The influence of different diagnostic approaches on familial aggregation of spelling disability

The influence of different diagnostic approaches on familial aggregation of spelling disability was investigated in three studies. In the first study, in a sample of 32 dyslexic children and their families, we found significa ntly incraeased rates of spelling-disabled sibs and parents by applying the IQ-discrepancy criterion. There was no evidence for the assumption that IQ -discrepancy and low achievement criteria define different subgroups of spe lling disorder regarding familial aggregation. In the second study, in a sa mple of 79 adults, it could be demonstrated that questionnaire data can be used as an appropriate method to classify adult probands as spelling disabl ed with a correct classification rate above 87%. In the third study, a subg roup of dyslexic boys could be characterized by a lack of the N1-component in visual evoked potentials which was most prominent in those boys whose sp elling scores were more than 1.5 standard deviations below their intelligen ce level. This subgroup could be interesting also for genetic research.