Han population.

The 5-hydroxytryptamine (5-HT) system is widely distributed in the central nervous system. A growing body of evidence has suggested that the neurotransmitter system is implicated in the functions of the prefrontal cortex. So far, several studies have revealed that some functional genetic variants in TPH2, 5-HT2A, and 5-HT6 genes are possibly related to executive function. To investigate the potential influences of TPH2, 5-HT2A, and 5-HT6 on the components of executive function, the authors performed a population-based study with standard cognitive paradigms in a young Chinese Han group. The results indicated that -703 G/T polymorphism of TPH2 was associated with the performance of response inhibition (p = .002) and the T allele carriers (TT and GT) had fewer errors than the noncarriers (GG) did in the response inhibition test. Furthermore, there were no significant associations of the T102C in 5-HT2A and T267C in 5-HT6 with the components of executive function after correcting for multiple tests (p > .05). The present study suggests that TPH2 contributes distinctively to the inhibition domain of executive function, whereas 5-HT2A and 5-HT6 show no striking effects on executive function in the Chinese Han population.

Polymorphisms in the DLG3 gene is not associated with non-syndromic mental retardation in the Chinese Han population of Qin-Ba mountain.

Discs-large-related 3 (DLG3), a member of the membrane-associated guanylate kinases (MAGUKs) protein family, playing an important role in regulating NMDA signal pathway and contributing to synaptic plasticity, may have an influence on the susceptibility of non-syndromic mental retardation (NSMR). To investigate the possible genetic contribution of DLG3 gene to the NSMR of Chinese Han population, we performed an association study of 556 subjects (118 NSMR, 116 borderline NSMR, and 322 controls in 275 males and 281 females) from Qin-Ba mountain region of Shaanxi province in the northwest of China by five common SNPs in the gene. The results showed that there was no positive association between the genetic variations of DLG3 and NSMR. In conclusion, the results of this study indicated that DLG3 did not associate with NSMR in Chinese Han population; however, further studies are needed.