Allelic contribution of Nrxn1 to autism-relevant behavioral phenotypes in mice

Author summaryDeletions of one of the two copies of the Neurexin1 (NRXN1) gene are among the most common genetic anomalies in autism spectrum disorder (ASD), a neurodevelopmental condition afflicting 1 in every 44 children in the United States. How NRXN1 deletions, which can occur at various positions across the gene, contribute to behaviors associated with autism remains unknown. Here we investigated mouse models carrying different deletions across the Nrxn1 gene, mimicking three distinct ASD-associated deletions observed in humans, and assessed autism-related mouse behaviors. We found that ASD-relevant behavioral traits in mice are dependent on the sex of the animal and the position of the deletion, and that losing one copy of the Nrxn1 gene (producing a similar genetic structure to humans with ASD) elicits behaviors akin to the core symptoms of autism: impaired social communication and restricted/repetitive behaviors. Additionally, circadian activity is markedly altered in mice lacking functional Nrxn1 product, consistent with sleep disturbance being the most common comorbidity in autism. Our findings support the importance of sex, genetic structure, and the amount of functional NRXN1 product in eliciting ASD-relevant behaviors, and the need for animal models carrying anomalies at multiple genes to elucidate the genetic underpinnings of autism. Copy number variations (CNVs) in the Neurexin 1 (NRXN1) gene, which encodes a presynaptic protein involved in neurotransmitter release, are some of the most frequently observed single-gene variants associated with autism spectrum disorder (ASD). To address the functional contribution of NRXN1 CNVs to behavioral phenotypes relevant to ASD, we carried out systematic behavioral phenotyping of an allelic series of Nrxn1 mouse models: one carrying promoter and exon 1 deletion abolishing Nrxn1 alpha transcription, one carrying exon 9 deletion disrupting Nrxn1 alpha protein translation, and one carrying an intronic deletion with no observable effect on Nrxn1 alpha expression. We found that homozygous loss of Nrxn1 alpha resulted in enhanced aggression in males, reduced affiliative social behaviors in females, and significantly altered circadian activities in both sexes. Heterozygous or homozygous loss of Nrxn1 alpha affected the preference for social novelty in male mice, and notably, enhanced repetitive motor skills and motor coordination in both sexes. In contrast, mice bearing an intronic deletion of Nrxn1 did not display alterations in any of the behaviors assessed. These findings demonstrate the importance of Nrxn1 alpha gene dosage in regulating social, circadian, and motor functions, and the variables of sex and genomic positioning of CNVs in the expression of autism-related phenotypes. Importantly, mice with heterozygous loss of Nrxn1, as found in numerous autistic individuals, show an elevated propensity to manifest autism-related phenotypes, supporting the use of models with this genomic architecture to study ASD etiology and assess additional genetic variants associated with autism.