The genomic background of patients and the Kif4-mutant mice exhibit a high embryonic mortality rate and developmental delay. (A) The pedigree chart of a Kif4 mutation-carrying family. Note that III-1, IV-1, and IV-2 (Kif4a^WT/Mut) exhibited no symptoms, whereas IV-3 (Kif4a^Mut/Y) showed global developmental delay, severe intellectual disability, and intractable seizure. (B) Illustration of the mouse KIF4 protein with its point mutation identified from the patients. LCR, low complexity region; CC, coiled coil; CXC, tesmin/TSO1-like CXC domain. (C) Coiled–coil prediction of the mouse KIF4 peptide from amino acid 524–732. Note that the Mut-KIF4 has a higher coil probability, as indicated with the asterisks. (D) Mouse mating strategy and the mortality rate. The embryonic mortality rate of Kif4 mutation-carrying mice (Mut, 26%) is significantly higher than that of wild-type mice (WT, 7%) Data are presented as mean ± SEM (n = 12 mating mouse pairs). ***P < 0.001 (Student’s t tests). (E) The composition of the offspring genotypes from the Kif4-mutant background exhibited a lower Kif4^Mut/Y pup population (n = 6 mating mouse pairs). (F) The photograph of Kif4^WT/Y and Kif4^Mut/Y mice at E16.5 and the statistical analysis results of embryo size. Data are presented as mean ± SEM (n = 8 mouse pairs). ****P < 0.0001 (Student’s t tests). (G) The postnatal weight comparison between Kif4^WT/Y and Kif4^Mut/Y mice from P3 to P14. Data are presented as mean ± SEM (n = 12 mouse pairs). *P < 0.05, **P < 0.01 (two-way ANOVA). (H) The assessment of Kif4^WT/Y and Kif4^Mut/Y mouse developmental milestones. Note that Surface Righting, Auditory, Open field, and Air Righting exhibited statistical significance. Data are presented as mean ± SEM (n = 12 mouse pairs). *P < 0.05, **P < 0.01, ***P < 0.001 (two-way ANOVA). (I) HE staining of sagittal mouse brain sections from the indicated genotypes at E16.5 and the corresponding statistical analysis of the hippocampal cell density. The red stars in the left panels indicate the hippocampus regions that are magnified in the right panels. Scale bars, 1000 μm (left panel) and 100 μm (right panel). Data are presented as mean ± SEM (n = 12 hippocampi from 6 mouse pairs). ****P < 0.0001 (Student’s t tests).