Neurodevelopmental disorders (NDDs) are a heterogeneous group of syndromes that typically manifest early in development. NDDs are characterized by intellectual disability/developmental delay (ID/DD) and resulting cognitive deficits. In our studies, we focus on Witteveen-Kolk Syndrome (WitKoS) characterized by mild ID, growth and feeding difficulties, autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD) and some types of language developmental delay (Balasubramanian et al., 2021). This syndrome is caused by heterozygous loss-of-function mutations in SIN3A, a gene that encodes for a transcriptional repressor and MeCP2 interactor. Preliminary studies performed in vivo proved that functional knockdown of Sin3a leads to reduced cortical neurogenesis and aberrant cortico-cortical projections in the developing mouse brain, as well as altered progenitor proliferation in the prefrontal cortex (Witteveen et al., 2016); however, little is known about the human-specific roles in corticogenesis. To shed light on the pathogenic molecular mechanisms, we generate dorsal forebrain and midbrain organoids from patient-derived iPSCs and characterize them in parallel with control organoids. To account for potential heterogeneity between patient iPSC lines, isogenic iPSC lines for SIN3A have been generated using CRISPR/Cas9-mediated genome editing. The characterization includes proliferation, migration and differentiation assays, through immunofluorescence analyses/morphometrics, as well as gene expression analyses, by means of RNA-seq. Preliminary data suggest that patient-derived dorsal forebrain organoids present a smaller size and an aberrant cytoarchitecture when compared to controls. A better understanding of the underlying biological mechanisms will open doors to investigate the possibility of therapeutic interventions and subsequent improvement of care.