[Show abstract][Hide abstract] ABSTRACT: While attention-deficit/hyperactivity disorder (ADHD) has been associated with both internalizing and externalizing childhood behaviour disorders, the specific relationship of these comorbid disorders to ADHD and reading problems is less well defined. The present study analysed data from the Australian Twin ADHD Project, which utilized DSM-IV-based ratings of ADHD, separation anxiety disorder, generalized anxiety disorder, depression, conduct disorder, and oppositional defiant disorder for twins and siblings aged 6 to 18 years. While differences between children with and without ADHD were demonstrated for those with separation anxiety disorder, generalized anxiety disorder, depression, conduct disorder, oppositional defiant disorder and a reading disorder, for all age groups, regression analysis of ADHD diagnostic subtypes by age and reading disorder showed that only generalized anxiety disorder remained significant after controlling for ADHD subtypes. Analysis of the mean reading disorder scores in children with and without ADHD showed that children with conduct disorder had significantly more reading problems, as did children with multiple comorbid disorders. In summary, both age and ADHD diagnosis were associated with variations in these comorbid disorders, and multiple comorbid disorders were associated with greater reading impairment.
ADHD Attention Deficit and Hyperactivity Disorders 11/2012;
[Show abstract][Hide abstract] ABSTRACT: It has been well recognized since the days of "minimal brain dysfunction" (Clements, 1966) that various developmental disorders have a shared aetiology. Poor motor coordination has been implicated as one of the factors in these relationships. This study examines the different patterns in symptomatology of five developmental disorders, namely developmental coordination disorder (DCD), attention-deficit/hyperactivity disorder (ADHD), reading disorder (RD), oppositional defiant disorder (ODD), and conduct disorder (CD) in order to build on the genetic work from Martin, Levy, Piek, and Hay (2006) and Martin, Piek, and Hay (2006) examining the overlap of these disorders. Latent class analysis was used on questionnaire data from 1304 families from the Australian twin ADHD project (ATAP) to examine the patterns of comorbidity of the five disorders. We confirmed and added detail to the shared symptoms between DCD, ADHD, RD, and ODD, but found no links between CD symptoms and any other disorders. Despite the close link previously identified with ODD and CD, this finding suggests a different aetiology for CD.
Human movement science 11/2009; 29(5):799-808. · 2.15 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The prevalence of attention-deficit/hyperactivity disorder (ADHD) has been estimated at 3-7% in the population. Children with this disorder are often characterized by symptoms of inattention and/or impulsivity and hyperactivity, which can significantly impact on many aspects of their behaviour and performance. This study investigated the characteristics of the SWAN Rating Scale and its discrimination of ADHD subtypes. This instrument was developed by Swanson and his colleagues and measures attentiveness and hyperactivity on a continuum, from attention problems to positive attention skills, using a seven-point scale of behaviour: "far below average" to "far above average". The Australian Twin Attention-Deficit/Hyperactivity Disorder Study consists of questionnaire data collected from families in 1990/2007. The Rasch model was used to measure the characteristics of items from the SWAN Rating Scale; how well these items discriminated between those with and without ADHD. The prevalence of each subtype was found to be 5.3% for inattentive ADHD, 4.3% for hyperactive ADHD and 4.6% for combined ADHD. A total of 14.2% of the cohort appeared to have ADHD. While the inattentive items appeared to be consistent with each other in their measurement behaviour and response patterns, the hyperactive items were less consistent. Further, the combined subtype appeared to be an entirely different type, with unique features unlike the other two subtypes. Further work is needed to distinguish the diagnostic features of each subtype of ADHD.
Child Psychiatry and Human Development 06/2009; 40(4):543-59. · 1.93 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: New attention-deficit/hyperactivity disorder (ADHD) subtypes identified through latent class analysis have been recently proposed. Here, we assess the accuracy of simple rules based on symptom counts for the assignment of youths to clinically relevant population-derived ADHD subtypes: severe inattentive (SI) and severe combined (SC).
Data from 9,675 twins and siblings from Missouri and Australia aged 7 to 19 years were analyzed using continuous and categorical models of ADHD symptoms using principal components analysis and subtyping by DSM-IV and by latent class criteria. Cut points were derived for classifying SI and SC subtypes by positive predictive value, negative predictive value, percent positive agreement, and Matthew coefficient of agreement.
