Hypokalemic periodic paralysis
| Hypokalemic periodic paralysis | |
|---|---|
| Classification and external resources | |
| Specialty | neurology |
| ICD-10 | G72.3 |
| ICD-9-CM | 359.3 |
| OMIM | 170400 613345 |
| DiseasesDB | 6465 |
| MedlinePlus | 000312 |
| MeSH | D020514 |
| GeneReviews | |
| Orphanet | 681 |
Hypokalemic periodic paralysis (hypoKPP) is a rare, autosomal dominant channelopathy characterized by muscle weakness or paralysis with a matching fall in potassium levels in the blood (primarily due to defect in a voltage-gated calcium channel). In individuals with this mutation, attacks often begin in adolescence and most commonly occur on awakening or after sleep or rest following strenuous exercise (attacks during exercise are rare), high carbohydrate meals, meals with high sodium content, sudden changes in temperature, and even excitement, noise, flashing lights and induced by cold temperatures. Weakness may be mild and limited to certain muscle groups, or more severe full-body paralysis. During an attack reflexes may be decreased or absent. Attacks may last for a few hours or persist for several days. Recovery is usually sudden when it occurs, due to release of potassium from swollen muscles as they recover. Some patients may fall into an abortive attack or develop chronic muscle weakness later in life.
Some people only develop symptoms of periodic paralysis due to hyperthyroidism (overactive thyroid). This entity is distinguished with thyroid function tests, and the diagnosis is instead called thyrotoxic periodic paralysis.
Mutations in the following genes can cause hypokalemic periodic paralysis:
An association with KCNE3 (voltage-gated potassium channel) has also been described, but is currently disputed, and excluded from the disease definition in OMIM.
Action potentials from the central nervous system cause end-plate potentials at the NMJ which causes sodium ions to enter and depolarise the muscle cells. This depolarisation propagates to the T-tubules where it triggers the entry of calcium ions via Cav1.1 as well as from the sarcoplasmic reticulum through the associated ryanodine receptor RyR1. This causes contraction (tensing) of the muscle. Depolarisation of the motor end plate causes potassium ions to leave the muscle cells, repolarising the muscle and closing the calcium channels. Calcium is pumped away from the contractile apparatus and the muscle relaxes.
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