Fig. 1.

a Normal nerve, transverse section, H&E 40 × ; (b) Normal nerve, transverse section, Sol. Cyan 40 × ; (c) Normal nerve, longitudinal section, H&E 40 × ; (d) normal nerve, longitudinal section, Sol. Cyan 40 × . All normal nerve sections highlight a normal population of myelinated nerve fibres of appropriate thickness; (e, f) patient 1: Sural Nerve biopsy (TS) at 9 years of age showing marked loss of large diameter (thickly myelinated) nerve fibres, thinly myelinated fibres for axon size, and clusters of thinly myelinated fibres (axonal sprouting) on H&E (e) and Sol. Cyan (f) in keeping with hypomyelinating neuropathy; (g, h) patient 2: Sural Nerve biopsy (TS) at 10 months of age showing modest loss of large diameter (thickly myelinated) fibres, presence of thinly myelinated fibres, clusters of thinly myelinated fibres and a rare onion bulb on H&E (g) and Sol.Cyan (h) consistent with hypomyelination; (i, j) Patient 7: Sural Nerve biopsy (LS) following death at 3 months of age (autopsy specimen). Demonstrates widespread, almost complete loss of myelinated fibres on H&E (i) and Sol. Cyan (j) with a few residual thinly myelinated fibres. k Patient 2: Electron microscopy (EM) highlighting clusters of thinly myelinated fibres with only a few residual appropriately myelinated fibres. Inset highlights single onion bulb in keeping with active demyelination. l. Patient 7: EM highlighting extensive loss of myelinated nerve fibres with a residual rare thinly myelinated fibre. m Electron Microscopy of a normal nerve showing a normal complement of large myelinated fibres and thinly myelinated fibres with proportionate axons