The fundamental building blocks of cortical development are established in human exencephaly

Background: The presence and status of progenitor/stem cells in excencephalic brain have not been previously examined. Methods: Brain sections of excencephalic 17-week fetus were stained for specific stem and mature cell markers. Results: The ventricles were open, the developing cerebral cortex was thin in the radial dimension, and the ventricular surface was undulated. There was a decreased ratio of subventricular/ventricular zone radial glia precursor cells (RGCs; PAX6⁺ and HOPX⁺ cells), a decreased number of intermediate progenitor cells (IPCs; TBR2⁺), a decreased number of neurons (MAP2⁺), and an increased number of astrocytes (S100b⁺), compared to the control. MAP2⁺ neurons, S100b⁺ astrocytes, and OLIG2⁺ oligodendrocytes were present within the subventricular zone. Conclusions: This indicates that the underlying condition did not initially preclude radial glial cells from undergoing asymmetric divisions that produce IPCs but halted the developmental progression. RGC and IPC presence in the developing cerebral cortex demonstrates that the fundamental building blocks of cortical formation had been established and that a normal sequence of developmental steps had been initiated in this case of exencephaly. These data expand our understanding of exencephaly etiology and highlight the status of cortical progenitor cells that may be linked to the disorder.