Association study for genes at chromosome 5p13-q11 in attention deficit hyperactivity disorder

Common and specific genes and peripheral biomarkers in children and adults with attention-deficit/hyperactivity disorder

OBJECTIVES

Elucidating the biological mechanisms involved in attention-deficit/hyperactivity disorder (ADHD) has been challenging. Relatively unexplored is the fact that these mechanisms can differ with age.

METHODS

We present an overview on the major differences between children and adults with ADHD, describing several studies from genomics to metabolomics performed in ADHD children and in adults (cADHD and aADHD, respectively). A systematic search (up until February 2016) was conducted.

RESULTS

From a PRISMA flow-chart, a total of 350 and 91 genomics and metabolomics studies were found to be elligible for cADHD and aADHD, respectively. For children, associations were found for genes belonging to dopaminergic (SLC6A3, DRD4 and MAOA) and neurodevelopmental (LPHN3 and DIRAS2) systems and OPRM1 (Yates corrected P = 0.016; OR = 2.27 95%CI: 1.15-4.47). Studies of adults have implicated circadian rhythms genes, HTR2A, MAOB and a more generic neurodevelopmental/neurite outgrowth network (BCHE, SNAP25, BAIAP2, NOS1/NO, KCNIP4 and SPOCK3; Yates corrected P = 0.007; OR = 3.30 95%CI: 1.33-8.29). In common among cADHD and aADHD, the most significant findings are for oxidative stress proteins (MAD, SOD, PON1, ARES, TOS, TAS and OSI), and, in the second level, DISC1, DBH, DDC, microRNA and adiponectin.

CONCLUSIONS

Through a convergent functional genomics, this review contributes to clarification of which genetic/biological mechanisms differ with age. The effects of some genes do not change throughout the lifetime, whereas others are linked to age-specific stages. Additional research and further studies are needed to generate firmer conclusions that might someday be useful for predicting the remission and persistence of the disorder. Despite the limitations, some of these genes/proteins could be potential useful biomarkers to discriminate cADHD from aADHD.

The SNP-set based association study identifies ITGA1 as a susceptibility gene of attention-deficit/hyperactivity disorder in Han Chinese

Genome-wide association studies, which detect the association between single-nucleotide polymorphisms (SNPs) and disease susceptibility, have been extensively applied to study attention-deficit/hyperactivity disorder (ADHD), but genome-wide significant associations have not been found yet. Genetic heterogeneity and insufficient genomic coverage may account for the missing heritability. We performed a two-stage association study for ADHD in the Han Chinese population. In the discovery stage, 1033 ADHD patients and 950 healthy controls were genotyped using both the Affymetrix Genome-Wide Human SNP Array 6.0 and the Illumina Infinium HumanExome BeadChip. The genotyped SNPs were combined to generate a powerful SNP set with better genomic coverage especially for the nonsynonymous variants. In addition to the association of single SNPs, we collected adjacent SNPs as SNP sets, which were determined by either genes or successive sliding windows, to evaluate their synergetic effect. The candidate susceptibility SNPs were further replicated in an independent cohort of 1441 ADHD patients and 1447 healthy controls. No genome-wide significant SNPs or gene-based SNP sets were found to be associated with ADHD. However, two continuous sliding windows located in ITGA1 (P-value=8.33E-7 and P-value=8.43E-7) were genome-wide significant. The quantitative trait analyses also demonstrated their association with ADHD core symptoms and executive functions. The association was further validated by follow-up replications for four selected SNPs: rs1979398 (P-value=2.64E-6), rs16880453 (P-value=3.58E-4), rs1531545 (P-value=7.62E-4) and rs4074793 (P-value=2.03E-4). Our results suggest that genetic variants in ITGA1 may be involved in the etiology of ADHD and the SNP-set based analysis is a promising strategy for the detection of underlying genetic risk factors.

