NTRK2 and microcephaly: Indeed, recent data have shown that overacidification of TrkB-containing organelles in the absence of the Christianson syndrome protein NHE6, an Na+/H+ exchanger known to underlie postnatal microcephaly, intellectual disability, epilepsy and autism52, 53, results in defective neuronal arborization52 akin to loss of AP-2 or ATG5 reported here.