pediatrics
Familial Periodic Paralysis
Introduction
Familial periodic paralysis is a rare autosomal dominant condition with considerable variation in penetrance. It is characterized by episodes of flaccid paralysis with loss of deep tendon reflexes and failure of muscle to respond to electrical stimulation. There are 4 forms: hypokalemic, hyperkalemic, thyrotoxic, and Andersen-Tawil syndrome. Diagnosis is indicated by history and is based on the results of an exercise test and genetic testing. Treatment depends on the form. Each form of familial periodic paralysis involves different genes and electrolyte channels. In hypokalemic periodic paralysis, 70% of affected people have a mutation in the alpha-subunit of the voltage-sensitive muscle calcium channel gene on chromosome 1q (HypoPP type 1). In some families, the mutation is in the alpha-subunit of the sodium channel gene on chromosome 17 (HypoPP type 2). Although the hypokalemic form is the most common form of familial periodic paralysis, it is nonetheless quite rare, with a prevalence of 1/100,000. Hyperkalemic periodic paralysis is due to mutations in the gene that encodes the alpha-subunit of the skeletal muscle sodium channel (SCN4A). In thyrotoxic periodic paralysis, the mutations and affected electrolyte channels are unknown, but this form usually involves Hypokalemia and is associated with symptoms of Andersen-Tawil syndrome is a rare, Autosomal Dominant disorder usually caused by mutations to the 