Family patterns of developmental dyslexia. Part III: Spelling errors as behavioral phenotype.

The major trends in current research on developmental dyslexia assume that impaired phonological processing is the core deficit in this disorder. Our earlier studies indicated that half of all dyslexic persons have significant deficits of bimanual motor coordination, and that impaired temporal resolution in motor action may identify a vertically transmitted behavioral phenotype in familial dyslexia. This report examines the relationship between spelling errors as a measure of impaired phonological processing and motor coordination deficits in the same dyslexia families.

Family patterns of developmental dyslexia, part II: behavioral phenotypes.

The motor control of bimanual coordination and motor speech was compared between first degree relatives from families with at least 2 dyslexic family members, and families where probands were the only affected family members. Half of affected relatives had motor coordination deficits; and they came from families in which probands also showed impaired motor coordination. By contrast, affected relatives without motor deficits came from dyslexia families where probands did not have motor deficits.

Family patterns of developmental dyslexia: clinical findings.

Two separate groups of dyslexia families were ascertained through probands attending special schools for dyslexic students. An additional control group of families was ascertained through randomly selected students attending public schools. The 3 groups were interviewed by questionnaire about the family's demographic characteristics, and about the incidence of reading and spelling disorders in all first and second order relatives.