CHIP: Defining a dimension of the vulnerability to attention deficit hyperactivity disorder (ADHD) using sibling and individual data of children in a community-based sample

Impact of obesity on cognitive outcome in children with sleep-disordered breathing

OBJECTIVES

The objective of this study was to evaluate the impact of obesity on cognitive impairment, in children with obstructive sleep apnoea (OSA), children with OSA and obesity, and in normal controls.

METHODS

Thirty-six children with OSA (group 1), 38 children with OSA and obesity (group 2) and 58 normal controls (group 3) were studied. The Total intelligence quotient (T-IQ), Verbal IQ (V-IQ) and the Performance IQ (P-IQ) scores were obtained using the Wechsler Intelligence Scale for Children - Third Edition Revised. All participants' parents filled out the questionnaire containing the attention deficit and hyperactive disorder rating scale to investigate symptoms of hyperactivity and attention deficit. Obese and non-obese children with sleep-disordered breathing (SDB) underwent polysomnography.

RESULTS

T-QI and P-QI scores were significantly lower in group 2 with higher performance impairment at the subtest compared to other groups. In obese children, V-IQ was significantly correlated with age of onset (r = 0.335, p = 0.05) and duration of SDB (r = -0.362, p = 0.02), while P-IQ and T-IQ were correlated with body mass index (BMI) percentile (r = -0.341, p = 0.03) and respiratory disturbance index (RDI) (r = -0.321, p = 0.05), respectively. RDI and BMI negatively influenced T-IQ in obese children with OSA. No correlation was found between sleep parameters and IQ scores or subtest scores in all groups.

CONCLUSIONS

Obese children with OSA showed higher cognitive impairment. Obesity has an additive and synergic action with that exerted by OSA, speeding up the onset of complications.

Phenotypic and genetic structure of anxiety sensitivity in adolescence and early adulthood

Anxiety sensitivity is a risk factor for emotional disorders. The structure of anxiety sensitivity was examined using phenotypic and genetic analyses. Self-reported anxiety sensitivity was measured at three time points from adolescence into young adulthood by 2651 individuals from the G1219 twin study. Confirmatory factor analyses revealed comparable statistical support for anxiety sensitivity models consisting of three or four dimensions across all time points. The three-factor model depicting Physical, Social and Mental anxiety-related concerns was favoured due to greater interpretability and parsimony. Multivariate quantitative genetic analyses supported a hierarchical structure with general genetic (.09-.61) and non-shared environmental (.39-.72) influences acting via a higher-order factor as well as dimension-specific genetic (.09-.21) and non-shared environmental (.23-.68) influences. The findings provide further evidence for a hierarchical structure underlying different dimensions of anxiety sensitivity.

The Latent Class Structure of ADHD Is Stable Across Informants

Previous studies have looked at the structure of attention-deficit/hyperactivity disorder (ADHD) using latent class analysis (LCA) of Child Behavior Checklist (CBCL) or Diagnostic and Statistical Manual of Mental Disorders (DSM) symptom structure. These studies have identified distinct classes of children with inattentive, hyperactive, or combined subtypes and have used these classes to refine genetic analyses. The objective of the current report is to determine if the latent class structure of ADHD subtypes is consistent across informant using the Conners' Rating Scales (CRS). LCA was applied to CRS forms from mother, father, and teacher reports of 1837, 1329 and 1048 latency aged Dutch twins, respectively. The optimal solution for boys was a 5-class solution for mothers, a 3-class solution for fathers, and a 4-class solution for teachers. For girls, a 4-class solution for mothers and a 3-class for fathers and teachers was optimal. Children placed into a class by one informant had markedly increased odds ratio of being placed into the same or similar class by the other informants. Results from LCA using Dutch twins with the CRS show stability across informants suggesting that more stable phenotypes may be accessible for genotyping using a multi-informant approach.

Genetic influences on the cognitive biases associated with anxiety and depression symptoms in adolescents

BACKGROUND

There is a substantial overlap between genes affecting anxiety and depression. Both anxiety and depression are associated with cognitive biases such as anxiety sensitivity and attributional style. Little, however, is known about the relationship between these variables and whether these too are genetically correlated.