Principal components analysis suggested two underlying factors: total number of symptoms and symptom type, with SI and SC latent class subtypes clearly mapping to distinct areas on a plot of these factors. Having six or more total symptoms and fewer than three hyperactive-impulsive symptoms accurately predicts the latent class SI subtype. The latent class SC subtype was best identified by 11 or more total symptoms and 4 or more hyperactive-impulsive. The DSM-IV ADHD subtype criteria accurately identified the SC subtype but only poorly for the SI subtype.
Symptom counts criteria allow the simple and accurate identification of subjects with severe ADHD subtypes defined by latent class analysis. Such simple symptom counts corresponding to screening cut points selected latent class-derived SI subtype subjects with greater precision than DSM-IV criteria.
Journal of the American Academy of Child and Adolescent Psychiatry 05/2009; 48(4):441-50. · 6.97 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Handedness refers to a consistent asymmetry in skill or preferential use between the hands and is related to lateralization within the brain of other functions such as language. Previous twin studies of handedness have yielded inconsistent results resulting from a general lack of statistical power to find significant effects. Here we present analyses from a large international collaborative study of handedness (assessed by writing/drawing or self report) in Australian and Dutch twins and their siblings (54,270 individuals from 25,732 families). Maximum likelihood analyses incorporating the effects of known covariates (sex, year of birth and birth weight) revealed no evidence of hormonal transfer, mirror imaging or twin specific effects. There were also no differences in prevalence between zygosity groups or between twins and their singleton siblings. Consistent with previous meta-analyses, additive genetic effects accounted for about a quarter (23.64%) of the variance (95%CI 20.17, 27.09%) with the remainder accounted for by non-shared environmental influences. The implications of these findings for handedness both as a primary phenotype and as a covariate in linkage and association analyses are discussed.
[Show abstract][Hide abstract] ABSTRACT: The high level of comorbidity between Developmental Coordination Disorder (DCD) and Attention Deficit Hyperactivity Disorder (ADHD) suggests that these disorders may have a shared etiology. We used a co-twin control design to study monozygotic (MZ) twins concordant and discordant for DCD and ADHD. In a total of 922 sets of MZ twins, 866 sets were eligible. We found equal numbers of DCD concordant and discordant sets; more ADHD concordant than discordant sets; nine sets in which both twins met criteria for DCD+ADHD; 773 sets of twins did not meet criteria for either DCD or ADHD. The only significant sex difference between groups was for ADHD discordant sets, with more males than females. For DCD groups there were no significant sex differences, with slightly more girls than boys affected in both groups. There was a greater number of oxygen perfusion complications in DCD affected than unaffected twins, suggesting that, given equal numbers of DCD concordant and discordant sets and a similar number of DCD girls and boys, the role of pre- and perinatal environmental factors is stronger in the etiology of DCD than in ADHD. Factors such as placental difficulties and hypoxia have also been related to cerebral palsy, which suggests that DCD may fall on the upper end of a continuum of movement disorder that includes cerebral palsy. The results suggest different etiological pathways for DCD and ADHD. Second born twins were at greater risk for oxygen perfusion difficulties in sets concordant for DCD, ADHD, and unaffected for either.
Journal of Pediatric Neurology. 08/2008; 6(3):209.
[Show abstract][Hide abstract] ABSTRACT: Cornish et al. (2008, this issue) provide an excellent review of Fragile X a common but very complex cause of intellectual disability. They report on a cohort of such males of normal intelligence quotient (IQ) and socioeconomic status (SES), but who have deficits in selective attention and growing impairment in response inhibition. This paper has theoretical views for our models of the mind and clinical implications for families where Fragile X may never have been considered as a possible cause of some of the problems in male and female family members and possibly as well for other disorders such as attention deficit hyperactivity disorder (ADHD) and autism.
[Show abstract][Hide abstract] ABSTRACT: The aim of this review is to describe the considerable advances in consolidating the empirical evidence on several key topics in the genetics of attention deficit hyperactivity disorder, namely the quantitative genetic studies of the nature of attention deficit hyperactivity disorder and its comorbidities, the molecular genetic studies that show modest but consistent effects of specific genotypes, and the growing recognition of genotype by environment interaction. Such interactions are studied to explain what happens when individuals with a susceptible genotype are exposed to a particular environment.
There have been a significant number of twin studies that have examined different models of the symptomatology of attention deficit hyperactivity disorder and how these symptoms are reported. Similarly, molecular genetic research is complicated by very different outcome measures, and study across the whole field is made more problematic by genotype by environment interaction effects. One of the most interesting areas of development is that of psychopharmacogenetics.
