In this study, we showed that childhood motor clumsiness, reported by parents, and poor performance in a simple motor test, assessed in adulthood, are strongly associated with childhood peer victimization, as reported by adult psychiatric patients. This association remained when diagnosis was controlled for. The present study extends previous findings to psychiatric patients at substantial risk for social and motor skills problems and peer victimization. Additionally, the clumsiness retrospectively reported by the parents was often observable in adulthood as poor vertical jump performance, suggesting deviant cerebellar development. Moreover, impaired visual perception, but none of the other domains of the FTF, was similarly associated with increased odds for peer victimization. A strong link between motor and visuospatial deficits exists both in the general population and in clumsy children . Thus the fact that "gross motor skills" and "visual perception" were the only two domains from the FTF that showed an association with increased peer victimization strengthens our findings.
Cerebellar dysfunction in neurodevelopmental disorders
Motor deficits in children with ADHD and ASD are well documented [30, 45, 46], and comorbidity between ASD, ADHD, and developmental coordination disorder has long been recognized . Children with a combination of motor coordination deficits and ADHD have less favorable outcomes and more autistic traits , including perceptual problems, supporting the concepts of Deficits in Attention, Motor control, and Perception (“DAMP”) [25, 30] and Early Symptomatic Syndromes Eliciting Neurodevelopmental Clinical Examinations (“ESSENCE”) . This also supports the idea that atypical brain development can explain the interrelatedness between these disorders .
Although motor abnormalities are common in ADHD and ASD and pivotal for the diagnosis of developmental coordination disorder, the underlying neurophysiologic impairments and type and persistence of motor problems appear to vary between the diagnostic groups and subgroups. Research in adults with ASD suggests a combination of cerebellar and basal ganglia deficits , and imaging studies of ASD and ADHD have consistently found cerebellar abnormalities [50–52]. The cerebellum controls sensorimotor coordination and is critical to timing computations in both motor and non-motor tasks . Working memory, the shifting of attention, implicit learning, emotional regulation, executive function and facial recognition all depend on cerebellar functioning [50, 54]. Moreover, symptoms of cerebellar lesions resemble the typical impairments of ASD .
In this study, the parents reported poor social skills in the majority of the cases (victims and non-victims), consistent with the social deficits related to ASD and to some extent to ADHD. However, poor gross motor skills in childhood but not poor social skills predicted peer victimization in the present study. Because poor social skills are frequent in both ADHD and ASD [56, 57], this by itself may explain the increased risk for peer victimization compared with normal controls [11, 12, 58]. Nevertheless, we propose that poor gross motor functioning constitutes an independent risk factor for peer victimization across various populations, regardless of provocative behaviors or anxiousness. Poor motor skills may manifest as impaired social skills, thereby contributing to peer victimization. Success in social interaction is largely a matter of timing and harmonious integration of verbal and non-verbal cues. In other words, cerebellar function may be critical for social success. Impairments in social functioning could be viewed as disintegrated motor skills, reflected by subtle aberrations in facial expressions, gaze, pitch, prosody, wording, posture, gestures, turn-taking, and sense of appropriate physical distance. Even slight signs of impairment, registered at a subliminal level, may affect others’ judgments and determine whether the person will be viewed as socially “normal” and attractive as a companion or considered “strange” and result in social exclusion or peer victimization. Preadolescents and adolescents are exceptionally sensitive to deviations , are easily embarrassed , and strive to conform to their peers [59, 61], possibly explaining why peer victimization peaks in the preteen years . We suggest that motor skills are associated with social likeability and that poor skills may contribute to the loneliness in adulthood reported by the victims in this study. Thus, the feeling of loneliness often reported by bullied children  seems to continue into adulthood.