Association between smoking behaviour and genetic variants of glial cell line-derived neurotrophic factor

Glial cell line-derived neurotrophic factor (GDNF) promotes development and differentiation of dopaminergic neurons, thus it has an important role in dopamine-related neuropsychiatric disorders. Since the role of dopamine system in smoking is well established, we hypothesized that GDNF gene variants may affect smoking behaviour. Self-reported data on smoking behaviour (never smoked, quit, occasional, or regular smokers) and level of nicotine addiction (Hooked on Nicotine Checklist and Fagerstrom Nicotine Addiction Scale), anxiety, as well as buccal samples were obtained from 930 Hungarian young adults (18-35 years). Genetic analysis involved eight GDNF single-nucleotide polymorphisms (SNP) (rs1981844, rs3812047, rs3096140, rs2973041, rs2910702, rs1549250, rs2973050 and rs11111). Allele-wise association analyses of the eight GDNF SNPs provided a significant association between smoking behaviour and rs3096140 (P=0.0039). The minor allele (C) was more frequent in those groups who smoked in some form (quit, occasional or regular smokers) as compared to those who never smoked (P = 0.0046). This result remained significant after Bonferroni correction for multiple testing. In the ever smoking group, no significant differences were found in the level of nicotine addiction by the alleles of these polymorphisms. Also, no significant interaction of rs3096140 and smoking categories were observed on anxiety mean scores. Although previous data demonstrated an association between GDNF rs2910704 and severity of methamphetamine use to the best of our knowledge, this is the first study on the role of GDNF genetic variations in smoking behaviour. Our results suggest that GDNF rs3096140 might be involved in the genetic background of smoking, independent of anxiety characteristics.

Serum brain-derived neurotrophic factor, glial-derived neurotrophic factor, nerve growth factor, and neurotrophin-3 levels in children with attention-deficit/hyperactivity disorder

It has been suggested that neurotrophins are involved in the etiopathogenesis of attention-deficit/hyperactivity disorder (ADHD). This study aimed to investigate whether there are differences in serum brain-derived neurotrophic factor (BDNF), glial-derived neurotrophic factor (GDNF), nerve growth factor (NGF), and neurotrophin-3 (NTF3) levels between children with ADHD and healthy controls. A total of 110 treatment-naive children with the combined presentation of ADHD and 44 healthy controls aged 8-18 years were enrolled in this study. The severity of ADHD symptoms was determined by scores on the Conners' Parent Rating Scale-Revised Short and Conners' Teacher Rating Scale-Revised Short. The severity of depression and anxiety symptoms of the children were evaluated by the self-report inventories. Serum levels of neurotrophins were measured using commercial enzyme-linked immunosorbent assay kits. The multivariate analysis of covariance (MANCOVA) revealed a significant main effect of groups in the levels of serum neurotrophins, an effect that was independent of age, sex, and the severity of the depression and anxiety. The analysis of covariance (ANCOVA) indicated that the mean serum GDNF and NTF3 levels of ADHD patients were significantly higher than that of controls. However, serum BDNF and NGF levels did not show any significant differences between groups. No correlations between the levels of serum neurotrophins and the severity of ADHD were observed. These results suggest that elevated serum GDNF and NTF3 levels may be related to ADHD in children.

Duplications of SLC1A3: Associated with ADHD and autism

We report four patients with a similar gain in 5p13.2 encompassing a single gene: SLC1A3. Behavioural problems resembling ADHD and/or autism-like features are observed which is in line with the glial glutamate transporter role of SLC1A3. We consider an association between SLC1A3 and the behavioural problems which can also be considered a contributing factor to behavioural problems in larger duplications overlapping the 5p13 microduplication syndrome region.

A genome-wide association study reveals susceptibility loci for myocardial infarction/coronary artery disease in Saudi Arabs

BACKGROUND

Multiple loci have been identified for coronary artery disease (CAD) by genome-wide association studies (GWAS), but no such studies on CAD incidence has been reported yet for any Middle Eastern population.