Two key developments have been integrative models of the genetics of attention deficit hyperactivity disorder and brain structure, which may have implications for future attention deficit hyperactivity disorder subtyping, and collaboration. This is not just within attention deficit hyperactivity disorder as in the IMAGE study, but also across disciplines.
Current opinion in psychiatry 07/2008; 21(4):356-61. · 3.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study aims to identify the family characteristics that promote the development of social skills in children with physical disabilities. Parents and teachers completed a range of questionnaires in an Australia‐wide study of 212 parents of children (5–12 years of age) with physical disabilities who attend mainstream schools. The relationships between parental attitudes, parental involvement, family relationships, teachers’ opinions, disability severity, and children’s social skills were tested using structural equation modelling. The results of this study show the importance of family characteristics for the development of social skills in children with physical disabilities. A strong link was found between aspects of healthy family relationships, especially high levels of parental involvement with schooling, and greater social skills development in children. In short, families with highly cohesive, idealised, and democratic family styles strongly influence children’s social skills by providing a safe and sound foundation for children to explore their social environment. Practical implications arising from this study are discussed.
International Journal of Disability. 12/2007; Development and Education(Vol. 54):381-397.
[Show abstract][Hide abstract] ABSTRACT: Previous research has demonstrated a link between attention-deficit/hyperactivity disorder (ADHD), developmental coordination disorder (DCD), and depression. The present study utilized a monozygotic (MZ) differences design to investigate differences in depressive symptomatology between MZ twins discordant for ADHD or DCD. This extends previous research as it controls for genetic effects and shared environmental influences and enables the investigation of nonshared environmental influences. In addition, children and adolescents with comorbid ADHD and DCD were compared on their level of depressive symptomatology to those with ADHD only, DCD only, and no ADHD or DCD. The parent-rated Strengths and Weaknesses of ADHD Symptoms and Normal Behavior, Developmental Coordination Disorder Questionnaire, and Sad Affect Scale were used to assess ADHD, DCD, and depressive symptomatology respectively. The results revealed higher levels of depressive symptomatology in MZ twins with ADHD or DCD compared to their nonaffected co-twins. In addition, children and adolescents with comorbid ADHD and DCD demonstrated higher levels of depressive symptomatology compared to those with ADHD only, DCD only, and no ADHD or DCD. The implications of these findings are discussed with emphasis on understanding and recognizing the relationship between ADHD, DCD, and depression in the assessment and intervention for children and adolescents with these disorders.
Twin Research and Human Genetics 09/2007; 10(4):587-96. · 1.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Children with autistic disorder (AD), mixed receptive-expressive language disorder (RELD), or developmental coordination disorder (DCD) have impairments in common. We assess which abilities differentiate the disorders. Children aged 3-13 years diagnosed with AD (n = 30), RELD (n = 30), or DCD (n = 22) were tested on measures of language, intelligence, social cognition, motor coordination, and executive functioning. Results indicate that the AD and DCD groups have poorer fine and gross motor coordination and better response inhibition than the RELD group. The AD and DCD groups differ in fine and gross motor coordination, emotion understanding, and theory of mind scores (AD always lower), but discriminant function analysis yielded a non-significant function and more classification errors for these groups. In terms of ability scores, the AD and DCD groups appear to differ more in severity than in kind.
[Show abstract][Hide abstract] ABSTRACT: When symptom rating scales are used in the general population, there is severe skewness, with many individuals having no symptoms. While this has major implications for genetic designs that require extremely discordant and concordant (EDAC) siblings, little is known of the genetics of scales which seek to differentiate within the "no ADHD symptom" group.
Parents of Australian twins completed two attention-deficit/hyperactivity disorder (ADHD) questionnaires, the Australian Twin Behaviour Rating Scale (ATBRS), based on conventional DSM-IV symptom scores, and the Strengths and Weaknesses of ADHD-Symptoms and Normal-Behavior (SWAN) scale, which includes above-average performance on attention and activity. The two scales were compared in two age groups of same-sex twins, 528 pairs aged 6 to 9 and 488 pairs aged 12 to 20.
Parents reported higher levels of activity and attention in their twins when reporting using the SWAN scale than when using the ATBRS, and while the monozygotic (MZ) correlations were similar on both scales, the dizygotic (DZ) correlations were consistently higher on the SWAN. On DSM-IV based scales, parents exaggerated differences within those sibling pairs in the "with few ADHD symptoms" category.
