What causes ATS?
In general the periodic paralyses are caused by abnormalities in the ion channels (especially the sodium, calcium and potassium channels) of the muscle membrane. The ion channels control the movement of sodium, chloride, potassium and calcium across the cell membrane and from one cell compartment to another. This movement of ions produces the electrical ‘spark’ which allows our muscles to move. All of the ATS mutations identified so far have been in a potassium ion channel. However it is evident that there are other, as yet unidentified, mutations which are responsible for ATS. There may be several variant mutations, producing similar but slightly different forms of the disorder, as occurs in the other forms of periodic paralysis, where several variants of each type have been identified.
Ion channels are tiny pores (openings) that allow ions (molecules) of sodium and potassium to move through the cell membrane. This movement of sodium and potassium ions from one side of the muscle membrane to the other creates an electrical current. For the muscles to work properly sodium and potassium ions must be kept in the correct ratio inside and outside the cell. ATS is caused by genetic mutations which cause a malfunction in certain potassium channels in the body. These ion channels fail to regulate the flow of ions properly when potassium levels in the blood change. The ratio of sodium and potassium inside and outside the cell become unbalanced. The muscles respond less when asked to move, which is felt as weakness. If the imbalance becomes pronounced the muscles quit responding at all, i.e. is paralyzed. Ion channels in the heart muscle are also affected, which leads to certain patterns of irregular heart rhythms. These unusual heart rhythms can be seen on an electrocardiogram
