Melkersson–Rosenthal syndrome is a rare neurological disorder characterized by recurring facial paralysis, swelling of the face and lips (usually the upper lip: cheilitis granulomatosis) and the development of folds and furrows in the tongue (fissured tongue).^: 799 Onset is in childhood or early adolescence. After recurrent attacks (ranging from days to years in between), swelling may persist and increase, eventually becoming permanent. The lip may become hard, cracked, and fissured with a reddish-brown discoloration. The cause of Melkersson–Rosenthal syndrome is unknown, but there may be a genetic predisposition. It has been noted to be especially prevalent among certain ethnic groups in Bolivia. It can be symptomatic of Crohn's disease or sarcoidosis. Approximately 400 cases have been reported worldwide.