METHODS

Self-reports of anxiety sensitivity, anxiety symptoms, attributional style and depression symptoms were obtained for over 1300 adolescent twin and sibling pairs at two time points. The magnitude of genetic and environmental influences on the measures was examined.

RESULTS

Strongest associations were found between anxiety sensitivity and anxiety ratings at both measurement times (r=.70, .72) and between anxiety and depression (r=.62 at both time points). Correlations between the cognitive biases were modest at time 1 (r=-.12) and slightly larger at time 2 (r=-.31). All measures showed moderate genetic influence. Generally genetic correlations reflected phenotypic correlations. Thus the highest genetic correlations were between anxiety sensitivity and anxiety ratings (.86, .87) and between anxiety and depression ratings (.77, .71). Interestingly, depression ratings also showed a high genetic correlation with anxiety sensitivity (.70, .76). Genetic correlations between the cognitive bias measures were moderate (-.31, -.46).

LIMITATIONS

The sample consists primarily of twins, there are limitations associated with the twin design.

CONCLUSIONS

Cognitive biases associated with depression and anxiety are not as genetically correlated as anxiety and depression ratings themselves. Further research into the cognitive processes related to anxiety and depression will facilitate understanding of the relationship between bias and symptoms.

Linkage to chromosome 1p36 for attention-deficit/hyperactivity disorder traits in school and home settings

BACKGROUND

Limited success has been achieved through previous attention-deficit/hyperactivity disorder (ADHD) linkage scans, which were all designed to map genes underlying the dichotomous phenotype. The International Multi-centre ADHD Genetics (IMAGE) project performed a whole genome linkage scan specifically designed to map ADHD quantitative trait loci (QTL).

METHODS

A set of 1094 single selected Caucasian ADHD nuclear families was genotyped on a highly accurate and informative single nucleotide polymorphism (SNP) panel. Two quantitative traits measuring the children's symptoms in home and school settings were collected and standardized according to a population sample of 8000 children to reflect the developmental nature and gender prevalence difference of ADHD. Univariate linkage test was performed on both traits and their mean score.

RESULTS

A significant common linkage locus was found at chromosome 1p36 with a locus-specific heritability of 5.1% and a genomewide empirical p < .04. Setting-specific suggestive linkage signals were also found: logarithm of odds (LOD) = 2.2 at 9p23 for home trait and LOD = 2.6 at 11q21 for school trait.

CONCLUSIONS

These results indicate that given large samples with proper phenotypic measures, searching for ADHD genes with a QTL strategy is an important alternative to using the clinical diagnosis. The fact that our linkage region 1p36 overlaps with the dyslexia QTL DYX8 further suggests it is potentially a pleiotropic locus for ADHD and dyslexia.

Links between parenting and extra-familial relationships: nature or nurture?

The current paper examined associations between parenting and both peer group characteristics and friendship quality within a genetically sensitive design. Participants were aged 12-19 years (approximately equal numbers of males and females), including 424 sibling pairs and 1185 twin pairs, of whom 328 were MZ, 311 were DZ same-sex, 463 were DZ opposite-sex and 83 were of unknown zygosity. The adolescents provided self-report questionnaire measures of parental discipline, friendship quality, and peer group characteristics. All three relationship measures were moderately to substantially heritable. The novel and provocative finding, that adolescents' genetic propensities are largely responsible for the overlap seen between parental discipline strategies and friendship quality, is discussed in terms of its implications for socialization theory and understanding of adolescent relationships.

Working toward a neurobiological account of ADHD: commentary on Gail Tripp and Jeff Wickens, dopamine transfer deficit

The dopamine transfer deficit model of attention deficit hyperactivity disorder (ADHD) is compared and contrasted with the existing dynamic developmental theory and the extended temporal difference (TD) model. The first two both identify learning deficits as a key problem in ADHD, but this mechanism would seem at least as likely to cause other neurodevelopmental disorders. Learning deficits also do not provide a natural account of ADHD performance worsening in longer trials, nor of stimulant action, nor of the high rate of test-retest inconsistency. The extended TD model is based on the quite different premise that there are very many underlying causes for the disorder, and computational simulation of it has supported the existence of two subtypes that involve no dopamine transfer deficit, as well as several subtypes that do. The three models have markedly different ways of accounting for key aspects of ADHD, including intra-individual variability, stimulant effects, and extinction deficits. The most important shortcoming of all the models is their limited treatment of state-regulation processes, which are very important in ADHD; this is partially addressed by the extended TD model's proposed dopamine appetite.

