PRNP and dementia: In contrast, patients with the second most frequent phenotype are homozygous for valine in codon 129 of the PRNP gene, accumulate Type 2 PrPSc and manifest a different disease course, with early ataxia, predominant extrapyramidal symptoms, relatively late-onset dementia in the extended course of the disease, and large plaque-like deposits of PrPSc [11, 75].