King syndrome: further clinical variability and review of the literature.

The King syndrome is characterized by a Noonan-like phenotype, the presence of a nonspecific myopathy and a predisposition to malignant hyperthermia. In some families, mild physical manifestations of the phenotype and/or elevated serum creatine phosphokinase (CPK) in relatives suggest the presence of an autosomal dominant myopathy with variable expressivity. We summarize the cases of 14 previously reported patients and describe a new patient, a 7-year-old girl, with the King syndrome and the unique findings of diaphragmatic eventration, tethered spinal cord, and severe paucity of type 2 skeletal muscle fibers. It has been proposed that the King syndrome represents a common phenotype that may result from several different slowly progressive congenital myopathies. This hypothesis, and the phenotypic overlap between the King and Noonan syndromes are discussed in light of the findings in this new patient.