In the hippocampus, although the total dendritic spines were similar to that of the wild type, the density of mushroom dendritic spines in Kif15-/- mice of 11 weeks old was still less than that in WT mice(Fig 1J,1M), suggesting that the Kif15-/- mice still had developmental delay in adulthood. This evidence concerns the gene KIF15 and Global developmental delay.