Marinesco-Sjögren syndrome (MSS) is a rare genetic disorder that affects multiple organ systems of the body. Common symptoms include difficulty coordinating voluntary movements due to degeneration (atrophy) of the cerebellum (cerebellar ataxia), clouding of the lenses of the eyes (cataracts), delays in the acquisition of skills requiring the coordination of muscular and mental activity (psychomotor development), diminished muscle tone (hypotonia), and progressive muscle weakness. Many affected individuals exhibit additional physical abnormalities. Although Marinesco-Sjögren syndrome can be associated with significant disability, lifespan is often unaffected. Marinesco-Sjögren syndrome is caused by mutations of the SIL1 gene and at least one other, presently unknown, gene.