Clumsiness and psychopathology: Causation or shared etiology? A twin study with the CBCL 6–18 questionnaire in a general school-age population sample

Abstract

In a sample of 398 twin pairs aged 8–17 belonging to the Italian Twin Registry we explored the extent to which physical clumsiness/motor problems covary with a broad spectrum of behavioral problems identified by the Child Behavior Checklist 6–18/DSM oriented scales, and the causes of such covariation. Only Anxiety and Attention Deficit Hyperactivity (ADH) Problems maintained significant correlation with Clumsiness after partialling out the effects of the other problem scales. By the co-twin control method we found no indication of clear, direct causal effect of Clumsiness upon Anxiety or ADH Problems, or vice versa. Twin bivariate analyses showed that the co-occurrence of motor problems and Anxiety/ADH Problems is best explained by genetic factors shared between Clumsiness and the behavioral problems phenotypes.

Introduction

The term “clumsiness” is often employed in developmental psychology and psychiatry to comprehensively indicate children who display below-the-norm competences in motor skills, without an easily identifiable neurological disorder. In children and adolescents with below-the-norm IQ, clumsiness is considered of clinical relevance when it manifests to an extent that is over and above the degree of motor impairment typically associated with mental retardation. Consistent with these views, both the DSM-IV and the ICD-10 (American Psychiatric Association, 2000; World Health Organization, 1992) define Developmental Coordination Disorder (DCD) as a chronic and sometimes permanent condition, whereby a significant impairment in the acquisition of motor skills interferes with a child’s motor coordination to an extent that is inappropriate for age and IQ, causing significant interference with academic achievement and/or daily activities. The DSM-IV (American Psychiatric Association, 2000) reports an estimated prevalence of 6% for DCD in children aged 5–11 years. Published studies, however, report a wide variation of DCD prevalence estimates, ranging from 1.7% to 13%, depending on the instruments and/or criteria adopted by different research groups. For instance, a recent general population study of 6990 children aged 7–8 employed: (a) three subtest of the Movement Assessment Battery for Children (Henderson & Sugden, 1992), (b) data from national handwriting tests, and (c) an Activities-of-Daily-Living measure, to quantify poor coordination and its impact upon daily life. By crossing the information yielded by these different sources, Lingam, Hunt, Golding, Jongmans, and Emond (2009) found that 1.7% children had DCD according to strict DSM-IV criteria, while 4.9% had probable-to-definite DCD.

In a general population study of 409 7-year-old children (Kadesjo & Gillberg, 1999), participants were individually assessed for motor coordination and parents and teachers were interviewed to gather developmental information. Data showed that severe variants of DCD were present in 4.9% of 7-year-olds, while another 8.6% would have moderate clumsiness. In the same study, children with moderate and severe DCD scored similarly in attentional, language, and reading problems, and both groups of DCD children differed markedly from those without DCD. The implication would be that cases of moderate and severe DCD – cumulatively accounting for some 13% of general population children – would constitute a sizable group deserving closer investigation, or clinical care (Kadesjo & Gillberg, 1999). A recent study of executive functioning (neuropsychological processes of working memory, set-shifting, and processing speed) by Piek et al. (2007) found that children with DCD have significantly poorer and slower performances than the control children in all tasks, supporting a theory of processing and timing deficit in DCD, possibly linked to cerebellar dysfunction (Piek, Dyck, Francis, & Conwell, 2007).

Although for a number of years it had been assumed that children with motor problems would grow out of their clumsiness, longitudinal studies tend to show the contrary, with many of these children displaying the same motor difficulties throughout adolescence (Green et al., 2006, Losse et al., 1991).

Different forms of childhood psychopathology can be associated with DCD/clumsiness.

