Noèlia Fernàndez-Castillo

Multicenter Analysis of the SLC6A3/DAT1 VNTR Haplotype in Persistent ADHD Suggests Differential Involvement of the Gene in Childhood and Persistent ADHD

Attention deficit/hyperactivity disorder (ADHD) is one of the most common neuropsychiatric disorders with a worldwide prevalence around 4–5% in children and 1–4% in adults. Although ADHD is highly heritable and familial risk may contribute most strongly to the persistent form of the disorder, there are few studies on the genetics of ADHD in adults. In this paper, we present the first results of the International Multicentre Persistent ADHD Genetics CollaboraTion (IMpACT) that has been set up with the goal of performing research into the genetics of persistent ADHD. In this study, we carried out a combined analysis as well as a meta-analysis of the association of the SLC6A3/DAT1 gene with persistent ADHD in 1440 patients and 1769 controls from IMpACT and an earlier report. DAT1, encoding the dopamine transporter, is one of the most frequently studied genes in ADHD, though results have been inconsistent. A variable number tandem repeat polymorphism (VNTR) in the 3′-untranslated region (UTR) of the gene and, more recently, a haplotype of this VNTR with another VNTR in intron 8 have been the target of most studies. Although the 10/10 genotype of the 3′-UTR VNTR and the 10-6 haplotype of the two VNTRs are thought to be risk factors for ADHD in children, we found the 9/9 genotype and the 9-6 haplotype associated with persistent ADHD. In conclusion, a differential association of DAT1 with ADHD in children and in adults might help explain the inconsistencies observed in earlier association studies. However, the data might also imply that DAT1 has a modulatory rather than causative role in ADHD.

Genetic analysis of 27 Spanish patients with hemiplegic migraine, basilar-type migraine and childhood periodic syndromes

Familial hemiplegic migraine (FHM) is a rare type of migraine with aura. Mutations in three genes have been described in FHM patients: CACNA1A (FHM1), ATP1A2 (FHM2) and SCN1A (FHM3). We screened 27 Spanish patients with hemiplegic migraine (HM), basilar-type migraine or childhood periodic syndromes (CPS) for mutations in these three genes. Two novel CACNA1A variants, p.Val581Met and p.Tyr1245Cys, and a previously annotated change, p.Cys1534Ser, were identified in individuals with HM, although they have not yet been proven to be pathogenic. Interestingly, p.Tyr1245Cys was detected in a patient displaying a changing, age-specific phenotype that began as benign paroxysmal torticollis of infancy, evolving into benign paroxysmal vertigo of childhood and later becoming HM. This is the first instance of a specific non-synonymous base change being described in a subject affected with CPS. The fact that the molecular screen identified non-synonymous changes in< 15± of our HM patients further stresses the genetic heterogeneity underlying the presumably monogenic forms of migraine.

The hemiplegic migraine-associated Y1245C mutation in CACNA1A results in a gain of channel function due to its effect on the voltage sensor and G-protein-mediated inhibition

Mutations in the gene encoding the pore-forming α1A subunit of P/Q Ca2+ channels (CACNA1A) are linked to familial hemiplegic migraine. CACNA1A Y1245C is the first missense mutation described in a subject affected with childhood periodic syndromes that evolved into hemiplegic migraine. Y1245C is also the first amino acid change described in any S1 segment of CACNA1A in a hemiplegic migraine background. We found that Y1245C induced a 9-mV left shift in the current–voltage activation curve, accelerated activation kinetics, and slowed deactivation kinetics within a wide range of voltage depolarizations. Y1245C also left-shifted the voltage-dependent steady-state inactivation with a significant increase in steepness, suggesting a direct effect on the P/Q channel voltage sensor. Moreover, Y1245C reduced Gβγ subunits-dependent channel inhibition probably by favoring Gβγ dissociation from the channel; an effect also observed using action-potential-like waveforms of different durations. The formation of a new disulfide bridge between cysteines may contribute to the Y1245C effects on activation and Gβγ inhibition of the channel, as they were significantly reversed by the sulphydryl-reducing agent dithiothreitol. Together, our data suggest that Y1245C alters the structure of the α1A voltage sensor producing an overall gain of channel function that may explain the observed clinical phenotypes.

Association study between the dat1 , dbh and drd2 genes and cocaine dependence in a Spanish sample

Drug addiction is a complex neuropsychiatric disorder involving the environmental and genetic factors. Genetic and physiological evidences suggest that the dopaminergic system may play an important role in cocaine abuse and dependence. Several association studies have focused on dopaminergic genes. We genotyped the Int8 and 3′UTR variable number of tandem repeats of the dopamine transporter gene (DAT1/SLC6A3), the TaqIA (rs1800497) and TaqIB (rs1079597) SNP polymorphisms within the dopamine receptor D2 gene and the 19-bp insertion/deletion and c.444G>A (rs1108580) polymorphisms of the dopamine β-hydroxylase gene (DBH) in a Spanish sample of 169 patients with cocaine addiction and 169 sex-matched controls. The case–control study showed a nominal overrepresentation of the 5R/5R genotype of the Int8 variable number of tandem repeats within DAT1 in cocaine abusers (P=0.016). However, no significant associations were detected when DAT1 haplotype frequencies or polymorphisms within the other dopaminergic genes were considered. Sample size is limited and further studies should be performed in a larger cohort.

