A study of 11 patients from 5 kindreds with Andersen’s syndrome (AS), a triad of potassium-sensitive periodic paralysis, ventricular dysrhythmias, and dysmorphic facial features, is reported from the Department of Neurology, University of Milan, Italy; University of Rochester, NY; University of Utah, Salt Lake City; Southwestern Medical Center, Scottish Rite Hospital, Dallas, TX; and Oregon Health Science University, Portland, OR. Episodic attacks of paralysis were associated with hypo-, normo-, or hyperkalemia. A prolonged QT interval (0.47 msec) on ECG was present in all patients and 4 had ventricular arrhythmias, one with cardiac arrest. Dysmorphic features included hypertelorism, broad nose, small mandible, clino- and syndactyly, and two patients had scoliosis. Genetic linkage analysis excluded linkage to the HyperKPP locus on chromosome 17 and the LQT1 locus on chromosome 11. Also, the common HypoKPP dihydropyridine mutations responsible for hypokalemic periodic paralysis were absent. AS is a unique autosomal dominant disorder, genetically distinct from the common forms of periodic paralysis and LQT syndromes. Partial manifestations of the syndrome occur in families, and a prolonged QT interval may be the only sign. 
COMMENT. Andersen’s syndrome is an autosomal dominant familial disorder characterized by hypo- or hyperkalemic periodic paralysis, prolonged QT interval with or without ventricular dysrhythmias, and facial dysmorphic features. Patients presenting with periodic weakness should have a cardiac workup for prolonged QT interval. Potassium challenges may precipitate life-threatening ventricular arrhythmia, and should be avoided in favor of graded exercise to provoke muscle weakness or serum potassium estimation at times of periodic paralysis.
Other metabolic syndromes which can present with dysmorphic features include Smith-Lemli-Opitz, Zellweger, and glutaric acidemia type II (see Menkes JH. In: Progress in Pediatric Neurology III, Millichap JG, ed. Chicago, PNB Publishers, 1997; pp533-535).