Mechanistically, the addition of EPIREGULIN did not appear to alter transcriptional programs but rather resulted in altered cell type proportions, as has also been observed for other factors that regulate brain size, such as abnormal spindle-like microcephaly-associated (ASPM), the most common recessive gene associated with human primary microcephaly (Johnson et al, 2018). This evidence concerns the gene ASPM and Primary microcephaly.