METHODS

In this study, we performed a GWAS for CAD and myocardial infarction (MI) incidence in 5668 Saudis of Arab descent using the Affymetrix Axiom Genotyping platform.

RESULTS

We describe SNPs at 16 loci that showed significant (P < 5 × 10(-8)) or suggestive GWAS association (P < 1 × 10(-5)) with CAD or MI, in the ethnic Saudi Arab population. Among the four variants reaching GWAS significance in the present study, the rs10738607_G [0.78(0.71-0.85); p = 2.17E-08] in CDNK2A/B gene was associated with CAD. Two other SNPs on the same gene, rs10757274_G [0.79(0.73-0.86); p = 2.98E-08] and rs1333045_C [0.79(0.73-0.86); p = 1.15E-08] as well as the rs9982601_T [1.38(1.23-1.55); p = 3.49E-08] on KCNE2 were associated with MI. These variants have been previously described in other populations. Several SNPs, including the rs7421388 (PLCL1) and rs12541758 (TRPA1) displaying a suggestive GWAS association (P < 1 × 10(-5)) with CAD as well as rs41411047 (RNF13), rs32793 (PDZD2) and rs4739066 (YTHDF3), similarly showing weak association with MI, were confirmed in an independent dataset. Furthermore, our estimation of heritability of CAD and MI based on observed genome-wide sharing in unrelated Saudi Arabs was approximately 33% and 44%, respectively.

CONCLUSIONS

Our study has identified susceptibility variants for CAD/MI in ethnic Arabs. These findings provide further insights into pathways contributing to the susceptibility for CAD and will enable more comprehensive genetic studies of these diseases in Middle East populations.

DNA methylation changes in the placenta are associated with fetal manganese exposure

Adequate micronutrient intake, including manganese (Mn), is important for fetal development. Both Mn deficiencies and excess exposures are associated with later-life disease, and Mn accumulates in the placenta. Placental functional alterations may alter fetal programming and lifelong health, and we hypothesized that prenatal exposures to Mn may alter placental function through epigenetic mechanisms. Using Illumina's HumanMethylation450 BeadArray, DNA methylation of >485,000 CpG loci genome-wide was interrogated in 61 placental samples and Mn associations assessed genome-wide via omnibus test (p=0.045). 713 loci were associated with Mn exposure (p<0.0001). Five significantly differentially-methylated (p<1.3×10(-7)) loci reside in neurodevelopmental, fetal growth and cancer-related genes. cg22284422, within the uncharacterized LOC284276 gene, was associated with birth weight; for every 10% increase in methylation, lower birth weights were observed, with an average decrease of 293.44g. Our observations suggest a link between prenatal micronutrient levels, placental epigenetic status and birth weight, although these preliminary results require validation.

Glutamatergic modulatory therapy for Tourette syndrome

Tourette syndrome (TS) is a neuropsychiatric disorder characterized by the presence of chronic, fluctuating motor and vocal (phonic) tics. The disorder is commonly associated with a variety of comorbidities including obsessive-compulsive disorder (OCD), attention deficit hyperactivity disorder (ADHD), school problems, anxiety, and depression. Therapeutically, if tics are causing psychosocial or physical problems, symptomatic medications are often prescribed, typically alpha-adrenergic agonists or dopamine antagonists. Recognizing that therapy is often ineffective and frequently associated with unacceptable side-effects, there is an ongoing effort to identify new tic-suppressing therapies. Several lines of evidence are presented that support the use of glutamate modulators in TS including glutamate's major role in cortico-striatal-thalamo-cortical circuits (CSTC), the recognized extensive interaction between glutamate and dopamine systems, results of familial genetic studies, and data from neurochemical analyses of postmortem brain samples. Since insufficient data is available to determine whether TS is definitively associated with a hyper- or hypo-glutamatergic state, potential treatment options using either glutamate antagonists or agonists are reviewed. Data from studies using these agents in the treatment of OCD are presented. If validated, modulation of the glutamate system could provide a valuable new pharmacological approach in the treatment of tics associated with Tourette syndrome.