Kaya Kvarme Jacobsen

Genetic Analyses of Dopamine Related Genes in Adult ADHD Patients Suggest an Association With the DRD5-Microsatellite Repeat, But Not With DRD4 or SLC6A3 VNTRs

Attention deficit hyperactivity disorder (ADHD) is a common and highly heritable psychiatric disorder in children and adults. Recent meta‐analyses have indicated an association between genes involved in dopaminergic signaling and childhood ADHD, but little is known about their possible role in adult ADHD. In this study of adults with ADHD, we evaluated the three most commonly studied ADHD candidate genetic polymorphisms; the dopamine receptor D4 (DRD4) exon 3 VNTR repeat, a microsatellite repeat 18.5 kb upstream of the DRD5 locus and the 3′UTR dopamine transporter SLC6A3 (DAT 1) VNTR. We examined 358 clinically diagnosed adult Norwegian ADHD patients (51% males) and 340 ethnically matched controls. We found a nominally significant overall association with adult ADHD for the DRD5 microsatellite marker (P = 0.04), and a trend toward increased risk associated with the 148‐bp allele consistent with recent meta‐analyses. The strongest overall association (P = 0.02) and increased risk for the 148‐bp allele [odds ratio (OR) = 1.27 (95% CI: 1.00–1.61)] were seen in the inattentive and combined inattentive/hyperactive group as previously reported for childhood ADHD. No association was found for the DRD4 or SLC6A3 polymorphisms in this patient sample. In conclusion, our results among adults with a clinical diagnosis of ADHD support an association between ADHD and the DRD5 locus, but not the DRD4 or SLC6A3 loci. It is possible that the latter polymorphisms are associated with a transient form of ADHD with better long‐term clinical outcome.

An international multicenter association study of the serotonin transporter gene in persistent ADHD.

Attention deficit hyperactivity disorder (ADHD) is a common behavioral disorder affecting children and adults. It has been suggested that gene variants related to serotonin neurotransmission are associated with ADHD. We tested the functional promoter polymorphism 5‐HTTLPR and seven single nucleotide polymorphisms in SLC6A4 for association with ADHD in 448 adult ADHD patients and 580 controls from Norway. Replication attempts were performed in a sample of 1454 Caucasian adult ADHD patients and 1302 controls from Germany, Spain, the Netherlands and USA, and a meta‐analysis was performed also including a previously published adult ADHD study. We found an association between ADHD and rs140700 [odds ratio (OR ) = 0.67; P = 0.01] and the short (S) allele of the 5‐HTTLPR (OR = 1.19; P = 0.06) in the Norwegian sample. Analysis of a possible gender effect suggested that the association might be restricted to females (rs140700: OR = 0.45; P = 0.00084). However, the meta‐analysis of 1894 cases and 1878 controls could not confirm the association for rs140700 [OR = 0.85, 95% confidence interval (CI) = 0.67–1.09; P = 0.20]. For 5‐HTTLPR, five of six samples showed a slight overrepresentation of the S allele in patients, but meta‐analysis refuted a strong effect (OR = 1.10, 95% CI = 1.00–1.21; P = 0.06). Neither marker showed any evidence of differential effects for ADHD subtype, gender or symptoms of depression/anxiety. In conclusion, our results do not support a major role for SLC6A4 common variants in persistent ADHD, although a modest effect of the 5‐HTTLPR and a role for rare variants cannot be excluded.

A genome-wide association study of bipolar disorder and comorbid migraine.

