In 2012, de Ligt et al. (2012) described a total of three individuals with severe intellectual disability who were found on a large‐scale study of exome sequencing to have germline de novo, likely pathogenic variants in CTNNB1. These patients were also found to share other clinical features, including microcephaly, limited or absent speech, and lower extremity spasticity. The gene discussed is CTNNB1; the disease is microcephaly.