PRNP and nervous system disorder: Tg mice overexpressing Mo-PrP with the D177N mutation (the human homologue of D178N in fCJD) along with the polymorphic amino acid substitution of M128V (the human homologue of M129V) 2 times higher than PrPC in WT mice were also reported to develop neurological disease around 150 days of age, with ataxia, kyphosis, and foot clasping (Table 1) [66].