Late-onset episodic ataxia type 2 associated with a novel loss-of-function mutation in the CACNA1A gene

We report a patient with typical features of episodic ataxia type 2 (EA2) but with onset in the sixth decade and associated interictal hand dystonia. He was found to bear the novel heterozygous missense mutation p.Gly638Asp (c.1913G>A) in the CACNA1A gene. Functional analysis of the mutation on P/Q channels expressed in HEK 293 cells revealed a reduction of Ca(2+) current densities, a left-shift in the apparent reversal potential, the slowing of inactivation kinetics and the increase in the rate of current recovery from inactivation. These results are consistent with a decrease in Ca(2+) permeability through mutant P/Q channels. To our knowledge, this is just the second patient with late onset EA2 linked to a CACNA1A mutation and the first to carry a loss-of-function missense mutation.

Association study of 37 genes related to serotonin and dopamine neurotransmission and neurotrophic factors in cocaine dependence

Cocaine dependence is a neuropsychiatric disorder in which both environmental and genetic factors are involved. Several processes, that include reward and neuroadaptations, mediate the transition from use to dependence. In this regard, dopamine and serotonin neurotransmission systems are clearly involved in reward and other cocaine‐related effects, whereas neurotrophic factors may be responsible for neuroadaptations associated with cocaine dependence. We examined the contribution to cocaine dependence of 37 genes related to the dopaminergic and serotoninergic systems, neurotrophic factors and their receptors through a case–control association study with 319 single nucleotide polymorphisms selected according to genetic coverage criteria in 432 cocaine‐dependent patients and 482 sex‐matched unrelated controls. Single marker analyses provided evidence for association of the serotonin receptor HTR2A with cocaine dependence [rs6561333; nominal P‐value adjusted for age = 1.9e−04, odds ratio = 1.72 (1.29–2.30)]. When patients were subdivided according to the presence or absence of psychotic symptoms, we confirmed the association between cocaine dependence and HTR2A in both subgroups of patients. Our data show additional evidence for the involvement of the serotoninergic system in the genetic susceptibility to cocaine dependence.

Genetics of aggressive behavior: An overview.

The Research Domain Criteria (RDoC) address three types of aggression: frustrative non‐reward, defensive aggression and offensive/proactive aggression. This review sought to present the evidence for genetic underpinnings of aggression and to determine to what degree prior studies have examined phenotypes that fit into the RDoC framework. Although the constructs of defensive and offensive aggression have been widely used in the animal genetics literature, the human literature is mostly agnostic with regard to all the RDoC constructs. We know from twin studies that about half the variance in behavior may be explained by genetic risk factors. This is true for both dimensional, trait‐like, measures of aggression and categorical definitions of psychopathology. The non‐shared environment seems to have a moderate influence with the effects of shared environment being unclear. Human molecular genetic studies of aggression are in an early stage. The most promising candidates are in the dopaminergic and serotonergic systems along with hormonal regulators. Genome‐wide association studies have not yet achieved genome‐wide significance, but current samples are too small to detect variants having the small effects one would expect for a complex disorder. The strongest molecular evidence for a genetic basis for aggression comes from animal models comparing aggressive and non‐aggressive strains or documenting the effects of gene knockouts. Although we have learned much from these prior studies, future studies should improve the measurement of aggression by using a systematic method of measurement such as that proposed by the RDoC initiative.

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.

Aggressive behavior in humans: Genes and pathways identified through association studies

Aggressive behavior has both genetic and environmental components. Many association studies have been performed to identify genetic factors underlying aggressive behaviors in humans. In this review we summarize the previous work performed in this field, considering both candidate gene (CGAS) and genome‐wide association studies (GWAS), excluding those performed in samples where the primary diagnosis is a psychiatric or neurological disorder other than an aggression‐related phenotype. Subsequently, we have studied the enrichment of pathways and functions in GWAS data. The results of our searches show that most CGAS have identified associations with genes involved in dopaminergic and serotonergic neurotransmission and in hormone regulation. On the other hand, GWAS have not yet identified genome‐wide significant associations, but top nominal findings are related to several signaling pathways, such as axon guidance or estrogen receptor signaling, and also to neurodevelopmental processes and synaptic plasticity. Future studies should use larger samples, homogeneous phenotypes and standardized measurements to identify genes that underlie aggressive behaviors in humans.

A mutation in the first intracellular loop of CACNA1A prevents P/Q channel modulation by SNARE proteins and lowers exocytosis

Familial hemiplegic migraine (FHM)-causing mutations in the gene encoding the P/Q Ca2+ channel α1A subunit (CACNA1A) locate to the pore and voltage sensor regions and normally involve gain-of-channel function. We now report on a mutation identified in the first intracellular loop of CACNA1A (α1A(A454T)) that does not cause FHM but is associated with the absence of sensorimotor symptoms in a migraine with aura pedigree. α1A(A454T) channels showed weakened regulation of voltage-dependent steady-state inactivation by CaVβ subunits. More interestingy, A454T mutation suppressed P/Q channel modulation by syntaxin 1A or SNAP-25 and decreased exocytosis. Our findings reveal the importance of I-II loop structural integrity in the functional interaction between P/Q channel and proteins of the vesicle-docking/fusion machinery, and that genetic variation in CACNA1A may be not only a cause but also a modifier of migraine phenotype.