Shank3B mutant mice display pitch discrimination enhancements and learning deficits.

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder characterized by a core set of atypical behaviors in social-communicative and repetitive-motor domains. Individual profiles are widely heterogeneous and include language skills ranging from nonverbal to hyperlexic. The causal mechanisms underlying ASD remain poorly understood but appear to include a complex combination of polygenic and environmental risk factors. SHANK3 (SH3 and multiple ankyrin repeat domains 3) is one of a subset of well-replicated ASD-risk genes (i.e., genes demonstrating ASD associations in multiple studies), with haploinsufficiency of SHANK3 following deletion or de novo mutation seen in about 1% of non-syndromic ASD. SHANK3 is a synaptic scaffolding protein enriched in the postsynaptic density of excitatory synapses. In order to more closely evaluate the contribution of SHANK3 to neurodevelopmental expression of ASD, a knockout mouse model with a mutation in the PDZ domain was developed. Initial research showed compulsive/repetitive behaviors and impaired social interactions in these mice, replicating two core ASD features. The current study was designed to further examine Shank3B heterozygous and homozygous knockout mice for behaviors that might map onto atypical language in ASD (e.g., auditory processing, and learning/memory). We report findings of repetitive and atypical aggressive social behaviors (replicating prior reports), novel evidence that Shank3B KO mice have atypical auditory processing (low-level enhancements that might have a direct relationship with heightened pitch discrimination seen in ASD), as well as robust learning impairments.

Auditory processing and morphological anomalies in medial geniculate nucleus of Cntnap2 mutant mice.

Genetic epidemiological studies support a role for CNTNAP2 in developmental language disorders such as autism spectrum disorder, specific language impairment, and dyslexia. Atypical language development and function represent a core symptom of autism spectrum disorder (ASD), with evidence suggesting that aberrant auditory processing-including impaired spectrotemporal processing and enhanced pitch perception-may both contribute to an anomalous language phenotype. Investigation of gene-brain-behavior relationships in social and repetitive ASD symptomatology have benefited from experimentation on the Cntnap2 knockout (KO) mouse. However, auditory-processing behavior and effects on neural structures within the central auditory pathway have not been assessed in this model. Thus, this study examined whether auditory-processing abnormalities were associated with mutation of the Cntnap2 gene in mice. Cntnap2 KO mice were assessed on auditory-processing tasks including silent gap detection, embedded tone detection, and pitch discrimination. Cntnap2 knockout mice showed deficits in silent gap detection but a surprising superiority in pitch-related discrimination as compared with controls. Stereological analysis revealed a reduction in the number and density of neurons, as well as a shift in neuronal size distribution toward smaller neurons, in the medial geniculate nucleus of mutant mice. These findings are consistent with a central role for CNTNAP2 in the ontogeny and function of neural systems subserving auditory processing and suggest that developmental disruption of these neural systems could contribute to the atypical language phenotype seen in autism spectrum disorder.