Another possible explanation for our findings could be the close association between poor motor skills and visual perceptual dysfunction. Visual perceptual dysfunction has been shown to be associated with the number of co-occurring disorders in children with developmental coordination disorder  and contribute to poor outcome in preterm born babies  and in children with hyperopia . Poor motor skills without visual perception dysfunction may represent a dimension of normality whereas the combination of the two reflects a neurological dysfunction with increased risk for social exclusion, and/or cognitive, behavioral and emotional disability. In a study on adults with either social phobia or obsessive-compulsive disorder (OCD), childhood peer victimization was much more often reported in the OCD group . Although both disorders have similar ages of onset, chronicity, and relationships with avoidant personality, OCD differs from social phobia by being associated with motor problems and soft neurological signs [67–69], including deficits in visuospatial skills . Interestingly, poor visuospatial skills predicted persistence in pediatric-onset OCD .
Associated risk factors
None of the established factors previously shown to be associated with peer victimization (e.g., education level, civil status, employment, general functioning, overweight, intelligence, reported social skills, internalization, depression, and antidepressant treatment) were implicated in this study. Notably, however, childhood Body Mass Index data were not obtained. By studying a sample at high risk for peer victimization, risk factors beyond the expected may be revealed, such as poor gross motor skills. Hence, our lack of findings about the established risk factors cannot be generalized to normally developing children.
Psychiatric patients are often targets of peer victimization in childhood. Bullying amongst normally developing children peaks in the pre teens, but children with both poor gross motor skills and psychiatric problems have often been bullied for a prolonged period of time. Prolonged peer rejection tends to result in poor self-esteem and may decrease the ability to appeal to others. In adult psychiatric patients a history of poor gross motor skills and peer victimization in childhood may indicate a severe and pervasive neuropsychiatric disorder with social skills deficits. In such cases the clinician should be aware that a range of support and treatments often are indicated.
Simple assessments of motor skills in pre school children should be helpful for identifying children at risk. Furthermore, the possibility should be explored whether early intervention programs using specialized physical education adapted for ‘clumsy’ children (e.g. ) reduce the risk of loneliness and peer rejection.
The patient group studied here may be perceived as marginal; on the other hand ADHD is not by any means a rare disorder in adults. ADHD has a chronic course in approximately 4% of the adult population  and can be diagnosed in almost one of four adult psychiatric outpatients [74, 75]. Concerning ASD, the prevalence rate in the general population exceeds 1% , and ASD frequently co-occurs with other psychiatric disorders. In a recent study, 70% of adults with ASD had experienced at least one episode of major depression . Possibly, the co-occurring disorders draw the clinician’s attention, whereas ADHD and ASD often remain un-diagnosed.
Nevertheless, this study has several limitations, partially due to lack of relevant instruments and the naturalistic setting. First, our retrospective use of FTF could interfere with the results, as the FTF was designed to be filled out by parents, when evaluating their children. Consequently, since parents may forget earlier signs of problematic behavior, false-negative responses may constitute a problem. However, false positive results seem less likely. In our experience, the parents recalled signs of atypical development remarkably well and our results are consistent with a previous report on children with ASD and ADHD that used the FTF . Secondly, we did not use any specific definition of peer victimization, but the concept of bullying is well known , and the patients never questioned the meaning of the wording. They knew whether or not they were victimized by peers and remembered how long it lasted and who where the perpetrators. Being victimized by peers is such a traumatic experience that it may reside as a humiliating memory throughout one’s life. Although some children may deny being victimized by peers or belittle it as “teasing”, we question whether this bias prevails into adulthood. In fact, self-reports of peer victimization by adults may be more reliable than children’s self-reports because the shame that hindered them in childhood may eventually subside. In this study we did not inquire about type of bullying that the participants had experienced, which is another limitation. Most of the participants were in their preteens during the eighties and nineties, thus cyber bullying had not emerged on the scene yet. The three-point scale to determine severity used in this study is not a validated method for measuring severity. However, the question is straightforward and the responses were dichotomized in the analyses; thus the peer victim group consisted of all participants who reported being bullied, regardless of severity. Attrition was partially attributed to the fact that many patients were originally investigated at other clinics and only referred to us for medication, thus providing a smaller proportion of patients to examine. Of the total sample, 21% were not included in the study because of missing data. However, no significant demographic differences were found between these individuals and those included in the study.