<unk>  is a genetic disorder which in the majority of cases is caused by mutations in the KCNJ2 gene. The condition is often inherited from a parent in an autosomal dominant manner, but may occur due to a new genetic mutation in the affected person. Two types of<unk>  have been described, distinguished by the genetic abnormality that is detected. Type 1<unk><unk> , accounting for about 60% of cases, is caused by mutations in the KCNJ2 gene. In type 2<unk><unk> , accounting for about 40% of cases, a KCNJ2 mutation is not identified. Mutations in a related gene encoding a similar potassium ion channel, KCNJ5, have been identified in some of those with type 2<unk><unk> , but in many cases a genetic mutation is not found. The protein made by the KCNJ2 gene forms an ion channel that transports potassium ions into muscle cells. This specific channel (the inward rectifier potassium channel Kir2.1) carries a potassium current known as IK1 which is responsible for setting the resting membrane potential of muscle cells and is therefore critical for maintaining the normal functions of skeletal and cardiac muscle. Pathogenic mutations in the KCNJ2 gene alter the usual structure and function of potassium channels or prevent the channels from being inserted correctly into the cell membrane. Many mutations prevent a molecule called PIP2 from binding to the channels and effectively regulating their activity. These changes disrupt the flow of potassium ions, leading to the periodic paralysis and abnormal heart rhythms characteristic of<unk> . Type OMIM Gene Notes Type 1<unk>  KCNJ2 Encodes inward rectifying potassium current Kir2.1 carrying the potassium current IK1. Type 2<unk>  KCNJ5 Also known as GIRK4, encodes G protein-sensitive inwardly rectifying potassium channels (Kir3.4) which carry the potassium current IK(ACh).
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