Agenesis of the corpus callosum and the establishment of handedness.

The goal of this study was to check whether an isolated agenesis of the corpus callosum, detected in utero with ultrasound recording, would impair the early development of unimanual and bimanual handedness. Twelve infants with isolated agenesis of the corpus callosum, either total (TACC) or partial (PACC) were tested for handedness at the end of their first year, and were compared to infants with typical development (TD), matched for age and sex. A majority of infants showed right-handedness at the unimanual grasping tasks, with no significant difference between the TD and ACC groups. When the object was presented to the left, the TACC infants were more likely to grasp the object with their right hand (with or without the left hand) than both the TD and the PACC infants who used mostly the ipsilateral left hand. The only significant difference between TD and ACC infants concerned bimanual coordination, as less ACC infants (especially TACC) succeeded at the bimanual task, compared with TD infants. In addition, the strategy of the former tended to be less right-handed than that of the latter. Our results confirm the role of the CC in bimanual coordination, indicating that the early emergence of bimanual coordination and, if confirmed, bimanual handedness, are likely to be delayed in the absence of corpus callosum, especially if agenesis is total. They do not support the idea that the CC is necessary for the early onset of handedness.