Gerstmann–Sträussler–Scheinker syndrome (GSS) is an extremely rare, always fatal (due to it being caused by prions) neurodegenerative disease that affects patients from 20 to 60 years in age.

[1] It is, however, classified with the transmissible spongiform encephalopathies (TSE) due to the causative role played by PRNP, the human prion protein.

[6] Symptoms start with slowly developing dysarthria (difficulty speaking) and cerebellar truncal ataxia (unsteadiness) and then the progressive dementia becomes more evident.

[9] The neuropathological findings of GSS include widespread deposition of amyloid plaques composed of abnormally folded prion protein.

[11] The P102L mutation, which causes a substitution of proline to a leucine in codon 102, has been found in the prion protein gene (PRNP, on chromosome 20) of most affected individuals.

[9] Testing for GSS involves a blood and DNA examination in order to attempt to detect the mutated gene at certain codons.

Nystagmus (rapid movement of the eyes in one direction, followed by a slower drift back to the original position) and deafness may develop.

Usually, the muscles that control breathing and coughing are impaired, resulting in a high risk of pneumonia, which is the most common cause of death.