Congenital Fiber Type Disproportion is a rare genetic disorder that affects the muscles of the body. It is characterized by a difference in the size of muscle fibers. Although there are no synonyms for the term itself, there are other terms used to describe the condition, including Congenital Fiber Type Disproportion Myopathy and Type 1 Fiber Predominance. These terms all refer to the same condition where type 1 muscle fibers are disproportionately larger than type 2 fibers. This results in muscle weakness, low muscle tone, and delayed motor development. Although there is no cure for this condition, physical therapy and exercise can help improve muscle strength and function.