Congenital fiber-type disproportion myopathy

Congenital fiber-type disproportion (CFTD) myopathy is a rare inherited muscle disorder classified among the congenital myopathies. It is defined by a characteristic finding on muscle biopsy in which type 1 (slow-twitch) muscle fibers are consistently and significantly smaller (at least 12–25% smaller) than type 2 (fast-twitch) fibers, without other major structural abnormalities. The condition primarily affects the skeletal muscular system and typically presents at birth or in early infancy with generalized muscle weakness (hypotonia), often described as a 'floppy infant.' Key clinical features include diffuse muscle weakness that is usually more prominent in proximal muscles, respiratory insufficiency of variable severity, feeding difficulties, delayed motor milestones, short stature, and skeletal abnormalities such as hip dislocation, joint contractures, scoliosis or kyphosis, and foot deformities. Facial weakness and a high-arched palate are also commonly observed. Some patients may develop ophthalmoplegia (weakness of eye muscles). The severity of CFTD is highly variable. Many affected individuals have a relatively mild and non-progressive or slowly progressive course, with some achieving independent ambulation, while others experience severe respiratory compromise requiring ventilatory support. Cardiomyopathy has been reported in a subset of patients, particularly those with certain genetic subtypes. Several genes have been implicated in CFTD, including TPM3 (tropomyosin 3), RYR1 (ryanodine receptor 1), ACTA1 (skeletal muscle alpha-actin), SELENON (formerly SEPN1), TPM2, and MYH7, reflecting genetic heterogeneity. Inheritance can be autosomal dominant or autosomal recessive depending on the causative gene. There is currently no cure or specific disease-modifying therapy for CFTD. Management is supportive and multidisciplinary, including physical therapy to maintain mobility and prevent contractures, respiratory support when needed, nutritional support for feeding difficulties, orthopedic interventions for skeletal complications, and regular cardiac monitoring in at-risk subtypes.

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