Congenital fiber-type disproportion (CFTD) refers to a group of myopathies histopathologically characterized by type 1 fiber atrophy often associated with type 1 fiber predominance. These changes are common to muscular dystrophy and other hereditary myopathies; therefore, it is important to rule out other conditions (based on histopathological features) prior to diagnosing CFTD.
Etiologically, CFTD is attributed to mutations in the α-skeletal actin 1 (ACTA1), α-tropomyosin 3 (TPM3), SEPN1, and RYR1 genes.
CFTD is clinically characterized by non-progressive proximal muscle weakness and is often associated with skeletal anomalies such as kyphoscoliosis, ankylosing spondylitis, and joint contractures. Serum CK levels remain normal. A small percentage of patients show severe symptoms including respiratory failure and mental retardation.