This disease is also known as spongiform encephalopathy (describing the typical microscopic changes in affected brain tissue). It is transmitted by a protein agent known as a prion (proteinaceous infectious agent) that resembles one of the genes in structure. About 90% of cases are sporadic and 5%-15% are hereditary with autosomal dominant transmission. In the hereditary form a gene with point mutation appears to be the cause. The sporadic cases do not show a detectable gene mutation and the mechanism of disease is not known. A similar disease in sheep is called scrapie. Another similar disease in New Guinea tribesmen was known as kuru. In C-J disease, most patients develop symptoms at age 40-60 years (so-called presenile dementia). Symptoms resemble those of Alzheimer’s disease to some degree, but the disease progresses much more rapidly and 90%-95% of patients die within one year. Besides mental changes there is ataxia and myoclonal muscle contractions. The major brain area affected is the cerebral cortex frontal lobe; occasionally patients have occipital lobe or cerebellar involvement. There is neuron death with vacuolization of their cytoplasm accompanied by proliferation of astrocytes and fibrosis but no inflammatory cell response. CSF usually does not show any abnormalities. Diagnosis is made by brain biopsy.