A Prospective Natural History and Outcome Measure Discovery Study of Charcot-Marie-Tooth Disease, Type 4J

This is a multicenter, longitudinal, prospective observational natural history study of subjects with a molecularly confirmed diagnosis of CMT4J. The study will enroll 20 subjects of any age into a uniform protocol for follow-up and evaluations. Subject visits will occur every 12 months + 4 weeks for up to 2 years.

Inclusion Criteria: 1. Male or female, all ages 2. A molecularly-confirmed diagnosis of CMT4J (confirmed by a CLIA certified, CE-marked, or equivalent lab): Genomic DNA mutation analysis demonstrating 1) bi-allelic pathogenic and/or likely pathogenic variants (by ACMG criteria) in the FIG4 gene, or 2) bi-allelic variants with one pathogenic and/or likely pathogenic variant in trans with a variant of uncertain significance if laboratory evidence and expert consensus exits in support of loss of FIG4 function exists. 3. Informed consent from patients 18 years or older who are able to provide consent and from caregivers; parent(s)/guardian(s) providing consent for subjects younger than 18 years at Screening and patients older than 18 years unable to provide informed consent 4. Informed assent of patients younger than 18 years at Screening who are able to provide assent 5. Able and willing to comply with the study protocol, including travel to Study Center, procedures, measurements and visits Exclusion Criteria: 1. Any known genetic abnormality, including chromosomal aberrations that confound the clinical phenotype 2. Current participation in an interventional or therapeutic study 3. Receiving an investigational drug within 90 days of the Baseline Visit 4. Prior or current treatment with gene or stem cell therapy 5. Any other diseases which may significantly interfere with the assessment of CMT4J 6. Have any other conditions, which, in the opinion of the Investigator or Sponsor would make the subject unsuitable for inclusion or could interfere with the subject participating in or completing the study