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Gerstmann-Straussler-Scheinker (GSS) syndrome is a very unusual degenerative disease of the brain. Like many degenerative diseases, it is inherited as a dominant genetic trait. However, unlike most genetic traits, GSS is also infectious, and may be transmitted to experimental animals by injecting them with brain material from GSS victims. The infectious agent responsible for GSS is similar to that of kuru, Creutzfeldt-Jakob disease, and the neurological disease of sheep, scrapie. The agents of these diseases have been termed 'prions' to distinguish them from conventional viruses. Unlike conventional viruses, however, prions seem to be composed almost entirely of protein, containing little or no genetic material like DNA or RNA. The prion protein is an aberrant form of a normal human protein; the gene for this protein is found on the short arm of chromosome 20. In many affected families, GSS takes the form of a disease which affects many parts of the brain, but predominantly the cerebral cortex, spinal cord and cerebellum. As more families are identified, however, and more is learned about GSS, it has become clear that the syndrome represents a range of disorders expressing differing ranges of symptoms. Genetic researchers have shown that in cases of GSS with symptoms of cerebellar involvement, patients have a mutation in the 102nd codon, or three-base piece of DNA coding for an amino acid in the prion protein. Researchers have now investigated a family in which the symptoms are not predominantly those of cerebellar involvement, but rather are those of involvement of the frontal lobes of the brain. The researchers found that the prion protein gene was aberrant in these cases as well, but unlike the cases with cerebellar symptoms, in these cases codon 117 was found to contain the mutation. In these cases, the codon was changed in such a way as to substitute the amino acid valine for alanine at this position in the prion protein. These results not only lend further support for the role of the prion protein as the agent responsible for Gerstmann-Straussler-Scheinker syndrome, but they also indicate that variations in the symptoms of the disease are likely to result from differing mutations in the prion protein gene. (Consumer Summary produced by Reliance Medical Information, Inc.)