SignificanceAll animals have associated microbial communities called microbiomes that influence the physiology and fitness of their host. It is unclear to what extent individual microbial species versus interactions between them influence the host. Here, we mapped all possible interactions between individual species of bacteria against Drosophila melanogaster fruit fly fitness traits. Our approach revealed that the same bacterial interactions that shape microbiome abundances also shape host fitness traits. The fitness traits of lifespan and fecundity showed a life history tradeoff, where equal total fitness can be gotten by either high fecundity over a short life or low fecundity over a long life. The microbiome interactions are as important as the individual species in shaping these fundamental aspects of fly physiology.

Attention deficit hyperactivity disorder (ADHD) is a highly heritable and heterogeneous disorder, which usually becomes apparent during the first few years of childhood. Imbalance in dopamine neurotransmission has been suggested as a factor predisposing to ADHD. However, evidence has suggested an interaction between dopamine and serotonin systems in the pathophysiology of the disorder. Studies using selective agonists of the different 5-HT receptors microinjected into selected brain structures have shown a positive modulating effect on the functional activities of the mesotelencephalic dopaminergic system. This suggests that some of the genetic predisposition to ADHD might be due to DNA variation at serotonin system genes. In this study, we investigated polymorphisms in HTR 1B and HTR 2A (which encode the serotonin receptors 5-HT 1B and 5-HT 2A respectively) in a European ADHD sample. Using haplotype based haplotype relative risk (HHRR) and transmission disequilibrium test (TDT) analyses, we observed significant preferential transmission of the allele 861G of the HTR 1B in the total sample (for HHRR; 2 = 7.4, P = 0.0065 and TDT; ( 2 = 6.4, P = 0.014). Analysis of HTR 2A failed to reveal evidence of association or linkage between the His452Tyr polymorphism and ADHD in the total sample. However, a significantly increased transmission of the allele 452His was observed in the Irish sample alone ( 2 = 4.9, P = 0.026). These preliminary data suggest an important role for the serotonin system in the development of ADHD. Further studies, preferentially including different ethnic groups are required to substantiate these findings.

Molecular genetic studies in attention deficit hyperactivity disorder (ADHD) have focussed on candidate genes within the dopamine system, which is thought to be the main site of action of stimulant drugs, the primary pharmacological treatment of the disorder. 1 Of particular interest are findings with the dopamine transporter gene (DAT1), since stimulant drugs interact directly with the transporter protein.2,3 To date, there have been eight published association studies of ADHD with a 480 basepair allele of a variable number tandem repeat (VNTR) polymorphism in the 3Ј-untranslated region of the gene, five 4-8 that support an association and three 9-11 against. We have analysed the same VNTR marker in a dataset of UK Caucasian children and an independent dataset of Turkish Caucasian children with DSM-IV ADHD, using the transmission disequilibrium test (TDT).12 Results from the UK ( In this study, we have taken a family-based association design to investigate the DAT1 VNTR marker in a dataset of UK Caucasian children and an independent dataset of Turkish Caucasian children. Cases were included if they had a diagnosis of ADHD under DSM-IV criteria and DNA from both parents available for genotyping. They were excluded if they had neurological disease or damage or congenital disorders known to cause hyperactivity. The UK sample consisted of 59 cases with the combined subtype, six the hyperactive/impulsive subtype and one the inattentive subtype of ADHD. Axis 1 co-morbidity other than oppositional defiant disorder and conduct disorder (ODD/CD) consisted of two cases with an affective disorder. The Turkish sample consisted of 111 complete trios with DSM-IV-ADHD combined type. Comorbid diagnoses other than ODD/CD were Tourette's syndrome and/or tics (TS/tics) in 34% and anxiety/depression in 8% of probands.Analysis was performed using the transmission disequilibrium test (TDT) of linkage in the presence of association.12 In order to further evaluate the evidence, we included data from other published reports and performed a combined analysis. The results of this study are shown in Table 1. When considered alone, data from the UK sample ( 2 = 6.12, P = 0.0.01, OR = 1.95), but not the Turkish sample ( 2 = 0.93, P = 0.335), support association and linkage between the DAT1 locus and ADHD.We are not alone in finding differences between datasets. Among previous published reports there have been five providing evidence for the association and three against. The reasons for this are unclear and require further investigation, but may relate to the statistical power of individual samples. To address this issue we combined available published data on the VNTR polymorphism and applied the TDT. Because the TDT is primarily a test of linkage, it is valid to analyse the combined data by adding the number of transmitted and non-transmitted alleles across different studies. As shown in Table 1, combined analysis provides evidence for association and linkage at an alphalevel of 0.06 and odds ratio of 1.15. Although diagnostic differences...

Recent family and twin study findings suggest that ADHD when comorbid with conduct problems may represent a particularly familial and heritable form of ADHD. Although several independent groups have shown association between the DRD4 7 repeat allele and ADHD, others have failed to replicate this finding. Previous TDT analyses of UK and Eire samples had also been negative. We set out to further examine the role of DRD4 but selecting a subgroup of children with ADHD and comorbid conduct problems. Families were recruited from Manchester, Ireland, Birmingham and London clinics. From these, 67 children who fulfilled diagnostic criteria for ADHD and who displayed conduct disorder symptoms were selected. TDT analysis, which had previously yielded negative results for the total sample, showed evidence of association between DRD4 and "ADHD with conduct problems" (7 repeat allele-24 transmissions, 13 non-transmissions; one-tailed P=0.05). These results provide further support for the role of DRD4 in ADHD. Furthermore, these results when considered together with family and twin study findings, suggest that those children with ADHD and comorbid conduct problems may be particularly informative for molecular genetic studies of ADHD. Further work is needed to examine these phenotype issues.

Abstract:With hundreds of species interacting with each other as well as with specific proteins and cells in the body, the gut microbiome is a complex ecosystem embedded within a complex organism. Microbiome impacts on host health can shape key aspects of fitness, such as development, 1 fecundity, 2 and lifespan, 3,4 while the host in turn can shape the microbiome. 5 However, complex interactions between microbes can make downstream effects unpredictable, such as when toxin-producing Clostridium species cause pathogenesis after antibiotics reduce gut diversity. 6 A pressing need exists to deconstruct the effects of gut diversity on host health, and new mathematical approaches are needed to quantify the complex patterns of interactions. Central to the microbiome-host relationship are questions of how bacterial diversity is maintained in the gut 7 and how this diversity impacts host fitness. 8 Here we show that interactions between bacteria are major determinants of host physiology and the maintenance of bacterial diversity. We performed a complete combinatorial dissection of the naturally low-diversity Drosophila gut microbiome using germ-free flies colonized with each possible combination of five core species of bacteria, forming a five-dimensional landscape in ecological state space. For each species combination, we measured the resulting bacterial community abundances and fly fitness traits including (i) development, (ii) reproduction, and (iii) lifespan. Notably, we found that the fly gut environment promotes bacterial diversity, which in turn accelerates development, reproduction, and aging. From these measurements we calculated the impact of bacterial interactions on fly fitness by adapting a combinatorial geometry approach, 9 to the microbiome. 10 We found that host phenotypes (e.g. lifespan) from single bacterial species are not predictive of host phenotypes in diverse communities. By contrast, higher-order interactions (involving 3, 4, and 5 species) are widely prevalent and impact both host physiology and the maintenance of bacterial diversity, as recently predicted by ecologists. 11 With regard to evolution, the impacts of bacterial interactions on gut community composition parallel the impacts on host fitness traits, providing a feedback that, propagated over time, may poise a population for emergence of co-evolving microbiome-host units.peer-reviewed)