Refining the attention deficit hyperactivity disorder phenotype for molecular genetic studies

It is well established that attention deficit hyperactivity disorder (ADHD) is a familial and highly heritable disorder. Consequently, much effort is being directed towards searching for specific susceptibility genes. There is a growing trend, across the field of complex disease genetics, towards undertaking secondary analyses based on refined phenotypic definitions and in testing whether specific susceptibility genes modify the phenotypic presentation of the disorder in question. It is crucial that good, empirically derived arguments are made before undertaking multiple analyses on different phenotype refinements. In this review article, we consider the evidence from genetic epidemiological studies as well as key clinical studies that provide guidance on examining the ADHD phenotype for the purpose of molecular genetic studies. Specifically, findings on categorical versus dimensional conceptualisations of ADHD, reporter effects, comorbidity, ADHD subtypes and persistence are reviewed. Current evidence suggests that for the purpose of identifying susceptibility genes for ADHD, parent and teachers should be used as informants and that focusing on the clinical diagnosis of ADHD is useful. There is also good empirical support in favour of examining antisocial behaviour in ADHD. Genetic studies of dimensional ADHD are useful for other complementary purposes.

Molecular genetics of attention-deficit/hyperactivity disorder

Results of behavioral genetic and molecular genetic studies have converged to suggest that both genetic and nongenetic factors contribute to the development of attention-deficit/hyperactivity disorder (ADHD). We review this literature, with a particular emphasis on molecular genetic studies. Family, twin, and adoption studies provide compelling evidence that genes play a strong role in mediating susceptibility to ADHD. This fact is most clearly seen in the 20 extant twin studies, which estimate the heritability of ADHD to be .76. Molecular genetic studies suggest that the genetic architecture of ADHD is complex. The few genome-wide scans conducted thus far are not conclusive. In contrast, the many candidate gene studies of ADHD have produced substantial evidence implicating several genes in the etiology of the disorder. For the eight genes for which the same variant has been studied in three or more case-control or family-based studies, seven show statistically significant evidence of association with ADHD on the basis of the pooled odds ratio across studies: DRD4, DRD5, DAT, DBH, 5-HTT, HTR1B, and SNAP-25.

Toward localizing genes underlying cerebral asymmetry and mental health

Genome investigations of autism, attention deficit hyperactivity disorder (ADHD), and dyslexia suggest possible genetic overlap. Atypical cerebral asymmetry (ACA), the absence of the left hemisphere dominance for language, may be a shared phenotype due to genes located in regions of overlap. A binomal test is used to evaluate whether linked regions overlap more than expected by chance for 15 genome-wide scans in autism, ADHD, and dyslexia. Significant evidence of linkage overlap (P = 10(-7)) is seen for autism, ADHD, and dyslexia for seven chromosomal regions (2p11-12, 5p13, 7q22-33, 9q33-34, 13q22, 16p13, and 17p11-q11). Linkage analysis of ACA and molecular markers for 270 sibling pairs with ADHD is conducted using the Haseman-Elston statistic. Linkage analysis supports ACA as a shared phenotype with risk genes located on 9q33-34 or 16p13 (P < 0.004). Further support stems from the overlap of these regions in schizophrenia, bipolar illness, specific language impairment (SLI), and handedness, all traits associated with ACA. Autism, ADHD, and dyslexia share regions of linkage overlap and ACA may be a shared phenotype for such genes similar to HLA in autoimmune disease. Because ACA is associated with certain aspects of creativity, such risk genes may also be enhancer genes for creativity.

