Recurrent deletions and duplications at chromosomal region 16p11.2 are variably associated with speech delay, autism spectrum disorder, developmental delay, schizophrenia, and cognitive impairments. Social communication deficits are a primary diagnostic symptom of autism. Here we investigated ultrasonic vocalizations (USVs) in young adult male 16p11.2 deletion mice during a novel three-phase male–female social interaction test that detects vocalizations emitted by a male in the presence of an estrous female, how the male changes its calling when the female is suddenly absent, and the extent to which calls resume when the female returns. Strikingly fewer vocalizations were detected in two independent cohorts of 16p11.2 heterozygous deletion males (+/−) during the first exposure to an unfamiliar estrous female, as compared to wildtype littermates (+/+). When the female was removed, +/+ emitted calls, but at a much lower level, whereas +/− males called minimally. Sensory and motor abnormalities were detected in +/−, including higher nociceptive thresholds, a complete absence of acoustic startle responses, and hearing loss in all +/− as confirmed by lack of auditory brainstem responses to frequencies between 8 and 100 kHz. Stereotyped circling and backflipping appeared in a small percentage of individuals, as previously reported. However, these sensory and motor phenotypes could not directly explain the low vocalizations in 16p11.2 deletion mice, since (a) +/− males displayed normal abilities to emit vocalizations when the female was subsequently reintroduced, and (b) +/− vocalized less than +/+ to social odor cues delivered on an inanimate cotton swab. Our findings support the concept that mouse USVs in social settings represent a response to social cues, and that 16p11.2 deletion mice are deficient in their initial USVs responses to novel social cues.

Chromosomal 16p11.2 deletion syndrome frequently presents with intellectual disabilities, speech delays, and autism. Here we investigated the Dolmetsch line of 16p11.2 heterozygous (+/2) mice on a range of cognitive tasks with different neuroanatomical substrates. Robust novel object recognition deficits were replicated in two cohorts of 16p11.2+/2 mice, confirming previous findings. A similarly robust deficit in object location memory was discovered in +/2, indicating impaired spatial novelty recognition. Generalizability of novelty recognition deficits in +/2 mice extended to preference for social novelty. Robust learning deficits and cognitive inflexibility were detected using Bussey-Saksida touchscreen operant chambers. During acquisition of pairwise visual discrimination, +/2 mice required significantly more training trials to reach criterion than wild-type littermates (+/+), and made more errors and correction errors than +/+. In the reversal phase, all +/+ reached criterion, whereas most +/2 failed to reach criterion by the 30-d cutoff. Contextual and cued fear conditioning were normal in +/2. These cognitive phenotypes may be relevant to some aspects of cognitive impairments in humans with 16p11.2 deletion, and support the use of 16p11.2+/2 mice as a model system for discovering treatments for cognitive impairments in 16p11.2 deletion syndrome.Recurrent heterozygous deletions of a 600-kb segment on human chromosome 16 is found in 0.4% of individuals with intellectual disability (Bijlsma et al. 2009;Hanson et al. 2015) and 0.6% of individuals with autism (Marshall et al. 2008;Weiss et al. 2008;Walsh and Bracken 2011). 16p11.2 deletion syndrome presents with a range of mild-to-severe cognitive impairments, with IQ scores averaging 2 SDs lower than controls, and a confirmed diagnosis of autism in 15% of affected individuals (Hanson et al.

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