Congenital myopathies are recognized by the clinical features of weakness and hypotonia, which may be obvious at birth or develop within the first weeks or months of life, thus sharing some characteristics with the congenital muscular dystrophies (discussed in Chapter 53). Classification has been based historically on skeletal muscle pathology, which in many cases remains useful in initial clinical workup, directing the choice of more conclusive genetic analyses. The main categories of congenital myopathies are nemaline myopathy, core myopathy, centronuclear myopathy (including X-linked myotubular myopathy), and congenital fiber-type disproportion myopathy (CFTD; see Table 54.1) [1,2]. A variety of additional phenotypes and genotypes are sometimes considered to be congenital myopathies (GeneTable)[3] but are omitted from the discussion here.