The SWAN may provide a more realistic description of the ADHD phenotype for the selection of twin and sibling pairs for genetic analysis.
[Show abstract][Hide abstract] ABSTRACT: This article describes the Australian Twin Attention-deficit/hyperactivity disorder (ADHD) Project (ATAP), the results of research conducted using this database and plans for future studies. Information has been actively collected from Australian families with twin children since 1991 for the ATAP database. The value of assessing siblings as well as twins is emphasized. Much work has gone into continuing the involvement of families in the study though this does become more difficult when twins reach maturity. The main focus of the project is ADHD in children and adolescents plus comorbid conditions including conduct disorder, oppositional defiant disorder, and generalized anxiety disorder. A major challenge has been how to retain continuity in the assessments, while at the same time covering changes in psychiatric classification, such as the move to Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV; American Psychiatric Association, 1994). Changes in the scale can affect the reports of twin similarity. Over the years, these twins have become part of other twin studies and future plans include linking different twin databases to investigate the relationships between childhood behavior and adult conditions. Recruitment, assessment and retention of twin families require a major commitment but create a significant resource for collaboration in areas outside the original aim.
Twin Research and Human Genetics 01/2007; 9(6):718-26. · 1.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We assessed if autism symptoms relate to ability deficits and achievement discrepancies in 29 children aged 4–13 years with a diagnosis of Autistic Disorder. Symptoms, intelligence, language, motor coordination and social cognition were assessed. Children with autism underachieve on all ability measures. There were significant achievement discrepancies between Performance IQ and theory of mind, fine and gross motor coordination. The most common discrepancy was between Performance IQ scores and motor coordination scores, which was observed in 86% of children. Early developmental abnormalities related to most abilities, social interaction symptoms related to motor coordination and receptive language, and symptoms related to discrepancies between PIQ and social cognitive abilities. Yes Yes
Journal of Developmental and Physical Disabilities 01/2007; · 0.89 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: There has been a significant increase in the number of twins and higher multiples so that one child in 33 is now a multiple. It is therefore not unusual for schools to have several sets of twins, as well as triplets and even higher multiples. By being the same age and in the same school year if not class, twins and higher multiples are not like brothers and sisters born closely together. Teachers and parents need to be aware of particular issues that may affect the physical, intellectual, personal, social and emotional development of multiple birth children, and to ensure that school policy and practice include this special group of children and parents. These issues include: preterm birth catch-up and implications for starting school; the balance of competition and cooperation among multiples; separation in school and the evidence from recent longitudinal studies; legislative and other initiatives on the development of school policy; the particular needs of higher multiples.
Early Human Development 07/2006; 82(6):397-403. · 2.02 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Attention Deficit Hyperactivity Disorder (ADHD) commonly co-occurs with Oppositional Defiant Disorder, Conduct Disorder and Reading Disability. Twin studies are an important approach to understanding and modelling potential causes of such comorbidity. Univariate and bivariate genetic models were fitted to maternal report data from 2040 families of twins from the Australian Twin ADHD Project. All measures showed a heritability of over 0.8 and little role for the common family environment, except for the combined subtype of ADHD with a heritability of 0.69 and a common environment of 0.19. About one-third of the genetic variance in ADHD was shared with the other behaviours, the largest overlap being with Oppositional Defiant Disorder. Common environmental effects were shared between the combined ADHD subtype and the other measures. Some implications of these findings for home and school are discussed.
International Journal of Disability Development and Education 04/2006; 53:1034-912. · 0.59 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: While there have been significant advances in both the behaviour genetics and molecular genetics of Attention Deficit Hyperactivity Disorder (ADHD), researchers are now beginning to develop hypotheses about relationships between phenotypes and genetic mechanisms. Twin studies are able to model genetic, shared environmental and non-shared environmental influences on aetiol-ogy. The present review describes recent behaviour genetic and latent class findings in relation to ADHD and its subtypes, including rater effects, comorbidity, and developmental effects, which have an impact on findings of high heritability. Molecular genetic studies have predominantly focused on dopamine genes, including dopamine receptor and transporter genes, because of animal and human studies indicating the importance of dopaminergic attention systems. The recent clinical use of noradrenergic reuptake inhibitors has also increased interest in noradrenergic genes. Adult ADHD and age-related genetic effects, in addition to "reading" genes, are reviewed in relation to comorbidity and developmental effects.
International Journal of Disability Development and Education 04/2006; 53:10005-16. · 0.59 Impact Factor