Congenital myopathies are a heterogenous group of primary muscle disorders that are present from birth, although their expression may be delayed until later in infancy or childhood. These conditions are rare. The most common are nemaline myopathy, central core disease, centronuclear/myotubular myopathies, and congenital fiber type disproportion (table 1).
Congenital myopathies share some common features, though severity is highly variable. Affected individuals usually present at birth or in infancy with hypotonia, weakness, hypoactive deep tendon reflexes, delayed motor milestones, and normal intelligence [1,2]. Prominent facial weakness and ptosis are often present; associated findings may include dysmorphic features such as dolichocephaly, a long, narrow face, and a high-arched palate. The weakness is usually generalized or more prominent in proximal and limb-girdle muscles. However, the weakness in some congenital myopathies predominantly affects distal muscles or axial and respiratory muscles. Muscle weakness tends to be stable or slowly progressive over time. In the most severe cases, the presentation is that of the floppy infant with a frog-leg posture and respiratory and bulbar weakness.
The specific congenital myopathies are characterized on the basis of their histologic and histochemical features. These conditions are caused by genetic abnormalities of muscle development. They are distinct from the metabolic myopathies, in which deficiencies of energy production in muscle result from defects in lipid metabolism, glycogenosis, or other metabolic pathways. (See "Causes of metabolic myopathies" and "Overview of inherited disorders of glucose and glycogen metabolism".)
No specific treatment is available for these disorders. Management consists of physical therapy, nutritional support, assisted ventilation if indicated, and genetic counseling.
Nemaline myopathy derives its name from the characteristic rod bodies in muscle that appear threadlike in longitudinal section.