Cited research: Neuron 66, 386–402 (2010)

Babies with a genetic disorder called primary autosomal-recessive microcephaly are born with unusually small brains. Five genes have been implicated, and it is thought that a defect in the pool of neural progenitor cells — the precursors of more specialized brain cells — is to blame.

Li-Huei Tsai at the Massachusetts Institute of Technology in Cambridge and her group showed how a protein encoded by one of these genes, Cdk5rap2, is linked to the defect by knocking it down in the neocortex of mouse embryos. This caused the progenitor-cell pool to shrink because more cells developed prematurely into neurons instead of replenishing the progenitor supply.

The team also found that, to do its job, Cdk5rap2 interacts with another protein, pericentrin. Malfunctioning pericentrin is associated with another disorder involving abnormal brain size. C.L.