Familial resemblance for cognitive abilities in families with P-type dyslexic, L-type dyslexic, or normal reading boys.

P-type dyslexic, L-type dyslexic, and normal reading boys, and their parents were administered a number of cognitive tasks. The P- and L-type dyslexic boys showed impaired performances on tasks representing a verbal/memory dimension. In addition, L-type dyslexics performed worse on a figure-rotation task, a result that supported the notion of a visuospatial deficit in this type of reading disturbance. The parents of P- and L-type dyslexics exhibited lowered performances on verbal/memory tasks, but they showed no evidence of impaired visuospatial functioning. Indices of familial resemblance revealed differential familial resemblances in the three types of families. In the families of P-type dyslexics, a high father-son effect was found for the visuospatial dimension. In the families of L-type dyslexics, moderately high single-parent/child effects were found for both fathers and mothers and for both the verbal/memory dimension and the visuospatial dimension. In the families of normal readers, only small single-parent/child effects were found.