A behavioral genetic investigation into directional motor skills and reading disability

Date of Completion

January 2003


Biology, Genetics|Psychology, Behavioral|Psychology, Developmental




The ability to rapidly articulate the complex sounds of speech depends, motorically, on changes in respiratory, laryngeal and pharyngeal morphology that arose with Homo sapiens. Motor skills, and more specifically, directional motor skills continued to develop to serve language and non language functions (e.g., hand preferences for tool use and gestures to express meaning/affect). ^ The present study explored a motor link that, based on evidence we have collected, serves as a biological basis for reading disability (RD). While other factors are undoubtedly involved, a genetic perceptual/motor component appears to be important in RD. We studied 300 elementary school, middle school and community college students. RDs were associated with a lack of motor directionality and a constellation of perceptual-motor patterns we have termed inverted directional processing (IDP). IDP is characterized by inconsistencies in laterality between sensory input, motor output and fine and gross motor movements. We developed the Young/Ginsburg Lateral Directional Assessment (YGLD) to detect and characterize IDP. It is our view that the diagnostic criteria used in previous studies of RDs do not represent biological phenotypes and that IDP does. Also, since the YGLD is not based on reading it is appropriate for preschool populations. ^ In addition, we have ascertained 12 Canadian (131 subjects; 62 affected) and 3 American families (141 subjects; 50 affected) with RD. Due to reports of genetic linkage of RD with DNA markers from 1p34-p36 and an association of a balanced translocation of 1p22;2q31 with dyslexia and delayed speech development, we genotyped our families with 12 STRP markers from the 1p region. Similarly, due to reports of an increased incidence of autoimmune disorders in dyslexics and linkage of dyslexia with DNA markers from 6p21 region (i.e., site of the HLA system), we genotyped our families with 11 markers in the 6p21-p12 region. We are unable to confirm or refute linkage of these markers with dyslexia. This may be attributed to small family size, lack of informative meioses, genetic heterogeneity and/or misdiagnosis. ^