CMT2B is caused by autosomal dominant mutations in the RAB7 gene.
CMT2B symptoms usually start to occur anywhere between the CMTers mid-teens and late 20s. CMTers who have CMT2B will usually experience more sensory loss than muscle weakness, but muscle weakness does occur. CMT2B is considered to be a length dependent CMT. Length dependent means that the longer nerves are more severely affected than the shorter nerves—the feet are more severely affected than the hands because the nerves that go to the feet (the sural nerve, for example), are significantly longer than the nerves that got to the hand (the ulnar nerve, for example). CMT2B progression and overall severity is widely variable.
CMTers who have CMT2B tend to experience severe calluses and ulcerations on their feet. Often, these ulcerations lead to toe amputations due to infections. The severe sensory loss causes the CMTer in this situation to not feel the otherwise painfully infected ulceration.
CMT2B shares many of the same clinical symptoms of a condition called Hereditary Sensory and Autonomic Neuropathy Type 1A, or HSAN-1A for short (OMIM 162400). Some categorize HSAN as another collection of CMT types, and some CMT clinics treat many HSANers.