DCD and ADHD: A genetic study of their shared aetiology
Introduction
Attention deficit hyperactivity disorder (ADHD) and developmental coordination disorder (DCD) are both childhood disorders identified in the DSM-IV (APA, 1994) which have a population prevalence of approximately 7% (Kadesjö and Gillberg, 1999, Milberger et al., 1996). Studies investigating ADHD have found that around 50% of ADHD cases also have motor problems severe enough to be diagnosed as DCD (Barkley, 1990, Piek et al., 1999, Pitcher et al., 2003). Further, children initially diagnosed with DCD have been found to also meet moderate to severe diagnosis for ADHD (Kadesjö & Gillberg, 1999).
Given the joint evolution of ADHD and DCD from the Minimal Brain Dysfunction classification, it is not surprising that these two disorders may be associated (Piek et al., 1999). Not only are they found together, but many studies report a higher prevalence of boys compared with girls for both ADHD (Eiraldi et al., 1997, Pennington and Ozonoff, 1996) and DCD (e.g., Henderson and Hall, 1982, Kadesjö and Gillberg, 1999). However other studies suggest there are equal numbers of boys and girls affected in DCD (e.g., Hoare & Larkin, 1991). Also, both disorders have been linked to psychosocial problems such as socially inappropriate behaviour, emotional problems, reduced academic performance, and reading and spelling difficulties (Levy et al., 2005, Taylor et al., 2004). Furthermore, when ADHD and DCD are comorbid, the outcome tends to be more severe than when each disorder occurs alone (e.g., Gillberg, 1992, Pitcher et al., 2003, Visser, 2003). This implies that there may be an exclusive shared aetiology of the comorbidity which is distinct from the factors influencing either of the separate disorders.
One of the difficulties in exploring the comorbidity of these two disorders is the difference between the bodies of research existing for each disorder. ADHD has been extensively researched (Voeller, 2004) with many genetic studies confirming the high heritability of ADHD and its subtypes (Levy & Hay, 2001). Several candidate loci, such as DAT1 (Chen et al., 2003), DRD4 (Langley et al., 2004), and MAO (Payton et al., 2001) have been identified and replicated. There are also many well developed measures in questionnaire or interview form and numerous neuropsychological measures, all of which are comprehensively covered in the recently revised European guidelines (Taylor et al., 2004). DCD, however, is much less extensively researched and what literature exists on it and its aetiology is often confusing. This confusion is often due to varying selection criteria, such as different cut-off scores being used in different studies (Piek & Edwards, 1997), and also due to the overlap that many symptoms of DCD have with other disorders such as learning difficulties (Peters, Barnett, & Henderson, 2001). Performance tests such as the Movement Assessment Battery for Children (Henderson & Sugden, 1992) and the McCarron Assessment of Neuromuscular Development (McCarron, 1997) are generally used to identify DCD. Recently, screening tools have been developed, such as the Developmental Coordination Disorder Questionnaire (Wilson, Kaplan, Crawford, Campbell, & Dewey, 2000), which allows the testing of much larger samples of children.
Although the link between ADHD and motor problems has been recognised for many years, there have been few studies that have investigated the motor problems in relation to the three distinct subtypes identified by the DSM-IV (APA, 1994). These subtypes are based on the behavioural symptomatology identified in the child; either predominantly inattentive (ADHD-PI), predominantly hyperactive/impulsive (ADHD-HI), or a combination of both types of symptoms (ADHD-C). One link that appears to have been established is that between inattentive symptomatology and poor motor skills, in particular fine motor control (McGee et al., 1992, Piek et al., 1999, Pitcher et al., 2003). There is also evidence that suggests that gross motor deficits are more likely to occur in ADHD-C compared to the ADHD-PI (Piek et al., 1999). Differences in the prevalence of boys and girls for different subtypes also suggests a greater relationship between DCD and ADHD-PI, as a greater proportion of girls are found with ADHD-PI compared with ADHD-C (Lahey et al., 1994).
The aim of the current study was to take validated questionnaire measures for both ADHD and DCD and look for a shared genetic heritability to both of them using quantitative genetic methodology in a very large twin sample. While this methodology is powerful, it does require extremely large sample sizes (Neale & Cardon, 1992). It can answer the question of why the two disorders co-occur at such a high frequency and with a different outcome than either disorder alone. By studying the heritability in this way we will be able to tease apart the genetic influences from the environmental effects acting upon the disorders to better understand how they come about. From looking at the comorbid disorder we can examine whether it is a general link between ADHD and DCD or whether particular subtypes of each are linked more strongly with each other. Specific comorbidities may point to particular aetiological pathways which can then be explored more fully. By studying the subtypes of the disorders we can also examine whether there are different factors influencing each one as well as common factors which act on all of them.
Different screening measures of ADHD were also tested against each other for equivalence and to explore the effect that different ADHD measures have on finding shared heritability between it and DCD. There has been much concern that different measures of ADHD may yield different genetic results. For example on some questionnaires, particularly short ones such as the Rutter A, parents may exaggerate differences between dizygotic twins and thus inflate the heritability (Thapar, Harrington, Ross, & McGuffin, 2000).
