SPAST and hereditary spastic paraplegia: The analysis comparing SPG4 vs. non-SPG4 among HSP subjects showed that in the L pre-central area, the measured levels of mI/Cr in subjects with non-SPG4 were significantly higher than those in subjects with SPG4 (0.58 ± 0.13 vs. 0.69 ± 0.11, p = 0.011, after adjustment for sex and age at T0).