Both migraine and bipolar affective disorder (BPAD) are complex phenotypes with significant genetic and nongenetic components. Epidemiological and clinical studies have showed a high degree of comorbidity between migraine and BPAD, and overlapping regions of linkage have been shown in numerous genome‐wide linkage studies. To identify susceptibility factors for the BPAD/migraine phenotype, we conducted a genome‐wide association study (GWAS) in 1001 cases with bipolar disorder collected through the NIMH Genetics Initiative for Bipolar Disorder and genotyped at 1 m single‐nucleotide polymorphisms (SNPs) as part of the Genetic Association Information Network (GAIN). We compared BPAD patients without any headache (n = 699) with BPAD patients with doctor diagnosed migraine (n = 56). The strongest evidence for association was found for several SNPs in a 317‐kb region encompassing the uncharacterized geneKIAA0564 {e.g. rs9566845 [OR = 4.98 (95% CI: 2.6–9.48), P = 7.7 × 10−8] and rs9566867 (P = 8.2 × 10−8)}. Although the level of signficance was significantly reduced when using the Fishers exact test (as a result of the low count of cases with migraine), rs9566845 P = 1.4 × 10−5 and rs9566867 P = 1.5 × 10−5, this region remained the most prominent finding. Furthermore, marker rs9566845 was genotyped and found associated with migraine in an independent Norwegian sample of adult attention deficit hyperactivity disorder (ADHD) patients with and without comorbid migraine (n = 131 and n = 324, respectively), OR = 2.42 (1.18–4.97), P = 0.013. This is the first GWAS examining patients with bipolar disorder and comorbid migraine. These data suggest that genetic variants in the KIAA0564 gene region may predispose to migraine headaches in subgroups of patients with both BPAD and ADHD.

Case-Control Genome-Wide Association Study of Persistent Attention-Deficit Hyperactivity Disorder Identifies FBXO33 as a Novel Susceptibility Gene for the Disorder

Attention-deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder with high heritability. At least 30% of patients diagnosed in childhood continue to suffer from ADHD during adulthood and genetic risk factors may play an essential role in the persistence of the disorder throughout lifespan. To date, genome-wide association studies (GWAS) of ADHD have been completed in seven independent datasets, six of which were pediatric samples and one on persistent ADHD using a DNA-pooling strategy, but none of them reported genome-wide significant associations. In an attempt to unravel novel genes for the persistence of ADHD into adulthood, we conducted the first two-stage GWAS in adults with ADHD. The discovery sample included 607 ADHD cases and 584 controls. Top signals were subsequently tested for replication in three independent follow-up samples of 2104 ADHD patients and 1901 controls. None of the findings exceeded the genome-wide threshold for significance (PGC<5e−08), but we found evidence for the involvement of the FBXO33 (F-box only protein 33) gene in combined ADHD in the discovery sample (P=9.02e−07) and in the joint analysis of both stages (P=9.7e−03). Additional evidence for a FBXO33 role in ADHD was found through gene-wise and pathway enrichment analyses in our genomic study. Risk alleles were associated with lower FBXO33 expression in lymphoblastoid cell lines and with reduced frontal gray matter volume in a sample of 1300 adult subjects. Our findings point for the first time at the ubiquitination machinery as a new disease mechanism for adult ADHD and establish a rationale for searching for additional risk variants in ubiquitination-related genes.

DIRAS2 is Associated with Adult ADHD, Related Traits, and Co-Morbid Disorders

Several linkage analyses implicated the chromosome 9q22 region in attention deficit/hyperactivity disorder (ADHD), a neurodevelopmental disease with remarkable persistence into adulthood. This locus contains the brain-expressed GTP-binding RAS-like 2 gene (DIRAS2) thought to regulate neurogenesis. As DIRAS2 is a positional and functional ADHD candidate gene, we conducted an association study in 600 patients suffering from adult ADHD (aADHD) and 420 controls. Replication samples consisted of 1035 aADHD patients and 1381 controls, as well as 166 families with a child affected from childhood ADHD. Given the high degree of co-morbidity with ADHD, we also investigated patients suffering from bipolar disorder (BD) (n=336) or personality disorders (PDs) (n=622). Twelve single-nucleotide polymorphisms (SNPs) covering the structural gene and the transcriptional control region of DIRAS2 were analyzed. Four SNPs and two haplotype blocks showed evidence of association with ADHD, with nominal p-values ranging from p=0.006 to p=0.05. In the adult replication samples, we obtained a consistent effect of rs1412005 and of a risk haplotype containing the promoter region (p=0.026). Meta-analysis resulted in a significant common OR of 1.12 (p=0.04) for rs1412005 and confirmed association with the promoter risk haplotype (OR=1.45, p=0.0003). Subsequent analysis in nuclear families with childhood ADHD again showed an association of the promoter haplotype block (p=0.02). rs1412005 also increased risk toward BD (p=0.026) and cluster B PD (p=0.031). Additional SNPs showed association with personality scores (p=0.008–0.048). Converging lines of evidence implicate genetic variance in the promoter region of DIRAS2 in the etiology of ADHD and co-morbid impulsive disorders.