Section snippets
Participants
The participants consisted of 1285 families of twins from the Australian Twin ADHD Project (ATAP) summarised in Levy and Hay (2001). Families were ascertained from the Australian Twin Registry (ATR: http://www.twins.org.au), a nation-wide, volunteer based database of twins and higher order multiple birth families born in Australia. Each family was sent a questionnaire package for returning by pre-paid mail. The project was approved by Curtin University Human Research Ethics Committee and by the
Prevalence
The prevalence of DCD using the published Canadian cut-off (Wilson et al., 2000) was 2% which was rather low compared with previous estimates of between 5% and 19% (APA, 1994, Henderson and Sugden, 1992, Kadesjö and Gillberg, 1999, Wright and Sugden, 1996). Using the mean ± 1.65sd method as used for the SWAN scale it was 8% which more closely approximates the prevalence given in DSM-IV of 6% (APA, 1994) and the recent Australian national survey (Graetz, Sawyer, Hazell, Arney, & Baghurst, 2001).
Discussion
The prevalence of both disorders was found to be comparable to those of previous studies. We found a higher rate of ADHD symptoms in boys than girls with a ratio of approximately 3:1 which is comparable to that found in previous studies.
The univariate analyses demonstrated that all of the subscales of ADHD and DCD have a substantial genetic component. For the ADHD data, both the SWAN and the ATBRS showed similar patterns with the inattentive and hyperactive/impulsive subtypes having substantial
Acknowledgments
This work was funded by a grant from the National Health and Medical Research Council of Australia. We would like to thank Grant Baynam and Kellie Bennett for their assistance with data collection and entry and the co-operation of so many families, as well as the Australian Twin Registry.
References (46)
- et al.
Patterns of comorbidity associated with subtypes of attention-deficit/hyperactivity disorder among 6- to 12-year-old children
Journal of the American Academy of Child and Adolescent Psychiatry
(1997) - et al.
Validity of DSM-IV ADHD subtypes in a nationally representative sample of Australian children and adolescents
Journal of the American Academy of Child and Adolescent Psychiatry
(2001) - et al.
Developmental coordination disorder in Swedish 7-year-old children
Journal of the American Academy of Child and Adolescent Psychiatry
(1999) - et al.
Validity of DSM-IV attention-deficit/hyperactivity disorder for younger children
Journal of the American Academy of Child and Adolescent Psychiatry
(1998) - et al.
Gender differences in ADHD subtype comorbidity
Journal of the American Academy of Child and Adolescent Psychiatry
(2005) - et al.
Attention-deficit hyperactivity disorder: A category or a continuum? Genetic analysis of a large-scale twin study
Journal of the American Academy of Child and Adolescent Psychiatry
(1997) - et al.
The relationship between motor coordination, executive functioning and attention in school aged children
Archives of Clinical Neuropsychology
(2004) - et al.
Motor flexibility problems as a marker for genetic susceptibility to attention deficit hyperactivity disorder
Biological Psychiatry
(2005) - et al.
Does the definition of ADHD affect heritability?
Journal of the American Academy of Child and Adolescent Psychiatry
(2000) Developmental coordination disorder: A review of research on subtypes and comorbidities
Human Movement Science
(2003)
Attention deficit hyperactivity disorder: A handbook for diagnosis and treatment
The dopamine transporter gene is associated with attention deficit hyperactivity disorder in a Taiwanese sample
Molecular Psychiatry
Reliably separating identical from fraternal twins
Archives of General Psychiatry
Deficits in attention, motor control and perception, and other syndromes attributed to minimal brain dysfunction
Learning to use statistical tests in psychology
Concomitants of clumsiness in young schoolchildren
Developmental Medicine and Child Neurology
Movement assessment battery for children
Kinaesthetic abilities of clumsy children
Developmental Medicine and Child Neurology
DSM-IV field trials for attention deficit hyperactivity disorder in children and adolescents
American Journal of Psychiatry
Association of the dopamine d4 receptor gene 7-repeat allele with neuropsychological test performance of children with ADHD
American Journal of Psychiatry
Twin sibling differences in parental reports of ADHD, speech, reading and behaviour problems
Journal of Child Psychology and Psychiatry
Cited by (145)
The adult developmental coordination disorders/dyspraxia checklist – German: adapted factor structure for the differentiation of DCD and ADHD
2022, Research in Developmental DisabilitiesINSERM's collective expertise on developmental coordination disorder or dyspraxia: Status of the main studies and recommendations
2021, Neuropsychiatrie de l'Enfance et de l'AdolescenceDevelopmental coordination disorder
2020, Handbook of Clinical NeurologyCitation Excerpt :By contrast, in their examination of 46 sets of monozygotic twins, Pearsall-Jones et al. (2008) found the same numbers of DCD concordant and discordant sets (n = 23). Researchers have also raised the possibility of a common genetic etiology between DCD and either attention deficit hyperactivity disorder (ADHD) (Martin et al., 2006) or autism spectrum disorder (ASD) (Lichtenstein et al., 2010). Despite the vertiginous development of sequencing and genomic analysis techniques over the past 10 years, there has been scant interest in how these might help us look for genes implicated in DCD.
Children with developmental coordination disorder show altered functional connectivity compared to peers
2020, NeuroImage: ClinicalLocomotor-cognitive dual-tasking in children with developmental coordination disorder
2024, Frontiers in Psychology