Quantification of the cellular composition of brain organoids showed a decrease in MAP2+ neurons within MID1 mutant organoids (M-OS/het, M-OS/male, J-OS/het, J-OS/hom, A-OS/het, A-OS/hom) compared to MID1 wildtype organoids (M-ctrl, J-ctrl, A-ctrl) (d30: Fig. 5b–d, Fig. S7d; d50: Fig. S7e–g), recapitulating microcephaly and hypoplasia of the cerebellum observed in OS patients. This evidence concerns the gene MID1 and microcephaly.