Figure 6.

Myotonic myopathy with secondary joint and bone anomalies is a dominantly expressed allelic disorder on the spectrum of SCN4A sodium channelopathies of skeletal muscle. The top row depicts the primary clinical manifestations, which may be overlapping in specific disorders (second row). Dashed lines are used to indicate fluctuating muscle weakness for myotonic myopathy and for myasthenic myopathy, as distinct from the more clearly demarcated attacks of classical periodic paralysis that usually have well-defined trigger factors (solid lines). The bars show the overlap of different functional defects of mutant sodium channels, with the more intense color indicating more severe changes. The final row indicates the inheritance pattern for expression of symptoms.