Shank3 mutations and HCN channelopathy: one size does not fit all

Abstract

Autism, from the Greek autos ("self") and ismos ("action") was initially described as a congenital lack of interest in other people. Approximately 1 in 88 children in the United States is currently diagnosed with autism spectrum disorder (ASD). ASD symptoms begin early in childhood and include social-interaction deficits and stereotyped, repetitive behavioral interests that interfere with daily activities. Recent large-scale genomic studies suggest an association between ASD and mutations in the SHANK3 gene (SH3 and multiple ankyrin repeat domains protein 3) (Leblond et al., 2014), which encodes a scaffolding protein enriched at the postsynaptic density fraction (PSD) of glutamatergic synapses. The full length SHANK3 protein contains several domains for protein–protein interactions: ANK domain, SH3 domain, PDZ domain, proline-rich region domain and SAM domain. In mice, the Shank3 gene has 22 exons, 6 intragenic promoters and 5 alternative splicing exons, resulting in diverse protein isoforms, namely isoforms lacking some interaction domains (Monteiro and Feng, 2017). Likely due to these intragenic promoters, multiple research groups have failed to fully delete all SHANK3 isoforms in mutant mouse lines.

Out of 13 mouse lines that have been generated with experimental Shank3 mutations, 9 mutant lines show aberrant social behaviors, and 9 display repetitive behavior. These mutant mice carrying experimental mutations are thus highly valuable for understanding Shank3 role, but also reveal that each mutation within the Shank3 gene has unique physiological impact and should perhaps be studied individually.