Prion disease (PrP-A117V) presenting with ataxia instead of dementia

Gerstmann-Sträussler-Scheinker disease (GSS) is caused by several different point mutations of the prion protein (PrP) gene, each of which generally produces a distinct clinical phenotype. An ataxic form of GSS is genetically linked to a mutation at codon 102 (CCG-->CTG) leading to the substitution of leucine for proline, while a "telencephalic" variant of GSS, in which dementia is the predominant symptom and ataxia is minimal, has been described in two kindreds with a mutation at codon 117 (GCA-->GTG) resulting in the substitution of valine for alanine. In this report, we present a family with ataxic GSS that has, however, the same mutation at codon 117 as is present in the telencephalic variant of GSS. Other than an additional silent mutation (GCA-->GCG) at codon 117 on the normal allele, there were no other mutations detected. At the polymorphic codon 129, valine was encoded by both alleles in the proband that we studied. Why this family with prion disease (PrP-A117V) should present with ataxia instead of dementia, which was found in two previously identified families with the same PrP gene mutation, remains to be established.