Júlia Pasqualini Genro

The Genomic Ancestry of Individuals from Different Geographical Regions of Brazil Is More Uniform Than Expected

Based on pre-DNA racial/color methodology, clinical and pharmacological trials have traditionally considered the different geographical regions of Brazil as being very heterogeneous. We wished to ascertain how such diversity of regional color categories correlated with ancestry. Using a panel of 40 validated ancestry-informative insertion-deletion DNA polymorphisms we estimated individually the European, African and Amerindian ancestry components of 934 self-categorized White, Brown or Black Brazilians from the four most populous regions of the Country. We unraveled great ancestral diversity between and within the different regions. Especially, color categories in the northern part of Brazil diverged significantly in their ancestry proportions from their counterparts in the southern part of the Country, indicating that diverse regional semantics were being used in the self-classification as White, Brown or Black. To circumvent these regional subjective differences in color perception, we estimated the general ancestry proportions of each of the four regions in a form independent of color considerations. For that, we multiplied the proportions of a given ancestry in a given color category by the official census information about the proportion of that color category in the specific region, to arrive at a “total ancestry” estimate. Once such a calculation was performed, there emerged a much higher level of uniformity than previously expected. In all regions studied, the European ancestry was predominant, with proportions ranging from 60.6% in the Northeast to 77.7% in the South. We propose that the immigration of six million Europeans to Brazil in the 19th and 20th centuries - a phenomenon described and intended as the “whitening of Brazil” - is in large part responsible for dissipating previous ancestry dissimilarities that reflected region-specific population histories. These findings, of both clinical and sociological importance for Brazil, should also be relevant to other countries with ancestrally admixed populations.

Attention-deficit/hyperactivity disorder and the dopaminergic hypotheses

Attention-deficit/hyperactivity disorder (ADHD) is a common psychiatric condition that affects approximately 5.3% of children worldwide. This disorder is defined by a combination of symptoms of inattention and hyperactivity/impulsivity. Diagnosis is based on impairment in these two domains determining several problems in personal and academic life. Although it is known that genetic and environmental factors are important in ADHD etiology, how these factors influence the brain and consequently behavior is still under debate. There seems to be a consensus in the literature that a fronto-subcortical dysfunction is responsible, at least in part, for the ADHD spectrum. Considering that these brain regions are rich in dopamine (DA), the DA hypothesis has an important role to understand ADHD pathophysiology. The main goal of the present review is to show evidence from different areas that support the idea that dysregulation in the DA system underlies ADHD. We discuss here evidences from animal models, pharmacology, brain imaging and genetics studies.

No significant association between response to methylphenidate and genes of the dopaminergic and serotonergic systems in a sample of Brazilian children with attention‐deficit/hyperactivity disorder

Few studies on pharmacogenetics of Attention‐Deficit/Hyperactivity Disorder (ADHD) have been conducted. Most of them evaluated dopaminergic genes resulting in positive and negative findings. We assessed effects of polymorphisms in candidate dopaminergic (DRD4, DAT1) and serotonergic genes (HTR1B, HTR2A, and 5‐HTT) on the response to treatment in 111 patients for whom methylphenidate (MPH) was prescribed. Outcome measures (Swanson, Nolan, and Pelham scale—version IV, Children Global Assessment Scale, Barkleys Stimulants Side Effects Rating Scale) were assessed at baseline and 1 month after the intervention. No significant association was detected between polymorphisms assessed and both response and side effects to MPH. Prospective multi‐site controlled studies with larger sample sizes are needed in order to disentangle the role of candidate genes in response to ADHD treatment.

