Electron microscopy of two cases with abundant white matter deposition of PrP amyloid in the frontal cortex. A, B, Case #31 with 6OPRI mutation shows small granular deposits in the axoplasm of a longitudinal section of a myelinated axon, and more substantial fibrillar electron dense deposits in a myelin sheath, that has become divided by these inclusions, raising the possibility of amyloid. C, D; Case #17 with an A117V mutation shows a cross section of a myelinated fibre with the axon (Ax) being separated from the para-axonal inclusion that led to a splitting of the myelin (My) sheath. The red box indicates the region shown in D with a characteristic electron dense deposition, raising the possibility of amyloid. Scale Bars: 1 μm (A, C), 0.5 μm (B, D).