The corpus callosum is the largest transverse white matter fiber tract connecting the two hemispheres of the brain. It plays an essential role in the interhemispheric transfer and bihemispheric coordination involved in perception and sensory-motor integration, as well as higher level cognition (e.g., memory, executive functioning). The corpus callosum forms prenatally (10-15 weeks gestation) and continues to develop through early adulthood. Damage to the corpus callosum throughout the lifespan, but especially later in life, can result in sensory and motor coordination deficits and produces disconnection syndromes.

However, individuals born with a partial or fully absent corpus callosum, known as Agenesis of the Corpus Callosum (ACC), do not exhibit a full disconnection syndrome and may, in fact, demonstrate many intact skills including broadly average intellectual abilities. Agenesis of the corpus callosum (ACC) is a relatively common congenital brain malformation that occurs in 1 out of ∼4000 live births (Glass, Shaw, Ma, & Sherr, 2008; Paul et al., 2007). There is significant heterogeneity in outcomes for these individuals, often related to the presence of additional neuropathology, and the presence of co-occurring medical and genetic conditions. In adults for whom ACC is the primary neurological finding, there is a core constellation of cognitive symptoms that include reduced interhemispheric transfer, slowed processing, and difficulty with complex novel problem solving (Brown & Paul, 2019). There is also an elevated likelihood of autism spectrum disorders in this population as well (Paul et al, 2014).

Modern ultrasound technology facilitates diagnosis of ACC in utero, offering a unique opportunity to study these individuals’ development from infancy. However, no studies to date have examined early development in this population using validated measures, leaving neuropsychologists, neurologists and primary care providers to make educated guesses about what families should expect and appropriate therapies/treatment.

This symposium presents a series of studies examining the early development of individuals with primary ACC across domains including language, adaptive skills, autism symptomology, and temperament/anxiety. We will provide the first in-depth prospective characterization of development in ACC relative to typically developing children at 6, 12, 18 and 24 months and discuss what these findings reveal about brain development and plasticity more broadly (e.g. how does early disruption in interhemispheric connection impact cognitive development across key domains?).

Finally, while ACC is defined specifically by corpus callosum anatomy, the corpus callosum has been implicated in other neurodevelopmental conditions (Paul, 2011). Utilizing extant comparison, we also assess how early development in ACC both overlaps and differs from two monogenic conditions (e.g. Fragile X and Down Syndrome) and a developmental behavioral diagnoses (e.g. autism) and discuss how early disruptions in interhemispheric transfer may contribute to shared behavioral phenotypes in these conditions.