Andersen syndrome includes a clinical triad with periodic paralysis, cardiac 
arrhythmia and dysmorphic features most often mild but relevant. It is a 
potassium channelopathy due to mutation of KCJN2 gene coding for Kir 2.1 
protein. We report a familial case with mutation R218W of Kir 2.1 and discuss 
the main phenotypic and genetic aspects of Andersen syndrome. Muscle 
manifestations are essentially a periodic paralysis most often of hypokaliemic 
type. Muscle biopsy reveals tubular aggregates but can be normal as it is shown 
in the same patient in our kindred. Our proband complained of paralytic attacks 
since childhood and at adult age she demonstrated a mild permanent deficit of 
pelvic girdle muscles as it has been described in other types of periodic 
paralysis after a long duration course. Cardiac manifestations may include in a 
variable manner a long QT syndrome, premature ventricular contractions, complex 
ventricular ectopy, polymorphic or bidirectional ventricular tachycardia. 
Imipramine had a positive effect on arrhythmia in our case. Dysmorphic features 
are often mild and have to be cautiously looked for as a clue to the diagnosis 
of Andersen syndrome. They can be easily overlooked if not systematically looked 
for. Clinical expressivity is variable including in the same family. In our 
observation, the daughter showed a complete triad, early expressed, which 
allowed the diagnosis. Her father was late diagnosed on ventricular dysrhytmia 
but without muscle manifestations and dysmorphic features. Since KCJN2 gene 
mutation identification, locus heterogeneity of Andersen syndrome was shown. 
Andersen syndrome kindreds without mutations in KCNJ2 were clinically 
indistinguishable from KCNJ2-associated subjects. KCNJ2 gene encodes the inward 
rectifier K+ channel Kir2.1 which plays an important role in maintaining 
membrane potential and during the terminal phase of cardiac action potential 
repolarization. Several studies showed a dominant negative effect of the 
mutation on Kir 2.1 channel function.