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Background: In order to fully specify the profiles of risk and protective factors of developmental disorders, a better understanding of the conditions under which they co-occur is required. So far, empirical evidence on comorbidities of specific learning disorders in arithmetic, reading and spelling is scarce. Methods: Prevalence and gender ratios of specific learning disorders in arithmetic (AD), reading (RD), and spelling (SD) and their co-occurrence were assessed in a large ( N = 2586) population-based sample of elementary school children and in a subsample of 293 children with at least one learning disorder (LD-sample). A questionnaire on familial transmission was given to a subsample of 256 parents of children with a learning disorder and 146 typically developing children. Results: The rates of deficits in arithmetic, reading, or spelling were four to five times higher in samples already experiencing marked problems in one academic domain compared to the full population. Thus, comorbidity of learning disorders was confirmed in a fairly standard school population. Rates of co-occurrence decreased for AD and RD, but not isolated SD when more stringent cutoff criteria were applied, suggesting that the comorbidity of arithmetic and spelling disorder may be more strongly biologically mediated than the comorbidity of arithmetic and reading disorder. We found a preponderance of girls with AD and boys with SD. These imbalanced gender ratios were especially marked for isolated problems, while for comorbid problems gender ratios were mostly balanced with the exception of deficits in arithmetic and reading (but not spelling) which were more typical for girls. The parental questionnaire provided evidence for disorder-specific familial transmission and co-segregation of arithmetic and literacy deficits. Conclusions: Comorbidities of learning disorders are not artificial. They are the result of a complex interplay between both general and disorder-specific aetiological factors. [ABSTRACT FROM AUTHOR]

Despite an expanding epidemiological evidence base, uncertainties remain over key aspects of the epidemiology of the ‘antisocial’ disorders in childhood and adolescence. We used cross-sectional data on a nationally representative sample of 10,438 5–15-year-olds drawn from the 1999 British Child Mental Health Survey to examine age trends, gender ratios and patterns of comorbidity in DSM-IV Conduct Disorder (CD) and Oppositional Defiant Disorder (ODD). CD was significantly more common in boys than girls, and increased in prevalence with age. Among children who met diagnostic criteria for CD, status violations and other non-aggressive conduct problems increased with age, while aggressive symptoms became less common. Gender differences in ODD varied by reporter. Estimates of age trends in ODD depended heavily on treatment of overlaps with CD. Following DSM-IV guidelines (where ODD is not diagnosed in the presence of CD), rates of ODD fell with age; if that constraint was released, clinically significant rates of oppositionality persisted at similar levels from early childhood to middle adolescence. CD and ODD showed high levels of overlap, and both diagnoses showed substantial comorbidity with other non-antisocial disorders. Results from this large-scale study confirm and extend previous findings in the epidemiology of the disruptive behaviour disorders. [ABSTRACT FROM AUTHOR]