The most dreaded complications of this disease are neurosyphilis and the involvement of the aortic valve and root.[1] Here, we report a patient with cerebral infarct and presumed latent syphilis with negative serum rapid plasma reagin (RPR) and syphilis-specific IgM tests, even though motile T pallidum was detected in the patient's cerebrospinal fluid (CSF) by RIT. The gene discussed is CD40LG; the disease is latent syphilis.