What is Congenital Fiber Type Disproportion

Congenital Fiber Type Disproportion (CFTD) is a rare congenital myopathy characterized by a specific imbalance in muscle fiber sizes, where type 1 (slow-twitch) fibers are significantly smaller than type 2 (fast-twitch) fibers. This condition primarily manifests as muscle weakness and low muscle tone, often present from birth or early infancy.

What are the symptoms and body systems affected by Congenital Fiber Type Disproportion?

The primary impact of Congenital Fiber Type Disproportion is on the skeletal muscles. Patients often experience generalized muscle weakness (hypotonia), which may affect motor development milestones like sitting, crawling, or walking. Other common clinical features include:

• Joint contractures (tightened joints) and scoliosis.


• High-arched palate and elongated face shape.


• Respiratory insufficiency, which may require monitoring of lung function.


• Hip dislocation, which is frequently observed in infants with the condition.

What causes Congenital Fiber Type Disproportion?

Congenital Fiber Type Disproportion is a genetic disorder. While the exact cause remains unknown in many cases, it has been linked to mutations in several genes, including TPM3, ACTA1, SELENON (formerly SEPN1), and RYR1. These genes are essential for the structure and function of muscle proteins, and their disruption leads to the characteristic fiber size imbalance.

How is Congenital Fiber Type Disproportion diagnosed and classified?

Diagnosis is usually confirmed through a muscle biopsy, which reveals that type 1 fibers are at least 12% to 25% smaller than type 2 fibers. Because Congenital Fiber Type Disproportion shares symptoms with other myopathies, clinicians use genetic testing to differentiate it from conditions like nemaline myopathy or central core disease. The prognosis for Congenital Fiber Type Disproportion varies; many patients show stable or slowly improving strength over time, though respiratory support may be necessary for some.

Is Congenital Fiber Type Disproportion common?

Congenital Fiber Type Disproportion is an extremely rare condition. While precise global prevalence data is not available, it is categorized as a rare disease affecting individuals regardless of gender or geographic location. Within the DiseaseMaps.org community, 17 people with Congenital Fiber Type Disproportion have connected to share their unique experiences and support one another.

Next steps

• Consult with a neuromuscular specialist or pediatric neurologist for a definitive diagnosis.


• Schedule a baseline evaluation with a pulmonologist to monitor respiratory health.


• Connect with the 17 other community members on DiseaseMaps.org to share lived experiences.


• Engage in physical and occupational therapy to maintain joint mobility and muscle function.

Medical disclaimer: This content is for informational purposes only and does not constitute professional medical advice, diagnosis, or treatment.

References

• NIH Genetic and Rare Diseases Information Center (GARD): Congenital fiber type disproportion.


• Orphanet: Congenital fiber type disproportion (ORPHA:1685).


• OMIM (Online Mendelian Inheritance in Man): #255310.


• National Institute of Neurological Disorders and Stroke (NINDS): Congenital Myopathies Overview.