Table 1.

Key features of CMT1A and HNPP

	CMT1A	HNPP
	Duplication of PMP22	Deletion of PMP22
Clinical features	Age of onset mainly in first two decades	Painless attacks of numbness, muscular weakness, and atrophy, recurrent and focal
	Presenting symptom is difficulty walking or running
		Preceded by minor compression on nerve
	Distal symmetrical muscle weakness and wasting, legs > arms
		Age at onset mostly in the second or third decade
	Pes cavus very frequent	Pes cavus found in 4-47% of patients
	Sensory symptoms (stocking-glove distribution) usually less prominent, legs > arms
		Full recovery in 50% of episodes, usually in days to weeks
	Pain more common than previously recognized	Sequelae rarely severe
		Large intrafamilial clinical variability
	Reflexes absent or depressed
	Large clinical variability between patients, even within family
Electrophysiological features	Homogeneous and diffuse MCV and SCV slowing	Increase in distal motor latencies, especially of median and peroneal nerve
	CMAP amplitudes reduced, especially distally in the legs
		Focal motor slowing at entrapment sites
	SNAP amplitudes frequently reduced to absent
		MCV normal to slightly reduced in other segments
		SCV decreased and SNAP amplitudes often reduced
Neuropathological features	Abnormal myelination over the whole nerve length	Segmental de-and remyelination
	Onion bulbs	Tomacula pathologic hallmark, but not pathognomonic
	Decreased density of myelinated nerve fibres
		Variable large-fibre loss

CMAP = compound muscle action potential. MCV = motor conduction velocity. SCV = sensory conduction velocity. SNAP = sensory nerve action potentials.