On postnatal day (P)4 (Fig. 1a, b), compared to control (ctrl), cKO mice exhibited a 40% decrease in cortical area (ctrl, 21 ± 1.0 mm2; cKO, 13 ± 0.8mm2, mean ± s.e.m, p = 1.3E−3, two-tailed unpaired t-test) and a 32% decrease in cortical plate (CP) thickness (ctrl, 947 ± 9.1 μm; cKO, 643 ± 12.1 μm, p = 2.05E−5), consistent with microcephaly in patients with KNL1 mutations. This evidence concerns the gene KNL1 and microcephaly.