Schizophrenia has been linked to severely damaging de novo mutations in synaptic junction proteins, neurotransmitter receptors, transcription factors, and chromatin remodeling proteins. In a patient with schizophrenia in the absence of a family history of severe mental illness, we identified de novo nonsense mutation, INO80D p.Q568X, associated with both a truncated protein and partial nonsense-mediated decay. Three experiments were undertaken to evaluate the consequences of the mutation. 1) In neural stem cells (iNSCs) differentiated from WTC11 iPSCs, CRISPRi knockdown of INO80D led to downregulation of three subunits of the AMPA-glutamate receptor, of multiple genes mutant in schizophrenia, and of genes of synaptic function. 2) INO80D p.Q568X iNSCs and neurons differentiated from patient-derived induced pluripotent stem cells (iPSCs) had significantly lower expression of neurogenesis genes compared to patient-derived cells with the mutation corrected by CRISPR-Cas9 gene editing. Patient-derived INO80D p.Q568X neurons had significantly higher expression of cell division genes compared to lines with the mutation corrected, consistent with the possibility that some of these cells may be undergoing mitosis, which is not normal for neurons. 3) Finally, on microelectrode array (MEA) plates, WTC11-derived glutamatergic neurons with reduced expression of INO80D had more rapid firing rate and increased average network burst duration, both features of neurons derived from patients with neurodevelopmental disorders. Overall, these findings suggest that partial loss of INO80D function due to de novo mutation may have disrupted normal neurodevelopment and contributed to the schizophrenia of this patient.
Sunshine et al. (Thu,) studied this question.