DRD4 rare variants in attention-deficit/hyperactivity disorder (ADHD) : further evidence from a birth cohort study

The dopamine receptor D4 (DRD4) is one of the most studied candidate genes for Attention-Deficit/Hyperactivity Disorder (ADHD). An excess of rare variants and non-synonymous mutations in the VNTR region of 7R allele in ADHD subjects was observed in previous studies with clinical samples. We hypothesize that genetic heterogeneity in the VNTR is an important factor in the pathophysiology of ADHD. The subjects included in the present study are members of the 1993 Pelotas Birth Cohort Study (N=5,249). We conducted an association study with the 4,101 subjects who had DNA samples collected. The hyperactivity-inattention scores were assessed through the parent version of the Strengths and Difficulties Questionnaire at 11 and 15 years of age. The contribution of allele’s length and rare variants to high hyperactivity/inattention scores predisposition was evaluated by multivariate logistic regression. No effect of allele length was observed on high scores of hyperactivity-inattention. By contrast, when resequencing/haplotyping was conducted in a subsample, all 7R rare variants as well as non-synonymous 7R rare variants were associated with high hyperactivity/inattention scores (OR=2.561; P=0.024 and OR=3.216; P=0.008 respectively). A trend for association was observed with 4R rare variants. New coding mutations covered 10 novel motifs and many of them are previously unreported deletions leading to different stop codons. Our findings suggest a contribution of DRD4 7R rare variants to high hyperactivity-inattention scores in a population-based sample from a large birth cohort. These findings provide further evidence for an effect of DRD4 7R rare variants and allelic heterogeneity in ADHD genetic susceptibility

CLOCK polymorphisms in attention-deficit/hyperactivity disorder (ADHD) : further evidence linking sleep and circadian disturbances and ADHD

Circadian and sleep disorders, short sleep duration, and evening chronotype are often present in attention-deficit/hyperactivity disorder (ADHD). CLOCK, considered the master gene in the circadian rhythm, has been explored by few studies. Understanding the relationship between ADHD and CLOCK may provide additional information to understand the correlation between ADHD and sleep problems. In this study, we aimed to explore the association between ADHD and CLOCK, using several genetic markers to comprehensively cover the gene extension. A total of 259 ADHD children and their parents from a Brazilian clinical sample were genotyped for eight single nucleotide polymorphisms (SNPs) in the CLOCK locus. We tested the individual markers and the haplotype effects using binary logistic regression. Binary logistic and linear regressions considering ADHD symptoms among ADHD cases were conducted as secondary analysis. As main result, the analysis showed a risk effect of the G-A-T-G-G-C-G-A (rs534654, rs1801260, rs6855837, rs34897046, rs11931061, rs3817444, rs4864548, rs726967) haplotype on ADHD. A suggestive association between ADHD and rs534654 was observed. The results suggest that the genetic susceptibility to circadian rhythm attributed to the CLOCK gene may play an important role on ADHD

O gene do transportador de dopamina e a suscetibilidade genética ao Transtorno de Déficit de Atenção/Hiperatividade em crianças