The serotonin transporter gene as a QTL for ADHD

Molecular studies of attention deficit hyperactivity disorder (ADHD) have identified susceptibility genes for the categorically diagnosed disorder using operational diagnostic criteria. Here, we take a QTL approach to mapping genes for ADHD using a composite continuous index of ADHD behavior in a large epidemiological sample. Previous studies of clinical ADHD suggest that two functional polymorphisms in the serotonin transporter gene (SLC6A4), one in the 5'-regulatory region of the gene (5-HTTLPR) and the other a VNTR (5-HTTVNTR) in the second intron, as well as a single nucleotide polymorphism in the 3'-untranslated region (3'-UTR SNP), may be associated with the disorder. Here, we investigate these polymorphisms as well as an additional ten SNPs spread across the gene. We found significant association with the long (L) allele of the 5-HTTLPR; P = 0.019, but neither the 5-HTTVNTR nor the 3'-UTR SNP were significantly associated. Significant associations (P < 0.05) were found for a further 5 the 10 other markers tested. We found evidence for two haplotype blocks spanning the region. We found strong evidence for association with the first haplotype block (comprised of four markers), with the significance of a combined primary and secondary test of association reaching an empirical P value = 0.0054 for the global test and an empirical P value = 0.00081 for the largest local test. Thus, we show here that SLC6A4, which has a major influence on brain serotonin availability, may be a QTL for ADHD.

Molecular genetics of attention-deficit hyperactivity disorder (ADHD): an update

Attention-deficit hyperactivity disorder (ADHD) is a heritable and behavioral condition of childhood, affecting 5-10% of school-age children worldwide. Affected patients exhibit various behavioral problems such as carelessness, restlessness, disobedience and failure to stay quiet in class. The etiology of ADHD is not known. However, family, twin and adoption studies have provided strong evidence for a genetic etiology of the disorder. A genome-wide scan has identified six chromosomal loci with LOD scores suggestive of linkage. Animal studies suggest the involvement of the brain dopamine pathway and its alteration in ADHD but there is no direct evidence to support this hypothesis. In addition, there are at least 20 candidate genes of small effect that have been studied but none of them appear to be the major gene causing ADHD. Medical intervention along with psychosocial therapy proved to be beneficial for controlling ADHD, although some undesirable side effects have been encountered during medical treatment. In the future, identification of environmental factors, study of additive gene effects and the interaction of genes and environmental factors may provide better insight into the pathophysiology of ADHD. This may lead to an effective new treatment strategy.

Attention deficit/hyperactivity disorder (ADHD): complex phenotype, simple genotype?

Complex genetic traits refer to those phenotypes not fitting patterns of Mendelian segregation and/or assortment but exhibiting a preferential familial clustering that cannot be explained by cultural or environmental causes. Attention-deficit/hyperactivity disorder (ADHD) is the most common neurodevelopmental disorder of childhood and probably the most controversial. ADHD has been considered a complex genetic trait based upon the absence of a clear-cut boundary between affected and unaffected status. Furthermore, its high comorbidity with other disorders strongly suggests complex epistatic or pleiotropic effects acting in common with the environmental influences. This implies that the same gene or genes is or are associated with different and concurrently occurring phenotypes. In this study, we will review clinical and epidemiological aspects related to the ADHD phenotype, which are considered either as categorical or continuous traits. We also will discuss genetic models underlying the complexity of this behavioral phenotype and the probable role of epistatic interactions between major genes contributing to the ADHD phenotype.

Parental familial vulnerability, family environment, and their interactions as predictors of depressive symptoms in adolescents

OBJECTIVE

Familial risk for depression results from both biological and social influences. These may also be associated with other characteristics, including alcohol use, smoking, and body mass index (BMI), and with environmental risks such as social problems, life events, and educational level, all of which may be associated with depression in offspring. The authors examined the links between (1) parental familial vulnerability to depression and (2) the role of associated parental characteristics on severe adolescent depressive symptoms. Third, the authors explored the influence of family environment variables. Fourth, the authors sought interactions between parental familial vulnerability and family environment.

METHOD

Questionnaires were obtained from 1,294 parents of 1,818 adolescent offspring.

RESULTS

The odds of severe adolescent depressive symptoms increased by a factor of 1.5 per standard deviation increase in parental familial vulnerability to depression (odds ratio [OR] = 1.50). Parental BMI (OR = 1.05) and educational level (OR = 2.60) had significant influences independent of parental vulnerability. Analyses indicated a significant interaction such that those with high parental familial vulnerability, whose parents also had no qualifications, had a threefold risk of severe depressive symptoms.

CONCLUSIONS

Adolescents with a family history of depression whose parents also lack qualifications may be a target for intervention.