The purpose of this study is to develop and validate a clinical outcome measure to evaluate disability and disease progression of children 3 years of age and younger (infants and toddlers) with various types of Charcot-Marie-Tooth disease (CMT).

Most forms of CMT begin in childhood and progress throughout a person's lifetime. Current research suggests that treatment to slow disease progression may be most effective if introduced early in a patient's life before muscle weakness and sensation loss develop, as it may be easier to slow disease progression than to reverse disability that is already in place. Clinical outcome measures have been developed for adults (CMT Neuropathy Score) and for children 3 years of age and older (CMT Pediatric Scale). However, no CMT-specific clinical outcome measure currently exists to measure disease severity or progression in children from birth to 3 years of age. It is the goal of this study to develop and validate the CMT Infant Scale (CMTInfS) to meet this need.

Inclusion Criteria (patients with CMT):

• Patient is ≤4 years of age
• Parent(s) or guardians have agreed for the child to take part in the study and have signed an informed consent form.
• Patient has known or probable inherited neuropathy
• Patient participates in the INC Natural History Study (INC 6601)

Inclusion Criteria (controls):

• Participant is ≤4 years of age
• Parent(s) or guardians have agreed for the child to take part in the study and have signed an informed consent form.
• Participant does NOT have an inherited neuropathy as determined by the investigator
• Participant is an unaffected friend or family member of a patient with CMT (patient does not have to be included in the study)

Exclusion Criteria (patients with CMT):

• Patient has a known condition of acquired neuropathy including toxic (e.g. medication related), metabolic (e.g. diabetic), immune mediated or inflammatory (AIDP or CIDP) neuropathies, a neuropathy related to leukodystrophy, or a congenital muscular dystrophy.
• Patient has a severe general medical condition, as determined by the site Principal Investigator.
• Patient has known normal nerve conductions of upper and lower limbs. This will be considered as exclusion criteria because it documents that the child does not have a large-fibre neuropathy. However, patients will not be required to have nerve conduction studies (NCS) or electromyography (EMG).

Patients who are 4 years of age and under who are also enrolled in the 6601 study and have performed all tasks to complete the CMTInfant Scale will be recruited for participation. Participation entails allow the information collected in the 6601 study be used for validation in the current study.