Given the microcephaly present in some of the affected individuals and the reduced brain size and skull width in the mouse model, this could be suggestive of decreased neuronal proliferation or reduced survival of the post-natal neurogenic population or of post-mitotic neurons as seen postnatally in biallelic loss of Bcl11a. 16Further studies are required to distinguish between these possible mechanisms in the heterozygous brain. The gene discussed is BCL11A; the disease is microcephaly.