O Transtorno de Déficit de Atenção/Hiperatividade (TDAH) está entre as doenças psiquiátricas mais comuns na infância e adolescência, afetando 5,3% de crianças em todo mundo. O TDAH é uma doença bastante heterogênea caracterizada por sintomas de desatenção, hiperatividade e impulsividade, determinando prejuízo significativo na qualidade de vida dos pacientes. A partir destes sintomas três tipos clínicos são reconhecidos: predominantemente desatento, predominantemente hiperativo-impulsivo e combinado (combinação dos sintomas de ambos os grupos). Embora sua etiologia ainda não esteja totalmente esclarecida, existem fortes evidências mostrando que os genes desempenham um papel importante na doença. O transportador de dopamina (DAT) é uma proteína plasmática de membrana que controla a neurotransmissão dopaminérgica através da recaptação da dopamina liberada pelos neurônios pré-sinapticos. O DAT também é o principal sítio de ação do metilfenidato, que é o estimulante mais usado no tratamento do TDAH. O metilfenidato bloqueia a ação do DAT aumentando as concentrações sinápticas de dopamina. Esta evidência justifica o gene transportador de dopamina (DAT1 ou SLC6A3) como um candidato central no TDAH. A grande maioria dos estudos de associação com este gene concentram-se na região 3 não traduzida do gene (3 UTR), principalmente com um polimorfismo de número variável de repetições em tandem (VNTR), mas os resultados são bastante controversos. Embora a explicação mais utilizada para explicar os resultados divergentes é que o polimorfismo está em desequilíbrio de ligação (DL) com outro sítio funcional, somente dois estudos em populações européias analisaram o gene como um todo. No presente estudo nós analisamos 16 polimorfismos ao longo do gene DAT1 no intuito de entender a estrutura do DL do gene e verificar se existe alguma transmissão preferencial das variantes estudadas (e haplótipos derivados) dos pais para os filhos afetados. A amostra foi composta de 243 famílias com pelo menos 1 filho afetado. Nós encontramos um padrão segmentado de DL com três blocos haplotípicos. Esta estrutura foi bastante similar aos resultados prévios descritos em populações européias. Na amostra total foi observada uma transmissão preferencial do haplótipo (A/C/C/C/A) derivado de 5 SNPs da região promotora (rs2550948, rs11564750, rs261759, rs2652511, rs2975223) dos pais para os filhos afetados (p=0,025). Esta associação haplotípica se mostrou mais forte quando a análise foi restrita ao subtipo clínico combinado (p=0,003). Não detectamos nenhuma outra associação com as demais variantes analisadas, incluindo o VNTR da região 3. Em primeiro lugar nossos resultados sugerem um papel importante da região promotora do gene DAT1 na suscetibilidade genética ao TDAH na nossa população. Em segundo lugar, eles também sugerem fortemente que a questão da heterogeneidade alélica deve ser considerada em doenças complexas como o TDAH, pois a estrutura do DL parece não explicar as inconsistências em relação a este gene.Attention-deficit/hyperactivity disorder (ADHD) is one of the most prevalent mental health disorders in childhood and adolescence, affecting 5.3% of children worldwide. ADHD is a very heterogeneous disorder characterized by symptoms of inattention, hyperactivity and impulsivity determining significant impairment across the life cycle. These symptoms define three clinical subtypes: mainly inattentive, mainly hyperactive-impulsive, or both combined. Although its etiology remains unclear, there is strong evidence supporting the role of genes in the disorder. The dopamine transporter (DAT) is a plasma membrane protein that controls dopaminergic neurotransmission by reuptake of released dopamine into presynaptic neurons. DAT is also the main target for methylphenidate (MPH), the most used stimulant for ADHD treatment. MPH blocks the action of DAT, increasing synaptic dopamine concentrations. This evidence justifies the dopamine transporter gene (DAT1 or SLC6A3) as a central candidate gene for ADHD. Most association studies of the DAT1 gene in ADHD are focused in the 3'- untranslated region of the gene (3'UTR) assessing mainly a variable number of tandem repeat (VNTR) polymorphism, but these investigations have reported discordant results. However, the most common explanation for these inconsistent results is variable linkage disequilibrium with an adjacent functional variant, only two studies in European populations have reported LD structure across the gene. In this study, we screened 16 polymorphisms across the DAT1 gene to understand LD structure in a Brazilian sample of families with ADHD probands and to verify if there were evidence for a biased transmission of alleles and haplotypes from parents to their affected children. The sample included 243 families with at least one affected child. We found a segmental pattern of LD with three haplotype blocks. Moreover, the LD structure observed here was very similar to those previous described for European populations. The promoter haplotype A/C/C/C/A derived from five SNPs (rs2550948, rs11564750, rs261759, rs2652511, rs2975223) in the 5' region was significantly more transmitted to ADHD probands (p=0.025). This association was strengthened when the analyses were restricted to patients with the combined type only (p=0.003). We observe no preferential transmission of any allele/haplotype at the 3' region of the gene, including the 3' VNTR. First, these results suggest a role for the promoter region in ADHD susceptibility in our Brazilian population. Second, allele heterogeneity should be highly considered in complex diseases like ADHD, because LD structure could not explain the inconsistencies about this gene in ADHD

Estudo de associação entre o polimorfismo -1021 C/T na região promotora do gene da dopamina beta-hidroxilase e o transtorno de déficit de atenção e hiperatividade

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Estudo de associação entre o loco da lipoproteína lipase e a esquizofrenia

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Estudo de associação entre o loco da lipoproteína lipase e a esquizofrenia

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The brazilian contribution to attention-deficit/hyperactivity disorder molecular genetics in children and adolescents

Attention-Deficit/Hyperactivity Disorder (ADHD) is a common psychiatric condition of children worldwide. This disorder is defined by a combination of symptoms of inattention and hyperactivity/impulsivity. Diagnosis is based on a sufficient number of symptoms causing impairment in these two domains determining several problems in personal and academic life. Although genetic and environmental factors are important in ADHD etiology, how these factors influence the brain and consequently behavior is still under debate. It seems to be consensus that a fronto-subcortical dysfunction is responsible, at least in part, for the ADHD phenotype spectrum. The main results from association and pharmacogenetic studies performed in Brazil are discussed. The investigations performed so far on ADHD genetics in Brazil and elsewhere are far from conclusive. New plausible biological hypotheses linked to neurotransmission and neurodevelopment, as well as new analytic approaches are needed to fully disclose the genetic component of the disorder