GSS is an extremely rare inherited disease found in only a few families around the world. It usually occurs between the ages of 35 and 55 but onset has been reported to occur as early as 25. The development of the disease in most individuals has been found to be a change in codon 102 with the substitution of leucine for proline on chromosome 20 in the Prnp gene. The trait is autosomal dominant. In the early stages of the disease individuals may experience a lack of muscle coordination at varying levels such as clumsiness, unsteadiness, and difficulty In walking. As the disease progresses, the lack of muscle coordination becomes more pronounced. Other symptoms that may occur are slurring of speech, involuntary eye movements, dementia, rigidity of muscle tone, visual disturbance that may lead to blindness, and occasionally deafness. As with other prion diseases, there is no cure and no treatment to slow down the development of symptoms. It is a slowly progressive condition that may last from two to ten years. The patient gradually suffers from severe disability and usually dies after going into a coma or suffering from a secondary infection, such as aspiration pneumonia caused by the inability to swallow.