Antisocial behaviour and spelling disability in a population sample of 13 year old twins.

The aetiology of the co-morbidity of specific spelling retardation and antisocial behaviour was investigated in a general population sample of 213 pairs of 13 year old same-sex twins. The rate of co-morbidity was 2.45 greater than that expected by chance. Using multiple regression it was shown that the heritability (hg2) of spelling disability was high whilst that for antisocial behaviour was not significant. A bivariate hg2 analysis showed that the co-morbidity was not due to common genetic factors. The data were not consistent with either one condition leading to the other nor with each resulting from a common origin linked with hyperactivity. The co-morbid children resembled the children with antisocial behaviour alone on family and social characteristics and the heritability of spelling disability is as high when co-morbid with antisocial behaviour as it is when occurring alone. It is concluded that co-morbidity arises by the genetic factors leading to spelling disability being associated with environmental factors leading to antisocial behaviour. The mechanisms are discussed whereby fathers genetically predisposed to spelling disability might create an adverse environment leading in some cases to antisocial behaviour in their children.