Exploring DRD4 and its interaction with SLC6A3 as possible risk factors for adult ADHD: a meta-analysis in four European populations

Attention‐deficit hyperactivity disorder (ADHD) is a common behavioral disorder affecting about 4–8% of children. ADHD persists into adulthood in around 65% of cases, either as the full condition or in partial remission with persistence of symptoms. Pharmacological, animal and molecular genetic studies support a role for genes of the dopaminergic system in ADHD due to its essential role in motor control, cognition, emotion, and reward. Based on these data, we analyzed two functional polymorphisms within the DRD4 gene (120 bp duplication in the promoter and 48 bp VNTR in exon 3) in a clinical sample of 1,608 adult ADHD patients and 2,352 controls of Caucasian origin from four European countries that had been recruited in the context of the International Multicentre persistent ADHD CollaboraTion (IMpACT). Single‐marker analysis of the two polymorphisms did not reveal association with ADHD. In contrast, multiple‐marker meta‐analysis showed a nominal association (P = 0.02) of the L‐4R haplotype (dup120bp‐48bpVNTR) with adulthood ADHD, especially with the combined clinical subtype. Since we previously described association between adulthood ADHD and the dopamine transporter SLC6A3 9R‐6R haplotype (3′UTR VNTR‐intron 8 VNTR) in the same dataset, we further tested for gene × gene interaction between DRD4 and SLC6A3. However, we detected no epistatic effects but our results rather suggest additive effects of the DRD4 risk haplotype and the SLC6A3 gene.

Common variants in the TPH1 and TPH2 regions are not associated with persistent ADHD in a combined sample of 1,636 adult cases and 1,923 controls from four European populations†

The tryptophan hydroxylase 1 and 2 (TPH1 and TPH2) genes encode the rate‐limiting enzymes in the serotonin biosynthesis. Genetic variants in both genes have been implicated in several psychiatric disorders. For attention‐deficit/hyperactivity disorder (ADHD) in children, the results are conflicting, and little is known about their role in adult ADHD patients. We therefore first genotype‐tagged all common variants within both genes in a Norwegian sample of 451 patients with a diagnosis of adult ADHD and 584 controls. Six of the single nucleotide polymorphisms (SNPs) were subsequently genotyped in three additional independent European Caucasian samples of adult ADHD cases and controls from the International Multicenter persistent ADHD Collaboration (IMpACT). None of the SNPs reached formal study‐wide significance in the total meta‐analysis sample of 1,636 cases and 1,923 controls, despite having a power of >80% to detect a variant conferring an OR = 1.25 at P = 0.001 level. Only the TPH1 SNP rs17794760 showed nominal significance [OR = 0.84 (0.71–1.00), P = 0.05]. In conclusion, in the single largest ADHD genetic study of TPH1 and TPH2 variants presented to date (n = 3,559 individuals), we did not find consistent evidence for a substantial effect of common genetic variants on persistent ADHD.

DISC1 in Adult ADHD Patients: An Association Study in Two European Samples

The DISC1 gene was named after its discovery in a Scottish pedigree with schizophrenia (SCZ) patients. However, subsequent studies have shown association of DISC1 variants with a range of different neurocognitive phenotypes and psychiatric disorders, including bipolar disorder (BPD), and major depression. Attention‐deficit/hyperactivity disorder (ADHD) shares some symptoms with BPD and ADHD patients often suffer from comorbid affective disorders. We wanted to examine the role of DISC1 in ADHD, and with comorbid symptoms of mood disorders. Eleven single nucleotide polymorphisms (SNPs) previously implicated in SCZ and BPD, and a DISC1 duplication involving exon 1, were genotyped in 561 adult ADHD cases and 713 controls of Norwegian ancestry. The intronic SNP rs1538979 was associated with ADHD in the Norwegian sample [odds ratio (OR): 1.33, 95% confidence interval (CI) 1.03–1.73, P = 0.03] and replicated in a Spanish adult ADHD sample of 694 cases and 735 controls, using the tagging SNP rs11122330 (meta‐analysis: P = 0.008, OR 1.25, 95% CI 1.06–1.47). In the Norwegian ADHD sample we also observed an association between the Phe607‐variant of rs6675281 and a positive score on the Mood Disorder Questionnaire (MDQ; OR = 1.44, 95% CI 1.08–1.93, P = 0.01). To our knowledge, this is the first study to show an association between DISC1 variants and ADHD. Our study suggests that further studies are warranted to resolve if DISC1 variation is involved in several common neurodevelopmental disorders including ADHD.