A common haplotype at the dopamine transporter gene 5′ region is associated with attention‐deficit/hyperactivity disorder

The dopamine transporter (DAT) is the major site of methylphenidate action, which is one of the main drugs used to treat attention‐deficit/hyperactivity disorder (ADHD). Most association studies with ADHD focused in a VNTR at the 3′‐untranslated region of the gene (3′UTR) presenting conflicting results. However, the most common explanation to inconsistent results is variable linkage disequilibrium with an adjacent functional variant, just a few number of DAT1 studies 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 243 children with ADHD. In the DSM‐IV combined subtype, we observed a preferential transmission of the haplotype A/C/C/C/A derived from five SNPs (rs2550948, rs11564750, rs261759, rs2652511, rs2975223) in 5′ region (P corrected = 0.018) and no association with any allele/haplotype at the 3′ region of the gene, including the 3′ VNTR and the VNTR of intron 8. These results suggest a role for the promoter region in ADHD susceptibility and that allele heterogeneity should be highly considered in DAT1 gene association studies highlighting the importance of this gene in the genetics of the disorder.

A current update on ADHD pharmacogenomics

Pharmacological treatment for attention deficit hyperactivity disorder, although highly effective, presents a marked variability in clinical response, optimal dosage needed and tolerability. Clinical and neurobiological investigations have juxtaposed findings on both response to medication and etiologic factors, generating the hypothesis that genetic factors may underlie differences in treatment outcome. Over the last decade, research has focused on the catecholaminergic system to investigate a potential role of genotype on pharmacological effect. Despite an increasing number of associations reported (for methylphenidate, nine in 2005, 24 in 2008 and 52 reported in the current article), the identification of clinically relevant genetic predictors of treatment response remains a challenge. At present, additional studies are required to allow for a shift from a trial-and-error approach to a more rational pharmacologic regimen that takes into account the likelihood of treatment effectiveness at the individual level.

Further evidence of the involvement of alpha-2A-adrenergic receptor gene (ADRA2A) in inattentive dimensional scores of attention-deficit/hyperactivity disorder

Further evidence of the involvement of alpha-2A-adrenergic receptor gene (ADRA2A) in inattentive dimensional scores of attention-deficit/hyperactivity disorder

The −1021 C/T DBH polymorphism is associated with neuropsychological performance among children and adolescents with ADHD†

Catecholaminergic imbalance has increasingly been implicated in the pathophysiology of attention‐deficit/hyperactivity disorder (ADHD). The enzyme dopamine‐β‐hydroxylase (DβH)—critical to catecholaminergic regulation—is under strong genetic control, with the −1021 C/T polymorphism accounting for up to 50% of the enzymatic activity. This work aimed to investigate association between this functional polymorphism and the performance of children and adolescents with ADHD in neuropsychological measures of executive function (EF). Sixty‐four drug‐naïve patients with ADHD undertook a Continuous Performance Test and the Wisconsin Card Sorting Test. By means of a factorial analysis, a composite measure of EF was extracted. Performance according to genotypic group was analyzed, including age as a confounder. In addition, a family‐based association test was conducted as a confirmatory analysis. Principal components analysis of neuropsychological measures loaded two factors that explained 83.8% of total variance. Cognitive performance, as measured by the composite score, showed significant difference between genotypic groups after adjustment for age (P = 0.002). The CC homozygosity was associated with a diminished global EF performance, a result that was corroborated by the intra‐familial analysis. The present study demonstrated an association between the neuropsychological performance of children with ADHD and a functional polymorphism in the promoter region of the DBH gene. The refinement of the ADHD phenotype by means of composite measures of EF can contribute to uncover the molecular underpinnings of ADHD.

Serotonin genes and attention deficit/hyperactivity disorder in a Brazilian sample : Preferential transmission of the HTR2A 452His allele to affected boys

Attention‐deficit hyperactivity disorder (ADHD) is one of the most common psychiatric disorders of childhood. The role of genetic factors in its etiology is strongly supported by family, adoption, and twin studies. Low serotonin activity has been associated in both animal and human studies with measures of impulsivity, aggression, and disinhibited behaviors, which make genes from the serotonin system reasonable candidates for ADHD susceptibility. In the present study, we investigated a polymorphism in the promoter region of the serotonin transporter (SLC6A4) and two polymorphisms (−1438 A > G and His452Tyr) in the serotonin 5‐HTR2A receptor gene using family based association analyses in a sample of 243 Brazilian ADHD children and adolescents and their parents. No linkage disequilibrium between the two HTR2A polymorphisms was detected in this sample (P = 0.76). Considering several evidences from animal models for sexual dimorphism in serotonin genes expression, analyses were performed separately for the whole sample and for male probands. No evidences for biased transmissions of both HTR2A −1438 A > G and SLC6A4 polymorphisms to ADHD youths were observed. Preferential transmission of the HTR2A His452 allele was observed only in families with affected boys (P = 0.04). Our results suggest that findings from ADHD association studies for serotonin genes might be understood in the context of a gender effect, which may help to explain conflicting results in these association studies.

