Congenital neuromuscular disease with uniform type-1 fibers, presenting early stage dystrophic muscle pathology.

We report two male siblings presenting with severe hypotonia, generalized muscle atrophy, multiple joint contractures and respiratory failure. The serum creatine kinase levels were within normal limits, 75 IU/l in the younger boy and 123 IU/l in the older one. Muscle biopsies at the age of 28 days in the younger boy and 48 days in the older one revealed dystrophic pathology with increased interstitial fibrous tissue, scattered basophilic fibers and an increased number of undeveloped type-2C fibers. Although the elder brother died from respiratory failure at 4 months of age, the younger child has been sustained with mechanical ventilation, and has been exhibiting non-progressive muscle symptoms. Upon re-biopsy of the younger sibling at the age of 3 years, neither basophilic regenerating fibers nor degenerating fibers were found. All muscle fibers were found to be extremely atrophic and behaved mostly like type-1 fibers, displaying the features of congenital neuromuscular disease with uniform type-1 fibers. Since early biopsies in congenital myopathies reveal numerous undifferentiated immature muscle fibers, it is difficult to make a definite diagnosis, unless we recognize disease-specific cytoplastic abnormalities of nemaline body formation and abnormalities of core structure.