Gerstmann–Sträussler–Scheinker syndrome  Gerstmann–Sträussler–Scheinker syndrome (GSS) is an extremely rare, usually familial, fatal neurodegenerative disease that affects patients from 20 to 60 years in age. It is exclusively heritable, and is found in only a few families all over the world (according to NINDS). It is, however, classified with the transmissible spongiform encephalopathies (TSE) due to the causative role played by PRNP, the human prion protein. GSS was first reported by the Austrian physicians Josef Gerstmann, Ernst Sträussler and Ilya Scheinker in 1936. Familial cases are associated with autosomal-dominant inheritance. Certain symptoms are common to GSS, such as progressive ataxia, pyramidal signs, and even adult-onset dementia; they progress more as the disease progresses. Symptoms start with slowly developing dysarthria (difficulty speaking) and cerebellar truncal ataxia (unsteadiness) and then the progressive dementia becomes more evident. Loss of memory can be the first symptom of GSS. Extrapyramidal and pyramidal symptoms and signs may occur and the disease may mimic spinocerebellar ataxias in the beginning stages. Myoclonus (spasmodic muscle contraction) is less frequently seen than in Creutzfeldt–Jakob disease. Many patients also exhibit nystagmus (involuntary movement of the eyes), visual disturbances, and even blindness or deafness. The neuropathological findings of GSS include widespread deposition of amyloid plaques composed of abnormally folded prion protein. Four clinical phenotypes are recognised: typical GSS, GSS with areflexia and paresthesia, pure dementia GSS and Creutzfeldt-Jakob disease-like GSS. GSS is one of a small number of diseases that are caused by prions, a class of pathogenic proteins highly resistant to proteases. A change in codon 102 from proline to leucine has been found in the prion protein gene ("PRNP", on chromosome 20) of most affected individuals. Therefore, it appears this genetic change is usually required for the development of the disease. GSS can be identified through genetic testing. Testing for GSS involves a blood and DNA examination in order to attempt to detect the mutated gene at certain codons.