A syndrome of short stature; generalized myotonia with contractures of major joints, microstomia, and muscle rigidity; ocular anomalies, mainly blepharophimosis; and characteristic facies marked by pinched or frozen smile puckered lips. Some degree of mental retardation occurs in about 25% of patients. The affected children usually appear normal at birth and the symptoms become recognizable at 1 to 3 years of age. Malignant hyperthermia is a potentially lethal hazard during anesthesia.