KCNJ2 (Kir2.1) Chromosome 17q23, potassium channel gene

ATS is the most recently characterized variant of periodic paralysis and is unique among the periodic paralyses because, in addition to skeletal muscle, other tissues are also affected (Cannon, 2002). Mutations in KCNJ2 (potassium channel gene) cause the cardiac, skeletal muscle, and developmental phenotypes of ATS (M. R. Donaldson, BA, J. L. Jensen, MS, M. Tristani–Firouzi, MD, R. Tawil, MD, S. Bendahhou, PhD, W. A. Suarez, et al., 2003 and Nikki M. Plaster, Rabi Tawil, Martin Tristani-Firouzi, Sonia Canun, Saýd Bendahhou, Akiko Tsunoda, Matthew R. Donaldson, et al., 2001).

The first reports of ATS were provided by Andersen (1971), describing a family with periodic paralysis, ventricular ectopy, and developmental abnormalities. Tawil R, Ptacek LJ, Pavlakis SG, et al. (1994), identified 15 similar cases from eight different kindreds, forming the basis for the current definition of ATS as a triad of potassium-sensitive periodic paralysis, ventricular arrhythmia and dysmorphic features. See link below:

HHMI:Research News: Cause of Rare Genetic Disorder Points to Faulty Ion Channel

Similar to other periodic paralyses, ATS inheritance is autosomal dominant, however, penetrance is highly variable. Cannon (2002), provides the following summary of clinical features:

Affected family members (proven genetically) often have only two or even one of the clinical features of AS. The skeletal muscle dysfunction in AS is similar to other forms of periodic paralysis. Attacks of weakness begin in the first or second decade. Serum potassium during a spontaneous attack is often low, but may be normal, and in some cases has even been high. Mild permanent weakness is another common feature of AS that was observed in 50% of patients. Myotonia is not present symptomatically or by EMG. The CK is usually normal, and the muscle biopsy typically shows mild chronic myopathy with tubular aggregates. Cardiac involvement in AS spans a wide spectrum of ventricular arrhythmias from asymptomatic long QT (LQT) to life-threatening ventricular tachycardia. In a series of 15 patients, the QT interval was prolonged in 12 [9]. Other cardiac defects observed in AS patients include ventricular ectopy, bi-directional ventricular tachycardia, and recurrent torsades de pointe. A constellation of distinctive dysmorphic features has been observed in AS. The most commonly involved structure is the face, which in AS may show low-set ears, broad nose, hypertelorism (wide-set eyes), and micrognathia (small mandible). Deformity of the digits also occurs with clinodactyly of the fingers or syndactyly of the toes. Less commonly occurring physical features include short stature, scoliosis, and high-arched palate.

Additional References:

Mutations in Kir2.1 cause the developmental and episodic electrical phenotypes of Andersen's syndrome Plaster NM, Tawil R, et al

Andersen-Tawil Syndrome Rabi Tawil, Shannon L Venance: March 19, 2007: GeneReviews.

Andersen's syndrome: a distinct periodic paralysis. Sansone V, Griggs RC, et al.

Andersen's syndrome: potassium-sensitive periodic paralysis, ventricular ectopy, and dysmorphic features Tawil R, Ptacek LJ, Pavlakis SG, DeVivo DC, Penn AS, Ozdemir C, Griggs RC.