Exome chip analyses in adult attention deficit hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is a highly heritable childhood-onset neuropsychiatric condition, often persisting into adulthood. The genetic architecture of ADHD, particularly in adults, is largely unknown. We performed an exome-wide scan of adult ADHD using the Illumina Human Exome Bead Chip, which interrogates over 250 000 common and rare variants. Participants were recruited by the International Multicenter persistent ADHD CollaboraTion (IMpACT). Statistical analyses were divided into 3 steps: (1) gene-level analysis of rare variants (minor allele frequency (MAF)<1%); (2) single marker association tests of common variants (MAF⩾1%), with replication of the top signals; and (3) pathway analyses. In total, 9365 individuals (1846 cases and 7519 controls) were examined. Replication of the most associated common variants was attempted in 9847 individuals (2077 cases and 7770 controls) using fixed-effects inverse variance meta-analysis. With a Bonferroni-corrected significance level of 1.82E−06, our analyses of rare coding variants revealed four study-wide significant loci: 6q22.1 locus (P=4.46E−08), where NT5DC1 and COL10A1 reside; the SEC23IP locus (P=6.47E−07); the PSD locus (P=7.58E−08) and ZCCHC4 locus (P=1.79E−06). No genome-wide significant association was observed among the common variants. The strongest signal was noted at rs9325032 in PPP2R2B (odds ratio=0.81, P=1.61E−05). Taken together, our data add to the growing evidence of general signal transduction molecules (NT5DC1, PSD, SEC23IP and ZCCHC4) having an important role in the etiology of ADHD. Although the biological implications of these findings need to be further explored, they highlight the possible role of cellular communication as a potential core component in the development of both adult and childhood forms of ADHD.

Epistatic and gene wide effects in YWHA and aromatic amino hydroxylase genes across ADHD and other common neuropsychiatric disorders: Association with YWHAE

Monoamines critically modulate neurophysiological functions affected in several neuropsychiatric disorders. We therefore examined genes encoding key enzymes of catecholamine and serotonin biosynthesis (tyrosine and tryptophan hydroxylases—TH and TPH1/2) as well as their regulatory 14‐3‐3 proteins (encoded by YWHA‐genes). Previous studies have focused mainly on the individual genes, but no analysis spanning this regulatory network has been reported. We explored interactions between these genes in Norwegian patients with adult attention deficit hyperactivity disorder (aADHD), followed by gene‐complex association tests in four major neuropsychiatric conditions; childhood ADHD (cADHD), bipolar disorder, schizophrenia, and major depressive disorder. For interaction analyses, we evaluated 55 SNPs across these genes in a sample of 583 aADHD patients and 637 controls. For the gene‐complex tests, we utilized the data from large‐scale studies of The Psychiatric Genomics Consortium (PGC). The four major neuropsychiatric disorders were examined for association with each of the genes individually as well as in three complexes as follows: (1) TPH1 and YWHA‐genes; (2) TH, TPH2 and YWHA‐genes; and (3) all genes together. The results show suggestive epistasis between YWHAE and two other 14‐3‐3‐genes ‐ YWHAZ, YWHAQ ‐ in aADHD (nominal P‐value of 0.0005 and 0.0008, respectively). In PGC data, association between YWHAE and schizophrenia was noted (P = 1.00E‐05), whereas the combination of TPH1 and YWHA‐genes revealed signs of association in cADHD, schizophrenia, and bipolar disorder. In conclusion, polymorphisms in the YWHA‐genes and their targets may exert a cumulative effect in ADHD and related neuropsychiatric conditions, warranting the need for further investigation of these gene‐complexes.