PRNP and Spastic paraparesis: GSS P105L (GSS105), a rare variant of GSS caused by a point mutation of PRNP at codon 105 (proline to leucine substitution), was first reported in Japan (Kitamoto, Amano, et al., 1993; Yamada et al., 1993) and is clinically characterized by gait disturbance (spastic paraparesis), dementia, or psychiatric disorders (Amano et al., 1992; Isshiki, Minagawa, & Yamauchi, 1994; Itoh et al., 1994; Kitamoto, Amano, et al., 1993; Kubo, Nishimura, Shikata, Kokubun, & Takasu, 1995; Nakazato, Ohno, Negishi, Hamaguchi, & Arai, 1991; Yamada et al., 1993).