Investigations for autoimmune causes of encephalitis all yielded negative results, including testing for antibodies to myelin oligodendrocyte glycoprotein aquaporin 4, N-methyl-d-aspartate (NMDA) receptor, contactin-associated protein-like 2 (CASPR2), leucine-rich glioma-inactivated 1 (LGI-1), gamma aminobutyric acid-B (GABA-B), dipeptidyl-peptidase-like protein 6 (DPPX), and immunoglobulin-like cell adhesion molecule 5 (IgLON5). The gene discussed is CNTNAP2; the disease is encephalitis.