Cross-platform validation of neurotransmitter release impairments in schizophrenia patient-derived <i>NRXN1</i> -mutant neurons

Heterozygous <i>NRXN1</i> deletions constitute the most prevalent currently known single-gene mutation associated with schizophrenia, and additionally predispose to multiple other neurodevelopmental disorders. Engineered heterozygous <i>NRXN1</i> deletions impaired neurotransmitter release in human neurons, suggesting a synaptic pathophysiological mechanism. Utilizing this observation for drug discovery, however, requires confidence in its robustness and validity. Here, we describe a multicenter effort to test the generality of this pivotal observation, using independent analyses at two laboratories of patient-derived and newly engineered human neurons with heterozygous <i>NRXN1</i> deletions. Using neurons transdifferentiated from induced pluripotent stem cells that were derived from schizophrenia patients carrying heterozygous <i>NRXN1</i> deletions, we observed the same synaptic impairment as in engineered <i>NRXN1</i>-deficient neurons. This impairment manifested as a large decrease in spontaneous synaptic events, in evoked synaptic responses, and in synaptic paired-pulse depression. <i>Nrxn1</i>-deficient mouse neurons generated from embryonic stem cells by the same method as human neurons did not exhibit impaired neurotransmitter release, suggesting a human-specific phenotype. Human <i>NRXN1</i> deletions produced a reproducible increase in the levels of CASK, an intracellular <i>NRXN1</i>-binding protein, and were associated with characteristic gene-expression changes. Thus, heterozygous <i>NRXN1</i> deletions robustly impair synaptic function in human neurons regardless of genetic background, enabling future drug discovery efforts.