Figure 78-1 The relationships of inherited neuropathies to each other and other syndromes. These Venn diagrams depict that dominantly inherited neuropathies can be separated into demyelinating and axonal forms (A); that inherited demyelinating diseases can be separated into those that cause PNS and/or CNS dysmyelination or demyelination (B); that inherited axonal diseases can be separated into those that cause combinations of a motor neuropathy, sensory neuropathy, or both sensory and motor neuropathy, each of which may also involve CNS axons. ALS, amyotrophic lateral sclerosis; AR-CMT, autosomal recessive Charcot-Marie-Tooth disease; GAN, giant axonal neuropathy; HMSN, hereditary motor and sensory neuropathy; NAD, neuroaxonal dystrophy; SPG, spastic paraplegia.

(Modified from Scherer SS. Finding the causes of inherited neuropathies. Arch Neurol 2006;63:812-6.)

As shown in Table 78-1 and Figure 78-1, multiple genes cause CMT1 and CMT2. The general principle is that myelinating Schwann cells and neurons express the genes that are mutated in CMT1 and CMT2, respectively. In keeping with the idea the DI-CMT could be an axonal or a demyelinating neuropathy, it is not clear in which cells the causal genes exert their deleterious effects.

Table 78-1 The molecular genetics of nonsyndromic inherited neuropathies*

HNPP, hereditary neuropathy with liability to pressure palsies; SMARD1, spinal muscular atrophy, distal, autosomal recessive 1.

* Dominant disorders are bolded; OMIM numbers are listed in parentheses; asterisks denote genes for which genetic testing is available (http://www.genetests.org).

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