Andersen cardiodysrhythmic periodic paralysis or Andersen-Tawil syndrome 
includes the distinct clinical features of periodic paralysis, cardiac 
arrhythmia, and facial and skeletal dysmorphisms and exhibits autosomal dominant 
inheritance. Mutations in the KCNJ2 gene, which encodes the human inward 
rectifier potassium channel Kir2.1, have been identified in the majority of 
cases. Despite well-established clinical and molecular characteristics, 
treatment is still case oriented, and timely diagnosis could be delayed because 
of the low incidence and phenotypic heterogeneity of this disease. This article 
describes the clinical and molecular features of 3 cases of Andersen-Tawil 
syndrome in 2 families. One of the mutations (G144D) was located in the pore 
selectivity filter residue (which is mutated recurrently) and was considered 
novel. Intermittent muscle weakness in childhood warrants careful evaluation of 
cardiac dysrhythmia and skeletal anomalies.