This allows for the following conclusions for clinical practice: (1) The spectrum of ARHGAP26-associated symptoms is broader than initially expected and also includes isolated cognitive impairment; (2) A positive ARHGAP26 antibody-test should prompt the search for an underlying malignancy; and (3) ARHGAP26-mediated autoimmune encephalopathy is a potential, yet rare differential diagnosis in patients with cognitive impairment. The gene discussed is ARHGAP26; the disease is Cognitive impairment.