Heterogeneity of nemaline myopathy. A follow-up study of 13 cases.

The marked heterogeneity of nemaline myopathy is again shown in the present series of 13 patients. Most children have a long-standing, mild, and slowly progressing proximal myopathy. Two brothers with extreme weakness died during the neonatal period of respiratory failure representing the X-linked variant. One adult with proximal weakness was also diagnosed as having nemaline myopathy. An unusual course was observed in 2 infants who initially had moderate weakness but subsequently developed severe generalized weakness including respiratory muscles. This led to irreversible respiratory failure requiring continuous ventilatory support for as long as 9 and 15 years, respectively. Although uncommon, the possibility of an imminent respiratory failure in initially weak infants should also be taken into account within the clinical spectrum of nemaline myopathy.