The birth of a human being requires billions of cell divisions to go from a fertilized egg to a baby. At each of these divisions, the genetic material of the mother cell duplicates itself to be equally distributed between the two new cells. In primary microcephaly, a rare but serious genetic disease, the ballet of cell division is dysregulated, preventing proper brain development. Scientists from the University of Geneva (UNIGE), in collaboration with Chinese scientists, have demonstrated how the mutation of a single protein, WDR62, prevents the proper formation of the cable network responsible for separating genetic material into two. As cell division is then slowed down, the brain does not have time to build itself completely. These results, to be read in the Journal of Cell Biology, shed new light on cell division, a phenomenon also involved in cancer development.