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Abstract Background Chromodomain helicase DNA-binding protein 8 (Chd8) is a high-confidence risk gene for autism spectrum disorder (ASD). However, how Chd8 haploinsufficiency impairs gene expression in the brain and impacts behavior at different stages of life is unknown. Methods We generated a mutant mouse line with an ASD-linked loss-of-function mutation in Chd8 (V986*; stop codon mutation). We examined the behavior of Chd8 mutant mice along with transcriptional changes in the cerebral cortex as a function of age, with a focus on one embryonic (E14.5) and three postnatal ages (1, 6, and 12 months). Results Chd8 V986*/+ mutant mice displayed macrocephaly, reduced rearing responses and reduced center time in the open field, and enhanced social novelty preference. Behavioral phenotypes were more evident in Chd8 V986*/+ mutant mice at 1 year of age. Pup survival was reduced in wild-type x Chd8 V986*/+ crosses when the mutant parent was female. Transcriptomic analyses indicated that pathways associated with synaptic and neuronal projections and sodium channel activity were reduced in the cortex of embryonic Chd8 V986*/+ mice and then equalized relative to wild-type mice in the postnatal period. At 12 months of age, expression of genes associated with endoplasmic reticulum (ER) stress, chaperone-mediated protein folding, and the unfolded protein response (UPR) were reduced in Chd8 V986*/+ mice, whereas genes associated with the c-MET signaling pathway were increased in expression. Limitations It is unclear whether the transcriptional changes observed with age in Chd8 V986*/+ mice reflect a direct effect of CHD8-regulated gene expression, or if CHD8 indirectly affects the expression of UPR/ER stress genes in adult mice as a consequence of neurodevelopmental abnormalities. Conclusions Collectively, these data suggest that UPR/ER stress pathways are reduced in the cerebral cortex of aged Chd8 V986*/+ mice. Our study uncovers neurodevelopmental and age-related phenotypes in Chd8 V986*/+ mice and highlights the importance of controlling for age when studying Chd8 haploinsufficient mice.

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