Key messages• Co-morbidity of motor problems with pervasive developmental disorder, a hyperkinetic disorder and/or a speech, language or learning disability varied between one fourth and one third of the children in this clinical sample.• Co-morbidity rates of motor problems in developmental and behavioural disorders are lower than previously reported • Co-morbidity of motor problems with pervasive developmental disorder, a hyperkinetic disorder and/or a speech, language or learning disability shows different patterns in boys and girls • It is recommended to asses motor skills in children with developmental disorders Word count main text: 3167 3 AbstractBackground: Few co-morbidity studies have been conducted since the Leeds Consensus Statement on Developmental Coordination Disorder (DCD) in 2006. In this Statement, international cut-offs and inclusion criteria were agreed and consequently the status of DCD changed. Furthermore, most existing comorbidity studies are small clinical studies, rather than epidemiological studies, resulting in a broad range of co-morbidity rates. DCD has a higher incidence for boys in comparison with girls, questions arise if this preponderance remains the same in combination with other developmental disorders. Therefore, in this study we aimed to determine co-morbidity and gender differences of motor problems in children with a pervasive developmental disorder, a hyperkinetic disorder and/or a speech, language or learning disability. Methods: Profiles of 3608 children (mean age 9y 1mo) referred to rehabilitation centres for behavioural, developmental and sensorineural disorders were studied.Results: Motor problems were reported in one fifth of the total sample. Comorbidity of motor problems in specific disorders varied between almost one fourth to more than one third. The male/female ratio was significantly higher in children with motor problems and 2 or more other disorders compared to children with motor problems and less than 2 other disorders.Conclusions: This study indicates that co-morbidity of motor problems with other clinical disorders is not exceptional and developmental deviance is seldom specific to one domain. However, current co-morbidity studies tend to overestimate the number of children with motor problems. In addition, there may be different patterns of symptoms between the genders. These findings stress the importance of assessing motor skills in children with various developmental disorders.

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