Attention-deficit/hyperactivity disorder: advancing on pharmacogenomics

Attention-deficit/hyperactivity disorder (ADHD) is a highly prevalent psychiatric disorder. An impressive volume of literature documents both a strong participation of genetics in its etiology and a high rate of response to medication. However, few studies on the pharmacogenomics of ADHD have been conducted to date. This systematic review aims to present a critical discussion of findings from recent investigations. The majority of studies have focused on individual polymorphisms of the dopaminergic genes, with special emphasis on variants of the dopamine transporter gene (DAT1). Almost all studies have assessed the effects of genes in the response to methylphenidate (MPH). Some preliminary results suggest an association between homozygosity for the 10-repeat allele at DAT1 and poor response to MPH. However, other studies have reported contrasting findings. Very few investigations addressed the role of non-dopaminergic genes or gene-gene interactions in ADHD pharmacogenomics. Recent findings suggesting an association between response to MPH and an MspI polymorphism in the promoter region of the alpha2A-adrenoceptor gene (ADRA2A) are discussed. Pharmacogenomic studies of ADHD are in their infancy, and comparability between studies is difficult due to the use of different methodological approaches. As such, multi-site collaborative efforts to obtain larger samples with standardized methodology should be encouraged.

Global pharmacogenomics: Impact of population diversity on the distribution of polymorphisms in the CYP2C cluster among Brazilians.

The impact of biogeographical ancestry, self-reported ‘race/color’ and geographical origin on the frequency distribution of 10 CYP2C functional polymorphisms (CYP2C8*2, *3, *4, CYP2C9*2, *3, *5, *11, CYP2C19*2, *3 and *17) and their haplotypes was assessed in a representative cohort of the Brazilian population (n=1034). TaqMan assays were used for allele discrimination at each CYP2C locus investigated. Individual proportions of European, African and Amerindian biogeographical ancestry were estimated using a panel of insertion-deletion polymorphisms. Multinomial log-linear models were applied to infer the statistical association between the CYP2C alleles and haplotypes (response variables), and biogeographical ancestry, self-reported Color and geographical origin (explanatory variables). The results showed that CYP2C19*3, CYP2C9*5 and CYP2C9*11 were rare alleles (<1%), the frequency of other variants ranged from 3.4% (CYP2C8*4) to 17.3% (CYP2C19*17). Two distinct haplotype blocks were identified: block 1 consists of three single nucleotide polymorphisms (SNPs) (CYP2C19*17, CYP2C19*2 and CYP2C9*2) and block 2 of six SNPs (CYP2C9*11, CYP2C9*3, CYP2C9*5, CYP2C8*2, CYP2C8*4 and CYP2C8*3). Diplotype analysis generated 41 haplotypes, of which eight had frequencies greater than 1% and together accounted for 96.4% of the overall genetic diversity. The distribution of CYP2C8 and CYP2C9 (but not CYP2C19) alleles, and of CYP2C haplotypes was significantly associated with self-reported Color and with the individual proportions of European and African genetic ancestry, irrespective of Color self-identification. The individual odds of having alleles CYP2C8*2, CYP2C8*3, CYP2C9*2 and CYP2C9*3, and haplotypes including these alleles, varied continuously as the proportion of European ancestry increased. Collectively, these data strongly suggest that the intrinsic heterogeneity of the Brazilian population must be acknowledged in the design and interpretation of pharmacogenomic studies of the CYP2C cluster in order to avoid spurious conclusions based on improper matching of study cohorts. This conclusion extends to other polymorphic pharmacogenes among Brazilians, and most likely to other admixed populations of the Americas.