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Congenital fiber type disproportion--30 years on
Nigel F Clarke1, Kathryn N North
1Institute for Neuromuscular Research, Children's Hospital at Westmead, Discipline of Paediatrics and Child Health, University of Sydney, Sydney, Australia.
Insights
Congenital fiber type disproportion (CFTD) is a distinct diagnostic entity. Its homogeneous phenotype and familial occurrence suggest a genetic basis, supporting its retention in clinical practice.
Area of Science:
- Neurology
- Muscle Biology
- Genetics
Background:
- Congenital fiber type disproportion (CFTD) was initially described 30 years ago.
- The histological pattern of CFTD is now recognized in various neurological disorders.
- This has led to questions about CFTD's status as a distinct nosological entity.
Observation:
- A literature review identified 67 cases of CFTD using strict exclusion criteria.
- Most patients presented with congenital weakness, hypotonia, and normal intelligence.
- Familial occurrence was noted in 43% of cases, suggesting a genetic basis.
Findings:
- CFTD presents with a relatively homogeneous phenotype, supporting its retention as a diagnostic entity.
- Common features include failure to thrive, contractures, and spinal deformities.
- Ophthalmoplegia and bulbar weakness are associated with a poorer prognosis, with 10% mortality from respiratory failure.
Implications:
- The findings support retaining CFTD as a distinct diagnostic entity due to its homogeneous phenotype.
- Familial occurrence highlights the likely genetic basis of CFTD.
- The study found no strong evidence to increase the diagnostic threshold for fiber size difference.
Abstract:
Thirty years ago, M. H. Brooke coined the term "congenital fiber type disproportion" (CFTD) to describe 12 children who had clinical features of a congenital myopathy and relative type 1 fiber hypotrophy on muscle biopsy. It is now clear that this histological pattern can accompany a wide range of neurological disorders, leading to disillusionment with CFTD as a distinct nosological entity. To determine whether the CFTD has clinical utility as a diagnostic entity, we have reviewed the literature for cases of type 1 fiber hypotrophy and have used strict exclusion criteria to identify 67 cases of CFTD. Most patients presented at birth with weakness and hypotonia, had normal intelligence, and followed a static or improving clinical course. In 43% of families, more than 1 individual was affected. Failure to thrive was common and 25% of patients had contractures or spinal deformities. Bulbar weakness and ophthalmoplegia were less common and cardiac involvement was rare. Twenty-five percent followed a severe course and 10% had died at the time of reporting, all from respiratory failure. Ophthalmoplegia and facial and bulbar weakness were significantly associated with a poorer prognosis. The relatively homogeneous phenotype supports the retention of CFTD as a distinct diagnostic entity and familial occurrence suggests a genetic basis. Regarding the diagnosis of CFTD, we found no strong evidence that the minimum difference between type 1 and type 2 fiber sizes should be increased from 12% to 25%. We also list the other reported causes of relative type 1 fiber hypotrophy to aid their exclusion from CFTD.
