CMFTD can be found in other forms of congenital
myopathy and other diseases (e.g., Duchenne Muscular Dystrophy,
Spinal Muscular Atrophy Syndrome, metabolic myopathies, central nervous system
diseases such as leukodystrophies, Lowe Syndrome, and Moebius
Syndrome); however, it also exists as a distinct diagnostic entity.
Generalized hypotonia and weakness are noticeable at birth, and failure to
thrive is common. The prognosis is often good because the disease is
usually not progressive. In some cases, improvement with age has been
reported. However, in approximately 25% of patients, the course is
severe, with death resulting from respiratory failure in approximately
10% of patients. Skeletal involvement is common and may present with
short stature, (kypho)scoliosis, contractures, joint laxity, and congenital
hip dislocation. Bulbar palsy and ophthalmoplegia are less common and
associated with a poor prognosis. Cardiac involvement (dilated
cardiomyopathy, arrhythmias) is rare, but can be significant and require
medical treatment or even heart transplant. In a minority of these patients,
facial anomalies (e.g., high arched palate) and insulin-resistant diabetes
mellitus have been reported. The diagnosis is confirmed by muscle biopsy,
which commonly shows small, atrophic type I fibers and compensatory
hypertrophic type II fibers. In CMFTD, type I fiber mean diameter should
be at least 12% smaller than that of type II fibers, although some groups
consider a difference of 25% more appropriate. Rarely, a small number of
type I fibers shows signs of hypertrophy.