OTX2 and microcephaly: Despite the low prevalence of microcephaly in patients with OTX1 or OTX2 variants, it is worth focusing on these OTX genes as potential causal genes for microcephaly, given the severity of the brain phenotypes observed in mice (Acampora et al., 1995; Matsuo et al., 1995; Ang et al., 1996; Simeone, 1998).