Next-generation cell-free DNA sequencing (Karius Test, Karius Inc, Redwood City, California, USA [43]) helped to establish the diagnosis of acute toxoplasmosis in one case of cerebral toxoplasmosis with high positive T. gondii IgM titers, but negative T. gondii IgG and negative T. gondii PCR in the patient’s CSF. The gene discussed is CD40LG; the disease is cerebral toxoplasmosis.