CHD8 haploinsufficiency alters the developmental trajectories of human excitatory and inhibitory neurons linking autism phenotypes with transient cellular defects
Chromodomain helicase DNA-binding 8 (CHD8) is one of the most frequently mutated genes causative of autism spectrum disorder (ASD). While its phenotypic spectrum often encompasses macrocephaly and hence implicates cortical abnormalities in this form of ASD, the neurodevelopmental impact of human CHD8 haploinsufficiency remains unexplored. Here we combined human cerebral organoids and single cell transcriptomics to define the effect of ASD-linked CHD8 mutations on human cortical development. We found that CHD8 haploinsufficiency causes a major disruption of neurodevelopmental trajectories with an accelerated generation of inhibitory neurons and a delayed production of excitatory neurons alongside the ensuing protraction of the proliferation phase. This imbalance leads to a significant enlargement of cerebral organoids aligned to the macrocephaly observed in patients with CHD8 mutations. By adopting an isogenic design of patient-specific mutations and mosaic cerebral organoids, we define genotype-phenotype relationships and uncover their cell-autonomous nature. Finally, our results assign different CHD8-dependent molecular defects to particular cell types, pointing to an abnormal and extended program of proliferation and alternative splicing specifically affected in, respectively, the radial glial and immature neuronal compartments. By identifying temporally restricted cell-type specific effects of human CHD8 mutations, our study uncovers developmental alterations as reproducible endophenotypes for neurodevelopmental disease modelling.