a Diagram of the pedigree, including a pair of monozygotic twins discordant for SA-B. DT1_A, affected twin; DT1_U, unaffected twin; C1, mother; C2, father. b Schematic protocol for the generation of cerebral organoids. c Overview of sample preparation for scRNA-seq. The 7-AAD− live single cells dissociated from two organoids of each iPSC clone were sorted into 384-well plates containing cell lysis buffer with barcoding primers. d t-distributed stochastic neighbor embedding (tSNE) plot according to cellular maturity based on the expression patterns of marker genes. e tSNE plots based on cellular maturity. Data from DT1_A and DT1_U are shown separately. Proportion of proliferative progenitors and postmitotic cells among the neuronal population (f) and of non-cycling cells and cycling cells among proliferative progenitors (g). h tSNE plot according to neuronal subtypes based on the expression patterns of marker genes. i tSNE plots based on the neuronal subtypes. Data from DT1_A and DT1_U are shown separately. The breakdown of postmitotic cells (j) and proliferative progenitors (k). Fisher’s exact test: **p < 0.01; ***p < 0.001; ****p < 0.0001; n.s. not significant (f, g, j and k). See also Figs. S2–4.