DCD is often reported to be associated with Attention Deficit Hyperactivity Disorder (ADHD) symptoms: according to some studies almost 50% children with DCD would also show moderate-to-severe ADHD (Kadesjo & Gillberg, 1999). Likewise, 30–50% of children with ADHD would display movement difficulties that closely resemble, or overlap with, those described for DCD (Piek et al., 1999, Pitcher et al., 2003) and the presence of both ADHD and DCD in childhood predict particularly poor psychosocial adjustment in early adulthood (Rasmussen & Gillberg, 2000). Only two studies examined the possibility of a shared etiology between ADHD and DCD. The first (Martin, Piek, & Hay, 2006) was based upon a large sample of children between 5 and 16 years of the Australian Volunteer Twin Registry assessed with the Developmental Coordination Questionnaire (DCDQ, Wilson, Kaplan, Crawford, Campbell, & Dewey, 2000): it reported a much smaller prevalence of DCD (2%) than the Kadesjo study, and substantial heritability (h² = .69) for the DCDQ. The genetic determinants shared between DCD and ADHD were small to moderate, with genetic correlations spanning between .29 and .51, depending upon which DCDQ subscales were analyzed for their covariation with different ADHD measures.

Shared common environmental effects explained the covariation between ADHD measured with the “Australian Twin Behaviour Rating Scale” (ATBRS; Levy, Hay, Waldman, & McStephen, 2001) and the DCDQ “control during movement” subscale, while shared additive genetic effects mainly explained the covariation between ADHD symptoms measured with the “Strengths and weaknesses of ADHD symptoms and normal behavior” scale (SWAN; Swanson et al., 2001) and the DCDQ “control during movement” subscale. For the covariation between the DCDQ “fine motor/handwriting” subscale and all the ADHD measures, analyses found a strong common genetic component. “Gross motor/planning” and “general coordination” subscales showed only moderate or non-significant correlations with ADHD, implying separate etiology. Finally, considering the DCDQ full scale and the ADHD measures, Martin et al. (2006) found a substantially shared etiology due both to additive genetic and common environmental factors.

The second study (Fliers et al., 2009) was based upon a clinical sample of 275 children with ADHD aged 5–19 years, and their siblings. The results indicated that the co-occurrence between ADHD and motor problems is largely familial in nature, but due to the sibling design it was impossible to discriminate between the action of shared genetic and/or shared environmental factors (Fliers et al., 2009).

DCD/clumsiness has been found associated with other disorders in addition to ADHD: Sigurdsson and colleagues (Sigurdsson, van Os, & Fombonne, 2002) have suggested that childhood motor skills impairment is a significant risk factor for anxiety in male adolescents. Consistent with this finding, Skinner and Piek found that DCD children and adolescents report significantly higher levels of both state and trait anxiety (Skinner & Piek, 2001), and up to 85% of children with DCD are reported by parents as having significant behavioral and emotional problems, as measured with the Strengths and Difficulties Questionnaire (Green et al., 2006). A study by Piek et al. (2007) investigated the association of depressive symptoms with DCD by using monozygotic twins discordant for DCD: since twins with DCD showed more depressive symptoms than their co-twins without DCD, idiosyncratic environmental experiences uniquely related to DCD (such as negative social feedback and academic difficulties) were suggested as a likely explanation for the association (Piek et al., 2007).

Finally, two studies found that DCD children scored significantly higher than typically-developing children on both Internalizing- and Externalizing problems on the Child Behavior Checklist (CBCL) (Dewey et al., 2002, Tseng et al., 2007).

The bulk of these data call for a more systematic approach to investigate the coexistence of clumsiness with childhood psychopathology. To do so, the full spectrum of problem behaviors in unselected (i.e., not clinical) populations should be taken into account, in order to allow better generalization of results and at least partially overcome the selection biases proper of clinical samples. Here, we explored the nature of the covariation between a psychometric index of Clumsiness and the new CBCL DSM oriented scales (DOS) in a general population sample of twins aged 8–17. First, we were interested in assessing the size of the covariation between six different problem behaviors mapped by the newly-established CBCL DOS and Clumsiness. Second, by the co-twin control method, and after partialling out the effects of other problem scales, we investigated whether the phenotypic correlations between different forms of psychopathology and Clumsiness could better be accounted for by direct causal effects, or by shared causal elements. Third, in absence of clear causal effects of CBCL DOS upon Clumsiness or vice versa, we investigated by bivariate twin analyses the nature of latent, causal elements that can simultaneously affect the risk for psychopathology and clumsiness in the developmental years.